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TOMOYO Linux Cross Reference
Linux/mm/swapfile.c

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  1 /*
  2  *  linux/mm/swapfile.c
  3  *
  4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  5  *  Swap reorganised 29.12.95, Stephen Tweedie
  6  */
  7 
  8 #include <linux/mm.h>
  9 #include <linux/hugetlb.h>
 10 #include <linux/mman.h>
 11 #include <linux/slab.h>
 12 #include <linux/kernel_stat.h>
 13 #include <linux/swap.h>
 14 #include <linux/vmalloc.h>
 15 #include <linux/pagemap.h>
 16 #include <linux/namei.h>
 17 #include <linux/shmem_fs.h>
 18 #include <linux/blkdev.h>
 19 #include <linux/random.h>
 20 #include <linux/writeback.h>
 21 #include <linux/proc_fs.h>
 22 #include <linux/seq_file.h>
 23 #include <linux/init.h>
 24 #include <linux/ksm.h>
 25 #include <linux/rmap.h>
 26 #include <linux/security.h>
 27 #include <linux/backing-dev.h>
 28 #include <linux/mutex.h>
 29 #include <linux/capability.h>
 30 #include <linux/syscalls.h>
 31 #include <linux/memcontrol.h>
 32 #include <linux/poll.h>
 33 #include <linux/oom.h>
 34 #include <linux/frontswap.h>
 35 #include <linux/swapfile.h>
 36 #include <linux/export.h>
 37 
 38 #include <asm/pgtable.h>
 39 #include <asm/tlbflush.h>
 40 #include <linux/swapops.h>
 41 #include <linux/page_cgroup.h>
 42 
 43 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
 44                                  unsigned char);
 45 static void free_swap_count_continuations(struct swap_info_struct *);
 46 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
 47 
 48 DEFINE_SPINLOCK(swap_lock);
 49 static unsigned int nr_swapfiles;
 50 atomic_long_t nr_swap_pages;
 51 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
 52 long total_swap_pages;
 53 static int least_priority;
 54 static atomic_t highest_priority_index = ATOMIC_INIT(-1);
 55 
 56 static const char Bad_file[] = "Bad swap file entry ";
 57 static const char Unused_file[] = "Unused swap file entry ";
 58 static const char Bad_offset[] = "Bad swap offset entry ";
 59 static const char Unused_offset[] = "Unused swap offset entry ";
 60 
 61 struct swap_list_t swap_list = {-1, -1};
 62 
 63 struct swap_info_struct *swap_info[MAX_SWAPFILES];
 64 
 65 static DEFINE_MUTEX(swapon_mutex);
 66 
 67 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
 68 /* Activity counter to indicate that a swapon or swapoff has occurred */
 69 static atomic_t proc_poll_event = ATOMIC_INIT(0);
 70 
 71 static inline unsigned char swap_count(unsigned char ent)
 72 {
 73         return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
 74 }
 75 
 76 /* returns 1 if swap entry is freed */
 77 static int
 78 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
 79 {
 80         swp_entry_t entry = swp_entry(si->type, offset);
 81         struct page *page;
 82         int ret = 0;
 83 
 84         page = find_get_page(swap_address_space(entry), entry.val);
 85         if (!page)
 86                 return 0;
 87         /*
 88          * This function is called from scan_swap_map() and it's called
 89          * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
 90          * We have to use trylock for avoiding deadlock. This is a special
 91          * case and you should use try_to_free_swap() with explicit lock_page()
 92          * in usual operations.
 93          */
 94         if (trylock_page(page)) {
 95                 ret = try_to_free_swap(page);
 96                 unlock_page(page);
 97         }
 98         page_cache_release(page);
 99         return ret;
100 }
101 
102 /*
103  * swapon tell device that all the old swap contents can be discarded,
104  * to allow the swap device to optimize its wear-levelling.
105  */
106 static int discard_swap(struct swap_info_struct *si)
107 {
108         struct swap_extent *se;
109         sector_t start_block;
110         sector_t nr_blocks;
111         int err = 0;
112 
113         /* Do not discard the swap header page! */
114         se = &si->first_swap_extent;
115         start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
116         nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
117         if (nr_blocks) {
118                 err = blkdev_issue_discard(si->bdev, start_block,
119                                 nr_blocks, GFP_KERNEL, 0);
120                 if (err)
121                         return err;
122                 cond_resched();
123         }
124 
125         list_for_each_entry(se, &si->first_swap_extent.list, list) {
126                 start_block = se->start_block << (PAGE_SHIFT - 9);
127                 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
128 
129                 err = blkdev_issue_discard(si->bdev, start_block,
130                                 nr_blocks, GFP_KERNEL, 0);
131                 if (err)
132                         break;
133 
134                 cond_resched();
135         }
136         return err;             /* That will often be -EOPNOTSUPP */
137 }
138 
139 /*
140  * swap allocation tell device that a cluster of swap can now be discarded,
141  * to allow the swap device to optimize its wear-levelling.
