TOMOYO Linux Cross Reference
Linux/kernel/futex.c

   /*
    *  Fast Userspace Mutexes (which I call "Futexes!").
    *  (C) Rusty Russell, IBM 2002
    *
    *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
    *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
    *
    *  Removed page pinning, fix privately mapped COW pages and other cleanups
    *  (C) Copyright 2003, 2004 Jamie Lokier
   *
   *  Robust futex support started by Ingo Molnar
   *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
   *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
   *
   *  PI-futex support started by Ingo Molnar and Thomas Gleixner
   *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   *
   *  PRIVATE futexes by Eric Dumazet
   *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
   *
   *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
   *  Copyright (C) IBM Corporation, 2009
   *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
   *
   *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
   *  enough at me, Linus for the original (flawed) idea, Matthew
   *  Kirkwood for proof-of-concept implementation.
   *
   *  "The futexes are also cursed."
   *  "But they come in a choice of three flavours!"
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation; either version 2 of the License, or
   *  (at your option) any later version.
   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to the Free Software
   *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  #include <linux/slab.h>
  #include <linux/poll.h>
  #include <linux/fs.h>
  #include <linux/file.h>
  #include <linux/jhash.h>
  #include <linux/init.h>
  #include <linux/futex.h>
  #include <linux/mount.h>
  #include <linux/pagemap.h>
  #include <linux/syscalls.h>
  #include <linux/signal.h>
  #include <linux/export.h>
  #include <linux/magic.h>
  #include <linux/pid.h>
  #include <linux/nsproxy.h>
  #include <linux/ptrace.h>
  #include <linux/sched/rt.h>
  #include <linux/sched/wake_q.h>
  #include <linux/sched/mm.h>
  #include <linux/hugetlb.h>
  #include <linux/freezer.h>
  #include <linux/bootmem.h>
  #include <linux/fault-inject.h>
  
  #include <asm/futex.h>
  
  #include "locking/rtmutex_common.h"
  
  /*
   * READ this before attempting to hack on futexes!
   *
   * Basic futex operation and ordering guarantees
   * =============================================
   *
   * The waiter reads the futex value in user space and calls
   * futex_wait(). This function computes the hash bucket and acquires
   * the hash bucket lock. After that it reads the futex user space value
   * again and verifies that the data has not changed. If it has not changed
   * it enqueues itself into the hash bucket, releases the hash bucket lock
   * and schedules.
   *
   * The waker side modifies the user space value of the futex and calls
   * futex_wake(). This function computes the hash bucket and acquires the
   * hash bucket lock. Then it looks for waiters on that futex in the hash
   * bucket and wakes them.
   *
   * In futex wake up scenarios where no tasks are blocked on a futex, taking
   * the hb spinlock can be avoided and simply return. In order for this
   * optimization to work, ordering guarantees must exist so that the waiter
   * being added to the list is acknowledged when the list is concurrently being
   * checked by the waker, avoiding scenarios like the following:
   *
   * CPU 0                               CPU 1
  * val = *futex;
  * sys_futex(WAIT, futex, val);
  *   futex_wait(futex, val);
  *   uval = *futex;
  *                                     *futex = newval;
  *                                     sys_futex(WAKE, futex);
  *                                       futex_wake(futex);
  *                                       if (queue_empty())
  *                                         return;
  *   if (uval == val)
  *      lock(hash_bucket(futex));
  *      queue();
  *     unlock(hash_bucket(futex));
  *     schedule();
  *
  * This would cause the waiter on CPU 0 to wait forever because it
  * missed the transition of the user space value from val to newval
  * and the waker did not find the waiter in the hash bucket queue.
  *
  * The correct serialization ensures that a waiter either observes
  * the changed user space value before blocking or is woken by a
  * concurrent waker:
  *
  * CPU 0                                 CPU 1
  * val = *futex;
  * sys_futex(WAIT, futex, val);
  *   futex_wait(futex, val);
  *
  *   waiters++; (a)
  *   smp_mb(); (A) <-- paired with -.
  *                                  |
  *   lock(hash_bucket(futex));      |
  *                                  |
  *   uval = *futex;                 |
  *                                  |        *futex = newval;
  *                                  |        sys_futex(WAKE, futex);
  *                                  |          futex_wake(futex);
  *                                  |
  *                                  `--------> smp_mb(); (B)
  *   if (uval == val)
  *     queue();
  *     unlock(hash_bucket(futex));
  *     schedule();                         if (waiters)
  *                                           lock(hash_bucket(futex));
  *   else                                    wake_waiters(futex);
  *     waiters--; (b)                        unlock(hash_bucket(futex));
  *
  * Where (A) orders the waiters increment and the futex value read through
  * atomic operations (see hb_waiters_inc) and where (B) orders the write
  * to futex and the waiters read -- this is done by the barriers for both
  * shared and private futexes in get_futex_key_refs().
  *
  * This yields the following case (where X:=waiters, Y:=futex):
  *
  *      X = Y = 0
  *
  *      w[X]=1          w[Y]=1
  *      MB              MB
  *      r[Y]=y          r[X]=x
  *
  * Which guarantees that x==0 && y==0 is impossible; which translates back into
  * the guarantee that we cannot both miss the futex variable change and the
  * enqueue.
  *
  * Note that a new waiter is accounted for in (a) even when it is possible that
  * the wait call can return error, in which case we backtrack from it in (b).
  * Refer to the comment in queue_lock().
  *
  * Similarly, in order to account for waiters being requeued on another
  * address we always increment the waiters for the destination bucket before
  * acquiring the lock. It then decrements them again  after releasing it -
  * the code that actually moves the futex(es) between hash buckets (requeue_futex)
  * will do the additional required waiter count housekeeping. This is done for
  * double_lock_hb() and double_unlock_hb(), respectively.
  */
 
 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
 int __read_mostly futex_cmpxchg_enabled;
 #endif
 
 /*
  * Futex flags used to encode options to functions and preserve them across
  * restarts.
  */
 #ifdef CONFIG_MMU
 # define FLAGS_SHARED           0x01
 #else
 /*
  * NOMMU does not have per process address space. Let the compiler optimize
  * code away.
  */
 # define FLAGS_SHARED           0x00
 #endif
 #define FLAGS_CLOCKRT           0x02
 #define FLAGS_HAS_TIMEOUT       0x04
 
 /*
  * Priority Inheritance state:
  */
 struct futex_pi_state {
         /*
          * list of 'owned' pi_state instances - these have to be
          * cleaned up in do_exit() if the task exits prematurely:
          */
         struct list_head list;
 
         /*
          * The PI object:
          */
         struct rt_mutex pi_mutex;
 
         struct task_struct *owner;
         atomic_t refcount;
 
         union futex_key key;
 };
 
 /**
  * struct futex_q - The hashed futex queue entry, one per waiting task
  * @list:               priority-sorted list of tasks waiting on this futex
  * @task:               the task waiting on the futex
  * @lock_ptr:           the hash bucket lock
  * @key:                the key the futex is hashed on
  * @pi_state:           optional priority inheritance state
  * @rt_waiter:          rt_waiter storage for use with requeue_pi
  * @requeue_pi_key:     the requeue_pi target futex key
  * @bitset:             bitset for the optional bitmasked wakeup
  *
  * We use this hashed waitqueue, instead of a normal wait_queue_t, so
  * we can wake only the relevant ones (hashed queues may be shared).
  *
  * A futex_q has a woken state, just like tasks have TASK_RUNNING.
  * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
  * The order of wakeup is always to make the first condition true, then
  * the second.
  *
  * PI futexes are typically woken before they are removed from the hash list via
  * the rt_mutex code. See unqueue_me_pi().
  */
 struct futex_q {
         struct plist_node list;
 
         struct task_struct *task;
         spinlock_t *lock_ptr;
         union futex_key key;
         struct futex_pi_state *pi_state;
         struct rt_mutex_waiter *rt_waiter;
         union futex_key *requeue_pi_key;
         u32 bitset;
 };
 
 static const struct futex_q futex_q_init = {
         /* list gets initialized in queue_me()*/
         .key = FUTEX_KEY_INIT,
         .bitset = FUTEX_BITSET_MATCH_ANY
 };
 
 /*
  * Hash buckets are shared by all the futex_keys that hash to the same
  * location.  Each key may have multiple futex_q structures, one for each task
  * waiting on a futex.
  */
 struct futex_hash_bucket {
         atomic_t waiters;
         spinlock_t lock;
         struct plist_head chain;
 } ____cacheline_aligned_in_smp;
 
 /*
  * The base of the bucket array and its size are always used together
  * (after initialization only in hash_futex()), so ensure that they
  * reside in the same cacheline.
  */
 static struct {
         struct futex_hash_bucket *queues;
         unsigned long            hashsize;
 } __futex_data __read_mostly __aligned(2*sizeof(long));
 #define futex_queues   (__futex_data.queues)
 #define futex_hashsize (__futex_data.hashsize)
 
 
 /*
  * Fault injections for futexes.
  */
 #ifdef CONFIG_FAIL_FUTEX
 
 static struct {
         struct fault_attr attr;
 
         bool ignore_private;
 } fail_futex = {
         .attr = FAULT_ATTR_INITIALIZER,
         .ignore_private = false,
 };
 
 static int __init setup_fail_futex(char *str)
 {
         return setup_fault_attr(&fail_futex.attr, str);
 }
 __setup("fail_futex=", setup_fail_futex);
 
 static bool should_fail_futex(bool fshared)
 {
         if (fail_futex.ignore_private && !fshared)
                 return false;
 
         return should_fail(&fail_futex.attr, 1);
 }
 
 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
 
 static int __init fail_futex_debugfs(void)
 {
         umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
         struct dentry *dir;
 
         dir = fault_create_debugfs_attr("fail_futex", NULL,
                                         &fail_futex.attr);
         if (IS_ERR(dir))
                 return PTR_ERR(dir);
 
         if (!debugfs_create_bool("ignore-private", mode, dir,
                                  &fail_futex.ignore_private)) {
                 debugfs_remove_recursive(dir);
                 return -ENOMEM;
         }
 
         return 0;
 }
 
 late_initcall(fail_futex_debugfs);
 
 #endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
 
 #else
 static inline bool should_fail_futex(bool fshared)
 {
         return false;
 }
 #endif /* CONFIG_FAIL_FUTEX */
 
 static inline void futex_get_mm(union futex_key *key)
 {
         mmgrab(key->private.mm);
         /*
          * Ensure futex_get_mm() implies a full barrier such that
          * get_futex_key() implies a full barrier. This is relied upon
          * as smp_mb(); (B), see the ordering comment above.
          */
         smp_mb__after_atomic();
 }
 
 /*
  * Reflects a new waiter being added to the waitqueue.
  */
 static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
 {
 #ifdef CONFIG_SMP
         atomic_inc(&hb->waiters);
         /*
          * Full barrier (A), see the ordering comment above.
          */
         smp_mb__after_atomic();
 #endif
 }
 
 /*
  * Reflects a waiter being removed from the waitqueue by wakeup
  * paths.
  */
 static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
 {
 #ifdef CONFIG_SMP
         atomic_dec(&hb->waiters);
 #endif
 }
 
 static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
 {
 #ifdef CONFIG_SMP
         return atomic_read(&hb->waiters);
 #else
         return 1;
 #endif
 }
 
 /**
  * hash_futex - Return the hash bucket in the global hash
  * @key:        Pointer to the futex key for which the hash is calculated
  *
  * We hash on the keys returned from get_futex_key (see below) and return the
  * corresponding hash bucket in the global hash.
  */
 static struct futex_hash_bucket *hash_futex(union futex_key *key)
 {
         u32 hash = jhash2((u32*)&key->both.word,
                           (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
                           key->both.offset);
         return &futex_queues[hash & (futex_hashsize - 1)];
 }
 
 
 /**
  * match_futex - Check whether two futex keys are equal
  * @key1:       Pointer to key1
  * @key2:       Pointer to key2
  *
  * Return 1 if two futex_keys are equal, 0 otherwise.
  */
 static inline int match_futex(union futex_key *key1, union futex_key *key2)
 {
         return (key1 && key2
                 && key1->both.word == key2->both.word
                 && key1->both.ptr == key2->both.ptr
                 && key1->both.offset == key2->both.offset);
 }
 
 /*
  * Take a reference to the resource addressed by a key.
  * Can be called while holding spinlocks.
  *
  */
 static void get_futex_key_refs(union futex_key *key)
 {
         if (!key->both.ptr)
                 return;
 
