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Linux/kernel/futex.c

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  1 /*
  2  *  Fast Userspace Mutexes (which I call "Futexes!").
  3  *  (C) Rusty Russell, IBM 2002
  4  *
  5  *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
  6  *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
  7  *
  8  *  Removed page pinning, fix privately mapped COW pages and other cleanups
  9  *  (C) Copyright 2003, 2004 Jamie Lokier
 10  *
 11  *  Robust futex support started by Ingo Molnar
 12  *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
 13  *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
 14  *
 15  *  PI-futex support started by Ingo Molnar and Thomas Gleixner
 16  *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 17  *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
 18  *
 19  *  PRIVATE futexes by Eric Dumazet
 20  *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
 21  *
 22  *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
 23  *  Copyright (C) IBM Corporation, 2009
 24  *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
 25  *
 26  *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
 27  *  enough at me, Linus for the original (flawed) idea, Matthew
 28  *  Kirkwood for proof-of-concept implementation.
 29  *
 30  *  "The futexes are also cursed."
 31  *  "But they come in a choice of three flavours!"
 32  *
 33  *  This program is free software; you can redistribute it and/or modify
 34  *  it under the terms of the GNU General Public License as published by
 35  *  the Free Software Foundation; either version 2 of the License, or
 36  *  (at your option) any later version.
 37  *
 38  *  This program is distributed in the hope that it will be useful,
 39  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 40  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 41  *  GNU General Public License for more details.
 42  *
 43  *  You should have received a copy of the GNU General Public License
 44  *  along with this program; if not, write to the Free Software
 45  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 46  */
 47 #include <linux/slab.h>
 48 #include <linux/poll.h>
 49 #include <linux/fs.h>
 50 #include <linux/file.h>
 51 #include <linux/jhash.h>
 52 #include <linux/init.h>
 53 #include <linux/futex.h>
 54 #include <linux/mount.h>
 55 #include <linux/pagemap.h>
 56 #include <linux/syscalls.h>
 57 #include <linux/signal.h>
 58 #include <linux/export.h>
 59 #include <linux/magic.h>
 60 #include <linux/pid.h>
 61 #include <linux/nsproxy.h>
 62 #include <linux/ptrace.h>
 63 #include <linux/sched/rt.h>
 64 #include <linux/sched/wake_q.h>
 65 #include <linux/sched/mm.h>
 66 #include <linux/hugetlb.h>
 67 #include <linux/freezer.h>
 68 #include <linux/bootmem.h>
 69 #include <linux/fault-inject.h>
 70 
 71 #include <asm/futex.h>
 72 
 73 #include "locking/rtmutex_common.h"
 74 
 75 /*
 76  * READ this before attempting to hack on futexes!
 77  *
 78  * Basic futex operation and ordering guarantees
 79  * =============================================
 80  *
 81  * The waiter reads the futex value in user space and calls
 82  * futex_wait(). This function computes the hash bucket and acquires
 83  * the hash bucket lock. After that it reads the futex user space value
 84  * again and verifies that the data has not changed. If it has not changed
 85  * it enqueues itself into the hash bucket, releases the hash bucket lock
 86  * and schedules.
 87  *
 88  * The waker side modifies the user space value of the futex and calls
 89  * futex_wake(). This function computes the hash bucket and acquires the
 90  * hash bucket lock. Then it looks for waiters on that futex in the hash
 91  * bucket and wakes them.
 92  *
 93  * In futex wake up scenarios where no tasks are blocked on a futex, taking
 94  * the hb spinlock can be avoided and simply return. In order for this
 95  * optimization to work, ordering guarantees must exist so that the waiter
 96  * being added to the list is acknowledged when the list is concurrently being
 97  * checked by the waker, avoiding scenarios like the following:
 98  *
 99  * CPU 0                               CPU 1
100  * val = *futex;
101  * sys_futex(WAIT, futex, val);
102  *   futex_wait(futex, val);
103  *   uval = *futex;
104  *                                     *futex = newval;
105  *                                     sys_futex(WAKE, futex);
106  *                                       futex_wake(futex);
107  *                                       if (queue_empty())
108  *                                         return;
109  *   if (uval == val)
110  *      lock(hash_bucket(futex));
111  *      queue();
112  *     unlock(hash_bucket(futex));
113  *     schedule();
114  *
115  * This would cause the waiter on CPU 0 to wait forever because it
116  * missed the transition of the user space value from val to newval
117  * and the waker did not find the waiter in the hash bucket queue.
118  *
119  * The correct serialization ensures that a waiter either observes
120  * the changed user space value before blocking or is woken by a
121  * concurrent waker:
122  *
123  * CPU 0                                 CPU 1
124  * val = *futex;
125  * sys_futex(WAIT, futex, val);
126  *   futex_wait(futex, val);
127  *
128  *   waiters++; (a)
129  *   smp_mb(); (A) <-- paired with -.
130  *                                  |
131  *   lock(hash_bucket(futex));      |
132  *                                  |
133  *   uval = *futex;                 |
134  *                                  |        *futex = newval;
135  *                                  |        sys_futex(WAKE, futex);
136  *                                  |          futex_wake(futex);
137  *                                  |
138  *                                  `--------> smp_mb(); (B)
139  *   if (uval == val)
140  *     queue();
141  *     unlock(hash_bucket(futex));
142  *     schedule();                         if (waiters)
143  *                                           lock(hash_bucket(futex));
144  *   else                                    wake_waiters(futex);
145  *     waiters--; (b)                        unlock(hash_bucket(futex));
146  *
147  * Where (A) orders the waiters increment and the futex value read through
148  * atomic operations (see hb_waiters_inc) and where (B) orders the write
149  * to futex and the waiters read -- this is done by the barriers for both
150  * shared and private futexes in get_futex_key_refs().
151  *
152  * This yields the following case (where X:=waiters, Y:=futex):
153  *
154  *      X = Y = 0
155  *
156  *      w[X]=1          w[Y]=1
157  *      MB              MB
158  *      r[Y]=y          r[X]=x
159  *
160  * Which guarantees that x==0 && y==0 is impossible; which translates back into
161  * the guarantee that we cannot both miss the futex variable change and the
162  * enqueue.
163  *
164  * Note that a new waiter is accounted for in (a) even when it is possible that
165  * the wait call can return error, in which case we backtrack from it in (b).
166  * Refer to the comment in queue_lock().
167  *
168  * Similarly, in order to account for waiters being requeued on another
169  * address we always increment the waiters for the destination bucket before
170  * acquiring the lock. It then decrements them again  after releasing it -
171  * the code that actually moves the futex(es) between hash buckets (requeue_futex)
172  * will do the additional required waiter count housekeeping. This is done for
173  * double_lock_hb() and double_unlock_hb(), respectively.
174  */
175 
176 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
177 int __read_mostly futex_cmpxchg_enabled;
178 #endif
179 
180 /*
181  * Futex flags used to encode options to functions and preserve them across
182  * restarts.
183  */
184 #ifdef CONFIG_MMU
185 # define FLAGS_SHARED           0x01
186 #else
187 /*
188  * NOMMU does not have per process address space. Let the compiler optimize
189  * code away.
190  */
191 # define FLAGS_SHARED           0x00
192 #endif
193 #define FLAGS_CLOCKRT           0x02
194 #define FLAGS_HAS_TIMEOUT       0x04
195 
196 /*
197  * Priority Inheritance state:
198  */
199 struct futex_pi_state {
200         /*
201          * list of 'owned' pi_state instances - these have to be
202          * cleaned up in do_exit() if the task exits prematurely:
203          */
204         struct list_head list;
205 
206         /*
207          * The PI object:
208          */
209         struct rt_mutex pi_mutex;
210 
211         struct task_struct *owner;
212         atomic_t refcount;
213 
214         union futex_key key;
215 } __randomize_layout;
216 
217 /**
218  * struct futex_q - The hashed futex queue entry, one per waiting task
219  * @list:               priority-sorted list of tasks waiting on this futex
220  * @task:               the task waiting on the futex
221  * @lock_ptr:           the hash bucket lock
222  * @key:                the key the futex is hashed on
223  * @pi_state:           optional priority inheritance state
224  * @rt_waiter:          rt_waiter storage for use with requeue_pi
225  * @requeue_pi_key:     the requeue_pi target futex key
226  * @bitset:             bitset for the optional bitmasked wakeup
227  *
228  * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
229  * we can wake only the relevant ones (hashed queues may be shared).
230  *
231  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
232  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
233  * The order of wakeup is always to make the first condition true, then
234  * the second.
235  *
236  * PI futexes are typically woken before they are removed from the hash list via
237  * the rt_mutex code. See unqueue_me_pi().
238  */
239 struct futex_q {
240         struct plist_node list;
241 
242         struct task_struct *task;
243         spinlock_t *lock_ptr;
244         union futex_key key;
245         struct futex_pi_state *pi_state;
246         struct rt_mutex_waiter *rt_waiter;
247         union futex_key *requeue_pi_key;
248         u32 bitset;
249 } __randomize_layout;
250 
251 static const struct futex_q futex_q_init = {
252         /* list gets initialized in queue_me()*/
253         .key = FUTEX_KEY_INIT,
254         .bitset = FUTEX_BITSET_MATCH_ANY
255 };
256 
257 /*
258  * Hash buckets are shared by all the futex_keys that hash to the same
259  * location.  Each key may have multiple futex_q structures, one for each task
260  * waiting on a futex.
261  */
262 struct futex_hash_bucket {
263         atomic_t waiters;
264         spinlock_t lock;
265         struct plist_head chain;
266 } ____cacheline_aligned_in_smp;
267 
268 /*
269  * The base of the bucket array and its size are always used together
270  * (after initialization only in hash_futex()), so ensure that they
271  * reside in the same cacheline.
272  */
273 static struct {
274         struct futex_hash_bucket *queues;
275         unsigned long            hashsize;
276 } __futex_data __read_mostly __aligned(2*sizeof(long));
277 #define futex_queues   (__futex_data.queues)
278 #define futex_hashsize (__futex_data.hashsize)
279 
280 
281 /*
282  * Fault injections for futexes.
283  */
284 #ifdef CONFIG_FAIL_FUTEX
285 
286 static struct {
287         struct fault_attr attr;
288 
289         bool ignore_private;
290 } fail_futex = {
291         .attr = FAULT_ATTR_INITIALIZER,
292         .ignore_private = false,
293 };
294 
295 static int __init setup_fail_futex(char *str)
296 {
297         return setup_fault_attr(&fail_futex.attr, str);
298 }
299 __setup("fail_futex=", setup_fail_futex);
300 
301 static bool should_fail_futex(bool fshared)
302 {
303         if (fail_futex.ignore_private && !fshared)
304                 return false;
305 
306         return should_fail(&fail_futex.attr, 1);
307 }
308 
309 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
310 
311 static int __init fail_futex_debugfs(void)
312 {
313         umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
314         struct dentry *dir;
315 
316         dir = fault_create_debugfs_attr("fail_futex", NULL,
317                                         &fail_futex.attr);
318         if (IS_ERR(dir))
319                 return PTR_ERR(dir);
320 
321         if (!debugfs_create_bool("ignore-private", mode, dir,
322                                  &fail_futex.ignore_private)) {
323                 debugfs_remove_recursive(dir);
324                 return -ENOMEM;
325         }
326 
327         return 0;
328 }
329 
330 late_initcall(fail_futex_debugfs);
331 
332 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
333 
334 #else
335 static inline bool should_fail_futex(bool fshared)
336 {
337         return false;
338 }
339 #endif /* CONFIG_FAIL_FUTEX */
340 
341 static inline void futex_get_mm(union futex_key *key)
342 {
343         mmgrab(key->private.mm);
344         /*
345          * Ensure futex_get_mm() implies a full barrier such that
346          * get_futex_key() implies a full barrier. This is relied upon
347          * as smp_mb(); (B), see the ordering comment above.
348          */
349         smp_mb__after_atomic();
350 }
351 
352 /*
353  * Reflects a new waiter being added to the waitqueue.
354  */
355 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
356 {
357 #ifdef CONFIG_SMP
358         atomic_inc(&hb->waiters);
359         /*
360          * Full barrier (A), see the ordering comment above.
361          */
362         smp_mb__after_atomic();
363 #endif
364 }
365 
366 /*
367  * Reflects a waiter being removed from the waitqueue by wakeup
368  * paths.
369  */
370 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
371 {
372 #ifdef CONFIG_SMP
373         atomic_dec(&hb->waiters);
374 #endif
375 }
376 
377 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
378 {
379 #ifdef CONFIG_SMP
380         return atomic_read(&hb->waiters);
381 #else
382         return 1;
383 #endif
384 }
385 
386 /**
387  * hash_futex - Return the hash bucket in the global hash
388  * @key:        Pointer to the futex key for which the hash is calculated
389  *
390  * We hash on the keys returned from get_futex_key (see below) and return the
391  * corresponding hash bucket in the global hash.
392  */
393 static struct futex_hash_bucket *hash_futex(union futex_key *key)
394 {
395         u32 hash = jhash2((u32*)&key->both.word,
396                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
397                           key->both.offset);
398         return &futex_queues[hash & (futex_hashsize - 1)];
399 }
400 
401 
402 /**
403  * match_futex - Check whether two futex keys are equal
404  * @key1:       Pointer to key1
405  * @key2:       Pointer to key2
406  *
407  * Return 1 if two futex_keys are equal, 0 otherwise.
408  */
409 static inline int match_futex(union futex_key *key1, union futex_key *key2)
410 {
411         return (key1 && key2
412                 && key1->both.word == key2->both.word
413                 && key1->both.ptr == key2->both.ptr
414                 && key1->both.offset == key2->both.offset);
415 }
416 
417 /*
418  * Take a reference to the resource addressed by a key.
419  * Can be called while holding spinlocks.
420  *
421  */
422 static void get_futex_key_refs(union futex_key *key)
423 {
424         if (!key->both.ptr)
425                 return;
426 
427         /*
428          * On MMU less systems futexes are always "private" as there is no per
429          * process address space. We need the smp wmb nevertheless - yes,
430          * arch/blackfin has MMU less SMP ...
431          */
432         if (!IS_ENABLED(CONFIG_MMU)) {
433                 smp_mb(); /* explicit smp_mb(); (B) */
434                 return;
435         }
436 
437         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
438         case FUT_OFF_INODE:
439                 ihold(key->shared.inode); /* implies smp_mb(); (B) */
440                 break;
441         case FUT_OFF_MMSHARED:
442                 futex_get_mm(key); /* implies smp_mb(); (B) */
443                 break;
444         default:
445                 /*
446                  * Private futexes do not hold reference on an inode or
447                  * mm, therefore the only purpose of calling get_futex_key_refs
448                  * is because we need the barrier for the lockless waiter check.