142  */
143 static void discard_swap_cluster(struct swap_info_struct *si,
144                                  pgoff_t start_page, pgoff_t nr_pages)
145 {
146         struct swap_extent *se = si->curr_swap_extent;
147         int found_extent = 0;
148 
149         while (nr_pages) {
150                 struct list_head *lh;
151 
152                 if (se->start_page <= start_page &&
153                     start_page < se->start_page + se->nr_pages) {
154                         pgoff_t offset = start_page - se->start_page;
155                         sector_t start_block = se->start_block + offset;
156                         sector_t nr_blocks = se->nr_pages - offset;
157 
158                         if (nr_blocks > nr_pages)
159                                 nr_blocks = nr_pages;
160                         start_page += nr_blocks;
161                         nr_pages -= nr_blocks;
162 
163                         if (!found_extent++)
164                                 si->curr_swap_extent = se;
165 
166                         start_block <<= PAGE_SHIFT - 9;
167                         nr_blocks <<= PAGE_SHIFT - 9;
168                         if (blkdev_issue_discard(si->bdev, start_block,
169                                     nr_blocks, GFP_NOIO, 0))
170                                 break;
171                 }
172 
173                 lh = se->list.next;
174                 se = list_entry(lh, struct swap_extent, list);
175         }
176 }
177 
178 static int wait_for_discard(void *word)
179 {
180         schedule();
181         return 0;
182 }
183 
184 #define SWAPFILE_CLUSTER        256
185 #define LATENCY_LIMIT           256
186 
187 static unsigned long scan_swap_map(struct swap_info_struct *si,
188                                    unsigned char usage)
189 {
190         unsigned long offset;
191         unsigned long scan_base;
192         unsigned long last_in_cluster = 0;
193         int latency_ration = LATENCY_LIMIT;
194         int found_free_cluster = 0;
195 
196         /*
197          * We try to cluster swap pages by allocating them sequentially
198          * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
199          * way, however, we resort to first-free allocation, starting
200          * a new cluster.  This prevents us from scattering swap pages
201          * all over the entire swap partition, so that we reduce
202          * overall disk seek times between swap pages.  -- sct
203          * But we do now try to find an empty cluster.  -Andrea
204          * And we let swap pages go all over an SSD partition.  Hugh
205          */
206 
207         si->flags += SWP_SCANNING;
208         scan_base = offset = si->cluster_next;
209 
210         if (unlikely(!si->cluster_nr--)) {
211                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
212                         si->cluster_nr = SWAPFILE_CLUSTER - 1;
213                         goto checks;
214                 }
215                 if (si->flags & SWP_DISCARDABLE) {
216                         /*
217                          * Start range check on racing allocations, in case
218                          * they overlap the cluster we eventually decide on
219                          * (we scan without swap_lock to allow preemption).
220                          * It's hardly conceivable that cluster_nr could be
221                          * wrapped during our scan, but don't depend on it.
222                          */
223                         if (si->lowest_alloc)
224                                 goto checks;
225                         si->lowest_alloc = si->max;
226                         si->highest_alloc = 0;
227                 }
228                 spin_unlock(&si->lock);
229 
230                 /*
231                  * If seek is expensive, start searching for new cluster from
232                  * start of partition, to minimize the span of allocated swap.
233                  * But if seek is cheap, search from our current position, so
234                  * that swap is allocated from all over the partition: if the
235                  * Flash Translation Layer only remaps within limited zones,
236                  * we don't want to wear out the first zone too quickly.