         /*
          * On MMU less systems futexes are always "private" as there is no per
          * process address space. We need the smp wmb nevertheless - yes,
          * arch/blackfin has MMU less SMP ...
          */
         if (!IS_ENABLED(CONFIG_MMU)) {
                 smp_mb(); /* explicit smp_mb(); (B) */
                 return;
         }
 
         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
         case FUT_OFF_INODE:
                 ihold(key->shared.inode); /* implies smp_mb(); (B) */
                 break;
         case FUT_OFF_MMSHARED:
                 futex_get_mm(key); /* implies smp_mb(); (B) */
                 break;
         default:
                 /*
                  * Private futexes do not hold reference on an inode or
                  * mm, therefore the only purpose of calling get_futex_key_refs
                  * is because we need the barrier for the lockless waiter check.
                  */
                 smp_mb(); /* explicit smp_mb(); (B) */
         }
 }
 
 /*
  * Drop a reference to the resource addressed by a key.
  * The hash bucket spinlock must not be held. This is
  * a no-op for private futexes, see comment in the get
  * counterpart.
  */
 static void drop_futex_key_refs(union futex_key *key)
 {
         if (!key->both.ptr) {
                 /* If we're here then we tried to put a key we failed to get */
                 WARN_ON_ONCE(1);
                 return;
         }
 
         if (!IS_ENABLED(CONFIG_MMU))
                 return;
 
         switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
         case FUT_OFF_INODE:
                 iput(key->shared.inode);
                 break;
         case FUT_OFF_MMSHARED:
                 mmdrop(key->private.mm);
                 break;
         }
 }
 
 /**
  * get_futex_key() - Get parameters which are the keys for a futex
  * @uaddr:      virtual address of the futex
  * @fshared:    0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
  * @key:        address where result is stored.
  * @rw:         mapping needs to be read/write (values: VERIFY_READ,
  *              VERIFY_WRITE)
  *
  * Return: a negative error code or 0
  *
  * The key words are stored in *key on success.
  *
  * For shared mappings, it's (page->index, file_inode(vma->vm_file),
  * offset_within_page).  For private mappings, it's (uaddr, current->mm).
  * We can usually work out the index without swapping in the page.
  *
  * lock_page() might sleep, the caller should not hold a spinlock.
  */
 static int
 get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
 {
         unsigned long address = (unsigned long)uaddr;
         struct mm_struct *mm = current->mm;
         struct page *page, *tail;
         struct address_space *mapping;
         int err, ro = 0;
 
         /*
          * The futex address must be "naturally" aligned.
          */
         key->both.offset = address % PAGE_SIZE;
         if (unlikely((address % sizeof(u32)) != 0))
                 return -EINVAL;
         address -= key->both.offset;
 
         if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
                 return -EFAULT;
 
         if (unlikely(should_fail_futex(fshared)))
                 return -EFAULT;
 
         /*
          * PROCESS_PRIVATE futexes are fast.
          * As the mm cannot disappear under us and the 'key' only needs
          * virtual address, we dont even have to find the underlying vma.
          * Note : We do have to check 'uaddr' is a valid user address,
          *        but access_ok() should be faster than find_vma()
          */
         if (!fshared) {
                 key->private.mm = mm;
                 key->private.address = address;
                 get_futex_key_refs(key);  /* implies smp_mb(); (B) */
                 return 0;
         }
 
 again:
         /* Ignore any VERIFY_READ mapping (futex common case) */
         if (unlikely(should_fail_futex(fshared)))
                 return -EFAULT;
 
         err = get_user_pages_fast(address, 1, 1, &page);
         /*
          * If write access is not required (eg. FUTEX_WAIT), try
          * and get read-only access.
          */
         if (err == -EFAULT && rw == VERIFY_READ) {
                 err = get_user_pages_fast(address, 1, 0, &page);
                 ro = 1;
         }
         if (err < 0)
                 return err;
         else
                 err = 0;
 
         /*
          * The treatment of mapping from this point on is critical. The page
          * lock protects many things but in this context the page lock
          * stabilizes mapping, prevents inode freeing in the shared
          * file-backed region case and guards against movement to swap cache.
          *
          * Strictly speaking the page lock is not needed in all cases being
          * considered here and page lock forces unnecessarily serialization
          * From this point on, mapping will be re-verified if necessary and
          * page lock will be acquired only if it is unavoidable
          *
          * Mapping checks require the head page for any compound page so the
          * head page and mapping is looked up now. For anonymous pages, it
          * does not matter if the page splits in the future as the key is
          * based on the address. For filesystem-backed pages, the tail is
          * required as the index of the page determines the key. For
          * base pages, there is no tail page and tail == page.
          */
         tail = page;
         page = compound_head(page);
         mapping = READ_ONCE(page->mapping);
 
         /*
          * If page->mapping is NULL, then it cannot be a PageAnon
          * page; but it might be the ZERO_PAGE or in the gate area or
          * in a special mapping (all cases which we are happy to fail);
          * or it may have been a good file page when get_user_pages_fast
          * found it, but truncated or holepunched or subjected to
          * invalidate_complete_page2 before we got the page lock (also
          * cases which we are happy to fail).  And we hold a reference,
          * so refcount care in invalidate_complete_page's remove_mapping
          * prevents drop_caches from setting mapping to NULL beneath us.
          *
          * The case we do have to guard against is when memory pressure made
          * shmem_writepage move it from filecache to swapcache beneath us:
          * an unlikely race, but we do need to retry for page->mapping.
          */
         if (unlikely(!mapping)) {
                 int shmem_swizzled;
 
                 /*
                  * Page lock is required to identify which special case above
                  * applies. If this is really a shmem page then the page lock
                  * will prevent unexpected transitions.
                  */
                 lock_page(page);
                 shmem_swizzled = PageSwapCache(page) || page->mapping;
                 unlock_page(page);
                 put_page(page);
 
                 if (shmem_swizzled)
                         goto again;
 
                 return -EFAULT;
         }
 
         /*
          * Private mappings are handled in a simple way.
          *
          * If the futex key is stored on an anonymous page, then the associated
          * object is the mm which is implicitly pinned by the calling process.
          *
          * NOTE: When userspace waits on a MAP_SHARED mapping, even if
          * it's a read-only handle, it's expected that futexes attach to
          * the object not the particular process.
          */
         if (PageAnon(page)) {
                 /*
                  * A RO anonymous page will never change and thus doesn't make
                  * sense for futex operations.
                  */
                 if (unlikely(should_fail_futex(fshared)) || ro) {
                         err = -EFAULT;
                         goto out;
                 }
 
                 key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
                 key->private.mm = mm;
                 key->private.address = address;
 
                 get_futex_key_refs(key); /* implies smp_mb(); (B) */
 
         } else {
                 struct inode *inode;
 
                 /*
                  * The associated futex object in this case is the inode and
                  * the page->mapping must be traversed. Ordinarily this should
                  * be stabilised under page lock but it's not strictly
                  * necessary in this case as we just want to pin the inode, not
                  * update the radix tree or anything like that.
                  *
                  * The RCU read lock is taken as the inode is finally freed
                  * under RCU. If the mapping still matches expectations then the
                  * mapping->host can be safely accessed as being a valid inode.
                  */
                 rcu_read_lock();
 
                 if (READ_ONCE(page->mapping) != mapping) {
                         rcu_read_unlock();
                         put_page(page);
 
                         goto again;
                 }
 
                 inode = READ_ONCE(mapping->host);
                 if (!inode) {
                         rcu_read_unlock();
                         put_page(page);
 
                         goto again;
                 }
 
                 /*
                  * Take a reference unless it is about to be freed. Previously
                  * this reference was taken by ihold under the page lock
                  * pinning the inode in place so i_lock was unnecessary. The
                  * only way for this check to fail is if the inode was
                  * truncated in parallel which is almost certainly an
                  * application bug. In such a case, just retry.
                  *
                  * We are not calling into get_futex_key_refs() in file-backed
                  * cases, therefore a successful atomic_inc return below will
                  * guarantee that get_futex_key() will still imply smp_mb(); (B).
                  */
                 if (!atomic_inc_not_zero(&inode->i_count)) {
                         rcu_read_unlock();
                         put_page(page);
 
                         goto again;
                 }
 
                 /* Should be impossible but lets be paranoid for now */
                 if (WARN_ON_ONCE(inode->i_mapping != mapping)) {
                         err = -EFAULT;
                         rcu_read_unlock();
                         iput(inode);
 
                         goto out;
                 }
 
                 key->both.offset |= FUT_OFF_INODE; /* inode-based key */
                 key->shared.inode = inode;
                 key->shared.pgoff = basepage_index(tail);
                 rcu_read_unlock();
         }
 
 out:
         put_page(page);
         return err;
 }
 
 static inline void put_futex_key(union futex_key *key)
 {
         drop_futex_key_refs(key);
 }
 
 /**
  * fault_in_user_writeable() - Fault in user address and verify RW access
  * @uaddr:      pointer to faulting user space address
  *
  * Slow path to fixup the fault we just took in the atomic write
  * access to @uaddr.
  *
  * We have no generic implementation of a non-destructive write to the
  * user address. We know that we faulted in the atomic pagefault
  * disabled section so we can as well avoid the #PF overhead by
  * calling get_user_pages() right away.
  */
 static int fault_in_user_writeable(u32 __user *uaddr)
 {
         struct mm_struct *mm = current->mm;
         int ret;
 
         down_read(&mm->mmap_sem);
         ret = fixup_user_fault(current, mm, (unsigned long)uaddr,
                                FAULT_FLAG_WRITE, NULL);
         up_read(&mm->mmap_sem);
 
         return ret < 0 ? ret : 0;
 }
 
 /**
  * futex_top_waiter() - Return the highest priority waiter on a futex
  * @hb:         the hash bucket the futex_q's reside in
  * @key:        the futex key (to distinguish it from other futex futex_q's)
  *
  * Must be called with the hb lock held.
  */
 static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
                                         union futex_key *key)
 {
         struct futex_q *this;
 
         plist_for_each_entry(this, &hb->chain, list) {
                 if (match_futex(&this->key, key))
                         return this;
         }
         return NULL;
 }
 
 static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
                                       u32 uval, u32 newval)
 {
         int ret;
 
         pagefault_disable();
         ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
         pagefault_enable();
 
         return ret;
 }
 
 static int get_futex_value_locked(u32 *dest, u32 __user *from)
 {
         int ret;
 
         pagefault_disable();
         ret = __get_user(*dest, from);
         pagefault_enable();
 
         return ret ? -EFAULT : 0;
 }
 
 
 /*
  * PI code:
  */
 static int refill_pi_state_cache(void)
 {
         struct futex_pi_state *pi_state;
 
         if (likely(current->pi_state_cache))
                 return 0;
 
         pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
 
         if (!pi_state)
                 return -ENOMEM;
 
         INIT_LIST_HEAD(&pi_state->list);
         /* pi_mutex gets initialized later */
         pi_state->owner = NULL;
         atomic_set(&pi_state->refcount, 1);
         pi_state->key = FUTEX_KEY_INIT;
 
         current->pi_state_cache = pi_state;
 
         return 0;
 }
 
 static struct futex_pi_state *alloc_pi_state(void)
 {
         struct futex_pi_state *pi_state = current->pi_state_cache;
 
         WARN_ON(!pi_state);
         current->pi_state_cache = NULL;
 
         return pi_state;
 }
 
 static void get_pi_state(struct futex_pi_state *pi_state)
 {
         WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
 }
 
 /*
  * Drops a reference to the pi_state object and frees or caches it
  * when the last reference is gone.
  *
  * Must be called with the hb lock held.
  */
 static void put_pi_state(struct futex_pi_state *pi_state)
 {
         if (!pi_state)
                 return;
 
         if (!atomic_dec_and_test(&pi_state->refcount))
                 return;
 
         /*
          * If pi_state->owner is NULL, the owner is most probably dying
          * and has cleaned up the pi_state already
          */
         if (pi_state->owner) {
                 raw_spin_lock_irq(&pi_state->owner->pi_lock);
                 list_del_init(&pi_state->list);
                 raw_spin_unlock_irq(&pi_state->owner->pi_lock);
 
                 rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
         }
 
         if (current->pi_state_cache)
                 kfree(pi_state);
         else {
                 /*
                  * pi_state->list is already empty.
                  * clear pi_state->owner.
                  * refcount is at 0 - put it back to 1.
                  */
                 pi_state->owner = NULL;
                 atomic_set(&pi_state->refcount, 1);
                 current->pi_state_cache = pi_state;
         }
 }
 