449                  */
450                 smp_mb(); /* explicit smp_mb(); (B) */
451         }
452 }
453 
454 /*
455  * Drop a reference to the resource addressed by a key.
456  * The hash bucket spinlock must not be held. This is
457  * a no-op for private futexes, see comment in the get
458  * counterpart.
459  */
460 static void drop_futex_key_refs(union futex_key *key)
461 {
462         if (!key->both.ptr) {
463                 /* If we're here then we tried to put a key we failed to get */
464                 WARN_ON_ONCE(1);
465                 return;
466         }
467 
468         if (!IS_ENABLED(CONFIG_MMU))
469                 return;
470 
471         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
472         case FUT_OFF_INODE:
473                 iput(key->shared.inode);
474                 break;
475         case FUT_OFF_MMSHARED:
476                 mmdrop(key->private.mm);
477                 break;
478         }
479 }
480 
481 /**
482  * get_futex_key() - Get parameters which are the keys for a futex
483  * @uaddr:      virtual address of the futex
484  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
485  * @key:        address where result is stored.
486  * @rw:         mapping needs to be read/write (values: VERIFY_READ,
487  *              VERIFY_WRITE)
488  *
489  * Return: a negative error code or 0
490  *
491  * The key words are stored in @key on success.
492  *
493  * For shared mappings, it's (page->index, file_inode(vma->vm_file),
494  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
495  * We can usually work out the index without swapping in the page.
496  *
497  * lock_page() might sleep, the caller should not hold a spinlock.
498  */
499 static int
500 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
501 {
502         unsigned long address = (unsigned long)uaddr;
503         struct mm_struct *mm = current->mm;
504         struct page *page, *tail;
505         struct address_space *mapping;
506         int err, ro = 0;
507 
508         /*
509          * The futex address must be "naturally" aligned.
510          */
511         key->both.offset = address % PAGE_SIZE;
512         if (unlikely((address % sizeof(u32)) != 0))
513                 return -EINVAL;
514         address -= key->both.offset;
515 
516         if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
517                 return -EFAULT;
518 
519         if (unlikely(should_fail_futex(fshared)))
520                 return -EFAULT;
521 
522         /*
523          * PROCESS_PRIVATE futexes are fast.
524          * As the mm cannot disappear under us and the 'key' only needs
525          * virtual address, we dont even have to find the underlying vma.
526          * Note : We do have to check 'uaddr' is a valid user address,
527          *        but access_ok() should be faster than find_vma()
528          */
529         if (!fshared) {
530                 key->private.mm = mm;
531                 key->private.address = address;
532                 get_futex_key_refs(key);  /* implies smp_mb(); (B) */
533                 return 0;
534         }
535 
536 again:
537         /* Ignore any VERIFY_READ mapping (futex common case) */
538         if (unlikely(should_fail_futex(fshared)))
539                 return -EFAULT;
540 
541         err = get_user_pages_fast(address, 1, 1, &page);
542         /*
543          * If write access is not required (eg. FUTEX_WAIT), try
544          * and get read-only access.
545          */
546         if (err == -EFAULT && rw == VERIFY_READ) {
547                 err = get_user_pages_fast(address, 1, 0, &page);
548                 ro = 1;
549         }
550         if (err < 0)
551                 return err;
552         else
553                 err = 0;
554 
555         /*
556          * The treatment of mapping from this point on is critical. The page
557          * lock protects many things but in this context the page lock
558          * stabilizes mapping, prevents inode freeing in the shared
559          * file-backed region case and guards against movement to swap cache.
560          *
561          * Strictly speaking the page lock is not needed in all cases being
562          * considered here and page lock forces unnecessarily serialization
563          * From this point on, mapping will be re-verified if necessary and
564          * page lock will be acquired only if it is unavoidable
565          *
566          * Mapping checks require the head page for any compound page so the
567          * head page and mapping is looked up now. For anonymous pages, it
568          * does not matter if the page splits in the future as the key is
569          * based on the address. For filesystem-backed pages, the tail is
570          * required as the index of the page determines the key. For
571          * base pages, there is no tail page and tail == page.
572          */
573         tail = page;
574         page = compound_head(page);
575         mapping = READ_ONCE(page->mapping);
576 
577         /*
578          * If page->mapping is NULL, then it cannot be a PageAnon
579          * page; but it might be the ZERO_PAGE or in the gate area or
580          * in a special mapping (all cases which we are happy to fail);
581          * or it may have been a good file page when get_user_pages_fast
582          * found it, but truncated or holepunched or subjected to
583          * invalidate_complete_page2 before we got the page lock (also
584          * cases which we are happy to fail).  And we hold a reference,
585          * so refcount care in invalidate_complete_page's remove_mapping
586          * prevents drop_caches from setting mapping to NULL beneath us.
587          *
588          * The case we do have to guard against is when memory pressure made
589          * shmem_writepage move it from filecache to swapcache beneath us:
590          * an unlikely race, but we do need to retry for page->mapping.
591          */
592         if (unlikely(!mapping)) {
593                 int shmem_swizzled;
594 
595                 /*
596                  * Page lock is required to identify which special case above
597                  * applies. If this is really a shmem page then the page lock
598                  * will prevent unexpected transitions.
599                  */
600                 lock_page(page);
601                 shmem_swizzled = PageSwapCache(page) || page->mapping;
602                 unlock_page(page);
603                 put_page(page);
604 
605                 if (shmem_swizzled)
606                         goto again;
607 
608                 return -EFAULT;
609         }
610 
611         /*
612          * Private mappings are handled in a simple way.
613          *
614          * If the futex key is stored on an anonymous page, then the associated
615          * object is the mm which is implicitly pinned by the calling process.
616          *
617          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
618          * it's a read-only handle, it's expected that futexes attach to
619          * the object not the particular process.
620          */
621         if (PageAnon(page)) {
622                 /*
623                  * A RO anonymous page will never change and thus doesn't make
624                  * sense for futex operations.
625                  */
626                 if (unlikely(should_fail_futex(fshared)) || ro) {
627                         err = -EFAULT;
628                         goto out;
629                 }
630 
631                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
632                 key->private.mm = mm;
633                 key->private.address = address;
634 
635                 get_futex_key_refs(key); /* implies smp_mb(); (B) */
636 
637         } else {
638                 struct inode *inode;
639 
640                 /*
641                  * The associated futex object in this case is the inode and
642                  * the page->mapping must be traversed. Ordinarily this should
643                  * be stabilised under page lock but it's not strictly
644                  * necessary in this case as we just want to pin the inode, not
645                  * update the radix tree or anything like that.
646                  *
647                  * The RCU read lock is taken as the inode is finally freed
648                  * under RCU. If the mapping still matches expectations then the
649                  * mapping->host can be safely accessed as being a valid inode.
650                  */
651                 rcu_read_lock();
652 
653                 if (READ_ONCE(page->mapping) != mapping) {
654                         rcu_read_unlock();
655                         put_page(page);
656 
657                         goto again;
658                 }
659 
660                 inode = READ_ONCE(mapping->host);
661                 if (!inode) {
662                         rcu_read_unlock();
663                         put_page(page);
664 
665                         goto again;
666                 }
667 
668                 /*
669                  * Take a reference unless it is about to be freed. Previously
670                  * this reference was taken by ihold under the page lock
671                  * pinning the inode in place so i_lock was unnecessary. The
672                  * only way for this check to fail is if the inode was
673                  * truncated in parallel which is almost certainly an
674                  * application bug. In such a case, just retry.
675                  *
676                  * We are not calling into get_futex_key_refs() in file-backed
677                  * cases, therefore a successful atomic_inc return below will
678                  * guarantee that get_futex_key() will still imply smp_mb(); (B).
679                  */
680                 if (!atomic_inc_not_zero(&inode->i_count)) {
681                         rcu_read_unlock();
682                         put_page(page);
683 
684                         goto again;
685                 }
686 
687                 /* Should be impossible but lets be paranoid for now */
688                 if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
689                         err = -EFAULT;
690                         rcu_read_unlock();
691                         iput(inode);
692 
693                         goto out;
694                 }
695 
696                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
697                 key->shared.inode = inode;
698                 key->shared.pgoff = basepage_index(tail);
699                 rcu_read_unlock();
700         }
701 
702 out:
703         put_page(page);
704         return err;
705 }
706 
707 static inline void put_futex_key(union futex_key *key)
708 {
709         drop_futex_key_refs(key);
710 }
711 
712 /**
713  * fault_in_user_writeable() - Fault in user address and verify RW access
714  * @uaddr:      pointer to faulting user space address
715  *
716  * Slow path to fixup the fault we just took in the atomic write
717  * access to @uaddr.
718  *
719  * We have no generic implementation of a non-destructive write to the
720  * user address. We know that we faulted in the atomic pagefault
721  * disabled section so we can as well avoid the #PF overhead by
722  * calling get_user_pages() right away.
723  */
724 static int fault_in_user_writeable(u32 __user *uaddr)
725 {
726         struct mm_struct *mm = current->mm;
727         int ret;
728 
729         down_read(&mm->mmap_sem);
730         ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
731                                FAULT_FLAG_WRITE, NULL);
732         up_read(&mm->mmap_sem);
733 
734         return ret < 0 ? ret : 0;
735 }
736 
737 /**
738  * futex_top_waiter() - Return the highest priority waiter on a futex
739  * @hb:         the hash bucket the futex_q's reside in
740  * @key:        the futex key (to distinguish it from other futex futex_q's)
741  *
742  * Must be called with the hb lock held.
743  */
744 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
745                                         union futex_key *key)
746 {
747         struct futex_q *this;
748 
749         plist_for_each_entry(this, &hb->chain, list) {
750                 if (match_futex(&this->key, key))
751                         return this;
752         }
753         return NULL;
754 }
755 
756 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
757                                       u32 uval, u32 newval)
758 {
759         int ret;
760 
761         pagefault_disable();
762         ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
763         pagefault_enable();
764 
765         return ret;
766 }
767 
768 static int get_futex_value_locked(u32 *dest, u32 __user *from)
769 {
770         int ret;
771 
772         pagefault_disable();
773         ret = __get_user(*dest, from);
774         pagefault_enable();
775 
776         return ret ? -EFAULT : 0;
777 }
778 
779 
780 /*
781  * PI code:
782  */
783 static int refill_pi_state_cache(void)
784 {
785         struct futex_pi_state *pi_state;
786 
787         if (likely(current->pi_state_cache))
788                 return 0;
789 
790         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
791 
792         if (!pi_state)
793                 return -ENOMEM;
794 
795         INIT_LIST_HEAD(&pi_state->list);
796         /* pi_mutex gets initialized later */
797         pi_state->owner = NULL;
798         atomic_set(&pi_state->refcount, 1);
799         pi_state->key = FUTEX_KEY_INIT;
800 
801         current->pi_state_cache = pi_state;
802 
803         return 0;
804 }
805 
806 static struct futex_pi_state *alloc_pi_state(void)
807 {
808         struct futex_pi_state *pi_state = current->pi_state_cache;
809 
810         WARN_ON(!pi_state);
811         current->pi_state_cache = NULL;
812 
813         return pi_state;
814 }
815 
816 static void get_pi_state(struct futex_pi_state *pi_state)
817 {
818         WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
819 }
820 
821 /*
822  * Drops a reference to the pi_state object and frees or caches it
823  * when the last reference is gone.
824  */
825 static void put_pi_state(struct futex_pi_state *pi_state)
826 {
827         if (!pi_state)
828                 return;
829 
830         if (!atomic_dec_and_test(&pi_state->refcount))
831                 return;
832 
833         /*
834          * If pi_state->owner is NULL, the owner is most probably dying
835          * and has cleaned up the pi_state already
836          */
837         if (pi_state->owner) {
838                 struct task_struct *owner;
839 
840                 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
841                 owner = pi_state->owner;
842                 if (owner) {
843                         raw_spin_lock(&owner->pi_lock);
844                         list_del_init(&pi_state->list);
845                         raw_spin_unlock(&owner->pi_lock);
846                 }
847                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
848                 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
849         }
850 
851         if (current->pi_state_cache) {
852                 kfree(pi_state);
853         } else {
854                 /*
855                  * pi_state->list is already empty.
856                  * clear pi_state->owner.
857                  * refcount is at 0 - put it back to 1.
858                  */
859                 pi_state->owner = NULL;
860                 atomic_set(&pi_state->refcount, 1);
861                 current->pi_state_cache = pi_state;
862         }
863 }
864 
865 #ifdef CONFIG_FUTEX_PI
866 
867 /*
868  * This task is holding PI mutexes at exit time => bad.
869  * Kernel cleans up PI-state, but userspace is likely hosed.
870  * (Robust-futex cleanup is separate and might save the day for userspace.)
871  */
872 void exit_pi_state_list(struct task_struct *curr)
873 {
874         struct list_head *next, *head = &curr->pi_state_list;
875         struct futex_pi_state *pi_state;
876         struct futex_hash_bucket *hb;
877         union futex_key key = FUTEX_KEY_INIT;
878 
879         if (!futex_cmpxchg_enabled)
880                 return;
881         /*
882          * We are a ZOMBIE and nobody can enqueue itself on
883          * pi_state_list anymore, but we have to be careful
884          * versus waiters unqueueing themselves:
885          */
886         raw_spin_lock_irq(&curr->pi_lock);
887         while (!list_empty(head)) {
888                 next = head->next;
889                 pi_state = list_entry(next, struct futex_pi_state, list);
890                 key = pi_state->key;
891                 hb = hash_futex(&key);
892 
893                 /*
894                  * We can race against put_pi_state() removing itself from the
895                  * list (a waiter going away). put_pi_state() will first
896                  * decrement the reference count and then modify the list, so
897                  * its possible to see the list entry but fail this reference
898                  * acquire.
899                  *
900                  * In that case; drop the locks to let put_pi_state() make
901                  * progress and retry the loop.