237                  */
238                 if (!(si->flags & SWP_SOLIDSTATE))
239                         scan_base = offset = si->lowest_bit;
240                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
241 
242                 /* Locate the first empty (unaligned) cluster */
243                 for (; last_in_cluster <= si->highest_bit; offset++) {
244                         if (si->swap_map[offset])
245                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
246                         else if (offset == last_in_cluster) {
247                                 spin_lock(&si->lock);
248                                 offset -= SWAPFILE_CLUSTER - 1;
249                                 si->cluster_next = offset;
250                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
251                                 found_free_cluster = 1;
252                                 goto checks;
253                         }
254                         if (unlikely(--latency_ration < 0)) {
255                                 cond_resched();
256                                 latency_ration = LATENCY_LIMIT;
257                         }
258                 }
259 
260                 offset = si->lowest_bit;
261                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
262 
263                 /* Locate the first empty (unaligned) cluster */
264                 for (; last_in_cluster < scan_base; offset++) {
265                         if (si->swap_map[offset])
266                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
267                         else if (offset == last_in_cluster) {
268                                 spin_lock(&si->lock);
269                                 offset -= SWAPFILE_CLUSTER - 1;
270                                 si->cluster_next = offset;
271                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
272                                 found_free_cluster = 1;
273                                 goto checks;
274                         }
275                         if (unlikely(--latency_ration < 0)) {
276                                 cond_resched();
277                                 latency_ration = LATENCY_LIMIT;
278                         }
279                 }
280 
281                 offset = scan_base;
282                 spin_lock(&si->lock);
283                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
284                 si->lowest_alloc = 0;
285         }
286 
287 checks:
288         if (!(si->flags & SWP_WRITEOK))
289                 goto no_page;
290         if (!si->highest_bit)
291                 goto no_page;
292         if (offset > si->highest_bit)
293                 scan_base = offset = si->lowest_bit;
294 
295         /* reuse swap entry of cache-only swap if not busy. */
296         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
297                 int swap_was_freed;
298                 spin_unlock(&si->lock);
299                 swap_was_freed = __try_to_reclaim_swap(si, offset);
300                 spin_lock(&si->lock);
301                 /* entry was freed successfully, try to use this again */
302                 if (swap_was_freed)
303                         goto checks;
304                 goto scan; /* check next one */
305         }
306 
307         if (si->swap_map[offset])
308                 goto scan;
309 
310         if (offset == si->lowest_bit)
311                 si->lowest_bit++;
312         if (offset == si->highest_bit)
313                 si->highest_bit--;
314         si->inuse_pages++;
315         if (si->inuse_pages == si->pages) {
316                 si->lowest_bit = si->max;
317                 si->highest_bit = 0;
318         }
319         si->swap_map[offset] = usage;
320         si->cluster_next = offset + 1;
321         si->flags -= SWP_SCANNING;
322 
323         if (si->lowest_alloc) {
324                 /*
325                  * Only set when SWP_DISCARDABLE, and there's a scan
326                  * for a free cluster in progress or just completed.
327                  */
328                 if (found_free_cluster) {
329                         /*
330                          * To optimize wear-levelling, discard the
331                          * old data of the cluster, taking care not to
332                          * discard any of its pages that have already
333                          * been allocated by racing tasks (offset has
334                          * already stepped over any at the beginning).
335                          */
336                         if (offset < si->highest_alloc &&
337                             si->lowest_alloc <= last_in_cluster)
338                                 last_in_cluster = si->lowest_alloc - 1;
339                         si->flags |= SWP_DISCARDING;
340                         spin_unlock(&si->lock);
341 
342                         if (offset < last_in_cluster)
343                                 discard_swap_cluster(si, offset,
344                                         last_in_cluster - offset + 1);
345 
346                         spin_lock(&si->lock);
347                         si->lowest_alloc = 0;
348                         si->flags &= ~SWP_DISCARDING;
349 
350                         smp_mb();       /* wake_up_bit advises this */
351                         wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
352 
353                 } else if (si->flags & SWP_DISCARDING) {
354                         /*
355                          * Delay using pages allocated by racing tasks
356                          * until the whole discard has been issued. We
357                          * could defer that delay until swap_writepage,
358                          * but it's easier to keep this self-contained.
359                          */
360                         spin_unlock(&si->lock);
361                         wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
362                                 wait_for_discard, TASK_UNINTERRUPTIBLE);
363                         spin_lock(&si->lock);
364                 } else {
365                         /*
366                          * Note pages allocated by racing tasks while
367                          * scan for a free cluster is in progress, so
368                          * that its final discard can exclude them.