 /*
  * Look up the task based on what TID userspace gave us.
  * We dont trust it.
  */
 static struct task_struct *futex_find_get_task(pid_t pid)
 {
         struct task_struct *p;
 
         rcu_read_lock();
         p = find_task_by_vpid(pid);
         if (p)
                 get_task_struct(p);
 
         rcu_read_unlock();
 
         return p;
 }
 
 /*
  * This task is holding PI mutexes at exit time => bad.
  * Kernel cleans up PI-state, but userspace is likely hosed.
  * (Robust-futex cleanup is separate and might save the day for userspace.)
  */
 void exit_pi_state_list(struct task_struct *curr)
 {
         struct list_head *next, *head = &curr->pi_state_list;
         struct futex_pi_state *pi_state;
         struct futex_hash_bucket *hb;
         union futex_key key = FUTEX_KEY_INIT;
 
         if (!futex_cmpxchg_enabled)
                 return;
         /*
          * We are a ZOMBIE and nobody can enqueue itself on
          * pi_state_list anymore, but we have to be careful
          * versus waiters unqueueing themselves:
          */
         raw_spin_lock_irq(&curr->pi_lock);
         while (!list_empty(head)) {
 
                 next = head->next;
                 pi_state = list_entry(next, struct futex_pi_state, list);
                 key = pi_state->key;
                 hb = hash_futex(&key);
                 raw_spin_unlock_irq(&curr->pi_lock);
 
                 spin_lock(&hb->lock);
 
                 raw_spin_lock_irq(&curr->pi_lock);
                 /*
                  * We dropped the pi-lock, so re-check whether this
                  * task still owns the PI-state:
                  */
                 if (head->next != next) {
                         spin_unlock(&hb->lock);
                         continue;
                 }
 
                 WARN_ON(pi_state->owner != curr);
                 WARN_ON(list_empty(&pi_state->list));
                 list_del_init(&pi_state->list);
                 pi_state->owner = NULL;
                 raw_spin_unlock_irq(&curr->pi_lock);
 
                 get_pi_state(pi_state);
                 spin_unlock(&hb->lock);
 
                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
                 put_pi_state(pi_state);
 
                 raw_spin_lock_irq(&curr->pi_lock);
         }
         raw_spin_unlock_irq(&curr->pi_lock);
 }
 
 /*
  * We need to check the following states:
  *
  *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
  *
  * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
  * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
  *
  * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
  *
  * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
  * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
  *
  * [6]  Found  | Found    | task      | 0         | 1      | Valid
  *
  * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
  *
  * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
  * [9]  Found  | Found    | task      | 0         | 0      | Invalid
  * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
  *
  * [1]  Indicates that the kernel can acquire the futex atomically. We
  *      came came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
  *
  * [2]  Valid, if TID does not belong to a kernel thread. If no matching
  *      thread is found then it indicates that the owner TID has died.
  *
  * [3]  Invalid. The waiter is queued on a non PI futex
  *
  * [4]  Valid state after exit_robust_list(), which sets the user space
  *      value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
  *
  * [5]  The user space value got manipulated between exit_robust_list()
  *      and exit_pi_state_list()
  *
  * [6]  Valid state after exit_pi_state_list() which sets the new owner in
  *      the pi_state but cannot access the user space value.
  *
  * [7]  pi_state->owner can only be NULL when the OWNER_DIED bit is set.
  *
  * [8]  Owner and user space value match
  *
  * [9]  There is no transient state which sets the user space TID to 0
  *      except exit_robust_list(), but this is indicated by the
  *      FUTEX_OWNER_DIED bit. See [4]
  *
  * [10] There is no transient state which leaves owner and user space
  *      TID out of sync.
  *
  *
  * Serialization and lifetime rules:
  *
  * hb->lock:
  *
  *      hb -> futex_q, relation
  *      futex_q -> pi_state, relation
  *
  *      (cannot be raw because hb can contain arbitrary amount
  *       of futex_q's)
  *
  * pi_mutex->wait_lock:
  *
  *      {uval, pi_state}
  *
  *      (and pi_mutex 'obviously')
  *
  * p->pi_lock:
  *
  *      p->pi_state_list -> pi_state->list, relation
  *
  * pi_state->refcount:
  *
  *      pi_state lifetime
  *
  *
  * Lock order:
  *
  *   hb->lock
  *     pi_mutex->wait_lock
  *       p->pi_lock
  *
  */
 
 /*
  * Validate that the existing waiter has a pi_state and sanity check
  * the pi_state against the user space value. If correct, attach to
  * it.
  */
 static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
                               struct futex_pi_state *pi_state,
                               struct futex_pi_state **ps)
 {
         pid_t pid = uval & FUTEX_TID_MASK;
         u32 uval2;
         int ret;
 
         /*
          * Userspace might have messed up non-PI and PI futexes [3]
          */
         if (unlikely(!pi_state))
                 return -EINVAL;
 
         /*
          * We get here with hb->lock held, and having found a
          * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
          * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
          * which in turn means that futex_lock_pi() still has a reference on
          * our pi_state.
          *
          * The waiter holding a reference on @pi_state also protects against
          * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
          * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
          * free pi_state before we can take a reference ourselves.
          */
         WARN_ON(!atomic_read(&pi_state->refcount));
 
         /*
          * Now that we have a pi_state, we can acquire wait_lock
          * and do the state validation.
          */
         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
 
         /*
          * Since {uval, pi_state} is serialized by wait_lock, and our current
          * uval was read without holding it, it can have changed. Verify it
          * still is what we expect it to be, otherwise retry the entire
          * operation.
          */
         if (get_futex_value_locked(&uval2, uaddr))
                 goto out_efault;
 
         if (uval != uval2)
                 goto out_eagain;
 
         /*
          * Handle the owner died case:
          */
         if (uval & FUTEX_OWNER_DIED) {
                 /*
                  * exit_pi_state_list sets owner to NULL and wakes the
                  * topmost waiter. The task which acquires the
                  * pi_state->rt_mutex will fixup owner.
                  */
                 if (!pi_state->owner) {
                         /*
                          * No pi state owner, but the user space TID
                          * is not 0. Inconsistent state. [5]
                          */
                         if (pid)
                                 goto out_einval;
                         /*
                          * Take a ref on the state and return success. [4]
                          */
                         goto out_attach;
                 }
 
                 /*
                  * If TID is 0, then either the dying owner has not
                  * yet executed exit_pi_state_list() or some waiter
                  * acquired the rtmutex in the pi state, but did not
                  * yet fixup the TID in user space.
                  *
                  * Take a ref on the state and return success. [6]
                  */
                 if (!pid)
                         goto out_attach;
         } else {
                 /*
                  * If the owner died bit is not set, then the pi_state
                  * must have an owner. [7]
                  */
                 if (!pi_state->owner)
                         goto out_einval;
         }
 
         /*
          * Bail out if user space manipulated the futex value. If pi
          * state exists then the owner TID must be the same as the
          * user space TID. [9/10]
          */
         if (pid != task_pid_vnr(pi_state->owner))
                 goto out_einval;
 
 out_attach:
         get_pi_state(pi_state);
         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
         *ps = pi_state;
         return 0;
 
 out_einval:
         ret = -EINVAL;
         goto out_error;
 
 out_eagain:
         ret = -EAGAIN;
         goto out_error;
 
 out_efault:
         ret = -EFAULT;
         goto out_error;
 
 out_error:
         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
         return ret;
 }
 
 /*
  * Lookup the task for the TID provided from user space and attach to
  * it after doing proper sanity checks.
  */
 static int attach_to_pi_owner(u32 uval, union futex_key *key,
                               struct futex_pi_state **ps)
 {
         pid_t pid = uval & FUTEX_TID_MASK;
         struct futex_pi_state *pi_state;
         struct task_struct *p;
 
         /*
          * We are the first waiter - try to look up the real owner and attach
          * the new pi_state to it, but bail out when TID = 0 [1]
          */
         if (!pid)
                 return -ESRCH;
         p = futex_find_get_task(pid);
         if (!p)
                 return -ESRCH;
 
         if (unlikely(p->flags & PF_KTHREAD)) {
                 put_task_struct(p);
                 return -EPERM;
         }
 
         /*
          * We need to look at the task state flags to figure out,
          * whether the task is exiting. To protect against the do_exit
          * change of the task flags, we do this protected by
          * p->pi_lock:
          */
         raw_spin_lock_irq(&p->pi_lock);
         if (unlikely(p->flags & PF_EXITING)) {
                 /*
                  * The task is on the way out. When PF_EXITPIDONE is
                  * set, we know that the task has finished the
                  * cleanup:
                  */
                 int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
 
                 raw_spin_unlock_irq(&p->pi_lock);
                 put_task_struct(p);
                 return ret;
         }
 
         /*
          * No existing pi state. First waiter. [2]
          *
          * This creates pi_state, we have hb->lock held, this means nothing can
          * observe this state, wait_lock is irrelevant.
          */
         pi_state = alloc_pi_state();
 
         /*
          * Initialize the pi_mutex in locked state and make @p
          * the owner of it:
          */
         rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
 
         /* Store the key for possible exit cleanups: */
         pi_state->key = *key;
 
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &p->pi_state_list);
         pi_state->owner = p;
         raw_spin_unlock_irq(&p->pi_lock);
 
         put_task_struct(p);
 
         *ps = pi_state;
 
         return 0;
 }
 
 static int lookup_pi_state(u32 __user *uaddr, u32 uval,
                            struct futex_hash_bucket *hb,
                            union futex_key *key, struct futex_pi_state **ps)
 {
         struct futex_q *top_waiter = futex_top_waiter(hb, key);
 
         /*
          * If there is a waiter on that futex, validate it and
          * attach to the pi_state when the validation succeeds.
          */
         if (top_waiter)
                 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
 
         /*
          * We are the first waiter - try to look up the owner based on
          * @uval and attach to it.
          */
         return attach_to_pi_owner(uval, key, ps);
 }
 
 static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
 {
         u32 uninitialized_var(curval);
 
         if (unlikely(should_fail_futex(true)))
                 return -EFAULT;
 
         if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
                 return -EFAULT;
 
         /* If user space value changed, let the caller retry */
         return curval != uval ? -EAGAIN : 0;
 }
 
 /**
  * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
  * @uaddr:              the pi futex user address
  * @hb:                 the pi futex hash bucket
  * @key:                the futex key associated with uaddr and hb
  * @ps:                 the pi_state pointer where we store the result of the
  *                      lookup
  * @task:               the task to perform the atomic lock work for.  This will
  *                      be "current" except in the case of requeue pi.
  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
  *
  * Return:
  *  0 - ready to wait;
  *  1 - acquired the lock;
  * <0 - error
  *
  * The hb->lock and futex_key refs shall be held by the caller.
  */
 static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
                                 union futex_key *key,
                                 struct futex_pi_state **ps,
                                 struct task_struct *task, int set_waiters)
 {
         u32 uval, newval, vpid = task_pid_vnr(task);
         struct futex_q *top_waiter;
         int ret;
 
         /*
          * Read the user space value first so we can validate a few
          * things before proceeding further.
          */
         if (get_futex_value_locked(&uval, uaddr))
                 return -EFAULT;
 
         if (unlikely(should_fail_futex(true)))
                 return -EFAULT;
 
         /*
          * Detect deadlocks.
          */
         if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
                 return -EDEADLK;
 
         if ((unlikely(should_fail_futex(true))))
                 return -EDEADLK;
 
         /*
          * Lookup existing state first. If it exists, try to attach to
          * its pi_state.
          */
         top_waiter = futex_top_waiter(hb, key);
         if (top_waiter)
                 return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
 
         /*
          * No waiter and user TID is 0. We are here because the
          * waiters or the owner died bit is set or called from
          * requeue_cmp_pi or for whatever reason something took the
          * syscall.
          */
         if (!(uval & FUTEX_TID_MASK)) {
                 /*
                  * We take over the futex. No other waiters and the user space
                  * TID is 0. We preserve the owner died bit.
                  */
                 newval = uval & FUTEX_OWNER_DIED;
                 newval |= vpid;
 
                 /* The futex requeue_pi code can enforce the waiters bit */
                 if (set_waiters)
                         newval |= FUTEX_WAITERS;
 
                 ret = lock_pi_update_atomic(uaddr, uval, newval);
                 /* If the take over worked, return 1 */
                 return ret < 0 ? ret : 1;
         }
 