902                  */
903                 if (!atomic_inc_not_zero(&pi_state->refcount)) {
904                         raw_spin_unlock_irq(&curr->pi_lock);
905                         cpu_relax();
906                         raw_spin_lock_irq(&curr->pi_lock);
907                         continue;
908                 }
909                 raw_spin_unlock_irq(&curr->pi_lock);
910 
911                 spin_lock(&hb->lock);
912                 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
913                 raw_spin_lock(&curr->pi_lock);
914                 /*
915                  * We dropped the pi-lock, so re-check whether this
916                  * task still owns the PI-state:
917                  */
918                 if (head->next != next) {
919                         /* retain curr->pi_lock for the loop invariant */
920                         raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
921                         spin_unlock(&hb->lock);
922                         put_pi_state(pi_state);
923                         continue;
924                 }
925 
926                 WARN_ON(pi_state->owner != curr);
927                 WARN_ON(list_empty(&pi_state->list));
928                 list_del_init(&pi_state->list);
929                 pi_state->owner = NULL;
930 
931                 raw_spin_unlock(&curr->pi_lock);
932                 raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
933                 spin_unlock(&hb->lock);
934 
935                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
936                 put_pi_state(pi_state);
937 
938                 raw_spin_lock_irq(&curr->pi_lock);
939         }
940         raw_spin_unlock_irq(&curr->pi_lock);
941 }
942 
943 #endif
944 
945 /*
946  * We need to check the following states:
947  *
948  *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
949  *
950  * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
951  * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
952  *
953  * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
954  *
955  * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
956  * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
957  *
958  * [6]  Found  | Found    | task      | 0         | 1      | Valid
959  *
960  * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
961  *
962  * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
963  * [9]  Found  | Found    | task      | 0         | 0      | Invalid
964  * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
965  *
966  * [1]  Indicates that the kernel can acquire the futex atomically. We
967  *      came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
968  *
969  * [2]  Valid, if TID does not belong to a kernel thread. If no matching
970  *      thread is found then it indicates that the owner TID has died.
971  *
972  * [3]  Invalid. The waiter is queued on a non PI futex
973  *
974  * [4]  Valid state after exit_robust_list(), which sets the user space
975  *      value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
976  *
977  * [5]  The user space value got manipulated between exit_robust_list()
978  *      and exit_pi_state_list()
979  *
980  * [6]  Valid state after exit_pi_state_list() which sets the new owner in
981  *      the pi_state but cannot access the user space value.
982  *
983  * [7]  pi_state->owner can only be NULL when the OWNER_DIED bit is set.
984  *
985  * [8]  Owner and user space value match
986  *
987  * [9]  There is no transient state which sets the user space TID to 0
988  *      except exit_robust_list(), but this is indicated by the
989  *      FUTEX_OWNER_DIED bit. See [4]
990  *
991  * [10] There is no transient state which leaves owner and user space
992  *      TID out of sync.
993  *
994  *
995  * Serialization and lifetime rules:
996  *
997  * hb->lock:
998  *
999  *      hb -> futex_q, relation
1000  *      futex_q -> pi_state, relation
1001  *
1002  *      (cannot be raw because hb can contain arbitrary amount
1003  *       of futex_q's)
1004  *
1005  * pi_mutex->wait_lock:
1006  *
1007  *      {uval, pi_state}
1008  *
1009  *      (and pi_mutex 'obviously')
1010  *
1011  * p->pi_lock:
1012  *
1013  *      p->pi_state_list -> pi_state->list, relation
1014  *
1015  * pi_state->refcount:
1016  *
1017  *      pi_state lifetime
1018  *
1019  *
1020  * Lock order:
1021  *
1022  *   hb->lock
1023  *     pi_mutex->wait_lock
1024  *       p->pi_lock
1025  *
1026  */
1027 
1028 /*
1029  * Validate that the existing waiter has a pi_state and sanity check
1030  * the pi_state against the user space value. If correct, attach to
1031  * it.
1032  */
1033 static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
1034                               struct futex_pi_state *pi_state,
1035                               struct futex_pi_state **ps)
1036 {
1037         pid_t pid = uval & FUTEX_TID_MASK;
1038         u32 uval2;
1039         int ret;
1040 
1041         /*
1042          * Userspace might have messed up non-PI and PI futexes [3]
1043          */
1044         if (unlikely(!pi_state))
1045                 return -EINVAL;
1046 
1047         /*
1048          * We get here with hb->lock held, and having found a
1049          * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
1050          * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
1051          * which in turn means that futex_lock_pi() still has a reference on
1052          * our pi_state.
1053          *
1054          * The waiter holding a reference on @pi_state also protects against
1055          * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
1056          * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
1057          * free pi_state before we can take a reference ourselves.
1058          */
1059         WARN_ON(!atomic_read(&pi_state->refcount));
1060 
1061         /*
1062          * Now that we have a pi_state, we can acquire wait_lock
1063          * and do the state validation.
1064          */
1065         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
1066 
1067         /*
1068          * Since {uval, pi_state} is serialized by wait_lock, and our current
1069          * uval was read without holding it, it can have changed. Verify it
1070          * still is what we expect it to be, otherwise retry the entire
1071          * operation.
1072          */
1073         if (get_futex_value_locked(&uval2, uaddr))
1074                 goto out_efault;
1075 
1076         if (uval != uval2)
1077                 goto out_eagain;
1078 
1079         /*
1080          * Handle the owner died case:
1081          */
1082         if (uval & FUTEX_OWNER_DIED) {
1083                 /*
1084                  * exit_pi_state_list sets owner to NULL and wakes the
1085                  * topmost waiter. The task which acquires the
1086                  * pi_state->rt_mutex will fixup owner.
1087                  */
1088                 if (!pi_state->owner) {
1089                         /*
1090                          * No pi state owner, but the user space TID
1091                          * is not 0. Inconsistent state. [5]
1092                          */
1093                         if (pid)
1094                                 goto out_einval;
1095                         /*
1096                          * Take a ref on the state and return success. [4]
1097                          */
1098                         goto out_attach;
1099                 }
1100 
1101                 /*
1102                  * If TID is 0, then either the dying owner has not
1103                  * yet executed exit_pi_state_list() or some waiter
1104                  * acquired the rtmutex in the pi state, but did not
1105                  * yet fixup the TID in user space.
1106                  *
1107                  * Take a ref on the state and return success. [6]
1108                  */
1109                 if (!pid)
1110                         goto out_attach;
1111         } else {
1112                 /*
1113                  * If the owner died bit is not set, then the pi_state
1114                  * must have an owner. [7]
1115                  */
1116                 if (!pi_state->owner)
1117                         goto out_einval;
1118         }
1119 
1120         /*
1121          * Bail out if user space manipulated the futex value. If pi
1122          * state exists then the owner TID must be the same as the
1123          * user space TID. [9/10]
1124          */
1125         if (pid != task_pid_vnr(pi_state->owner))
1126                 goto out_einval;
1127 
1128 out_attach:
1129         get_pi_state(pi_state);
1130         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1131         *ps = pi_state;
1132         return 0;
1133 
1134 out_einval:
1135         ret = -EINVAL;
1136         goto out_error;
1137 
1138 out_eagain:
1139         ret = -EAGAIN;
1140         goto out_error;
1141 
1142 out_efault:
1143         ret = -EFAULT;
1144         goto out_error;
1145 
1146 out_error:
1147         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1148         return ret;
1149 }
1150 
1151 /*
1152  * Lookup the task for the TID provided from user space and attach to
1153  * it after doing proper sanity checks.
1154  */
1155 static int attach_to_pi_owner(u32 uval, union futex_key *key,
1156                               struct futex_pi_state **ps)
1157 {
1158         pid_t pid = uval & FUTEX_TID_MASK;
1159         struct futex_pi_state *pi_state;
1160         struct task_struct *p;
1161 
1162         /*
1163          * We are the first waiter - try to look up the real owner and attach
1164          * the new pi_state to it, but bail out when TID = 0 [1]
1165          */
1166         if (!pid)
1167                 return -ESRCH;
1168         p = find_get_task_by_vpid(pid);
1169         if (!p)
1170                 return -ESRCH;
1171 
1172         if (unlikely(p->flags & PF_KTHREAD)) {
1173                 put_task_struct(p);
1174                 return -EPERM;
1175         }
1176 
1177         /*
1178          * We need to look at the task state flags to figure out,
1179          * whether the task is exiting. To protect against the do_exit
1180          * change of the task flags, we do this protected by
1181          * p->pi_lock:
1182          */
1183         raw_spin_lock_irq(&p->pi_lock);
1184         if (unlikely(p->flags & PF_EXITING)) {
1185                 /*
1186                  * The task is on the way out. When PF_EXITPIDONE is
1187                  * set, we know that the task has finished the
1188                  * cleanup:
1189                  */
1190                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
1191 
1192                 raw_spin_unlock_irq(&p->pi_lock);
1193                 put_task_struct(p);
1194                 return ret;
1195         }
1196 
1197         /*
1198          * No existing pi state. First waiter. [2]
1199          *
1200          * This creates pi_state, we have hb->lock held, this means nothing can
1201          * observe this state, wait_lock is irrelevant.
1202          */
1203         pi_state = alloc_pi_state();
1204 
1205         /*
1206          * Initialize the pi_mutex in locked state and make @p
1207          * the owner of it:
1208          */
1209         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
1210 
1211         /* Store the key for possible exit cleanups: */
1212         pi_state->key = *key;
1213 
1214         WARN_ON(!list_empty(&pi_state->list));
1215         list_add(&pi_state->list, &p->pi_state_list);
1216         /*
1217          * Assignment without holding pi_state->pi_mutex.wait_lock is safe
1218          * because there is no concurrency as the object is not published yet.
1219          */
1220         pi_state->owner = p;
1221         raw_spin_unlock_irq(&p->pi_lock);
1222 
1223         put_task_struct(p);
1224 
1225         *ps = pi_state;
1226 
1227         return 0;
1228 }
1229 
1230 static int lookup_pi_state(u32 __user *uaddr, u32 uval,
1231                            struct futex_hash_bucket *hb,
1232                            union futex_key *key, struct futex_pi_state **ps)
1233 {
1234         struct futex_q *top_waiter = futex_top_waiter(hb, key);
1235 
1236         /*
1237          * If there is a waiter on that futex, validate it and
1238          * attach to the pi_state when the validation succeeds.
1239          */
1240         if (top_waiter)
1241                 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1242 
1243         /*
1244          * We are the first waiter - try to look up the owner based on
1245          * @uval and attach to it.
1246          */
1247         return attach_to_pi_owner(uval, key, ps);
1248 }
1249 
1250 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
1251 {
1252         u32 uninitialized_var(curval);
1253 
1254         if (unlikely(should_fail_futex(true)))
1255                 return -EFAULT;
1256 
1257         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
1258                 return -EFAULT;
1259 
1260         /* If user space value changed, let the caller retry */
1261         return curval != uval ? -EAGAIN : 0;
1262 }
1263 
1264 /**
1265  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
1266  * @uaddr:              the pi futex user address
1267  * @hb:                 the pi futex hash bucket
1268  * @key:                the futex key associated with uaddr and hb
1269  * @ps:                 the pi_state pointer where we store the result of the
1270  *                      lookup
1271  * @task:               the task to perform the atomic lock work for.  This will
1272  *                      be "current" except in the case of requeue pi.
1273  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1274  *
1275  * Return:
1276  *  -  0 - ready to wait;
1277  *  -  1 - acquired the lock;
1278  *  - <0 - error
1279  *
1280  * The hb->lock and futex_key refs shall be held by the caller.
1281  */
1282 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
1283                                 union futex_key *key,
1284                                 struct futex_pi_state **ps,
1285                                 struct task_struct *task, int set_waiters)
1286 {
1287         u32 uval, newval, vpid = task_pid_vnr(task);
1288         struct futex_q *top_waiter;
1289         int ret;
1290 
1291         /*
1292          * Read the user space value first so we can validate a few
1293          * things before proceeding further.
1294          */
1295         if (get_futex_value_locked(&uval, uaddr))
1296                 return -EFAULT;
1297 
1298         if (unlikely(should_fail_futex(true)))
1299                 return -EFAULT;
1300 
1301         /*
1302          * Detect deadlocks.
1303          */
1304         if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
1305                 return -EDEADLK;
1306 
1307         if ((unlikely(should_fail_futex(true))))
1308                 return -EDEADLK;
1309 
1310         /*
1311          * Lookup existing state first. If it exists, try to attach to
1312          * its pi_state.
1313          */
1314         top_waiter = futex_top_waiter(hb, key);
1315         if (top_waiter)
1316                 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
1317 
1318         /*
1319          * No waiter and user TID is 0. We are here because the
1320          * waiters or the owner died bit is set or called from
1321          * requeue_cmp_pi or for whatever reason something took the
1322          * syscall.
1323          */
1324         if (!(uval & FUTEX_TID_MASK)) {
1325                 /*
1326                  * We take over the futex. No other waiters and the user space
1327                  * TID is 0. We preserve the owner died bit.
1328                  */
1329                 newval = uval & FUTEX_OWNER_DIED;
1330                 newval |= vpid;
1331 
1332                 /* The futex requeue_pi code can enforce the waiters bit */
1333                 if (set_waiters)
1334                         newval |= FUTEX_WAITERS;
1335 
1336                 ret = lock_pi_update_atomic(uaddr, uval, newval);
1337                 /* If the take over worked, return 1 */
1338                 return ret < 0 ? ret : 1;
1339         }
1340 
1341         /*
1342          * First waiter. Set the waiters bit before attaching ourself to
1343          * the owner. If owner tries to unlock, it will be forced into
1344          * the kernel and blocked on hb->lock.
1345          */
1346         newval = uval | FUTEX_WAITERS;
1347         ret = lock_pi_update_atomic(uaddr, uval, newval);
1348         if (ret)
1349                 return ret;
1350         /*
1351          * If the update of the user space value succeeded, we try to
1352          * attach to the owner. If that fails, no harm done, we only
1353          * set the FUTEX_WAITERS bit in the user space variable.
1354          */
1355         return attach_to_pi_owner(uval, key, ps);
1356 }
1357 
1358 /**
1359  * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
1360  * @q:  The futex_q to unqueue
1361  *
1362  * The q->lock_ptr must not be NULL and must be held by the caller.
1363  */
1364 static void __unqueue_futex(struct futex_q *q)
1365 {
1366         struct futex_hash_bucket *hb;
1367 
1368         if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
1369             || WARN_ON(plist_node_empty(&q->list)))
1370                 return;
1371 
1372         hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
1373         plist_del(&q->list, &hb->chain);
1374         hb_waiters_dec(hb);
1375 }
1376 
1377 /*
1378  * The hash bucket lock must be held when this is called.
1379  * Afterwards, the futex_q must not be accessed. Callers
1380  * must ensure to later call wake_up_q() for the actual
1381  * wakeups to occur.
1382  */
1383 static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
1384 {
1385         struct task_struct *p = q->task;
1386 
1387         if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
1388                 return;
1389 
1390         /*
1391          * Queue the task for later wakeup for after we've released
1392          * the hb->lock. wake_q_add() grabs reference to p.