369                          */
370                         if (offset < si->lowest_alloc)
371                                 si->lowest_alloc = offset;
372                         if (offset > si->highest_alloc)
373                                 si->highest_alloc = offset;
374                 }
375         }
376         return offset;
377 
378 scan:
379         spin_unlock(&si->lock);
380         while (++offset <= si->highest_bit) {
381                 if (!si->swap_map[offset]) {
382                         spin_lock(&si->lock);
383                         goto checks;
384                 }
385                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
386                         spin_lock(&si->lock);
387                         goto checks;
388                 }
389                 if (unlikely(--latency_ration < 0)) {
390                         cond_resched();
391                         latency_ration = LATENCY_LIMIT;
392                 }
393         }
394         offset = si->lowest_bit;
395         while (++offset < scan_base) {
396                 if (!si->swap_map[offset]) {
397                         spin_lock(&si->lock);
398                         goto checks;
399                 }
400                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
401                         spin_lock(&si->lock);
402                         goto checks;
403                 }
404                 if (unlikely(--latency_ration < 0)) {
405                         cond_resched();
406                         latency_ration = LATENCY_LIMIT;
407                 }
408         }
409         spin_lock(&si->lock);
410 
411 no_page:
412         si->flags -= SWP_SCANNING;
413         return 0;
414 }
415 
416 swp_entry_t get_swap_page(void)
417 {
418         struct swap_info_struct *si;
419         pgoff_t offset;
420         int type, next;
421         int wrapped = 0;
422         int hp_index;
423 
424         spin_lock(&swap_lock);
425         if (atomic_long_read(&nr_swap_pages) <= 0)
426                 goto noswap;
427         atomic_long_dec(&nr_swap_pages);
428 
429         for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
430                 hp_index = atomic_xchg(&highest_priority_index, -1);
431                 /*
432                  * highest_priority_index records current highest priority swap
433                  * type which just frees swap entries. If its priority is
434                  * higher than that of swap_list.next swap type, we use it.  It
435                  * isn't protected by swap_lock, so it can be an invalid value
436                  * if the corresponding swap type is swapoff. We double check
437                  * the flags here. It's even possible the swap type is swapoff
438                  * and swapon again and its priority is changed. In such rare
439                  * case, low prority swap type might be used, but eventually
440                  * high priority swap will be used after several rounds of
441                  * swap.
442                  */
443                 if (hp_index != -1 && hp_index != type &&
444                     swap_info[type]->prio < swap_info[hp_index]->prio &&
445                     (swap_info[hp_index]->flags & SWP_WRITEOK)) {
446                         type = hp_index;
447                         swap_list.next = type;
448                 }
449 
450                 si = swap_info[type];
451                 next = si->next;
452                 if (next < 0 ||
453                     (!wrapped && si->prio != swap_info[next]->prio)) {
454                         next = swap_list.head;
455                         wrapped++;
456                 }
457 
458                 spin_lock(&si->lock);
459                 if (!si->highest_bit) {
460                         spin_unlock(&si->lock);
461                         continue;
462                 }
463                 if (!(si->flags & SWP_WRITEOK)) {
464                         spin_unlock(&si->lock);
465                         continue;
466                 }
467 
468                 swap_list.next = next;
469 
470                 spin_unlock(&swap_lock);
471                 /* This is called for allocating swap entry for cache */
472                 offset = scan_swap_map(si, SWAP_HAS_CACHE);
473                 spin_unlock(&si->lock);
474                 if (offset)
475                         return swp_entry(type, offset);
476                 spin_lock(&swap_lock);
477                 next = swap_list.next;
478         }
479 
480         atomic_long_inc(&nr_swap_pages);
481 noswap:
482         spin_unlock(&swap_lock);
483         return (swp_entry_t) {0};
484 }
485 
486 /* The only caller of this function is now susupend routine */
487 swp_entry_t get_swap_page_of_type(int type)
488 {
489         struct swap_info_struct *si;
490         pgoff_t offset;
491 
492         si = swap_info[type];
493         spin_lock(&si->lock);
494         if (si && (si->flags & SWP_WRITEOK)) {
495                 atomic_long_dec(&nr_swap_pages);
496                 /* This is called for allocating swap entry, not cache */
497                 offset = scan_swap_map(si, 1);
498                 if (offset) {
499                         spin_unlock(&si->lock);
500                         return swp_entry(type, offset);
501                 }
502                 atomic_long_inc(&nr_swap_pages);
503         }
504         spin_unlock(&si->lock);
505         return (swp_entry_t) {0};
506 }
507 
508 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
509 {
510         struct swap_info_struct *p;
511         unsigned long offset, type;
512 
513         if (!entry.val)
514                 goto out;
515         type = swp_type(entry);
516         if (type >= nr_swapfiles)
517                 goto bad_nofile;
518         p = swap_info[type];
519         if (!(p->flags & SWP_USED))
520                 goto bad_device;
521         offset = swp_offset(entry);
522         if (offset >= p->max)
523                 goto bad_offset;
524         if (!p->swap_map[offset])
525                 goto bad_free;
526         spin_lock(&p->lock);
527         return p;
528 
529 bad_free:
530         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
531         goto out;
532 bad_offset:
533         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
534         goto out;
535 bad_device:
536         printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
537         goto out;
538 bad_nofile:
539         printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
540 out:
541         return NULL;
542 }
543 
544 /*
545  * This swap type frees swap entry, check if it is the highest priority swap
546  * type which just frees swap entry. get_swap_page() uses
547  * highest_priority_index to search highest priority swap type. The
548  * swap_info_struct.lock can't protect us if there are multiple swap types
549  * active, so we use atomic_cmpxchg.