         /*
          * First waiter. Set the waiters bit before attaching ourself to
          * the owner. If owner tries to unlock, it will be forced into
          * the kernel and blocked on hb->lock.
          */
         newval = uval | FUTEX_WAITERS;
         ret = lock_pi_update_atomic(uaddr, uval, newval);
         if (ret)
                 return ret;
         /*
          * If the update of the user space value succeeded, we try to
          * attach to the owner. If that fails, no harm done, we only
          * set the FUTEX_WAITERS bit in the user space variable.
          */
         return attach_to_pi_owner(uval, key, ps);
 }
 
 /**
  * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
  * @q:  The futex_q to unqueue
  *
  * The q->lock_ptr must not be NULL and must be held by the caller.
  */
 static void __unqueue_futex(struct futex_q *q)
 {
         struct futex_hash_bucket *hb;
 
         if (WARN_ON_SMP(!q->lock_ptr || !spin_is_locked(q->lock_ptr))
             || WARN_ON(plist_node_empty(&q->list)))
                 return;
 
         hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
         plist_del(&q->list, &hb->chain);
         hb_waiters_dec(hb);
 }
 
 /*
  * The hash bucket lock must be held when this is called.
  * Afterwards, the futex_q must not be accessed. Callers
  * must ensure to later call wake_up_q() for the actual
  * wakeups to occur.
  */
 static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
 {
         struct task_struct *p = q->task;
 
         if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
                 return;
 
         /*
          * Queue the task for later wakeup for after we've released
          * the hb->lock. wake_q_add() grabs reference to p.
          */
         wake_q_add(wake_q, p);
         __unqueue_futex(q);
         /*
          * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
          * is written, without taking any locks. This is possible in the event
          * of a spurious wakeup, for example. A memory barrier is required here
          * to prevent the following store to lock_ptr from getting ahead of the
          * plist_del in __unqueue_futex().
          */
         smp_store_release(&q->lock_ptr, NULL);
 }
 
 /*
  * Caller must hold a reference on @pi_state.
  */
 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
 {
         u32 uninitialized_var(curval), newval;
         struct task_struct *new_owner;
         bool postunlock = false;
         DEFINE_WAKE_Q(wake_q);
         int ret = 0;
 
         new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
         if (WARN_ON_ONCE(!new_owner)) {
                 /*
                  * As per the comment in futex_unlock_pi() this should not happen.
                  *
                  * When this happens, give up our locks and try again, giving
                  * the futex_lock_pi() instance time to complete, either by
                  * waiting on the rtmutex or removing itself from the futex
                  * queue.
                  */
                 ret = -EAGAIN;
                 goto out_unlock;
         }
 
         /*
          * We pass it to the next owner. The WAITERS bit is always kept
          * enabled while there is PI state around. We cleanup the owner
          * died bit, because we are the owner.
          */
         newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
 
         if (unlikely(should_fail_futex(true)))
                 ret = -EFAULT;
 
         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)) {
                 ret = -EFAULT;
 
         } else if (curval != uval) {
                 /*
                  * If a unconditional UNLOCK_PI operation (user space did not
                  * try the TID->0 transition) raced with a waiter setting the
                  * FUTEX_WAITERS flag between get_user() and locking the hash
                  * bucket lock, retry the operation.
                  */
                 if ((FUTEX_TID_MASK & curval) == uval)
                         ret = -EAGAIN;
                 else
                         ret = -EINVAL;
         }
 
         if (ret)
                 goto out_unlock;
 
         /*
          * This is a point of no return; once we modify the uval there is no
          * going back and subsequent operations must not fail.
          */
 
         raw_spin_lock(&pi_state->owner->pi_lock);
         WARN_ON(list_empty(&pi_state->list));
         list_del_init(&pi_state->list);
         raw_spin_unlock(&pi_state->owner->pi_lock);
 
         raw_spin_lock(&new_owner->pi_lock);
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &new_owner->pi_state_list);
         pi_state->owner = new_owner;
         raw_spin_unlock(&new_owner->pi_lock);
 
         postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
 
 out_unlock:
         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
 
         if (postunlock)
                 rt_mutex_postunlock(&wake_q);
 
         return ret;
 }
 
 /*
  * Express the locking dependencies for lockdep:
  */
 static inline void
 double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
 {
         if (hb1 <= hb2) {
                 spin_lock(&hb1->lock);
                 if (hb1 < hb2)
                         spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
         } else { /* hb1 > hb2 */
                 spin_lock(&hb2->lock);
                 spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
         }
 }
 
 static inline void
 double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
 {
         spin_unlock(&hb1->lock);
         if (hb1 != hb2)
                 spin_unlock(&hb2->lock);
 }
 
 /*
  * Wake up waiters matching bitset queued on this futex (uaddr).
  */
 static int
 futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
 {
         struct futex_hash_bucket *hb;
         struct futex_q *this, *next;
         union futex_key key = FUTEX_KEY_INIT;
         int ret;
         DEFINE_WAKE_Q(wake_q);
 
         if (!bitset)
                 return -EINVAL;
 
         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out;
 
         hb = hash_futex(&key);
 
         /* Make sure we really have tasks to wakeup */
         if (!hb_waiters_pending(hb))
                 goto out_put_key;
 
         spin_lock(&hb->lock);
 
         plist_for_each_entry_safe(this, next, &hb->chain, list) {
                 if (match_futex (&this->key, &key)) {
                         if (this->pi_state || this->rt_waiter) {
                                 ret = -EINVAL;
                                 break;
                         }
 
                         /* Check if one of the bits is set in both bitsets */
                         if (!(this->bitset & bitset))
                                 continue;
 
                         mark_wake_futex(&wake_q, this);
                         if (++ret >= nr_wake)
                                 break;
                 }
         }
 
         spin_unlock(&hb->lock);
         wake_up_q(&wake_q);
 out_put_key:
         put_futex_key(&key);
 out:
         return ret;
 }
 
 /*
  * Wake up all waiters hashed on the physical page that is mapped
  * to this virtual address:
  */
 static int
 futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
               int nr_wake, int nr_wake2, int op)
 {
         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
         struct futex_hash_bucket *hb1, *hb2;
         struct futex_q *this, *next;
         int ret, op_ret;
         DEFINE_WAKE_Q(wake_q);
 
 retry:
         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out;
         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
         if (unlikely(ret != 0))
                 goto out_put_key1;
 
         hb1 = hash_futex(&key1);
         hb2 = hash_futex(&key2);
 
 retry_private:
         double_lock_hb(hb1, hb2);
         op_ret = futex_atomic_op_inuser(op, uaddr2);
         if (unlikely(op_ret < 0)) {
 
                 double_unlock_hb(hb1, hb2);
 
 #ifndef CONFIG_MMU
                 /*
                  * we don't get EFAULT from MMU faults if we don't have an MMU,
                  * but we might get them from range checking
                  */
                 ret = op_ret;
                 goto out_put_keys;
 #endif
 
                 if (unlikely(op_ret != -EFAULT)) {
                         ret = op_ret;
                         goto out_put_keys;
                 }
 
                 ret = fault_in_user_writeable(uaddr2);
                 if (ret)
                         goto out_put_keys;
 
                 if (!(flags & FLAGS_SHARED))
                         goto retry_private;
 
                 put_futex_key(&key2);
                 put_futex_key(&key1);
                 goto retry;
         }
 
         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
                 if (match_futex (&this->key, &key1)) {
                         if (this->pi_state || this->rt_waiter) {
                                 ret = -EINVAL;
                                 goto out_unlock;
                         }
                         mark_wake_futex(&wake_q, this);
                         if (++ret >= nr_wake)
                                 break;
                 }
         }
 
         if (op_ret > 0) {
                 op_ret = 0;
                 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
                         if (match_futex (&this->key, &key2)) {
                                 if (this->pi_state || this->rt_waiter) {
                                         ret = -EINVAL;
                                         goto out_unlock;
                                 }
                                 mark_wake_futex(&wake_q, this);
                                 if (++op_ret >= nr_wake2)
                                         break;
                         }
                 }
                 ret += op_ret;
         }
 
 out_unlock:
         double_unlock_hb(hb1, hb2);
         wake_up_q(&wake_q);
 out_put_keys:
         put_futex_key(&key2);
 out_put_key1:
         put_futex_key(&key1);
 out:
         return ret;
 }
 
 /**
  * requeue_futex() - Requeue a futex_q from one hb to another
  * @q:          the futex_q to requeue
  * @hb1:        the source hash_bucket
  * @hb2:        the target hash_bucket
  * @key2:       the new key for the requeued futex_q
  */
 static inline
 void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
                    struct futex_hash_bucket *hb2, union futex_key *key2)
 {
 
         /*
          * If key1 and key2 hash to the same bucket, no need to
          * requeue.
          */
         if (likely(&hb1->chain != &hb2->chain)) {
                 plist_del(&q->list, &hb1->chain);
                 hb_waiters_dec(hb1);
                 hb_waiters_inc(hb2);
                 plist_add(&q->list, &hb2->chain);
                 q->lock_ptr = &hb2->lock;
         }
         get_futex_key_refs(key2);
         q->key = *key2;
 }
 
 /**
  * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
  * @q:          the futex_q
  * @key:        the key of the requeue target futex
  * @hb:         the hash_bucket of the requeue target futex
  *
  * During futex_requeue, with requeue_pi=1, it is possible to acquire the
  * target futex if it is uncontended or via a lock steal.  Set the futex_q key
  * to the requeue target futex so the waiter can detect the wakeup on the right
  * futex, but remove it from the hb and NULL the rt_waiter so it can detect
  * atomic lock acquisition.  Set the q->lock_ptr to the requeue target hb->lock
  * to protect access to the pi_state to fixup the owner later.  Must be called
  * with both q->lock_ptr and hb->lock held.
  */
 static inline
 void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
                            struct futex_hash_bucket *hb)
 {
         get_futex_key_refs(key);
         q->key = *key;
 
         __unqueue_futex(q);
 
         WARN_ON(!q->rt_waiter);
         q->rt_waiter = NULL;
 
         q->lock_ptr = &hb->lock;
 
         wake_up_state(q->task, TASK_NORMAL);
 }
 
 /**
  * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
  * @pifutex:            the user address of the to futex
  * @hb1:                the from futex hash bucket, must be locked by the caller
  * @hb2:                the to futex hash bucket, must be locked by the caller
  * @key1:               the from futex key
  * @key2:               the to futex key
  * @ps:                 address to store the pi_state pointer
  * @set_waiters:        force setting the FUTEX_WAITERS bit (1) or not (0)
  *
  * Try and get the lock on behalf of the top waiter if we can do it atomically.
  * Wake the top waiter if we succeed.  If the caller specified set_waiters,
  * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
  * hb1 and hb2 must be held by the caller.
  *
  * Return:
  *  0 - failed to acquire the lock atomically;
  * >0 - acquired the lock, return value is vpid of the top_waiter
  * <0 - error
  */
 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
                                  struct futex_hash_bucket *hb1,
                                  struct futex_hash_bucket *hb2,
                                  union futex_key *key1, union futex_key *key2,
                                  struct futex_pi_state **ps, int set_waiters)
 {
         struct futex_q *top_waiter = NULL;
         u32 curval;
         int ret, vpid;
 
         if (get_futex_value_locked(&curval, pifutex))
                 return -EFAULT;
 
         if (unlikely(should_fail_futex(true)))
                 return -EFAULT;
 
         /*
          * Find the top_waiter and determine if there are additional waiters.
          * If the caller intends to requeue more than 1 waiter to pifutex,
          * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
          * as we have means to handle the possible fault.  If not, don't set
          * the bit unecessarily as it will force the subsequent unlock to enter
          * the kernel.
          */
         top_waiter = futex_top_waiter(hb1, key1);
 
         /* There are no waiters, nothing for us to do. */
         if (!top_waiter)
                 return 0;
 
         /* Ensure we requeue to the expected futex. */
         if (!match_futex(top_waiter->requeue_pi_key, key2))
                 return -EINVAL;
 
         /*
          * Try to take the lock for top_waiter.  Set the FUTEX_WAITERS bit in
          * the contended case or if set_waiters is 1.  The pi_state is returned
          * in ps in contended cases.
          */
         vpid = task_pid_vnr(top_waiter->task);
         ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
                                    set_waiters);
         if (ret == 1) {
                 requeue_pi_wake_futex(top_waiter, key2, hb2);
                 return vpid;
         }
         return ret;
 }
 