1393          */
1394         wake_q_add(wake_q, p);
1395         __unqueue_futex(q);
1396         /*
1397          * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
1398          * is written, without taking any locks. This is possible in the event
1399          * of a spurious wakeup, for example. A memory barrier is required here
1400          * to prevent the following store to lock_ptr from getting ahead of the
1401          * plist_del in __unqueue_futex().
1402          */
1403         smp_store_release(&q->lock_ptr, NULL);
1404 }
1405 
1406 /*
1407  * Caller must hold a reference on @pi_state.
1408  */
1409 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
1410 {
1411         u32 uninitialized_var(curval), newval;
1412         struct task_struct *new_owner;
1413         bool postunlock = false;
1414         DEFINE_WAKE_Q(wake_q);
1415         int ret = 0;
1416 
1417         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
1418         if (WARN_ON_ONCE(!new_owner)) {
1419                 /*
1420                  * As per the comment in futex_unlock_pi() this should not happen.
1421                  *
1422                  * When this happens, give up our locks and try again, giving
1423                  * the futex_lock_pi() instance time to complete, either by
1424                  * waiting on the rtmutex or removing itself from the futex
1425                  * queue.
1426                  */
1427                 ret = -EAGAIN;
1428                 goto out_unlock;
1429         }
1430 
1431         /*
1432          * We pass it to the next owner. The WAITERS bit is always kept
1433          * enabled while there is PI state around. We cleanup the owner
1434          * died bit, because we are the owner.
1435          */
1436         newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
1437 
1438         if (unlikely(should_fail_futex(true)))
1439                 ret = -EFAULT;
1440 
1441         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
1442                 ret = -EFAULT;
1443 
1444         } else if (curval != uval) {
1445                 /*
1446                  * If a unconditional UNLOCK_PI operation (user space did not
1447                  * try the TID->0 transition) raced with a waiter setting the
1448                  * FUTEX_WAITERS flag between get_user() and locking the hash
1449                  * bucket lock, retry the operation.
1450                  */
1451                 if ((FUTEX_TID_MASK & curval) == uval)
1452                         ret = -EAGAIN;
1453                 else
1454                         ret = -EINVAL;
1455         }
1456 
1457         if (ret)
1458                 goto out_unlock;
1459 
1460         /*
1461          * This is a point of no return; once we modify the uval there is no
1462          * going back and subsequent operations must not fail.
1463          */
1464 
1465         raw_spin_lock(&pi_state->owner->pi_lock);
1466         WARN_ON(list_empty(&pi_state->list));
1467         list_del_init(&pi_state->list);
1468         raw_spin_unlock(&pi_state->owner->pi_lock);
1469 
1470         raw_spin_lock(&new_owner->pi_lock);
1471         WARN_ON(!list_empty(&pi_state->list));
1472         list_add(&pi_state->list, &new_owner->pi_state_list);
1473         pi_state->owner = new_owner;
1474         raw_spin_unlock(&new_owner->pi_lock);
1475 
1476         postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
1477 
1478 out_unlock:
1479         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
1480 
1481         if (postunlock)
1482                 rt_mutex_postunlock(&wake_q);
1483 
1484         return ret;
1485 }
1486 
1487 /*
1488  * Express the locking dependencies for lockdep:
1489  */
1490 static inline void
1491 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1492 {
1493         if (hb1 <= hb2) {
1494                 spin_lock(&hb1->lock);
1495                 if (hb1 < hb2)
1496                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
1497         } else { /* hb1 > hb2 */
1498                 spin_lock(&hb2->lock);
1499                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
1500         }
1501 }
1502 
1503 static inline void
1504 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
1505 {
1506         spin_unlock(&hb1->lock);
1507         if (hb1 != hb2)
1508                 spin_unlock(&hb2->lock);
1509 }
1510 
1511 /*
1512  * Wake up waiters matching bitset queued on this futex (uaddr).
1513  */
1514 static int
1515 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
1516 {
1517         struct futex_hash_bucket *hb;
1518         struct futex_q *this, *next;
1519         union futex_key key = FUTEX_KEY_INIT;
1520         int ret;
1521         DEFINE_WAKE_Q(wake_q);
1522 
1523         if (!bitset)
1524                 return -EINVAL;
1525 
1526         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
1527         if (unlikely(ret != 0))
1528                 goto out;
1529 
1530         hb = hash_futex(&key);
1531 
1532         /* Make sure we really have tasks to wakeup */
1533         if (!hb_waiters_pending(hb))
1534                 goto out_put_key;
1535 
1536         spin_lock(&hb->lock);
1537 
1538         plist_for_each_entry_safe(this, next, &hb->chain, list) {
1539                 if (match_futex (&this->key, &key)) {
1540                         if (this->pi_state || this->rt_waiter) {
1541                                 ret = -EINVAL;
1542                                 break;
1543                         }
1544 
1545                         /* Check if one of the bits is set in both bitsets */
1546                         if (!(this->bitset & bitset))
1547                                 continue;
1548 
1549                         mark_wake_futex(&wake_q, this);
1550                         if (++ret >= nr_wake)
1551                                 break;
1552                 }
1553         }
1554 
1555         spin_unlock(&hb->lock);
1556         wake_up_q(&wake_q);
1557 out_put_key:
1558         put_futex_key(&key);
1559 out:
1560         return ret;
1561 }
1562 
1563 static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
1564 {
1565         unsigned int op =         (encoded_op & 0x70000000) >> 28;
1566         unsigned int cmp =        (encoded_op & 0x0f000000) >> 24;
1567         int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
1568         int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
1569         int oldval, ret;
1570 
1571         if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
1572                 if (oparg < 0 || oparg > 31) {
1573                         char comm[sizeof(current->comm)];
1574                         /*
1575                          * kill this print and return -EINVAL when userspace
1576                          * is sane again
1577                          */
1578                         pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
1579                                         get_task_comm(comm, current), oparg);
1580                         oparg &= 31;
1581                 }
1582                 oparg = 1 << oparg;
1583         }
1584 
1585         if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
1586                 return -EFAULT;
1587 
1588         ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
1589         if (ret)
1590                 return ret;
1591 
1592         switch (cmp) {
1593         case FUTEX_OP_CMP_EQ:
1594                 return oldval == cmparg;
1595         case FUTEX_OP_CMP_NE:
1596                 return oldval != cmparg;
1597         case FUTEX_OP_CMP_LT:
1598                 return oldval < cmparg;
1599         case FUTEX_OP_CMP_GE:
1600                 return oldval >= cmparg;
1601         case FUTEX_OP_CMP_LE:
1602                 return oldval <= cmparg;
1603         case FUTEX_OP_CMP_GT:
1604                 return oldval > cmparg;
1605         default:
1606                 return -ENOSYS;
1607         }
1608 }
1609 
1610 /*
1611  * Wake up all waiters hashed on the physical page that is mapped
1612  * to this virtual address:
1613  */
1614 static int
1615 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
1616               int nr_wake, int nr_wake2, int op)
1617 {
1618         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1619         struct futex_hash_bucket *hb1, *hb2;
1620         struct futex_q *this, *next;
1621         int ret, op_ret;
1622         DEFINE_WAKE_Q(wake_q);
1623 
1624 retry:
1625         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1626         if (unlikely(ret != 0))
1627                 goto out;
1628         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
1629         if (unlikely(ret != 0))
1630                 goto out_put_key1;
1631 
1632         hb1 = hash_futex(&key1);
1633         hb2 = hash_futex(&key2);
1634 
1635 retry_private:
1636         double_lock_hb(hb1, hb2);
1637         op_ret = futex_atomic_op_inuser(op, uaddr2);
1638         if (unlikely(op_ret < 0)) {
1639 
1640                 double_unlock_hb(hb1, hb2);
1641 
1642 #ifndef CONFIG_MMU
1643                 /*
1644                  * we don't get EFAULT from MMU faults if we don't have an MMU,
1645                  * but we might get them from range checking
1646                  */
1647                 ret = op_ret;
1648                 goto out_put_keys;
1649 #endif
1650 
1651                 if (unlikely(op_ret != -EFAULT)) {
1652                         ret = op_ret;
1653                         goto out_put_keys;
1654                 }
1655 
1656                 ret = fault_in_user_writeable(uaddr2);
1657                 if (ret)
1658                         goto out_put_keys;
1659 
1660                 if (!(flags & FLAGS_SHARED))
1661                         goto retry_private;
1662 
1663                 put_futex_key(&key2);
1664                 put_futex_key(&key1);
1665                 goto retry;
1666         }
1667 
1668         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
1669                 if (match_futex (&this->key, &key1)) {
1670                         if (this->pi_state || this->rt_waiter) {
1671                                 ret = -EINVAL;
1672                                 goto out_unlock;
1673                         }
1674                         mark_wake_futex(&wake_q, this);
1675                         if (++ret >= nr_wake)
1676                                 break;
1677                 }
1678         }
1679 
1680         if (op_ret > 0) {
1681                 op_ret = 0;
1682                 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
1683                         if (match_futex (&this->key, &key2)) {
1684                                 if (this->pi_state || this->rt_waiter) {
1685                                         ret = -EINVAL;
1686                                         goto out_unlock;
1687                                 }
1688                                 mark_wake_futex(&wake_q, this);
1689                                 if (++op_ret >= nr_wake2)
1690                                         break;
1691                         }
1692                 }
1693                 ret += op_ret;
1694         }
1695 
1696 out_unlock:
1697         double_unlock_hb(hb1, hb2);
1698         wake_up_q(&wake_q);
1699 out_put_keys:
1700         put_futex_key(&key2);
1701 out_put_key1:
1702         put_futex_key(&key1);
1703 out:
1704         return ret;
1705 }
1706 
1707 /**
1708  * requeue_futex() - Requeue a futex_q from one hb to another
1709  * @q:          the futex_q to requeue
1710  * @hb1:        the source hash_bucket
1711  * @hb2:        the target hash_bucket
1712  * @key2:       the new key for the requeued futex_q
1713  */
1714 static inline
1715 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
1716                    struct futex_hash_bucket *hb2, union futex_key *key2)
1717 {
1718 
1719         /*
1720          * If key1 and key2 hash to the same bucket, no need to
1721          * requeue.
1722          */
1723         if (likely(&hb1->chain != &hb2->chain)) {
1724                 plist_del(&q->list, &hb1->chain);
1725                 hb_waiters_dec(hb1);
1726                 hb_waiters_inc(hb2);
1727                 plist_add(&q->list, &hb2->chain);
1728                 q->lock_ptr = &hb2->lock;
1729         }
1730         get_futex_key_refs(key2);
1731         q->key = *key2;
1732 }
1733 
1734 /**
1735  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
1736  * @q:          the futex_q
1737  * @key:        the key of the requeue target futex
1738  * @hb:         the hash_bucket of the requeue target futex
1739  *
1740  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
1741  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
1742  * to the requeue target futex so the waiter can detect the wakeup on the right
1743  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
1744  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
1745  * to protect access to the pi_state to fixup the owner later.  Must be called
1746  * with both q->lock_ptr and hb->lock held.
1747  */
1748 static inline
1749 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
1750                            struct futex_hash_bucket *hb)
1751 {
1752         get_futex_key_refs(key);
1753         q->key = *key;
1754 
1755         __unqueue_futex(q);
1756 
1757         WARN_ON(!q->rt_waiter);
1758         q->rt_waiter = NULL;
1759 
1760         q->lock_ptr = &hb->lock;
1761 
1762         wake_up_state(q->task, TASK_NORMAL);
1763 }
1764 
1765 /**
1766  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
1767  * @pifutex:            the user address of the to futex
1768  * @hb1:                the from futex hash bucket, must be locked by the caller
1769  * @hb2:                the to futex hash bucket, must be locked by the caller
1770  * @key1:               the from futex key
1771  * @key2:               the to futex key
1772  * @ps:                 address to store the pi_state pointer
1773  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
1774  *
1775  * Try and get the lock on behalf of the top waiter if we can do it atomically.
1776  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
1777  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
1778  * hb1 and hb2 must be held by the caller.
1779  *
1780  * Return:
1781  *  -  0 - failed to acquire the lock atomically;
1782  *  - >0 - acquired the lock, return value is vpid of the top_waiter
1783  *  - <0 - error
1784  */
1785 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
1786                                  struct futex_hash_bucket *hb1,
1787                                  struct futex_hash_bucket *hb2,
1788                                  union futex_key *key1, union futex_key *key2,
1789                                  struct futex_pi_state **ps, int set_waiters)
1790 {
1791         struct futex_q *top_waiter = NULL;
1792         u32 curval;
1793         int ret, vpid;
1794 
1795         if (get_futex_value_locked(&curval, pifutex))
1796                 return -EFAULT;
1797 
1798         if (unlikely(should_fail_futex(true)))
1799                 return -EFAULT;
1800 
1801         /*
1802          * Find the top_waiter and determine if there are additional waiters.
1803          * If the caller intends to requeue more than 1 waiter to pifutex,
1804          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
1805          * as we have means to handle the possible fault.  If not, don't set
1806          * the bit unecessarily as it will force the subsequent unlock to enter
1807          * the kernel.
1808          */
1809         top_waiter = futex_top_waiter(hb1, key1);
1810 
1811         /* There are no waiters, nothing for us to do. */
1812         if (!top_waiter)
1813                 return 0;
1814 
1815         /* Ensure we requeue to the expected futex. */
1816         if (!match_futex(top_waiter->requeue_pi_key, key2))
1817                 return -EINVAL;
1818 
1819         /*
1820          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
1821          * the contended case or if set_waiters is 1.  The pi_state is returned
1822          * in ps in contended cases.
1823          */
1824         vpid = task_pid_vnr(top_waiter->task);
1825         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
1826                                    set_waiters);
1827         if (ret == 1) {
1828                 requeue_pi_wake_futex(top_waiter, key2, hb2);
1829                 return vpid;
1830         }
1831         return ret;
1832 }
1833 
1834 /**
1835  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
1836  * @uaddr1:     source futex user address
1837  * @flags:      futex flags (FLAGS_SHARED, etc.)
1838  * @uaddr2:     target futex user address
1839  * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
1840  * @nr_requeue: number of waiters to requeue (0-INT_MAX)
1841  * @cmpval:     @uaddr1 expected value (or %NULL)
1842  * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
1843  *              pi futex (pi to pi requeue is not supported)
1844  *
1845  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
1846  * uaddr2 atomically on behalf of the top waiter.