550  */
551 static void set_highest_priority_index(int type)
552 {
553         int old_hp_index, new_hp_index;
554 
555         do {
556                 old_hp_index = atomic_read(&highest_priority_index);
557                 if (old_hp_index != -1 &&
558                         swap_info[old_hp_index]->prio >= swap_info[type]->prio)
559                         break;
560                 new_hp_index = type;
561         } while (atomic_cmpxchg(&highest_priority_index,
562                 old_hp_index, new_hp_index) != old_hp_index);
563 }
564 
565 static unsigned char swap_entry_free(struct swap_info_struct *p,
566                                      swp_entry_t entry, unsigned char usage)
567 {
568         unsigned long offset = swp_offset(entry);
569         unsigned char count;
570         unsigned char has_cache;
571 
572         count = p->swap_map[offset];
573         has_cache = count & SWAP_HAS_CACHE;
574         count &= ~SWAP_HAS_CACHE;
575 
576         if (usage == SWAP_HAS_CACHE) {
577                 VM_BUG_ON(!has_cache);
578                 has_cache = 0;
579         } else if (count == SWAP_MAP_SHMEM) {
580                 /*
581                  * Or we could insist on shmem.c using a special
582                  * swap_shmem_free() and free_shmem_swap_and_cache()...
583                  */
584                 count = 0;
585         } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
586                 if (count == COUNT_CONTINUED) {
587                         if (swap_count_continued(p, offset, count))
588                                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
589                         else
590                                 count = SWAP_MAP_MAX;
591                 } else
592                         count--;
593         }
594 
595         if (!count)
596                 mem_cgroup_uncharge_swap(entry);
597 
598         usage = count | has_cache;
599         p->swap_map[offset] = usage;
600 
601         /* free if no reference */
602         if (!usage) {
603                 if (offset < p->lowest_bit)
604                         p->lowest_bit = offset;
605                 if (offset > p->highest_bit)
606                         p->highest_bit = offset;
607                 set_highest_priority_index(p->type);
608                 atomic_long_inc(&nr_swap_pages);
609                 p->inuse_pages--;
610                 frontswap_invalidate_page(p->type, offset);
611                 if (p->flags & SWP_BLKDEV) {
612                         struct gendisk *disk = p->bdev->bd_disk;
613                         if (disk->fops->swap_slot_free_notify)
614                                 disk->fops->swap_slot_free_notify(p->bdev,
615                                                                   offset);
616                 }
617         }
618 
619         return usage;
620 }
621 
622 /*
623  * Caller has made sure that the swapdevice corresponding to entry
624  * is still around or has not been recycled.
625  */
626 void swap_free(swp_entry_t entry)
627 {
628         struct swap_info_struct *p;
629 
630         p = swap_info_get(entry);
631         if (p) {
632                 swap_entry_free(p, entry, 1);
633                 spin_unlock(&p->lock);
634         }
635 }
636 
637 /*
638  * Called after dropping swapcache to decrease refcnt to swap entries.
639  */
640 void swapcache_free(swp_entry_t entry, struct page *page)
641 {
642         struct swap_info_struct *p;
643         unsigned char count;
644 
645         p = swap_info_get(entry);
646         if (p) {
647                 count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
648                 if (page)
649                         mem_cgroup_uncharge_swapcache(page, entry, count != 0);
650                 spin_unlock(&p->lock);
651         }
652 }
653 
654 /*
655  * How many references to page are currently swapped out?
656  * This does not give an exact answer when swap count is continued,
657  * but does include the high COUNT_CONTINUED flag to allow for that.