 /**
  * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
  * @uaddr1:     source futex user address
  * @flags:      futex flags (FLAGS_SHARED, etc.)
  * @uaddr2:     target futex user address
  * @nr_wake:    number of waiters to wake (must be 1 for requeue_pi)
  * @nr_requeue: number of waiters to requeue (0-INT_MAX)
  * @cmpval:     @uaddr1 expected value (or %NULL)
  * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
  *              pi futex (pi to pi requeue is not supported)
  *
  * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
  * uaddr2 atomically on behalf of the top waiter.
  *
  * Return:
  * >=0 - on success, the number of tasks requeued or woken;
  *  <0 - on error
  */
 static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
                          u32 __user *uaddr2, int nr_wake, int nr_requeue,
                          u32 *cmpval, int requeue_pi)
 {
         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
         int drop_count = 0, task_count = 0, ret;
         struct futex_pi_state *pi_state = NULL;
         struct futex_hash_bucket *hb1, *hb2;
         struct futex_q *this, *next;
         DEFINE_WAKE_Q(wake_q);
 
         if (requeue_pi) {
                 /*
                  * Requeue PI only works on two distinct uaddrs. This
                  * check is only valid for private futexes. See below.
                  */
                 if (uaddr1 == uaddr2)
                         return -EINVAL;
 
                 /*
                  * requeue_pi requires a pi_state, try to allocate it now
                  * without any locks in case it fails.
                  */
                 if (refill_pi_state_cache())
                         return -ENOMEM;
                 /*
                  * requeue_pi must wake as many tasks as it can, up to nr_wake
                  * + nr_requeue, since it acquires the rt_mutex prior to
                  * returning to userspace, so as to not leave the rt_mutex with
                  * waiters and no owner.  However, second and third wake-ups
                  * cannot be predicted as they involve race conditions with the
                  * first wake and a fault while looking up the pi_state.  Both
                  * pthread_cond_signal() and pthread_cond_broadcast() should
                  * use nr_wake=1.
                  */
                 if (nr_wake != 1)
                         return -EINVAL;
         }
 
 retry:
         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out;
         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
                             requeue_pi ? VERIFY_WRITE : VERIFY_READ);
         if (unlikely(ret != 0))
                 goto out_put_key1;
 
         /*
          * The check above which compares uaddrs is not sufficient for
          * shared futexes. We need to compare the keys:
          */
         if (requeue_pi && match_futex(&key1, &key2)) {
                 ret = -EINVAL;
                 goto out_put_keys;
         }
 
         hb1 = hash_futex(&key1);
         hb2 = hash_futex(&key2);
 
 retry_private:
         hb_waiters_inc(hb2);
         double_lock_hb(hb1, hb2);
 
         if (likely(cmpval != NULL)) {
                 u32 curval;
 
                 ret = get_futex_value_locked(&curval, uaddr1);
 
                 if (unlikely(ret)) {
                         double_unlock_hb(hb1, hb2);
                         hb_waiters_dec(hb2);
 
                         ret = get_user(curval, uaddr1);
                         if (ret)
                                 goto out_put_keys;
 
                         if (!(flags & FLAGS_SHARED))
                                 goto retry_private;
 
                         put_futex_key(&key2);
                         put_futex_key(&key1);
                         goto retry;
                 }
                 if (curval != *cmpval) {
                         ret = -EAGAIN;
                         goto out_unlock;
                 }
         }
 
         if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
                 /*
                  * Attempt to acquire uaddr2 and wake the top waiter. If we
                  * intend to requeue waiters, force setting the FUTEX_WAITERS
                  * bit.  We force this here where we are able to easily handle
                  * faults rather in the requeue loop below.
                  */
                 ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
                                                  &key2, &pi_state, nr_requeue);
 
                 /*
                  * At this point the top_waiter has either taken uaddr2 or is
                  * waiting on it.  If the former, then the pi_state will not
                  * exist yet, look it up one more time to ensure we have a
                  * reference to it. If the lock was taken, ret contains the
                  * vpid of the top waiter task.
                  * If the lock was not taken, we have pi_state and an initial
                  * refcount on it. In case of an error we have nothing.
                  */
                 if (ret > 0) {
                         WARN_ON(pi_state);
                         drop_count++;
                         task_count++;
                         /*
                          * If we acquired the lock, then the user space value
                          * of uaddr2 should be vpid. It cannot be changed by
                          * the top waiter as it is blocked on hb2 lock if it
                          * tries to do so. If something fiddled with it behind
                          * our back the pi state lookup might unearth it. So
                          * we rather use the known value than rereading and
                          * handing potential crap to lookup_pi_state.
                          *
                          * If that call succeeds then we have pi_state and an
                          * initial refcount on it.
                          */
                         ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state);
                 }
 
                 switch (ret) {
                 case 0:
                         /* We hold a reference on the pi state. */
                         break;
 
                         /* If the above failed, then pi_state is NULL */
                 case -EFAULT:
                         double_unlock_hb(hb1, hb2);
                         hb_waiters_dec(hb2);
                         put_futex_key(&key2);
                         put_futex_key(&key1);
                         ret = fault_in_user_writeable(uaddr2);
                         if (!ret)
                                 goto retry;
                         goto out;
                 case -EAGAIN:
                         /*
                          * Two reasons for this:
                          * - Owner is exiting and we just wait for the
                          *   exit to complete.
                          * - The user space value changed.
                          */
                         double_unlock_hb(hb1, hb2);
                         hb_waiters_dec(hb2);
                         put_futex_key(&key2);
                         put_futex_key(&key1);
                         cond_resched();
                         goto retry;
                 default:
                         goto out_unlock;
                 }
         }
 
         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
                 if (task_count - nr_wake >= nr_requeue)
                         break;
 
                 if (!match_futex(&this->key, &key1))
                         continue;
 
                 /*
                  * FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
                  * be paired with each other and no other futex ops.
                  *
                  * We should never be requeueing a futex_q with a pi_state,
                  * which is awaiting a futex_unlock_pi().
                  */
                 if ((requeue_pi && !this->rt_waiter) ||
                     (!requeue_pi && this->rt_waiter) ||
                     this->pi_state) {
                         ret = -EINVAL;
                         break;
                 }
 
                 /*
                  * Wake nr_wake waiters.  For requeue_pi, if we acquired the
                  * lock, we already woke the top_waiter.  If not, it will be
                  * woken by futex_unlock_pi().
                  */
                 if (++task_count <= nr_wake && !requeue_pi) {
                         mark_wake_futex(&wake_q, this);
                         continue;
                 }
 
                 /* Ensure we requeue to the expected futex for requeue_pi. */
                 if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
                         ret = -EINVAL;
                         break;
                 }
 
                 /*
                  * Requeue nr_requeue waiters and possibly one more in the case
                  * of requeue_pi if we couldn't acquire the lock atomically.
                  */
                 if (requeue_pi) {
                         /*
                          * Prepare the waiter to take the rt_mutex. Take a
                          * refcount on the pi_state and store the pointer in
                          * the futex_q object of the waiter.
                          */
                         get_pi_state(pi_state);
                         this->pi_state = pi_state;
                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
                                                         this->rt_waiter,
                                                         this->task);
                         if (ret == 1) {
                                 /*
                                  * We got the lock. We do neither drop the
                                  * refcount on pi_state nor clear
                                  * this->pi_state because the waiter needs the
                                  * pi_state for cleaning up the user space
                                  * value. It will drop the refcount after
                                  * doing so.
                                  */
                                 requeue_pi_wake_futex(this, &key2, hb2);
                                 drop_count++;
                                 continue;
                         } else if (ret) {
                                 /*
                                  * rt_mutex_start_proxy_lock() detected a
                                  * potential deadlock when we tried to queue
                                  * that waiter. Drop the pi_state reference
                                  * which we took above and remove the pointer
                                  * to the state from the waiters futex_q
                                  * object.
                                  */
                                 this->pi_state = NULL;
                                 put_pi_state(pi_state);
                                 /*
                                  * We stop queueing more waiters and let user
                                  * space deal with the mess.
                                  */
                                 break;
                         }
                 }
                 requeue_futex(this, hb1, hb2, &key2);
                 drop_count++;
         }
 
         /*
          * We took an extra initial reference to the pi_state either
          * in futex_proxy_trylock_atomic() or in lookup_pi_state(). We
          * need to drop it here again.
          */
         put_pi_state(pi_state);
 
 out_unlock:
         double_unlock_hb(hb1, hb2);
         wake_up_q(&wake_q);
         hb_waiters_dec(hb2);
 
         /*
          * drop_futex_key_refs() must be called outside the spinlocks. During
          * the requeue we moved futex_q's from the hash bucket at key1 to the
          * one at key2 and updated their key pointer.  We no longer need to
          * hold the references to key1.
          */
         while (--drop_count >= 0)
                 drop_futex_key_refs(&key1);
 
 out_put_keys:
         put_futex_key(&key2);
 out_put_key1:
         put_futex_key(&key1);
 out:
         return ret ? ret : task_count;
 }
 
 /* The key must be already stored in q->key. */
 static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
         __acquires(&hb->lock)
 {
         struct futex_hash_bucket *hb;
 
         hb = hash_futex(&q->key);
 
         /*
          * Increment the counter before taking the lock so that
          * a potential waker won't miss a to-be-slept task that is
          * waiting for the spinlock. This is safe as all queue_lock()
          * users end up calling queue_me(). Similarly, for housekeeping,
          * decrement the counter at queue_unlock() when some error has
          * occurred and we don't end up adding the task to the list.
          */
         hb_waiters_inc(hb);
 
         q->lock_ptr = &hb->lock;
 
         spin_lock(&hb->lock); /* implies smp_mb(); (A) */
         return hb;
 }
 
 static inline void
 queue_unlock(struct futex_hash_bucket *hb)
         __releases(&hb->lock)
 {
         spin_unlock(&hb->lock);
         hb_waiters_dec(hb);
 }
 
 static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
 {
         int prio;
 
         /*
          * The priority used to register this element is
          * - either the real thread-priority for the real-time threads
          * (i.e. threads with a priority lower than MAX_RT_PRIO)
          * - or MAX_RT_PRIO for non-RT threads.
          * Thus, all RT-threads are woken first in priority order, and
          * the others are woken last, in FIFO order.
          */
         prio = min(current->normal_prio, MAX_RT_PRIO);
 
         plist_node_init(&q->list, prio);
         plist_add(&q->list, &hb->chain);
         q->task = current;
 }
 
 /**
  * queue_me() - Enqueue the futex_q on the futex_hash_bucket
  * @q:  The futex_q to enqueue
  * @hb: The destination hash bucket
  *
  * The hb->lock must be held by the caller, and is released here. A call to
  * queue_me() is typically paired with exactly one call to unqueue_me().  The
  * exceptions involve the PI related operations, which may use unqueue_me_pi()
  * or nothing if the unqueue is done as part of the wake process and the unqueue
  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
  * an example).
  */
 static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
         __releases(&hb->lock)
 {
         __queue_me(q, hb);
         spin_unlock(&hb->lock);
 }
 
 /**
  * unqueue_me() - Remove the futex_q from its futex_hash_bucket
  * @q:  The futex_q to unqueue
  *
  * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
  * be paired with exactly one earlier call to queue_me().
  *
  * Return:
  *   1 - if the futex_q was still queued (and we removed unqueued it);
  *   0 - if the futex_q was already removed by the waking thread
  */
 static int unqueue_me(struct futex_q *q)
 {
         spinlock_t *lock_ptr;
         int ret = 0;
 
         /* In the common case we don't take the spinlock, which is nice. */
 retry:
         /*
          * q->lock_ptr can change between this read and the following spin_lock.
          * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
          * optimizing lock_ptr out of the logic below.
          */
         lock_ptr = READ_ONCE(q->lock_ptr);
         if (lock_ptr != NULL) {
                 spin_lock(lock_ptr);
                 /*
                  * q->lock_ptr can change between reading it and
                  * spin_lock(), causing us to take the wrong lock.  This
                  * corrects the race condition.
                  *
                  * Reasoning goes like this: if we have the wrong lock,
                  * q->lock_ptr must have changed (maybe several times)
                  * between reading it and the spin_lock().  It can
                  * change again after the spin_lock() but only if it was
                  * already changed before the spin_lock().  It cannot,
                  * however, change back to the original value.  Therefore
                  * we can detect whether we acquired the correct lock.
                  */
                 if (unlikely(lock_ptr != q->lock_ptr)) {
                         spin_unlock(lock_ptr);
                         goto retry;
                 }
                 __unqueue_futex(q);
 