1847  *
1848  * Return:
1849  *  - >=0 - on success, the number of tasks requeued or woken;
1850  *  -  <0 - on error
1851  */
1852 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
1853                          u32 __user *uaddr2, int nr_wake, int nr_requeue,
1854                          u32 *cmpval, int requeue_pi)
1855 {
1856         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
1857         int drop_count = 0, task_count = 0, ret;
1858         struct futex_pi_state *pi_state = NULL;
1859         struct futex_hash_bucket *hb1, *hb2;
1860         struct futex_q *this, *next;
1861         DEFINE_WAKE_Q(wake_q);
1862 
1863         if (nr_wake < 0 || nr_requeue < 0)
1864                 return -EINVAL;
1865 
1866         /*
1867          * When PI not supported: return -ENOSYS if requeue_pi is true,
1868          * consequently the compiler knows requeue_pi is always false past
1869          * this point which will optimize away all the conditional code
1870          * further down.
1871          */
1872         if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
1873                 return -ENOSYS;
1874 
1875         if (requeue_pi) {
1876                 /*
1877                  * Requeue PI only works on two distinct uaddrs. This
1878                  * check is only valid for private futexes. See below.
1879                  */
1880                 if (uaddr1 == uaddr2)
1881                         return -EINVAL;
1882 
1883                 /*
1884                  * requeue_pi requires a pi_state, try to allocate it now
1885                  * without any locks in case it fails.
1886                  */
1887                 if (refill_pi_state_cache())
1888                         return -ENOMEM;
1889                 /*
1890                  * requeue_pi must wake as many tasks as it can, up to nr_wake
1891                  * + nr_requeue, since it acquires the rt_mutex prior to
1892                  * returning to userspace, so as to not leave the rt_mutex with
1893                  * waiters and no owner.  However, second and third wake-ups
1894                  * cannot be predicted as they involve race conditions with the
1895                  * first wake and a fault while looking up the pi_state.  Both
1896                  * pthread_cond_signal() and pthread_cond_broadcast() should
1897                  * use nr_wake=1.
1898                  */
1899                 if (nr_wake != 1)
1900                         return -EINVAL;
1901         }
1902 
1903 retry:
1904         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
1905         if (unlikely(ret != 0))
1906                 goto out;
1907         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
1908                             requeue_pi ? VERIFY_WRITE : VERIFY_READ);
1909         if (unlikely(ret != 0))
1910                 goto out_put_key1;
1911 
1912         /*
1913          * The check above which compares uaddrs is not sufficient for
1914          * shared futexes. We need to compare the keys:
1915          */
1916         if (requeue_pi && match_futex(&key1, &key2)) {
1917                 ret = -EINVAL;
1918                 goto out_put_keys;
1919         }
1920 
1921         hb1 = hash_futex(&key1);
1922         hb2 = hash_futex(&key2);
1923 
1924 retry_private:
1925         hb_waiters_inc(hb2);
1926         double_lock_hb(hb1, hb2);
1927 
1928         if (likely(cmpval != NULL)) {
1929                 u32 curval;
1930 
1931                 ret = get_futex_value_locked(&curval, uaddr1);
1932 
1933                 if (unlikely(ret)) {
1934                         double_unlock_hb(hb1, hb2);
1935                         hb_waiters_dec(hb2);
1936 
1937                         ret = get_user(curval, uaddr1);
1938                         if (ret)
1939                                 goto out_put_keys;
1940 
1941                         if (!(flags & FLAGS_SHARED))
1942                                 goto retry_private;
1943 
1944                         put_futex_key(&key2);
1945                         put_futex_key(&key1);
1946                         goto retry;
1947                 }
1948                 if (curval != *cmpval) {
1949                         ret = -EAGAIN;
1950                         goto out_unlock;
1951                 }
1952         }
1953 
1954         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
1955                 /*
1956                  * Attempt to acquire uaddr2 and wake the top waiter. If we
1957                  * intend to requeue waiters, force setting the FUTEX_WAITERS
1958                  * bit.  We force this here where we are able to easily handle
1959                  * faults rather in the requeue loop below.
1960                  */
1961                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
1962                                                  &key2, &pi_state, nr_requeue);
1963 
1964                 /*
1965                  * At this point the top_waiter has either taken uaddr2 or is
1966                  * waiting on it.  If the former, then the pi_state will not
1967                  * exist yet, look it up one more time to ensure we have a
1968                  * reference to it. If the lock was taken, ret contains the
1969                  * vpid of the top waiter task.
1970                  * If the lock was not taken, we have pi_state and an initial
1971                  * refcount on it. In case of an error we have nothing.
1972                  */
1973                 if (ret > 0) {
1974                         WARN_ON(pi_state);
1975                         drop_count++;
1976                         task_count++;
1977                         /*
1978                          * If we acquired the lock, then the user space value
1979                          * of uaddr2 should be vpid. It cannot be changed by
1980                          * the top waiter as it is blocked on hb2 lock if it
1981                          * tries to do so. If something fiddled with it behind
1982                          * our back the pi state lookup might unearth it. So
1983                          * we rather use the known value than rereading and
1984                          * handing potential crap to lookup_pi_state.
1985                          *
1986                          * If that call succeeds then we have pi_state and an
1987                          * initial refcount on it.
1988                          */
1989                         ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state);
1990                 }
1991 
1992                 switch (ret) {
1993                 case 0:
1994                         /* We hold a reference on the pi state. */
1995                         break;
1996 
1997                         /* If the above failed, then pi_state is NULL */
1998                 case -EFAULT:
1999                         double_unlock_hb(hb1, hb2);
2000                         hb_waiters_dec(hb2);
2001                         put_futex_key(&key2);
2002                         put_futex_key(&key1);
2003                         ret = fault_in_user_writeable(uaddr2);
2004                         if (!ret)
2005                                 goto retry;
2006                         goto out;
2007                 case -EAGAIN:
2008                         /*
2009                          * Two reasons for this:
2010                          * - Owner is exiting and we just wait for the
2011                          *   exit to complete.
2012                          * - The user space value changed.
2013                          */
2014                         double_unlock_hb(hb1, hb2);
2015                         hb_waiters_dec(hb2);
2016                         put_futex_key(&key2);
2017                         put_futex_key(&key1);
2018                         cond_resched();
2019                         goto retry;
2020                 default:
2021                         goto out_unlock;
2022                 }
2023         }
2024 
2025         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
2026                 if (task_count - nr_wake >= nr_requeue)
2027                         break;
2028 
2029                 if (!match_futex(&this->key, &key1))
2030                         continue;
2031 
2032                 /*
2033                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
2034                  * be paired with each other and no other futex ops.
2035                  *
2036                  * We should never be requeueing a futex_q with a pi_state,
2037                  * which is awaiting a futex_unlock_pi().
2038                  */
2039                 if ((requeue_pi && !this->rt_waiter) ||
2040                     (!requeue_pi && this->rt_waiter) ||
2041                     this->pi_state) {
2042                         ret = -EINVAL;
2043                         break;
2044                 }
2045 
2046                 /*
2047                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
2048                  * lock, we already woke the top_waiter.  If not, it will be
2049                  * woken by futex_unlock_pi().
2050                  */
2051                 if (++task_count <= nr_wake && !requeue_pi) {
2052                         mark_wake_futex(&wake_q, this);
2053                         continue;
2054                 }
2055 
2056                 /* Ensure we requeue to the expected futex for requeue_pi. */
2057                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
2058                         ret = -EINVAL;
2059                         break;
2060                 }
2061 
2062                 /*
2063                  * Requeue nr_requeue waiters and possibly one more in the case
2064                  * of requeue_pi if we couldn't acquire the lock atomically.
2065                  */
2066                 if (requeue_pi) {
2067                         /*
2068                          * Prepare the waiter to take the rt_mutex. Take a
2069                          * refcount on the pi_state and store the pointer in
2070                          * the futex_q object of the waiter.
2071                          */
2072                         get_pi_state(pi_state);
2073                         this->pi_state = pi_state;
2074                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
2075                                                         this->rt_waiter,
2076                                                         this->task);
2077                         if (ret == 1) {
2078                                 /*
2079                                  * We got the lock. We do neither drop the
2080                                  * refcount on pi_state nor clear
2081                                  * this->pi_state because the waiter needs the
2082                                  * pi_state for cleaning up the user space
2083                                  * value. It will drop the refcount after
2084                                  * doing so.
2085                                  */
2086                                 requeue_pi_wake_futex(this, &key2, hb2);
2087                                 drop_count++;
2088                                 continue;
2089                         } else if (ret) {
2090                                 /*
2091                                  * rt_mutex_start_proxy_lock() detected a
2092                                  * potential deadlock when we tried to queue
2093                                  * that waiter. Drop the pi_state reference
2094                                  * which we took above and remove the pointer
2095                                  * to the state from the waiters futex_q
2096                                  * object.
2097                                  */
2098                                 this->pi_state = NULL;
2099                                 put_pi_state(pi_state);
2100                                 /*
2101                                  * We stop queueing more waiters and let user
2102                                  * space deal with the mess.
2103                                  */
2104                                 break;
2105                         }
2106                 }
2107                 requeue_futex(this, hb1, hb2, &key2);
2108                 drop_count++;
2109         }
2110 
2111         /*
2112          * We took an extra initial reference to the pi_state either
2113          * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
2114          * need to drop it here again.
2115          */
2116         put_pi_state(pi_state);
2117 
2118 out_unlock:
2119         double_unlock_hb(hb1, hb2);
2120         wake_up_q(&wake_q);
2121         hb_waiters_dec(hb2);
2122 
2123         /*
2124          * drop_futex_key_refs() must be called outside the spinlocks. During
2125          * the requeue we moved futex_q's from the hash bucket at key1 to the
2126          * one at key2 and updated their key pointer.  We no longer need to
2127          * hold the references to key1.
2128          */
2129         while (--drop_count >= 0)
2130                 drop_futex_key_refs(&key1);
2131 
2132 out_put_keys:
2133         put_futex_key(&key2);
2134 out_put_key1:
2135         put_futex_key(&key1);
2136 out:
2137         return ret ? ret : task_count;
2138 }
2139 
2140 /* The key must be already stored in q->key. */
2141 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
2142         __acquires(&hb->lock)
2143 {
2144         struct futex_hash_bucket *hb;
2145 
2146         hb = hash_futex(&q->key);
2147 
2148         /*
2149          * Increment the counter before taking the lock so that
2150          * a potential waker won't miss a to-be-slept task that is
2151          * waiting for the spinlock. This is safe as all queue_lock()
2152          * users end up calling queue_me(). Similarly, for housekeeping,
2153          * decrement the counter at queue_unlock() when some error has
2154          * occurred and we don't end up adding the task to the list.
2155          */
2156         hb_waiters_inc(hb);
2157 
2158         q->lock_ptr = &hb->lock;
2159 
2160         spin_lock(&hb->lock); /* implies smp_mb(); (A) */
2161         return hb;
2162 }
2163 
2164 static inline void
2165 queue_unlock(struct futex_hash_bucket *hb)
2166         __releases(&hb->lock)
2167 {
2168         spin_unlock(&hb->lock);
2169         hb_waiters_dec(hb);
2170 }
2171 
2172 static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2173 {
2174         int prio;
2175 
2176         /*
2177          * The priority used to register this element is
2178          * - either the real thread-priority for the real-time threads
2179          * (i.e. threads with a priority lower than MAX_RT_PRIO)
2180          * - or MAX_RT_PRIO for non-RT threads.
2181          * Thus, all RT-threads are woken first in priority order, and
2182          * the others are woken last, in FIFO order.
2183          */
2184         prio = min(current->normal_prio, MAX_RT_PRIO);
2185 
2186         plist_node_init(&q->list, prio);
2187         plist_add(&q->list, &hb->chain);
2188         q->task = current;
2189 }
2190 
2191 /**
2192  * queue_me() - Enqueue the futex_q on the futex_hash_bucket
2193  * @q:  The futex_q to enqueue
2194  * @hb: The destination hash bucket
2195  *
2196  * The hb->lock must be held by the caller, and is released here. A call to
2197  * queue_me() is typically paired with exactly one call to unqueue_me().  The
2198  * exceptions involve the PI related operations, which may use unqueue_me_pi()
2199  * or nothing if the unqueue is done as part of the wake process and the unqueue
2200  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
2201  * an example).
2202  */
2203 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
2204         __releases(&hb->lock)
2205 {
2206         __queue_me(q, hb);
2207         spin_unlock(&hb->lock);
2208 }
2209 
2210 /**
2211  * unqueue_me() - Remove the futex_q from its futex_hash_bucket
2212  * @q:  The futex_q to unqueue
2213  *
2214  * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
2215  * be paired with exactly one earlier call to queue_me().
2216  *
2217  * Return:
2218  *  - 1 - if the futex_q was still queued (and we removed unqueued it);
2219  *  - 0 - if the futex_q was already removed by the waking thread
2220  */
2221 static int unqueue_me(struct futex_q *q)
2222 {
2223         spinlock_t *lock_ptr;
2224         int ret = 0;
2225 
2226         /* In the common case we don't take the spinlock, which is nice. */
2227 retry:
2228         /*
2229          * q->lock_ptr can change between this read and the following spin_lock.
2230          * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
2231          * optimizing lock_ptr out of the logic below.
2232          */
2233         lock_ptr = READ_ONCE(q->lock_ptr);
2234         if (lock_ptr != NULL) {
2235                 spin_lock(lock_ptr);
2236                 /*
2237                  * q->lock_ptr can change between reading it and
2238                  * spin_lock(), causing us to take the wrong lock.  This
2239                  * corrects the race condition.
2240                  *
2241                  * Reasoning goes like this: if we have the wrong lock,
2242                  * q->lock_ptr must have changed (maybe several times)
2243                  * between reading it and the spin_lock().  It can
2244                  * change again after the spin_lock() but only if it was
2245                  * already changed before the spin_lock().  It cannot,
2246                  * however, change back to the original value.  Therefore
2247                  * we can detect whether we acquired the correct lock.
2248                  */
2249                 if (unlikely(lock_ptr != q->lock_ptr)) {
2250                         spin_unlock(lock_ptr);
2251                         goto retry;
2252                 }
2253                 __unqueue_futex(q);
2254 
2255                 BUG_ON(q->pi_state);
2256 
2257                 spin_unlock(lock_ptr);
2258                 ret = 1;
2259         }
2260 
2261         drop_futex_key_refs(&q->key);
2262         return ret;
2263 }
2264 
2265 /*
2266  * PI futexes can not be requeued and must remove themself from the
2267  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
2268  * and dropped here.