658  */
659 int page_swapcount(struct page *page)
660 {
661         int count = 0;
662         struct swap_info_struct *p;
663         swp_entry_t entry;
664 
665         entry.val = page_private(page);
666         p = swap_info_get(entry);
667         if (p) {
668                 count = swap_count(p->swap_map[swp_offset(entry)]);
669                 spin_unlock(&p->lock);
670         }
671         return count;
672 }
673 
674 /*
675  * We can write to an anon page without COW if there are no other references
676  * to it.  And as a side-effect, free up its swap: because the old content
677  * on disk will never be read, and seeking back there to write new content
678  * later would only waste time away from clustering.
679  */
680 int reuse_swap_page(struct page *page)
681 {
682         int count;
683 
684         VM_BUG_ON(!PageLocked(page));
685         if (unlikely(PageKsm(page)))
686                 return 0;
687         count = page_mapcount(page);
688         if (count <= 1 && PageSwapCache(page)) {
689                 count += page_swapcount(page);
690                 if (count == 1 && !PageWriteback(page)) {
691                         delete_from_swap_cache(page);
692                         SetPageDirty(page);
693                 }
694         }
695         return count <= 1;
696 }
697 
698 /*
699  * If swap is getting full, or if there are no more mappings of this page,
700  * then try_to_free_swap is called to free its swap space.
701  */
702 int try_to_free_swap(struct page *page)
703 {
704         VM_BUG_ON(!PageLocked(page));
705 
706         if (!PageSwapCache(page))
707                 return 0;
708         if (PageWriteback(page))
709                 return 0;
710         if (page_swapcount(page))
711                 return 0;
712 
713         /*
714          * Once hibernation has begun to create its image of memory,
715          * there's a danger that one of the calls to try_to_free_swap()
716          * - most probably a call from __try_to_reclaim_swap() while
717          * hibernation is allocating its own swap pages for the image,
718          * but conceivably even a call from memory reclaim - will free
719          * the swap from a page which has already been recorded in the
720          * image as a clean swapcache page, and then reuse its swap for
721          * another page of the image.  On waking from hibernation, the
722          * original page might be freed under memory pressure, then
723          * later read back in from swap, now with the wrong data.
724          *
725          * Hibration suspends storage while it is writing the image
726          * to disk so check that here.
727          */
728         if (pm_suspended_storage())
729                 return 0;
730 
731         delete_from_swap_cache(page);
732         SetPageDirty(page);
733         return 1;
734 }
735 
736 /*
737  * Free the swap entry like above, but also try to
738  * free the page cache entry if it is the last user.
739  */
740 int free_swap_and_cache(swp_entry_t entry)
741 {
742         struct swap_info_struct *p;
743         struct page *page = NULL;
744 
745         if (non_swap_entry(entry))
746                 return 1;
747 
748         p = swap_info_get(entry);
749         if (p) {
750                 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
751                         page = find_get_page(swap_address_space(entry),
752                                                 entry.val);
753                         if (page && !trylock_page(page)) {
754                                 page_cache_release(page);
755                                 page = NULL;
756                         }
757                 }
758                 spin_unlock(&p->lock);
759         }
760         if (page) {
761                 /*
762                  * Not mapped elsewhere, or swap space full? Free it!
763                  * Also recheck PageSwapCache now page is locked (above).
764                  */
765                 if (PageSwapCache(page) && !PageWriteback(page) &&
766                                 (!page_mapped(page) || vm_swap_full())) {
767                         delete_from_swap_cache(page);
768                         SetPageDirty(page);
769                 }
770                 unlock_page(page);
771                 page_cache_release(page);
772         }
773         return p != NULL;
774 }
775 
776 #ifdef CONFIG_HIBERNATION
777 /*
778  * Find the swap type that corresponds to given device (if any).
779  *
780  * @offset - number of the PAGE_SIZE-sized block of the device, starting
781  * from 0, in which the swap header is expected to be located.
782  *
783  * This is needed for the suspend to disk (aka swsusp).
784  */
785 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
786 {
787         struct block_device *bdev = NULL;
788         int type;
789 
790         if (device)
791                 bdev = bdget(device);
792 
793         spin_lock(&swap_lock);
794         for (type = 0; type < nr_swapfiles; type++) {
795                 struct swap_info_struct *sis = swap_info[type];
796 
797                 if (!(sis->flags & SWP_WRITEOK))
798                         continue;
799 
800                 if (!bdev) {
801                         if (bdev_p)
802                                 *bdev_p = bdgrab(sis->bdev);
803 
804                         spin_unlock(&swap_lock);
805                         return type;
806                 }
807                 if (bdev == sis->bdev) {
808                         struct swap_extent *se = &sis->first_swap_extent;
809 
810                         if (se->start_block == offset) {
811                                 if (bdev_p)
812                                         *bdev_p = bdgrab(sis->bdev);
813 
814                                 spin_unlock(&swap_lock);
815                                 bdput(bdev);
816                                 return type;
817                         }
818                 }
819         }
820         spin_unlock(&swap_lock);
821         if (bdev)
822                 bdput(bdev);
823 
824         return -ENODEV;
825 }
826 
827 /*
828  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
829  * corresponding to given index in swap_info (swap type).