                 BUG_ON(q->pi_state);
 
                 spin_unlock(lock_ptr);
                 ret = 1;
         }
 
         drop_futex_key_refs(&q->key);
         return ret;
 }
 
 /*
  * PI futexes can not be requeued and must remove themself from the
  * hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
  * and dropped here.
  */
 static void unqueue_me_pi(struct futex_q *q)
         __releases(q->lock_ptr)
 {
         __unqueue_futex(q);
 
         BUG_ON(!q->pi_state);
         put_pi_state(q->pi_state);
         q->pi_state = NULL;
 
         spin_unlock(q->lock_ptr);
 }
 
 /*
  * Fixup the pi_state owner with the new owner.
  *
  * Must be called with hash bucket lock held and mm->sem held for non
  * private futexes.
  */
 static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
                                 struct task_struct *newowner)
 {
         u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
         struct futex_pi_state *pi_state = q->pi_state;
         u32 uval, uninitialized_var(curval), newval;
         struct task_struct *oldowner;
         int ret;
 
         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
 
         oldowner = pi_state->owner;
         /* Owner died? */
         if (!pi_state->owner)
                 newtid |= FUTEX_OWNER_DIED;
 
         /*
          * We are here either because we stole the rtmutex from the
          * previous highest priority waiter or we are the highest priority
          * waiter but have failed to get the rtmutex the first time.
          *
          * We have to replace the newowner TID in the user space variable.
          * This must be atomic as we have to preserve the owner died bit here.
          *
          * Note: We write the user space value _before_ changing the pi_state
          * because we can fault here. Imagine swapped out pages or a fork
          * that marked all the anonymous memory readonly for cow.
          *
          * Modifying pi_state _before_ the user space value would leave the
          * pi_state in an inconsistent state when we fault here, because we
          * need to drop the locks to handle the fault. This might be observed
          * in the PID check in lookup_pi_state.
          */
 retry:
         if (get_futex_value_locked(&uval, uaddr))
                 goto handle_fault;
 
         for (;;) {
                 newval = (uval & FUTEX_OWNER_DIED) | newtid;
 
                 if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
                         goto handle_fault;
                 if (curval == uval)
                         break;
                 uval = curval;
         }
 
         /*
          * We fixed up user space. Now we need to fix the pi_state
          * itself.
          */
         if (pi_state->owner != NULL) {
                 raw_spin_lock(&pi_state->owner->pi_lock);
                 WARN_ON(list_empty(&pi_state->list));
                 list_del_init(&pi_state->list);
                 raw_spin_unlock(&pi_state->owner->pi_lock);
         }
 
         pi_state->owner = newowner;
 
         raw_spin_lock(&newowner->pi_lock);
         WARN_ON(!list_empty(&pi_state->list));
         list_add(&pi_state->list, &newowner->pi_state_list);
         raw_spin_unlock(&newowner->pi_lock);
         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
 
         return 0;
 
         /*
          * To handle the page fault we need to drop the locks here. That gives
          * the other task (either the highest priority waiter itself or the
          * task which stole the rtmutex) the chance to try the fixup of the
          * pi_state. So once we are back from handling the fault we need to
          * check the pi_state after reacquiring the locks and before trying to
          * do another fixup. When the fixup has been done already we simply
          * return.
          *
          * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
          * drop hb->lock since the caller owns the hb -> futex_q relation.
          * Dropping the pi_mutex->wait_lock requires the state revalidate.
          */
 handle_fault:
         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
         spin_unlock(q->lock_ptr);
 
         ret = fault_in_user_writeable(uaddr);
 
         spin_lock(q->lock_ptr);
         raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
 
         /*
          * Check if someone else fixed it for us:
          */
         if (pi_state->owner != oldowner) {
                 ret = 0;
                 goto out_unlock;
         }
 
         if (ret)
                 goto out_unlock;
 
         goto retry;
 
 out_unlock:
         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
         return ret;
 }
 
 static long futex_wait_restart(struct restart_block *restart);
 
 /**
  * fixup_owner() - Post lock pi_state and corner case management
  * @uaddr:      user address of the futex
  * @q:          futex_q (contains pi_state and access to the rt_mutex)
  * @locked:     if the attempt to take the rt_mutex succeeded (1) or not (0)
  *
  * After attempting to lock an rt_mutex, this function is called to cleanup
  * the pi_state owner as well as handle race conditions that may allow us to
  * acquire the lock. Must be called with the hb lock held.
  *
  * Return:
  *  1 - success, lock taken;
  *  0 - success, lock not taken;
  * <0 - on error (-EFAULT)
  */
 static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
 {
         int ret = 0;
 
         if (locked) {
                 /*
                  * Got the lock. We might not be the anticipated owner if we
                  * did a lock-steal - fix up the PI-state in that case:
                  *
                  * We can safely read pi_state->owner without holding wait_lock
                  * because we now own the rt_mutex, only the owner will attempt
                  * to change it.
                  */
                 if (q->pi_state->owner != current)
                         ret = fixup_pi_state_owner(uaddr, q, current);
                 goto out;
         }
 
         /*
          * Paranoia check. If we did not take the lock, then we should not be
          * the owner of the rt_mutex.
          */
         if (rt_mutex_owner(&q->pi_state->pi_mutex) == current) {
                 printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
                                 "pi-state %p\n", ret,
                                 q->pi_state->pi_mutex.owner,
                                 q->pi_state->owner);
         }
 
 out:
         return ret ? ret : locked;
 }
 
 /**
  * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
  * @hb:         the futex hash bucket, must be locked by the caller
  * @q:          the futex_q to queue up on
  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
  */
 static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
                                 struct hrtimer_sleeper *timeout)
 {
         /*
          * The task state is guaranteed to be set before another task can
          * wake it. set_current_state() is implemented using smp_store_mb() and
          * queue_me() calls spin_unlock() upon completion, both serializing
          * access to the hash list and forcing another memory barrier.
          */
         set_current_state(TASK_INTERRUPTIBLE);
         queue_me(q, hb);
 
         /* Arm the timer */
         if (timeout)
                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
 
         /*
          * If we have been removed from the hash list, then another task
          * has tried to wake us, and we can skip the call to schedule().
          */
         if (likely(!plist_node_empty(&q->list))) {
                 /*
                  * If the timer has already expired, current will already be
                  * flagged for rescheduling. Only call schedule if there
                  * is no timeout, or if it has yet to expire.
                  */
                 if (!timeout || timeout->task)
                         freezable_schedule();
         }
         __set_current_state(TASK_RUNNING);
 }
 
 /**
  * futex_wait_setup() - Prepare to wait on a futex
  * @uaddr:      the futex userspace address
  * @val:        the expected value
  * @flags:      futex flags (FLAGS_SHARED, etc.)
  * @q:          the associated futex_q
  * @hb:         storage for hash_bucket pointer to be returned to caller
  *
  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
  * compare it with the expected value.  Handle atomic faults internally.
  * Return with the hb lock held and a q.key reference on success, and unlocked
  * with no q.key reference on failure.
  *
  * Return:
  *  0 - uaddr contains val and hb has been locked;
  * <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
  */
 static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
                            struct futex_q *q, struct futex_hash_bucket **hb)
 {
         u32 uval;
         int ret;
 
         /*
          * Access the page AFTER the hash-bucket is locked.
          * Order is important:
          *
          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
          *
          * The basic logical guarantee of a futex is that it blocks ONLY
          * if cond(var) is known to be true at the time of blocking, for
          * any cond.  If we locked the hash-bucket after testing *uaddr, that
          * would open a race condition where we could block indefinitely with
          * cond(var) false, which would violate the guarantee.
          *
          * On the other hand, we insert q and release the hash-bucket only
          * after testing *uaddr.  This guarantees that futex_wait() will NOT
          * absorb a wakeup if *uaddr does not match the desired values
          * while the syscall executes.
          */
 retry:
         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, VERIFY_READ);
         if (unlikely(ret != 0))
                 return ret;
 
 retry_private:
         *hb = queue_lock(q);
 
         ret = get_futex_value_locked(&uval, uaddr);
 
         if (ret) {
                 queue_unlock(*hb);
 
                 ret = get_user(uval, uaddr);
                 if (ret)
                         goto out;
 
                 if (!(flags & FLAGS_SHARED))
                         goto retry_private;
 
                 put_futex_key(&q->key);
                 goto retry;
         }
 
         if (uval != val) {
                 queue_unlock(*hb);
                 ret = -EWOULDBLOCK;
         }
 
 out:
         if (ret)
                 put_futex_key(&q->key);
         return ret;
 }
 
 static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
                       ktime_t *abs_time, u32 bitset)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct restart_block *restart;
         struct futex_hash_bucket *hb;
         struct futex_q q = futex_q_init;
         int ret;
 
         if (!bitset)
                 return -EINVAL;
         q.bitset = bitset;
 
         if (abs_time) {
                 to = &timeout;
 
                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
                                       HRTIMER_MODE_ABS);
                 hrtimer_init_sleeper(to, current);
                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
                                              current->timer_slack_ns);
         }
 
 retry:
         /*
          * Prepare to wait on uaddr. On success, holds hb lock and increments
          * q.key refs.
          */
         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
         if (ret)
                 goto out;
 
         /* queue_me and wait for wakeup, timeout, or a signal. */
         futex_wait_queue_me(hb, &q, to);
 
         /* If we were woken (and unqueued), we succeeded, whatever. */
         ret = 0;
         /* unqueue_me() drops q.key ref */
         if (!unqueue_me(&q))
                 goto out;
         ret = -ETIMEDOUT;
         if (to && !to->task)
                 goto out;
 
         /*
          * We expect signal_pending(current), but we might be the
          * victim of a spurious wakeup as well.
          */
         if (!signal_pending(current))
                 goto retry;
 
         ret = -ERESTARTSYS;
         if (!abs_time)
                 goto out;
 
         restart = &current->restart_block;
         restart->fn = futex_wait_restart;
         restart->futex.uaddr = uaddr;
         restart->futex.val = val;
         restart->futex.time = *abs_time;
         restart->futex.bitset = bitset;
         restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
 
         ret = -ERESTART_RESTARTBLOCK;
 
 out:
         if (to) {
                 hrtimer_cancel(&to->timer);
                 destroy_hrtimer_on_stack(&to->timer);
         }
         return ret;
 }
 
 
 static long futex_wait_restart(struct restart_block *restart)
 {
         u32 __user *uaddr = restart->futex.uaddr;
         ktime_t t, *tp = NULL;
 
         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
                 t = restart->futex.time;
                 tp = &t;
         }
         restart->fn = do_no_restart_syscall;
 
         return (long)futex_wait(uaddr, restart->futex.flags,
                                 restart->futex.val, tp, restart->futex.bitset);
 }
 
 
 /*
  * Userspace tried a 0 -> TID atomic transition of the futex value
  * and failed. The kernel side here does the whole locking operation:
  * if there are waiters then it will block as a consequence of relying
  * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
  * a 0 value of the futex too.).
  *
  * Also serves as futex trylock_pi()'ing, and due semantics.
  */
 static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
                          ktime_t *time, int trylock)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct futex_pi_state *pi_state = NULL;
         struct rt_mutex_waiter rt_waiter;
         struct futex_hash_bucket *hb;
         struct futex_q q = futex_q_init;
         int res, ret;
 
         if (refill_pi_state_cache())
                 return -ENOMEM;
 
         if (time) {
                 to = &timeout;
                 hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
                                       HRTIMER_MODE_ABS);
                 hrtimer_init_sleeper(to, current);
                 hrtimer_set_expires(&to->timer, *time);
         }
 
 retry:
         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, VERIFY_WRITE);
         if (unlikely(ret != 0))
                 goto out;
 
 retry_private:
         hb = queue_lock(&q);
 
         ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
         if (unlikely(ret)) {
                 /*
                  * Atomic work succeeded and we got the lock,
                  * or failed. Either way, we do _not_ block.
                  */
                 switch (ret) {
                 case 1:
                         /* We got the lock. */
                         ret = 0;
                         goto out_unlock_put_key;
                 case -EFAULT:
                         goto uaddr_faulted;
                 case -EAGAIN:
                         /*
                          * Two reasons for this:
                          * - Task is exiting and we just wait for the
                          *   exit to complete.
                          * - The user space value changed.
                          */
                         queue_unlock(hb);
                         put_futex_key(&q.key);
                         cond_resched();
                         goto retry;
                 default:
                         goto out_unlock_put_key;
                 }
         }
 