2269  */
2270 static void unqueue_me_pi(struct futex_q *q)
2271         __releases(q->lock_ptr)
2272 {
2273         __unqueue_futex(q);
2274 
2275         BUG_ON(!q->pi_state);
2276         put_pi_state(q->pi_state);
2277         q->pi_state = NULL;
2278 
2279         spin_unlock(q->lock_ptr);
2280 }
2281 
2282 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
2283                                 struct task_struct *argowner)
2284 {
2285         struct futex_pi_state *pi_state = q->pi_state;
2286         u32 uval, uninitialized_var(curval), newval;
2287         struct task_struct *oldowner, *newowner;
2288         u32 newtid;
2289         int ret;
2290 
2291         lockdep_assert_held(q->lock_ptr);
2292 
2293         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2294 
2295         oldowner = pi_state->owner;
2296 
2297         /*
2298          * We are here because either:
2299          *
2300          *  - we stole the lock and pi_state->owner needs updating to reflect
2301          *    that (@argowner == current),
2302          *
2303          * or:
2304          *
2305          *  - someone stole our lock and we need to fix things to point to the
2306          *    new owner (@argowner == NULL).
2307          *
2308          * Either way, we have to replace the TID in the user space variable.
2309          * This must be atomic as we have to preserve the owner died bit here.
2310          *
2311          * Note: We write the user space value _before_ changing the pi_state
2312          * because we can fault here. Imagine swapped out pages or a fork
2313          * that marked all the anonymous memory readonly for cow.
2314          *
2315          * Modifying pi_state _before_ the user space value would leave the
2316          * pi_state in an inconsistent state when we fault here, because we
2317          * need to drop the locks to handle the fault. This might be observed
2318          * in the PID check in lookup_pi_state.
2319          */
2320 retry:
2321         if (!argowner) {
2322                 if (oldowner != current) {
2323                         /*
2324                          * We raced against a concurrent self; things are
2325                          * already fixed up. Nothing to do.
2326                          */
2327                         ret = 0;
2328                         goto out_unlock;
2329                 }
2330 
2331                 if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
2332                         /* We got the lock after all, nothing to fix. */
2333                         ret = 0;
2334                         goto out_unlock;
2335                 }
2336 
2337                 /*
2338                  * Since we just failed the trylock; there must be an owner.
2339                  */
2340                 newowner = rt_mutex_owner(&pi_state->pi_mutex);
2341                 BUG_ON(!newowner);
2342         } else {
2343                 WARN_ON_ONCE(argowner != current);
2344                 if (oldowner == current) {
2345                         /*
2346                          * We raced against a concurrent self; things are
2347                          * already fixed up. Nothing to do.
2348                          */
2349                         ret = 0;
2350                         goto out_unlock;
2351                 }
2352                 newowner = argowner;
2353         }
2354 
2355         newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
2356         /* Owner died? */
2357         if (!pi_state->owner)
2358                 newtid |= FUTEX_OWNER_DIED;
2359 
2360         if (get_futex_value_locked(&uval, uaddr))
2361                 goto handle_fault;
2362 
2363         for (;;) {
2364                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
2365 
2366                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
2367                         goto handle_fault;
2368                 if (curval == uval)
2369                         break;
2370                 uval = curval;
2371         }
2372 
2373         /*
2374          * We fixed up user space. Now we need to fix the pi_state
2375          * itself.
2376          */
2377         if (pi_state->owner != NULL) {
2378                 raw_spin_lock(&pi_state->owner->pi_lock);
2379                 WARN_ON(list_empty(&pi_state->list));
2380                 list_del_init(&pi_state->list);
2381                 raw_spin_unlock(&pi_state->owner->pi_lock);
2382         }
2383 
2384         pi_state->owner = newowner;
2385 
2386         raw_spin_lock(&newowner->pi_lock);
2387         WARN_ON(!list_empty(&pi_state->list));
2388         list_add(&pi_state->list, &newowner->pi_state_list);
2389         raw_spin_unlock(&newowner->pi_lock);
2390         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2391 
2392         return 0;
2393 
2394         /*
2395          * To handle the page fault we need to drop the locks here. That gives
2396          * the other task (either the highest priority waiter itself or the
2397          * task which stole the rtmutex) the chance to try the fixup of the
2398          * pi_state. So once we are back from handling the fault we need to
2399          * check the pi_state after reacquiring the locks and before trying to
2400          * do another fixup. When the fixup has been done already we simply
2401          * return.
2402          *
2403          * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
2404          * drop hb->lock since the caller owns the hb -> futex_q relation.
2405          * Dropping the pi_mutex->wait_lock requires the state revalidate.
2406          */
2407 handle_fault:
2408         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2409         spin_unlock(q->lock_ptr);
2410 
2411         ret = fault_in_user_writeable(uaddr);
2412 
2413         spin_lock(q->lock_ptr);
2414         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2415 
2416         /*
2417          * Check if someone else fixed it for us:
2418          */
2419         if (pi_state->owner != oldowner) {
2420                 ret = 0;
2421                 goto out_unlock;
2422         }
2423 
2424         if (ret)
2425                 goto out_unlock;
2426 
2427         goto retry;
2428 
2429 out_unlock:
2430         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
2431         return ret;
2432 }
2433 
2434 static long futex_wait_restart(struct restart_block *restart);
2435 
2436 /**
2437  * fixup_owner() - Post lock pi_state and corner case management
2438  * @uaddr:      user address of the futex
2439  * @q:          futex_q (contains pi_state and access to the rt_mutex)
2440  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
2441  *
2442  * After attempting to lock an rt_mutex, this function is called to cleanup
2443  * the pi_state owner as well as handle race conditions that may allow us to
2444  * acquire the lock. Must be called with the hb lock held.
2445  *
2446  * Return:
2447  *  -  1 - success, lock taken;
2448  *  -  0 - success, lock not taken;
2449  *  - <0 - on error (-EFAULT)
2450  */
2451 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
2452 {
2453         int ret = 0;
2454 
2455         if (locked) {
2456                 /*
2457                  * Got the lock. We might not be the anticipated owner if we
2458                  * did a lock-steal - fix up the PI-state in that case:
2459                  *
2460                  * Speculative pi_state->owner read (we don't hold wait_lock);
2461                  * since we own the lock pi_state->owner == current is the
2462                  * stable state, anything else needs more attention.
2463                  */
2464                 if (q->pi_state->owner != current)
2465                         ret = fixup_pi_state_owner(uaddr, q, current);
2466                 goto out;
2467         }
2468 
2469         /*
2470          * If we didn't get the lock; check if anybody stole it from us. In
2471          * that case, we need to fix up the uval to point to them instead of
2472          * us, otherwise bad things happen. [10]
2473          *
2474          * Another speculative read; pi_state->owner == current is unstable
2475          * but needs our attention.
2476          */
2477         if (q->pi_state->owner == current) {
2478                 ret = fixup_pi_state_owner(uaddr, q, NULL);
2479                 goto out;
2480         }
2481 
2482         /*
2483          * Paranoia check. If we did not take the lock, then we should not be
2484          * the owner of the rt_mutex.
2485          */
2486         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) {
2487                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
2488                                 "pi-state %p\n", ret,
2489                                 q->pi_state->pi_mutex.owner,
2490                                 q->pi_state->owner);
2491         }
2492 
2493 out:
2494         return ret ? ret : locked;
2495 }
2496 
2497 /**
2498  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
2499  * @hb:         the futex hash bucket, must be locked by the caller
2500  * @q:          the futex_q to queue up on
2501  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
2502  */
2503 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
2504                                 struct hrtimer_sleeper *timeout)
2505 {
2506         /*
2507          * The task state is guaranteed to be set before another task can
2508          * wake it. set_current_state() is implemented using smp_store_mb() and
2509          * queue_me() calls spin_unlock() upon completion, both serializing
2510          * access to the hash list and forcing another memory barrier.
2511          */
2512         set_current_state(TASK_INTERRUPTIBLE);
2513         queue_me(q, hb);
2514 
2515         /* Arm the timer */
2516         if (timeout)
2517                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
2518 
2519         /*
2520          * If we have been removed from the hash list, then another task
2521          * has tried to wake us, and we can skip the call to schedule().
2522          */
2523         if (likely(!plist_node_empty(&q->list))) {
2524                 /*
2525                  * If the timer has already expired, current will already be
2526                  * flagged for rescheduling. Only call schedule if there
2527                  * is no timeout, or if it has yet to expire.
2528                  */
2529                 if (!timeout || timeout->task)
2530                         freezable_schedule();
2531         }
2532         __set_current_state(TASK_RUNNING);
2533 }
2534 
2535 /**
2536  * futex_wait_setup() - Prepare to wait on a futex
2537  * @uaddr:      the futex userspace address
2538  * @val:        the expected value
2539  * @flags:      futex flags (FLAGS_SHARED, etc.)
2540  * @q:          the associated futex_q
2541  * @hb:         storage for hash_bucket pointer to be returned to caller
2542  *
2543  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
2544  * compare it with the expected value.  Handle atomic faults internally.
2545  * Return with the hb lock held and a q.key reference on success, and unlocked
2546  * with no q.key reference on failure.
2547  *
2548  * Return:
2549  *  -  0 - uaddr contains val and hb has been locked;
2550  *  - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
2551  */
2552 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
2553                            struct futex_q *q, struct futex_hash_bucket **hb)
2554 {
2555         u32 uval;
2556         int ret;
2557 
2558         /*
2559          * Access the page AFTER the hash-bucket is locked.
2560          * Order is important:
2561          *
2562          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
2563          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
2564          *
2565          * The basic logical guarantee of a futex is that it blocks ONLY
2566          * if cond(var) is known to be true at the time of blocking, for
2567          * any cond.  If we locked the hash-bucket after testing *uaddr, that
2568          * would open a race condition where we could block indefinitely with
2569          * cond(var) false, which would violate the guarantee.
2570          *
2571          * On the other hand, we insert q and release the hash-bucket only
2572          * after testing *uaddr.  This guarantees that futex_wait() will NOT
2573          * absorb a wakeup if *uaddr does not match the desired values
2574          * while the syscall executes.
2575          */
2576 retry:
2577         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
2578         if (unlikely(ret != 0))
2579                 return ret;
2580 
2581 retry_private:
2582         *hb = queue_lock(q);
2583 
2584         ret = get_futex_value_locked(&uval, uaddr);
2585 
2586         if (ret) {
2587                 queue_unlock(*hb);
2588 
2589                 ret = get_user(uval, uaddr);
2590                 if (ret)
2591                         goto out;
2592 
2593                 if (!(flags & FLAGS_SHARED))
2594                         goto retry_private;
2595 
2596                 put_futex_key(&q->key);
2597                 goto retry;
2598         }
2599 
2600         if (uval != val) {
2601                 queue_unlock(*hb);
2602                 ret = -EWOULDBLOCK;
2603         }
2604 
2605 out:
2606         if (ret)
2607                 put_futex_key(&q->key);
2608         return ret;
2609 }
2610 
2611 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
2612                       ktime_t *abs_time, u32 bitset)
2613 {
2614         struct hrtimer_sleeper timeout, *to = NULL;
2615         struct restart_block *restart;
2616         struct futex_hash_bucket *hb;
2617         struct futex_q q = futex_q_init;
2618         int ret;
2619 
2620         if (!bitset)
2621                 return -EINVAL;
2622         q.bitset = bitset;
2623 
2624         if (abs_time) {
2625                 to = &timeout;
2626 
2627                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
2628                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
2629                                       HRTIMER_MODE_ABS);
2630                 hrtimer_init_sleeper(to, current);
2631                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
2632                                              current->timer_slack_ns);
2633         }
2634 
2635 retry:
2636         /*
2637          * Prepare to wait on uaddr. On success, holds hb lock and increments
2638          * q.key refs.
2639          */
2640         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
2641         if (ret)
2642                 goto out;
2643 
2644         /* queue_me and wait for wakeup, timeout, or a signal. */
2645         futex_wait_queue_me(hb, &q, to);
2646 
2647         /* If we were woken (and unqueued), we succeeded, whatever. */
2648         ret = 0;
2649         /* unqueue_me() drops q.key ref */
2650         if (!unqueue_me(&q))
2651                 goto out;
2652         ret = -ETIMEDOUT;
2653         if (to && !to->task)
2654                 goto out;
2655 
2656         /*
2657          * We expect signal_pending(current), but we might be the
2658          * victim of a spurious wakeup as well.
2659          */
2660         if (!signal_pending(current))
2661                 goto retry;
2662 
2663         ret = -ERESTARTSYS;
2664         if (!abs_time)
2665                 goto out;
2666 
2667         restart = &current->restart_block;
2668         restart->fn = futex_wait_restart;
2669         restart->futex.uaddr = uaddr;
2670         restart->futex.val = val;
2671         restart->futex.time = *abs_time;
2672         restart->futex.bitset = bitset;
2673         restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
2674 
2675         ret = -ERESTART_RESTARTBLOCK;
2676 
2677 out:
2678         if (to) {
2679                 hrtimer_cancel(&to->timer);
2680                 destroy_hrtimer_on_stack(&to->timer);
2681         }
2682         return ret;
2683 }
2684 
2685 
2686 static long futex_wait_restart(struct restart_block *restart)
2687 {
2688         u32 __user *uaddr = restart->futex.uaddr;
2689         ktime_t t, *tp = NULL;
2690 
2691         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
2692                 t = restart->futex.time;
2693                 tp = &t;
2694         }
2695         restart->fn = do_no_restart_syscall;
2696 
2697         return (long)futex_wait(uaddr, restart->futex.flags,
2698                                 restart->futex.val, tp, restart->futex.bitset);
2699 }
2700 
2701 
2702 /*
2703  * Userspace tried a 0 -> TID atomic transition of the futex value
2704  * and failed. The kernel side here does the whole locking operation:
2705  * if there are waiters then it will block as a consequence of relying
2706  * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
2707  * a 0 value of the futex too.).
2708  *
2709  * Also serves as futex trylock_pi()'ing, and due semantics.
2710  */
2711 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
2712                          ktime_t *time, int trylock)
2713 {
2714         struct hrtimer_sleeper timeout, *to = NULL;
2715         struct futex_pi_state *pi_state = NULL;
2716         struct rt_mutex_waiter rt_waiter;
2717         struct futex_hash_bucket *hb;
2718         struct futex_q q = futex_q_init;
2719         int res, ret;
2720 
2721         if (!IS_ENABLED(CONFIG_FUTEX_PI))
2722                 return -ENOSYS;
2723 
2724         if (refill_pi_state_cache())
2725                 return -ENOMEM;
2726 
2727         if (time) {
2728                 to = &timeout;
2729                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
2730                                       HRTIMER_MODE_ABS);
2731                 hrtimer_init_sleeper(to, current);
2732                 hrtimer_set_expires(&to->timer, *time);
2733         }
2734 
2735 retry:
2736         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
2737         if (unlikely(ret != 0))
2738                 goto out;
2739 
2740 retry_private:
2741         hb = queue_lock(&q);
2742 
2743         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
2744         if (unlikely(ret)) {
2745                 /*
2746                  * Atomic work succeeded and we got the lock,
2747                  * or failed. Either way, we do _not_ block.