830  */
831 sector_t swapdev_block(int type, pgoff_t offset)
832 {
833         struct block_device *bdev;
834 
835         if ((unsigned int)type >= nr_swapfiles)
836                 return 0;
837         if (!(swap_info[type]->flags & SWP_WRITEOK))
838                 return 0;
839         return map_swap_entry(swp_entry(type, offset), &bdev);
840 }
841 
842 /*
843  * Return either the total number of swap pages of given type, or the number
844  * of free pages of that type (depending on @free)
845  *
846  * This is needed for software suspend
847  */
848 unsigned int count_swap_pages(int type, int free)
849 {
850         unsigned int n = 0;
851 
852         spin_lock(&swap_lock);
853         if ((unsigned int)type < nr_swapfiles) {
854                 struct swap_info_struct *sis = swap_info[type];
855 
856                 spin_lock(&sis->lock);
857                 if (sis->flags & SWP_WRITEOK) {
858                         n = sis->pages;
859                         if (free)
860                                 n -= sis->inuse_pages;
861                 }
862                 spin_unlock(&sis->lock);
863         }
864         spin_unlock(&swap_lock);
865         return n;
866 }
867 #endif /* CONFIG_HIBERNATION */
868 
869 /*
870  * No need to decide whether this PTE shares the swap entry with others,
871  * just let do_wp_page work it out if a write is requested later - to
872  * force COW, vm_page_prot omits write permission from any private vma.
873  */
874 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
875                 unsigned long addr, swp_entry_t entry, struct page *page)
876 {
877         struct page *swapcache;
878         struct mem_cgroup *memcg;
879         spinlock_t *ptl;
880         pte_t *pte;
881         int ret = 1;
882 
883         swapcache = page;
884         page = ksm_might_need_to_copy(page, vma, addr);
885         if (unlikely(!page))
886                 return -ENOMEM;
887 
888         if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
889                                          GFP_KERNEL, &memcg)) {
890                 ret = -ENOMEM;
891                 goto out_nolock;
892         }
893 
894         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
895         if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
896                 mem_cgroup_cancel_charge_swapin(memcg);
897                 ret = 0;
898                 goto out;
899         }
900 
901         dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
902         inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
903         get_page(page);
904         set_pte_at(vma->vm_mm, addr, pte,
905                    pte_mkold(mk_pte(page, vma->vm_page_prot)));
906         if (page == swapcache)
907                 page_add_anon_rmap(page, vma, addr);
908         else /* ksm created a completely new copy */
909                 page_add_new_anon_rmap(page, vma, addr);
910         mem_cgroup_commit_charge_swapin(page, memcg);
911         swap_free(entry);
912         /*
913          * Move the page to the active list so it is not
914          * immediately swapped out again after swapon.
915          */
916         activate_page(page);
917 out:
918         pte_unmap_unlock(pte, ptl);
919 out_nolock:
920         if (page != swapcache) {
921                 unlock_page(page);
922                 put_page(page);
923         }
924         return ret;
925 }
926 
927 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
928                                 unsigned long addr, unsigned long end,
929                                 swp_entry_t entry, struct page *page)
930 {
931         pte_t swp_pte = swp_entry_to_pte(entry);
932         pte_t *pte;
933         int ret = 0;
934 
935         /*
936          * We don't actually need pte lock while scanning for swp_pte: since
937          * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
938          * page table while we're scanning; though it could get zapped, and on
939          * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
940          * of unmatched parts which look like swp_pte, so unuse_pte must
941          * recheck under pte lock.  Scanning without pte lock lets it be
942          * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
943          */
944         pte = pte_offset_map(pmd, addr);
945         do {
946                 /*
947                  * swapoff spends a _lot_ of time in this loop!
948                  * Test inline before going to call unuse_pte.