         WARN_ON(!q.pi_state);
 
         /*
          * Only actually queue now that the atomic ops are done:
          */
         __queue_me(&q, hb);
 
         if (trylock) {
                 ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
                 /* Fixup the trylock return value: */
                 ret = ret ? 0 : -EWOULDBLOCK;
                 goto no_block;
         }
 
         rt_mutex_init_waiter(&rt_waiter);
 
         /*
          * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
          * hold it while doing rt_mutex_start_proxy(), because then it will
          * include hb->lock in the blocking chain, even through we'll not in
          * fact hold it while blocking. This will lead it to report -EDEADLK
          * and BUG when futex_unlock_pi() interleaves with this.
          *
          * Therefore acquire wait_lock while holding hb->lock, but drop the
          * latter before calling rt_mutex_start_proxy_lock(). This still fully
          * serializes against futex_unlock_pi() as that does the exact same
          * lock handoff sequence.
          */
         raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
         spin_unlock(q.lock_ptr);
         ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
         raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
 
         if (ret) {
                 if (ret == 1)
                         ret = 0;
 
                 spin_lock(q.lock_ptr);
                 goto no_block;
         }
 
 
         if (unlikely(to))
                 hrtimer_start_expires(&to->timer, HRTIMER_MODE_ABS);
 
         ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
 
         spin_lock(q.lock_ptr);
         /*
          * If we failed to acquire the lock (signal/timeout), we must
          * first acquire the hb->lock before removing the lock from the
          * rt_mutex waitqueue, such that we can keep the hb and rt_mutex
          * wait lists consistent.
          *
          * In particular; it is important that futex_unlock_pi() can not
          * observe this inconsistency.
          */
         if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
                 ret = 0;
 
 no_block:
         /*
          * Fixup the pi_state owner and possibly acquire the lock if we
          * haven't already.
          */
         res = fixup_owner(uaddr, &q, !ret);
         /*
          * If fixup_owner() returned an error, proprogate that.  If it acquired
          * the lock, clear our -ETIMEDOUT or -EINTR.
          */
         if (res)
                 ret = (res < 0) ? res : 0;
 
         /*
          * If fixup_owner() faulted and was unable to handle the fault, unlock
          * it and return the fault to userspace.
          */
         if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current)) {
                 pi_state = q.pi_state;
                 get_pi_state(pi_state);
         }
 
         /* Unqueue and drop the lock */
         unqueue_me_pi(&q);
 
         if (pi_state) {
                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
                 put_pi_state(pi_state);
         }
 
         goto out_put_key;
 
 out_unlock_put_key:
         queue_unlock(hb);
 
 out_put_key:
         put_futex_key(&q.key);
 out:
         if (to) {
                 hrtimer_cancel(&to->timer);
                 destroy_hrtimer_on_stack(&to->timer);
         }
         return ret != -EINTR ? ret : -ERESTARTNOINTR;
 
 uaddr_faulted:
         queue_unlock(hb);
 
         ret = fault_in_user_writeable(uaddr);
         if (ret)
                 goto out_put_key;
 
         if (!(flags & FLAGS_SHARED))
                 goto retry_private;
 
         put_futex_key(&q.key);
         goto retry;
 }
 
 /*
  * Userspace attempted a TID -> 0 atomic transition, and failed.
  * This is the in-kernel slowpath: we look up the PI state (if any),
  * and do the rt-mutex unlock.
  */
 static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
 {
         u32 uninitialized_var(curval), uval, vpid = task_pid_vnr(current);
         union futex_key key = FUTEX_KEY_INIT;
         struct futex_hash_bucket *hb;
         struct futex_q *top_waiter;
         int ret;
 
 retry:
         if (get_user(uval, uaddr))
                 return -EFAULT;
         /*
          * We release only a lock we actually own:
          */
         if ((uval & FUTEX_TID_MASK) != vpid)
                 return -EPERM;
 
         ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, VERIFY_WRITE);
         if (ret)
                 return ret;
 
         hb = hash_futex(&key);
         spin_lock(&hb->lock);
 
         /*
          * Check waiters first. We do not trust user space values at
          * all and we at least want to know if user space fiddled
          * with the futex value instead of blindly unlocking.
          */
         top_waiter = futex_top_waiter(hb, &key);
         if (top_waiter) {
                 struct futex_pi_state *pi_state = top_waiter->pi_state;
 
                 ret = -EINVAL;
                 if (!pi_state)
                         goto out_unlock;
 
                 /*
                  * If current does not own the pi_state then the futex is
                  * inconsistent and user space fiddled with the futex value.
                  */
                 if (pi_state->owner != current)
                         goto out_unlock;
 
                 get_pi_state(pi_state);
                 /*
                  * By taking wait_lock while still holding hb->lock, we ensure
                  * there is no point where we hold neither; and therefore
                  * wake_futex_pi() must observe a state consistent with what we
                  * observed.
                  */
                 raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
                 spin_unlock(&hb->lock);
 
                 ret = wake_futex_pi(uaddr, uval, pi_state);
 
                 put_pi_state(pi_state);
 
                 /*
                  * Success, we're done! No tricky corner cases.
                  */
                 if (!ret)
                         goto out_putkey;
                 /*
                  * The atomic access to the futex value generated a
                  * pagefault, so retry the user-access and the wakeup:
                  */
                 if (ret == -EFAULT)
                         goto pi_faulted;
                 /*
                  * A unconditional UNLOCK_PI op raced against a waiter
                  * setting the FUTEX_WAITERS bit. Try again.
                  */
                 if (ret == -EAGAIN) {
                         put_futex_key(&key);
                         goto retry;
                 }
                 /*
                  * wake_futex_pi has detected invalid state. Tell user
                  * space.
                  */
                 goto out_putkey;
         }
 
         /*
          * We have no kernel internal state, i.e. no waiters in the
          * kernel. Waiters which are about to queue themselves are stuck
          * on hb->lock. So we can safely ignore them. We do neither
          * preserve the WAITERS bit not the OWNER_DIED one. We are the
          * owner.
          */
         if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
                 spin_unlock(&hb->lock);
                 goto pi_faulted;
         }
 
         /*
          * If uval has changed, let user space handle it.
          */
         ret = (curval == uval) ? 0 : -EAGAIN;
 
 out_unlock:
         spin_unlock(&hb->lock);
 out_putkey:
         put_futex_key(&key);
         return ret;
 
 pi_faulted:
         put_futex_key(&key);
 
         ret = fault_in_user_writeable(uaddr);
         if (!ret)
                 goto retry;
 
         return ret;
 }
 
 /**
  * handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
  * @hb:         the hash_bucket futex_q was original enqueued on
  * @q:          the futex_q woken while waiting to be requeued
  * @key2:       the futex_key of the requeue target futex
  * @timeout:    the timeout associated with the wait (NULL if none)
  *
  * Detect if the task was woken on the initial futex as opposed to the requeue
  * target futex.  If so, determine if it was a timeout or a signal that caused
  * the wakeup and return the appropriate error code to the caller.  Must be
  * called with the hb lock held.
  *
  * Return:
  *  0 = no early wakeup detected;
  * <0 = -ETIMEDOUT or -ERESTARTNOINTR
  */
 static inline
 int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
                                    struct futex_q *q, union futex_key *key2,
                                    struct hrtimer_sleeper *timeout)
 {
         int ret = 0;
 
         /*
          * With the hb lock held, we avoid races while we process the wakeup.
          * We only need to hold hb (and not hb2) to ensure atomicity as the
          * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
          * It can't be requeued from uaddr2 to something else since we don't
          * support a PI aware source futex for requeue.
          */
         if (!match_futex(&q->key, key2)) {
                 WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
                 /*
                  * We were woken prior to requeue by a timeout or a signal.
                  * Unqueue the futex_q and determine which it was.
                  */
                 plist_del(&q->list, &hb->chain);
                 hb_waiters_dec(hb);
 
                 /* Handle spurious wakeups gracefully */
                 ret = -EWOULDBLOCK;
                 if (timeout && !timeout->task)
                         ret = -ETIMEDOUT;
                 else if (signal_pending(current))
                         ret = -ERESTARTNOINTR;
         }
         return ret;
 }
 
 /**
  * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
  * @uaddr:      the futex we initially wait on (non-pi)
  * @flags:      futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
  *              the same type, no requeueing from private to shared, etc.
  * @val:        the expected value of uaddr
  * @abs_time:   absolute timeout
  * @bitset:     32 bit wakeup bitset set by userspace, defaults to all
  * @uaddr2:     the pi futex we will take prior to returning to user-space
  *
  * The caller will wait on uaddr and will be requeued by futex_requeue() to
  * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
  * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
  * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
  * without one, the pi logic would not know which task to boost/deboost, if
  * there was a need to.
  *
  * We call schedule in futex_wait_queue_me() when we enqueue and return there
  * via the following--
  * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
  * 2) wakeup on uaddr2 after a requeue
  * 3) signal
  * 4) timeout
  *
  * If 3, cleanup and return -ERESTARTNOINTR.
  *
  * If 2, we may then block on trying to take the rt_mutex and return via:
  * 5) successful lock
  * 6) signal
  * 7) timeout
  * 8) other lock acquisition failure
  *
  * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
  *
  * If 4 or 7, we cleanup and return with -ETIMEDOUT.
  *
  * Return:
  *  0 - On success;
  * <0 - On error
  */
 static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
                                  u32 val, ktime_t *abs_time, u32 bitset,
                                  u32 __user *uaddr2)
 {
         struct hrtimer_sleeper timeout, *to = NULL;
         struct futex_pi_state *pi_state = NULL;
         struct rt_mutex_waiter rt_waiter;
         struct futex_hash_bucket *hb;
         union futex_key key2 = FUTEX_KEY_INIT;
         struct futex_q q = futex_q_init;
         int res, ret;
 
         if (uaddr == uaddr2)
                 return -EINVAL;
 
         if (!bitset)
                 return -EINVAL;
 
         if (abs_time) {
                 to = &timeout;
                 hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
                                       CLOCK_REALTIME : CLOCK_MONOTONIC,
                                       HRTIMER_MODE_ABS);
                 hrtimer_init_sleeper(to, current);
                 hrtimer_set_expires_range_ns(&to->timer, *abs_time,
                                              current->timer_slack_ns);
         }
 
         /*
          * The waiter is allocated on our stack, manipulated by the requeue
          * code while we sleep on uaddr.
          */
         rt_mutex_init_waiter(&rt_waiter);
 
         ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
         if (unlikely(ret != 0))
                 goto out;
 
         q.bitset = bitset;
         q.rt_waiter = &rt_waiter;
         q.requeue_pi_key = &key2;
 
         /*
          * Prepare to wait on uaddr. On success, increments q.key (key1) ref
          * count.
          */
         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
         if (ret)
                 goto out_key2;
 
         /*
          * The check above which compares uaddrs is not sufficient for
          * shared futexes. We need to compare the keys:
          */
         if (match_futex(&q.key, &key2)) {
                 queue_unlock(hb);
                 ret = -EINVAL;
                 goto out_put_keys;
         }
 
         /* Queue the futex_q, drop the hb lock, wait for wakeup. */
         futex_wait_queue_me(hb, &q, to);
 
         spin_lock(&hb->lock);
         ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
         spin_unlock(&hb->lock);
         if (ret)
                 goto out_put_keys;
 
         /*
          * In order for us to be here, we know our q.key == key2, and since
          * we took the hb->lock above, we also know that futex_requeue() has
          * completed and we no longer have to concern ourselves with a wakeup
          * race with the atomic proxy lock acquisition by the requeue code. The
          * futex_requeue dropped our key1 reference and incremented our key2
          * reference count.
          */
 
         /* Check if the requeue code acquired the second futex for us. */
         if (!q.rt_waiter) {
                 /*
                  * Got the lock. We might not be the anticipated owner if we
                  * did a lock-steal - fix up the PI-state in that case.
                  */
                 if (q.pi_state && (q.pi_state->owner != current)) {
                         spin_lock(q.lock_ptr);
                         ret = fixup_pi_state_owner(uaddr2, &q, current);
                         if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
                                 pi_state = q.pi_state;
                                 get_pi_state(pi_state);
                         }
                         /*
                          * Drop the reference to the pi state which
                          * the requeue_pi() code acquired for us.
                          */
                         put_pi_state(q.pi_state);
                         spin_unlock(q.lock_ptr);
                 }
         } else {
                 struct rt_mutex *pi_mutex;
 