2748                  */
2749                 switch (ret) {
2750                 case 1:
2751                         /* We got the lock. */
2752                         ret = 0;
2753                         goto out_unlock_put_key;
2754                 case -EFAULT:
2755                         goto uaddr_faulted;
2756                 case -EAGAIN:
2757                         /*
2758                          * Two reasons for this:
2759                          * - Task is exiting and we just wait for the
2760                          *   exit to complete.
2761                          * - The user space value changed.
2762                          */
2763                         queue_unlock(hb);
2764                         put_futex_key(&q.key);
2765                         cond_resched();
2766                         goto retry;
2767                 default:
2768                         goto out_unlock_put_key;
2769                 }
2770         }
2771 
2772         WARN_ON(!q.pi_state);
2773 
2774         /*
2775          * Only actually queue now that the atomic ops are done:
2776          */
2777         __queue_me(&q, hb);
2778 
2779         if (trylock) {
2780                 ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
2781                 /* Fixup the trylock return value: */
2782                 ret = ret ? 0 : -EWOULDBLOCK;
2783                 goto no_block;
2784         }
2785 
2786         rt_mutex_init_waiter(&rt_waiter);
2787 
2788         /*
2789          * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
2790          * hold it while doing rt_mutex_start_proxy(), because then it will
2791          * include hb->lock in the blocking chain, even through we'll not in
2792          * fact hold it while blocking. This will lead it to report -EDEADLK
2793          * and BUG when futex_unlock_pi() interleaves with this.
2794          *
2795          * Therefore acquire wait_lock while holding hb->lock, but drop the
2796          * latter before calling rt_mutex_start_proxy_lock(). This still fully
2797          * serializes against futex_unlock_pi() as that does the exact same
2798          * lock handoff sequence.
2799          */
2800         raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
2801         spin_unlock(q.lock_ptr);
2802         ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
2803         raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
2804 
2805         if (ret) {
2806                 if (ret == 1)
2807                         ret = 0;
2808 
2809                 spin_lock(q.lock_ptr);
2810                 goto no_block;
2811         }
2812 
2813 
2814         if (unlikely(to))
2815                 hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
2816 
2817         ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
2818 
2819         spin_lock(q.lock_ptr);
2820         /*
2821          * If we failed to acquire the lock (signal/timeout), we must
2822          * first acquire the hb->lock before removing the lock from the
2823          * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
2824          * wait lists consistent.
2825          *
2826          * In particular; it is important that futex_unlock_pi() can not
2827          * observe this inconsistency.
2828          */
2829         if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
2830                 ret = 0;
2831 
2832 no_block:
2833         /*
2834          * Fixup the pi_state owner and possibly acquire the lock if we
2835          * haven't already.
2836          */
2837         res = fixup_owner(uaddr, &q, !ret);
2838         /*
2839          * If fixup_owner() returned an error, proprogate that.  If it acquired
2840          * the lock, clear our -ETIMEDOUT or -EINTR.
2841          */
2842         if (res)
2843                 ret = (res < 0) ? res : 0;
2844 
2845         /*
2846          * If fixup_owner() faulted and was unable to handle the fault, unlock
2847          * it and return the fault to userspace.
2848          */
2849         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
2850                 pi_state = q.pi_state;
2851                 get_pi_state(pi_state);
2852         }
2853 
2854         /* Unqueue and drop the lock */
2855         unqueue_me_pi(&q);
2856 
2857         if (pi_state) {
2858                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
2859                 put_pi_state(pi_state);
2860         }
2861 
2862         goto out_put_key;
2863 
2864 out_unlock_put_key:
2865         queue_unlock(hb);
2866 
2867 out_put_key:
2868         put_futex_key(&q.key);
2869 out:
2870         if (to) {
2871                 hrtimer_cancel(&to->timer);
2872                 destroy_hrtimer_on_stack(&to->timer);
2873         }
2874         return ret != -EINTR ? ret : -ERESTARTNOINTR;
2875 
2876 uaddr_faulted:
2877         queue_unlock(hb);
2878 
2879         ret = fault_in_user_writeable(uaddr);
2880         if (ret)
2881                 goto out_put_key;
2882 
2883         if (!(flags & FLAGS_SHARED))
2884                 goto retry_private;
2885 
2886         put_futex_key(&q.key);
2887         goto retry;
2888 }
2889 
2890 /*
2891  * Userspace attempted a TID -> 0 atomic transition, and failed.
2892  * This is the in-kernel slowpath: we look up the PI state (if any),
2893  * and do the rt-mutex unlock.
2894  */
2895 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
2896 {
2897         u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
2898         union futex_key key = FUTEX_KEY_INIT;
2899         struct futex_hash_bucket *hb;
2900         struct futex_q *top_waiter;
2901         int ret;
2902 
2903         if (!IS_ENABLED(CONFIG_FUTEX_PI))
2904                 return -ENOSYS;
2905 
2906 retry:
2907         if (get_user(uval, uaddr))
2908                 return -EFAULT;
2909         /*
2910          * We release only a lock we actually own:
2911          */
2912         if ((uval & FUTEX_TID_MASK) != vpid)
2913                 return -EPERM;
2914 
2915         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
2916         if (ret)
2917                 return ret;
2918 
2919         hb = hash_futex(&key);
2920         spin_lock(&hb->lock);
2921 
2922         /*
2923          * Check waiters first. We do not trust user space values at
2924          * all and we at least want to know if user space fiddled
2925          * with the futex value instead of blindly unlocking.
2926          */
2927         top_waiter = futex_top_waiter(hb, &key);
2928         if (top_waiter) {
2929                 struct futex_pi_state *pi_state = top_waiter->pi_state;
2930 
2931                 ret = -EINVAL;
2932                 if (!pi_state)
2933                         goto out_unlock;
2934 
2935                 /*
2936                  * If current does not own the pi_state then the futex is
2937                  * inconsistent and user space fiddled with the futex value.
2938                  */
2939                 if (pi_state->owner != current)
2940                         goto out_unlock;
2941 
2942                 get_pi_state(pi_state);
2943                 /*
2944                  * By taking wait_lock while still holding hb->lock, we ensure
2945                  * there is no point where we hold neither; and therefore
2946                  * wake_futex_pi() must observe a state consistent with what we
2947                  * observed.
2948                  */
2949                 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
2950                 spin_unlock(&hb->lock);
2951 
2952                 /* drops pi_state->pi_mutex.wait_lock */
2953                 ret = wake_futex_pi(uaddr, uval, pi_state);
2954 
2955                 put_pi_state(pi_state);
2956 
2957                 /*
2958                  * Success, we're done! No tricky corner cases.
2959                  */
2960                 if (!ret)
2961                         goto out_putkey;
2962                 /*
2963                  * The atomic access to the futex value generated a
2964                  * pagefault, so retry the user-access and the wakeup:
2965                  */
2966                 if (ret == -EFAULT)
2967                         goto pi_faulted;
2968                 /*
2969                  * A unconditional UNLOCK_PI op raced against a waiter
2970                  * setting the FUTEX_WAITERS bit. Try again.
2971                  */
2972                 if (ret == -EAGAIN) {
2973                         put_futex_key(&key);
2974                         goto retry;
2975                 }
2976                 /*
2977                  * wake_futex_pi has detected invalid state. Tell user
2978                  * space.
2979                  */
2980                 goto out_putkey;
2981         }
2982 
2983         /*
2984          * We have no kernel internal state, i.e. no waiters in the
2985          * kernel. Waiters which are about to queue themselves are stuck
2986          * on hb->lock. So we can safely ignore them. We do neither
2987          * preserve the WAITERS bit not the OWNER_DIED one. We are the
2988          * owner.
2989          */
2990         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
2991                 spin_unlock(&hb->lock);
2992                 goto pi_faulted;
2993         }
2994 
2995         /*
2996          * If uval has changed, let user space handle it.
2997          */
2998         ret = (curval == uval) ? 0 : -EAGAIN;
2999 
3000 out_unlock:
3001         spin_unlock(&hb->lock);
3002 out_putkey:
3003         put_futex_key(&key);
3004         return ret;
3005 
3006 pi_faulted:
3007         put_futex_key(&key);
3008 
3009         ret = fault_in_user_writeable(uaddr);
3010         if (!ret)
3011                 goto retry;
3012 
3013         return ret;
3014 }
3015 
3016 /**
3017  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
3018  * @hb:         the hash_bucket futex_q was original enqueued on
3019  * @q:          the futex_q woken while waiting to be requeued
3020  * @key2:       the futex_key of the requeue target futex
3021  * @timeout:    the timeout associated with the wait (NULL if none)
3022  *
3023  * Detect if the task was woken on the initial futex as opposed to the requeue
3024  * target futex.  If so, determine if it was a timeout or a signal that caused
3025  * the wakeup and return the appropriate error code to the caller.  Must be
3026  * called with the hb lock held.
3027  *
3028  * Return:
3029  *  -  0 = no early wakeup detected;
3030  *  - <0 = -ETIMEDOUT or -ERESTARTNOINTR
3031  */
3032 static inline
3033 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
3034                                    struct futex_q *q, union futex_key *key2,
3035                                    struct hrtimer_sleeper *timeout)
3036 {
3037         int ret = 0;
3038 
3039         /*
3040          * With the hb lock held, we avoid races while we process the wakeup.
3041          * We only need to hold hb (and not hb2) to ensure atomicity as the
3042          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
3043          * It can't be requeued from uaddr2 to something else since we don't
3044          * support a PI aware source futex for requeue.
3045          */
3046         if (!match_futex(&q->key, key2)) {
3047                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
3048                 /*
3049                  * We were woken prior to requeue by a timeout or a signal.
3050                  * Unqueue the futex_q and determine which it was.
3051                  */
3052                 plist_del(&q->list, &hb->chain);
3053                 hb_waiters_dec(hb);
3054 
3055                 /* Handle spurious wakeups gracefully */
3056                 ret = -EWOULDBLOCK;
3057                 if (timeout && !timeout->task)
3058                         ret = -ETIMEDOUT;
3059                 else if (signal_pending(current))
3060                         ret = -ERESTARTNOINTR;
3061         }
3062         return ret;
3063 }
3064 
3065 /**
3066  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
3067  * @uaddr:      the futex we initially wait on (non-pi)
3068  * @flags:      futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
3069  *              the same type, no requeueing from private to shared, etc.
3070  * @val:        the expected value of uaddr
3071  * @abs_time:   absolute timeout
3072  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
3073  * @uaddr2:     the pi futex we will take prior to returning to user-space
3074  *
3075  * The caller will wait on uaddr and will be requeued by futex_requeue() to
3076  * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
3077  * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
3078  * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
3079  * without one, the pi logic would not know which task to boost/deboost, if
3080  * there was a need to.
3081  *
3082  * We call schedule in futex_wait_queue_me() when we enqueue and return there
3083  * via the following--
3084  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
3085  * 2) wakeup on uaddr2 after a requeue
3086  * 3) signal
3087  * 4) timeout
3088  *
3089  * If 3, cleanup and return -ERESTARTNOINTR.
3090  *
3091  * If 2, we may then block on trying to take the rt_mutex and return via:
3092  * 5) successful lock
3093  * 6) signal
3094  * 7) timeout
3095  * 8) other lock acquisition failure
3096  *
3097  * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
3098  *
3099  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
3100  *
3101  * Return:
3102  *  -  0 - On success;
3103  *  - <0 - On error
3104  */
3105 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
3106                                  u32 val, ktime_t *abs_time, u32 bitset,
3107                                  u32 __user *uaddr2)
3108 {
3109         struct hrtimer_sleeper timeout, *to = NULL;
3110         struct futex_pi_state *pi_state = NULL;
3111         struct rt_mutex_waiter rt_waiter;
3112         struct futex_hash_bucket *hb;
3113         union futex_key key2 = FUTEX_KEY_INIT;
3114         struct futex_q q = futex_q_init;
3115         int res, ret;
3116 
3117         if (!IS_ENABLED(CONFIG_FUTEX_PI))
3118                 return -ENOSYS;
3119 
3120         if (uaddr == uaddr2)
3121                 return -EINVAL;
3122 
3123         if (!bitset)
3124                 return -EINVAL;
3125 
3126         if (abs_time) {
3127                 to = &timeout;
3128                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
3129                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
3130                                       HRTIMER_MODE_ABS);
3131                 hrtimer_init_sleeper(to, current);
3132                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
3133                                              current->timer_slack_ns);
3134         }
3135 
3136         /*
3137          * The waiter is allocated on our stack, manipulated by the requeue
3138          * code while we sleep on uaddr.
3139          */
3140         rt_mutex_init_waiter(&rt_waiter);
3141 
3142         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
3143         if (unlikely(ret != 0))
3144                 goto out;
3145 
3146         q.bitset = bitset;
3147         q.rt_waiter = &rt_waiter;
3148         q.requeue_pi_key = &key2;
3149 
3150         /*
3151          * Prepare to wait on uaddr. On success, increments q.key (key1) ref
3152          * count.
3153          */
3154         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
3155         if (ret)
3156                 goto out_key2;
3157 
3158         /*
3159          * The check above which compares uaddrs is not sufficient for
3160          * shared futexes. We need to compare the keys:
3161          */
3162         if (match_futex(&q.key, &key2)) {
3163                 queue_unlock(hb);
3164                 ret = -EINVAL;
3165                 goto out_put_keys;
3166         }
3167 
3168         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
3169         futex_wait_queue_me(hb, &q, to);
3170 
3171         spin_lock(&hb->lock);
3172         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
3173         spin_unlock(&hb->lock);
3174         if (ret)
3175                 goto out_put_keys;
3176 
3177         /*
3178          * In order for us to be here, we know our q.key == key2, and since
3179          * we took the hb->lock above, we also know that futex_requeue() has
3180          * completed and we no longer have to concern ourselves with a wakeup
3181          * race with the atomic proxy lock acquisition by the requeue code. The
3182          * futex_requeue dropped our key1 reference and incremented our key2
3183          * reference count.
3184          */
3185 
3186         /* Check if the requeue code acquired the second futex for us. */
3187         if (!q.rt_waiter) {
3188                 /*
3189                  * Got the lock. We might not be the anticipated owner if we
3190                  * did a lock-steal - fix up the PI-state in that case.
3191                  */
3192                 if (q.pi_state && (q.pi_state->owner != current)) {
3193                         spin_lock(q.lock_ptr);
3194                         ret = fixup_pi_state_owner(uaddr2, &q, current);
3195                         if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3196                                 pi_state = q.pi_state;
3197                                 get_pi_state(pi_state);
3198                         }
3199                         /*
3200                          * Drop the reference to the pi state which
3201                          * the requeue_pi() code acquired for us.
3202                          */
3203                         put_pi_state(q.pi_state);
3204                         spin_unlock(q.lock_ptr);
3205                 }
3206         } else {
3207                 struct rt_mutex *pi_mutex;
3208 
3209                 /*
3210                  * We have been woken up by futex_unlock_pi(), a timeout, or a
3211                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
3212                  * the pi_state.
3213                  */
3214                 WARN_ON(!q.pi_state);
3215                 pi_mutex = &q.pi_state->pi_mutex;
3216                 ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
3217 
3218                 spin_lock(q.lock_ptr);
3219                 if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
3220                         ret = 0;
3221 
3222                 debug_rt_mutex_free_waiter(&rt_waiter);
3223                 /*
3224                  * Fixup the pi_state owner and possibly acquire the lock if we
3225                  * haven't already.
3226                  */
3227                 res = fixup_owner(uaddr2, &q, !ret);
3228                 /*
3229                  * If fixup_owner() returned an error, proprogate that.  If it
3230                  * acquired the lock, clear -ETIMEDOUT or -EINTR.
3231                  */
3232                 if (res)
3233                         ret = (res < 0) ? res : 0;
3234 
3235                 /*
3236                  * If fixup_pi_state_owner() faulted and was unable to handle
3237                  * the fault, unlock the rt_mutex and return the fault to
3238                  * userspace.
3239                  */
3240                 if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
3241                         pi_state = q.pi_state;
3242                         get_pi_state(pi_state);
3243                 }
3244 
3245                 /* Unqueue and drop the lock. */
3246                 unqueue_me_pi(&q);
3247         }
3248 
3249         if (pi_state) {
3250                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
3251                 put_pi_state(pi_state);
3252         }
3253 
3254         if (ret == -EINTR) {
3255                 /*
3256                  * We've already been requeued, but cannot restart by calling
3257                  * futex_lock_pi() directly. We could restart this syscall, but
3258                  * it would detect that the user space "val" changed and return
3259                  * -EWOULDBLOCK.  Save the overhead of the restart and return
3260                  * -EWOULDBLOCK directly.
3261                  */
3262                 ret = -EWOULDBLOCK;
3263         }
3264 
3265 out_put_keys:
3266         put_futex_key(&q.key);
3267 out_key2:
3268         put_futex_key(&key2);
3269 
3270 out:
3271         if (to) {
3272                 hrtimer_cancel(&to->timer);
3273                 destroy_hrtimer_on_stack(&to->timer);
3274         }
3275         return ret;
3276 }
3277 
3278 /*
3279  * Support for robust futexes: the kernel cleans up held futexes at
3280  * thread exit time.
3281  *
3282  * Implementation: user-space maintains a per-thread list of locks it
3283  * is holding. Upon do_exit(), the kernel carefully walks this list,
3284  * and marks all locks that are owned by this thread with the
3285  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
3286  * always manipulated with the lock held, so the list is private and
3287  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
3288  * field, to allow the kernel to clean up if the thread dies after
3289  * acquiring the lock, but just before it could have added itself to
3290  * the list. There can only be one such pending lock.
3291  */
3292 
3293 /**
3294  * sys_set_robust_list() - Set the robust-futex list head of a task
3295  * @head:       pointer to the list-head
3296  * @len:        length of the list-head, as userspace expects
3297  */
3298 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
3299                 size_t, len)
3300 {
3301         if (!futex_cmpxchg_enabled)
3302                 return -ENOSYS;
3303         /*
3304          * The kernel knows only one size for now:
3305          */
3306         if (unlikely(len != sizeof(*head)))
3307                 return -EINVAL;
3308 
3309         current->robust_list = head;
3310 
3311         return 0;
3312 }
3313 
3314 /**
3315  * sys_get_robust_list() - Get the robust-futex list head of a task
3316  * @pid:        pid of the process [zero for current task]
3317  * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
3318  * @len_ptr:    pointer to a length field, the kernel fills in the header size
3319  */
3320 SYSCALL_DEFINE3(get_robust_list, int, pid,
3321                 struct robust_list_head __user * __user *, head_ptr,
3322                 size_t __user *, len_ptr)
3323 {
3324         struct robust_list_head __user *head;
3325         unsigned long ret;
3326         struct task_struct *p;
3327 
3328         if (!futex_cmpxchg_enabled)
3329                 return -ENOSYS;
3330 
3331         rcu_read_lock();
3332 
3333         ret = -ESRCH;
3334         if (!pid)
3335                 p = current;
3336         else {
3337                 p = find_task_by_vpid(pid);
3338                 if (!p)
3339                         goto err_unlock;
3340         }
3341 
3342         ret = -EPERM;
3343         if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
3344                 goto err_unlock;
3345 
3346         head = p->robust_list;
3347         rcu_read_unlock();
3348 
3349         if (put_user(sizeof(*head), len_ptr))
3350                 return -EFAULT;
3351         return put_user(head, head_ptr);
3352 
3353 err_unlock:
3354         rcu_read_unlock();
3355 
3356         return ret;
3357 }
3358 
3359 /*
3360  * Process a futex-list entry, check whether it's owned by the
3361  * dying task, and do notification if so:
3362  */
3363 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
3364 {
3365         u32 uval, uninitialized_var(nval), mval;
3366 
3367 retry:
3368         if (get_user(uval, uaddr))
3369                 return -1;
3370 
3371         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
3372                 /*
3373                  * Ok, this dying thread is truly holding a futex
3374                  * of interest. Set the OWNER_DIED bit atomically
3375                  * via cmpxchg, and if the value had FUTEX_WAITERS
3376                  * set, wake up a waiter (if any). (We have to do a
3377                  * futex_wake() even if OWNER_DIED is already set -
3378                  * to handle the rare but possible case of recursive
3379                  * thread-death.) The rest of the cleanup is done in
3380                  * userspace.
3381                  */
3382                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
3383                 /*
3384                  * We are not holding a lock here, but we want to have
3385                  * the pagefault_disable/enable() protection because
3386                  * we want to handle the fault gracefully. If the
3387                  * access fails we try to fault in the futex with R/W
3388                  * verification via get_user_pages. get_user() above
3389                  * does not guarantee R/W access. If that fails we
3390                  * give up and leave the futex locked.
3391                  */
3392                 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
3393                         if (fault_in_user_writeable(uaddr))
3394                                 return -1;
3395                         goto retry;
3396                 }
3397                 if (nval != uval)
3398                         goto retry;
3399 
3400                 /*
3401                  * Wake robust non-PI futexes here. The wakeup of
3402                  * PI futexes happens in exit_pi_state():
3403                  */
3404                 if (!pi && (uval & FUTEX_WAITERS))
3405                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
3406         }
3407         return 0;
3408 }
3409 
3410 /*
3411  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
3412  */
3413 static inline int fetch_robust_entry(struct robust_list __user **entry,
3414                                      struct robust_list __user * __user *head,
3415                                      unsigned int *pi)
3416 {
3417         unsigned long uentry;
3418 
3419         if (get_user(uentry, (unsigned long __user *)head))
3420                 return -EFAULT;
3421 
3422         *entry = (void __user *)(uentry & ~1UL);
3423         *pi = uentry & 1;
3424 
3425         return 0;
3426 }
3427 
3428 /*
3429  * Walk curr->robust_list (very carefully, it's a userspace list!)
3430  * and mark any locks found there dead, and notify any waiters.
3431  *
3432  * We silently return on any sign of list-walking problem.
3433  */
3434 void exit_robust_list(struct task_struct *curr)
3435 {
3436         struct robust_list_head __user *head = curr->robust_list;
3437         struct robust_list __user *entry, *next_entry, *pending;
3438         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
3439         unsigned int uninitialized_var(next_pi);
3440         unsigned long futex_offset;
3441         int rc;
3442 
3443         if (!futex_cmpxchg_enabled)
3444                 return;
3445 
3446         /*
3447          * Fetch the list head (which was registered earlier, via
3448          * sys_set_robust_list()):
3449          */
3450         if (fetch_robust_entry(&entry, &head->list.next, &pi))
3451                 return;
3452         /*
3453          * Fetch the relative futex offset:
3454          */
3455         if (get_user(futex_offset, &head->futex_offset))
3456                 return;
3457         /*
3458          * Fetch any possibly pending lock-add first, and handle it
3459          * if it exists:
3460          */
3461         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
3462                 return;
3463 
3464         next_entry = NULL;      /* avoid warning with gcc */
3465         while (entry != &head->list) {
3466                 /*
3467                  * Fetch the next entry in the list before calling
3468                  * handle_futex_death:
3469                  */
3470                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
3471                 /*
3472                  * A pending lock might already be on the list, so
3473                  * don't process it twice:
3474                  */
3475                 if (entry != pending)
3476                         if (handle_futex_death((void __user *)entry + futex_offset,
3477                                                 curr, pi))
3478                                 return;
3479                 if (rc)
3480                         return;
3481                 entry = next_entry;
3482                 pi = next_pi;
3483                 /*
3484                  * Avoid excessively long or circular lists:
3485                  */
3486                 if (!--limit)
3487                         break;
3488 
3489                 cond_resched();
3490         }
3491 
3492         if (pending)
3493                 handle_futex_death((void __user *)pending + futex_offset,
3494                                    curr, pip);
3495 }
3496 
3497 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
3498                 u32 __user *uaddr2, u32 val2, u32 val3)
3499 {
3500         int cmd = op & FUTEX_CMD_MASK;
3501         unsigned int flags = 0;
3502 
3503         if (!(op & FUTEX_PRIVATE_FLAG))
3504                 flags |= FLAGS_SHARED;
3505 
3506         if (op & FUTEX_CLOCK_REALTIME) {
3507                 flags |= FLAGS_CLOCKRT;
3508                 if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
3509                     cmd != FUTEX_WAIT_REQUEUE_PI)
3510                         return -ENOSYS;
3511         }
3512 
3513         switch (cmd) {
3514         case FUTEX_LOCK_PI:
3515         case FUTEX_UNLOCK_PI:
3516         case FUTEX_TRYLOCK_PI:
3517         case FUTEX_WAIT_REQUEUE_PI:
3518         case FUTEX_CMP_REQUEUE_PI:
3519                 if (!futex_cmpxchg_enabled)
3520                         return -ENOSYS;
3521         }
3522 
3523         switch (cmd) {
3524         case FUTEX_WAIT:
3525                 val3 = FUTEX_BITSET_MATCH_ANY;
3526         case FUTEX_WAIT_BITSET:
3527                 return futex_wait(uaddr, flags, val, timeout, val3);
3528         case FUTEX_WAKE:
3529                 val3 = FUTEX_BITSET_MATCH_ANY;
3530         case FUTEX_WAKE_BITSET:
3531                 return futex_wake(uaddr, flags, val, val3);
3532         case FUTEX_REQUEUE:
3533                 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
3534         case FUTEX_CMP_REQUEUE:
3535                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
3536         case FUTEX_WAKE_OP:
3537                 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
3538         case FUTEX_LOCK_PI:
3539                 return futex_lock_pi(uaddr, flags, timeout, 0);
3540         case FUTEX_UNLOCK_PI:
3541                 return futex_unlock_pi(uaddr, flags);
3542         case FUTEX_TRYLOCK_PI:
3543                 return futex_lock_pi(uaddr, flags, NULL, 1);
3544         case FUTEX_WAIT_REQUEUE_PI:
3545                 val3 = FUTEX_BITSET_MATCH_ANY;
3546                 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
3547                                              uaddr2);
3548         case FUTEX_CMP_REQUEUE_PI:
3549                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
3550         }
3551         return -ENOSYS;
3552 }
3553 
3554 
3555 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
3556                 struct timespec __user *, utime, u32 __user *, uaddr2,
3557                 u32, val3)
3558 {
3559         struct timespec ts;
3560         ktime_t t, *tp = NULL;
3561         u32 val2 = 0;
3562         int cmd = op & FUTEX_CMD_MASK;
3563 
3564         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
3565                       cmd == FUTEX_WAIT_BITSET ||
3566                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
3567                 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
3568                         return -EFAULT;
3569                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
3570                         return -EFAULT;
3571                 if (!timespec_valid(&ts))
3572                         return -EINVAL;
3573 
3574                 t = timespec_to_ktime(ts);
3575                 if (cmd == FUTEX_WAIT)
3576                         t = ktime_add_safe(ktime_get(), t);
3577                 tp = &t;
3578         }
3579         /*
3580          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
3581          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
3582          */
3583         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
3584             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
3585                 val2 = (u32) (unsigned long) utime;
3586 
3587         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
3588 }
3589 
3590 static void __init futex_detect_cmpxchg(void)
3591 {
3592 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
3593         u32 curval;
3594 
3595         /*
3596          * This will fail and we want it. Some arch implementations do
3597          * runtime detection of the futex_atomic_cmpxchg_inatomic()
3598          * functionality. We want to know that before we call in any
3599          * of the complex code paths. Also we want to prevent
3600          * registration of robust lists in that case. NULL is
3601          * guaranteed to fault and we get -EFAULT on functional
3602          * implementation, the non-functional ones will return
3603          * -ENOSYS.
3604          */
3605         if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
3606                 futex_cmpxchg_enabled = 1;
3607 #endif
3608 }
3609 
3610 static int __init futex_init(void)
3611 {
3612         unsigned int futex_shift;
3613         unsigned long i;
3614 
3615 #if CONFIG_BASE_SMALL
3616         futex_hashsize = 16;
3617 #else
3618         futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
3619 #endif
3620 
3621         futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
3622                                                futex_hashsize, 0,
3623                                                futex_hashsize < 256 ? HASH_SMALL : 0,
3624                                                &futex_shift, NULL,
3625                                                futex_hashsize, futex_hashsize);
3626         futex_hashsize = 1UL << futex_shift;
3627 
3628         futex_detect_cmpxchg();
3629 
3630         for (i = 0; i < futex_hashsize; i++) {
3631                 atomic_set(&futex_queues[i].waiters, 0);
3632                 plist_head_init(&futex_queues[i].chain);
3633                 spin_lock_init(&futex_queues[i].lock);
3634         }
3635 
3636         return 0;
3637 }
3638 core_initcall(futex_init);
3639 

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