                 /*
                  * We have been woken up by futex_unlock_pi(), a timeout, or a
                  * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
                  * the pi_state.
                  */
                 WARN_ON(!q.pi_state);
                 pi_mutex = &q.pi_state->pi_mutex;
                 ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
 
                 spin_lock(q.lock_ptr);
                 if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
                         ret = 0;
 
                 debug_rt_mutex_free_waiter(&rt_waiter);
                 /*
                  * Fixup the pi_state owner and possibly acquire the lock if we
                  * haven't already.
                  */
                 res = fixup_owner(uaddr2, &q, !ret);
                 /*
                  * If fixup_owner() returned an error, proprogate that.  If it
                  * acquired the lock, clear -ETIMEDOUT or -EINTR.
                  */
                 if (res)
                         ret = (res < 0) ? res : 0;
 
                 /*
                  * If fixup_pi_state_owner() faulted and was unable to handle
                  * the fault, unlock the rt_mutex and return the fault to
                  * userspace.
                  */
                 if (ret && rt_mutex_owner(&q.pi_state->pi_mutex) == current) {
                         pi_state = q.pi_state;
                         get_pi_state(pi_state);
                 }
 
                 /* Unqueue and drop the lock. */
                 unqueue_me_pi(&q);
         }
 
         if (pi_state) {
                 rt_mutex_futex_unlock(&pi_state->pi_mutex);
                 put_pi_state(pi_state);
         }
 
         if (ret == -EINTR) {
                 /*
                  * We've already been requeued, but cannot restart by calling
                  * futex_lock_pi() directly. We could restart this syscall, but
                  * it would detect that the user space "val" changed and return
                  * -EWOULDBLOCK.  Save the overhead of the restart and return
                  * -EWOULDBLOCK directly.
                  */
                 ret = -EWOULDBLOCK;
         }
 
 out_put_keys:
         put_futex_key(&q.key);
 out_key2:
         put_futex_key(&key2);
 
 out:
         if (to) {
                 hrtimer_cancel(&to->timer);
                 destroy_hrtimer_on_stack(&to->timer);
         }
         return ret;
 }
 
 /*
  * Support for robust futexes: the kernel cleans up held futexes at
  * thread exit time.
  *
  * Implementation: user-space maintains a per-thread list of locks it
  * is holding. Upon do_exit(), the kernel carefully walks this list,
  * and marks all locks that are owned by this thread with the
  * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
  * always manipulated with the lock held, so the list is private and
  * per-thread. Userspace also maintains a per-thread 'list_op_pending'
  * field, to allow the kernel to clean up if the thread dies after
  * acquiring the lock, but just before it could have added itself to
  * the list. There can only be one such pending lock.
  */
 
 /**
  * sys_set_robust_list() - Set the robust-futex list head of a task
  * @head:       pointer to the list-head
  * @len:        length of the list-head, as userspace expects
  */
 SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
                 size_t, len)
 {
         if (!futex_cmpxchg_enabled)
                 return -ENOSYS;
         /*
          * The kernel knows only one size for now:
          */
         if (unlikely(len != sizeof(*head)))
                 return -EINVAL;
 
         current->robust_list = head;
 
         return 0;
 }
 
 /**
  * sys_get_robust_list() - Get the robust-futex list head of a task
  * @pid:        pid of the process [zero for current task]
  * @head_ptr:   pointer to a list-head pointer, the kernel fills it in
  * @len_ptr:    pointer to a length field, the kernel fills in the header size
  */
 SYSCALL_DEFINE3(get_robust_list, int, pid,
                 struct robust_list_head __user * __user *, head_ptr,
                 size_t __user *, len_ptr)
 {
         struct robust_list_head __user *head;
         unsigned long ret;
         struct task_struct *p;
 
         if (!futex_cmpxchg_enabled)
                 return -ENOSYS;
 
         rcu_read_lock();
 
         ret = -ESRCH;
         if (!pid)
                 p = current;
         else {
                 p = find_task_by_vpid(pid);
                 if (!p)
                         goto err_unlock;
         }
 
         ret = -EPERM;
         if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
                 goto err_unlock;
 
         head = p->robust_list;
         rcu_read_unlock();
 
         if (put_user(sizeof(*head), len_ptr))
                 return -EFAULT;
         return put_user(head, head_ptr);
 
 err_unlock:
         rcu_read_unlock();
 
         return ret;
 }
 
 /*
  * Process a futex-list entry, check whether it's owned by the
  * dying task, and do notification if so:
  */
 int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
 {
         u32 uval, uninitialized_var(nval), mval;
 
 retry:
         if (get_user(uval, uaddr))
                 return -1;
 
         if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
                 /*
                  * Ok, this dying thread is truly holding a futex
                  * of interest. Set the OWNER_DIED bit atomically
                  * via cmpxchg, and if the value had FUTEX_WAITERS
                  * set, wake up a waiter (if any). (We have to do a
                  * futex_wake() even if OWNER_DIED is already set -
                  * to handle the rare but possible case of recursive
                  * thread-death.) The rest of the cleanup is done in
                  * userspace.
                  */
                 mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
                 /*
                  * We are not holding a lock here, but we want to have
                  * the pagefault_disable/enable() protection because
                  * we want to handle the fault gracefully. If the
                  * access fails we try to fault in the futex with R/W
                  * verification via get_user_pages. get_user() above
                  * does not guarantee R/W access. If that fails we
                  * give up and leave the futex locked.
                  */
                 if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
                         if (fault_in_user_writeable(uaddr))
                                 return -1;
                         goto retry;
                 }
                 if (nval != uval)
                         goto retry;
 
                 /*
                  * Wake robust non-PI futexes here. The wakeup of
                  * PI futexes happens in exit_pi_state():
                  */
                 if (!pi && (uval & FUTEX_WAITERS))
                         futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
         }
         return 0;
 }
 
 /*
  * Fetch a robust-list pointer. Bit 0 signals PI futexes:
  */
 static inline int fetch_robust_entry(struct robust_list __user **entry,
                                      struct robust_list __user * __user *head,
                                      unsigned int *pi)
 {
         unsigned long uentry;
 
         if (get_user(uentry, (unsigned long __user *)head))
                 return -EFAULT;
 
         *entry = (void __user *)(uentry & ~1UL);
         *pi = uentry & 1;
 
         return 0;
 }
 
 /*
  * Walk curr->robust_list (very carefully, it's a userspace list!)
  * and mark any locks found there dead, and notify any waiters.
  *
  * We silently return on any sign of list-walking problem.
  */
 void exit_robust_list(struct task_struct *curr)
 {
         struct robust_list_head __user *head = curr->robust_list;
         struct robust_list __user *entry, *next_entry, *pending;
         unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
         unsigned int uninitialized_var(next_pi);
         unsigned long futex_offset;
         int rc;
 
         if (!futex_cmpxchg_enabled)
                 return;
 
         /*
          * Fetch the list head (which was registered earlier, via
          * sys_set_robust_list()):
          */
         if (fetch_robust_entry(&entry, &head->list.next, &pi))
                 return;
         /*
          * Fetch the relative futex offset:
          */
         if (get_user(futex_offset, &head->futex_offset))
                 return;
         /*
          * Fetch any possibly pending lock-add first, and handle it
          * if it exists:
          */
         if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
                 return;
 
         next_entry = NULL;      /* avoid warning with gcc */
         while (entry != &head->list) {
                 /*
                  * Fetch the next entry in the list before calling
                  * handle_futex_death:
                  */
                 rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
                 /*
                  * A pending lock might already be on the list, so
                  * don't process it twice:
                  */
                 if (entry != pending)
                         if (handle_futex_death((void __user *)entry + futex_offset,
                                                 curr, pi))
                                 return;
                 if (rc)
                         return;
                 entry = next_entry;
                 pi = next_pi;
                 /*
                  * Avoid excessively long or circular lists:
                  */
                 if (!--limit)
                         break;
 
                 cond_resched();
         }
 
         if (pending)
                 handle_futex_death((void __user *)pending + futex_offset,
                                    curr, pip);
 }
 
 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
                 u32 __user *uaddr2, u32 val2, u32 val3)
 {
         int cmd = op & FUTEX_CMD_MASK;
         unsigned int flags = 0;
 
         if (!(op & FUTEX_PRIVATE_FLAG))
                 flags |= FLAGS_SHARED;
 
         if (op & FUTEX_CLOCK_REALTIME) {
                 flags |= FLAGS_CLOCKRT;
                 if (cmd != FUTEX_WAIT && cmd != FUTEX_WAIT_BITSET && \
                     cmd != FUTEX_WAIT_REQUEUE_PI)
                         return -ENOSYS;
         }
 
         switch (cmd) {
         case FUTEX_LOCK_PI:
         case FUTEX_UNLOCK_PI:
         case FUTEX_TRYLOCK_PI:
         case FUTEX_WAIT_REQUEUE_PI:
         case FUTEX_CMP_REQUEUE_PI:
                 if (!futex_cmpxchg_enabled)
                         return -ENOSYS;
         }
 
         switch (cmd) {
         case FUTEX_WAIT:
                 val3 = FUTEX_BITSET_MATCH_ANY;
         case FUTEX_WAIT_BITSET:
                 return futex_wait(uaddr, flags, val, timeout, val3);
         case FUTEX_WAKE:
                 val3 = FUTEX_BITSET_MATCH_ANY;
         case FUTEX_WAKE_BITSET:
                 return futex_wake(uaddr, flags, val, val3);
         case FUTEX_REQUEUE:
                 return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
         case FUTEX_CMP_REQUEUE:
                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
         case FUTEX_WAKE_OP:
                 return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
         case FUTEX_LOCK_PI:
                 return futex_lock_pi(uaddr, flags, timeout, 0);
         case FUTEX_UNLOCK_PI:
                 return futex_unlock_pi(uaddr, flags);
         case FUTEX_TRYLOCK_PI:
                 return futex_lock_pi(uaddr, flags, NULL, 1);
         case FUTEX_WAIT_REQUEUE_PI:
                 val3 = FUTEX_BITSET_MATCH_ANY;
                 return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
                                              uaddr2);
         case FUTEX_CMP_REQUEUE_PI:
                 return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
         }
         return -ENOSYS;
 }
 
 
 SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
                 struct timespec __user *, utime, u32 __user *, uaddr2,
                 u32, val3)
 {
         struct timespec ts;
         ktime_t t, *tp = NULL;
         u32 val2 = 0;
         int cmd = op & FUTEX_CMD_MASK;
 
         if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
                       cmd == FUTEX_WAIT_BITSET ||
                       cmd == FUTEX_WAIT_REQUEUE_PI)) {
                 if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
                         return -EFAULT;
                 if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
                         return -EFAULT;
                 if (!timespec_valid(&ts))
                         return -EINVAL;
 
                 t = timespec_to_ktime(ts);
                 if (cmd == FUTEX_WAIT)
                         t = ktime_add_safe(ktime_get(), t);
                 tp = &t;
         }
         /*
          * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
          * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
          */
         if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
             cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
                 val2 = (u32) (unsigned long) utime;
 
         return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
 }
 
 static void __init futex_detect_cmpxchg(void)
 {
 #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
         u32 curval;
 
         /*
          * This will fail and we want it. Some arch implementations do
          * runtime detection of the futex_atomic_cmpxchg_inatomic()
          * functionality. We want to know that before we call in any
          * of the complex code paths. Also we want to prevent
          * registration of robust lists in that case. NULL is
          * guaranteed to fault and we get -EFAULT on functional
          * implementation, the non-functional ones will return
          * -ENOSYS.
          */
         if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
                 futex_cmpxchg_enabled = 1;
 #endif
 }
 
 static int __init futex_init(void)
 {
         unsigned int futex_shift;
         unsigned long i;
 
 #if CONFIG_BASE_SMALL
         futex_hashsize = 16;
 #else
         futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
 #endif
 
         futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
                                                futex_hashsize, 0,
                                                futex_hashsize < 256 ? HASH_SMALL : 0,
                                                &futex_shift, NULL,
                                                futex_hashsize, futex_hashsize);
         futex_hashsize = 1UL << futex_shift;
 
         futex_detect_cmpxchg();
 
         for (i = 0; i < futex_hashsize; i++) {
                 atomic_set(&futex_queues[i].waiters, 0);
                 plist_head_init(&futex_queues[i].chain);
                 spin_lock_init(&futex_queues[i].lock);
         }
 
         return 0;
 }
 core_initcall(futex_init);