949                  */
950                 if (unlikely(pte_same(*pte, swp_pte))) {
951                         pte_unmap(pte);
952                         ret = unuse_pte(vma, pmd, addr, entry, page);
953                         if (ret)
954                                 goto out;
955                         pte = pte_offset_map(pmd, addr);
956                 }
957         } while (pte++, addr += PAGE_SIZE, addr != end);
958         pte_unmap(pte - 1);
959 out:
960         return ret;
961 }
962 
963 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
964                                 unsigned long addr, unsigned long end,
965                                 swp_entry_t entry, struct page *page)
966 {
967         pmd_t *pmd;
968         unsigned long next;
969         int ret;
970 
971         pmd = pmd_offset(pud, addr);
972         do {
973                 next = pmd_addr_end(addr, end);
974                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
975                         continue;
976                 ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
977                 if (ret)
978                         return ret;
979         } while (pmd++, addr = next, addr != end);
980         return 0;
981 }
982 
983 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
984                                 unsigned long addr, unsigned long end,
985                                 swp_entry_t entry, struct page *page)
986 {
987         pud_t *pud;
988         unsigned long next;
989         int ret;
990 
991         pud = pud_offset(pgd, addr);
992         do {
993                 next = pud_addr_end(addr, end);
994                 if (pud_none_or_clear_bad(pud))
995                         continue;
996                 ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
997                 if (ret)
998                         return ret;
999         } while (pud++, addr = next, addr != end);
1000         return 0;
1001 }
1002 
1003 static int unuse_vma(struct vm_area_struct *vma,
1004                                 swp_entry_t entry, struct page *page)
1005 {
1006         pgd_t *pgd;
1007         unsigned long addr, end, next;
1008         int ret;
1009 
1010         if (page_anon_vma(page)) {
1011                 addr = page_address_in_vma(page, vma);
1012                 if (addr == -EFAULT)
1013                         return 0;
1014                 else
1015                         end = addr + PAGE_SIZE;
1016         } else {
1017                 addr = vma->vm_start;
1018                 end = vma->vm_end;
1019         }
1020 
1021         pgd = pgd_offset(vma->vm_mm, addr);
1022         do {
1023                 next = pgd_addr_end(addr, end);
1024                 if (pgd_none_or_clear_bad(pgd))
1025                         continue;
1026                 ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1027                 if (ret)
1028                         return ret;
1029         } while (pgd++, addr = next, addr != end);
1030         return 0;
1031 }
1032 
1033 static int unuse_mm(struct mm_struct *mm,
1034                                 swp_entry_t entry, struct page *page)
1035 {
1036         struct vm_area_struct *vma;
1037         int ret = 0;
1038 
1039         if (!down_read_trylock(&mm->mmap_sem)) {
1040                 /*
1041                  * Activate page so shrink_inactive_list is unlikely to unmap
1042                  * its ptes while lock is dropped, so swapoff can make progress.
1043                  */
1044                 activate_page(page);
1045                 unlock_page(page);
1046                 down_read(&mm->mmap_sem);
1047                 lock_page(page);
1048         }
1049         for (vma = mm->mmap; vma; vma = vma->vm_next) {
1050                 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1051                         break;
1052         }
1053         up_read(&mm->mmap_sem);
1054         return (ret < 0)? ret: 0;
1055 }
1056 
1057 /*
1058  * Scan swap_map (or frontswap_map if frontswap parameter is true)
1059  * from current position to next entry still in use.
1060  * Recycle to start on reaching the end, returning 0 when empty.
1061  */
1062 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1063                                         unsigned int prev, bool frontswap)
1064 {
1065         unsigned int max = si->max;
1066         unsigned int i = prev;
1067         unsigned char count;
1068 
1069         /*
1070          * No need for swap_lock here: we're just looking
1071          * for whether an entry is in use, not modifying it; false
1072          * hits are okay, and sys_swapoff() has already prevented new
1073          * allocations from this area (while holding swap_lock).
1074          */
1075         for (;;) {
1076                 if (++i >= max) {
1077                         if (!prev) {
1078                                 i = 0;
1079                                 break;
1080                         }
1081                         /*
1082                          * No entries in use at top of swap_map,
1083                          * loop back to start and recheck there.
1084                          */
1085                         max = prev + 1;
1086                         prev = 0;
1087                         i = 1;
1088                 }
1089                 if (frontswap) {
1090                         if (frontswap_test(si, i))
1091                                 break;
1092                         else
1093                                 continue;
1094                 }
1095                 count = si->swap_map[i];
1096                 if (count && swap_count(count) != SWAP_MAP_BAD)
1097                         break;
1098         }
1099         return i;
1100 }
1101 
1102 /*
1103  * We completely avoid races by reading each swap page in advance,
1104  * and then search for the process using it.  All the necessary
1105  * page table adjustments can then be made atomically.
1106  *
1107  * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1108  * pages_to_unuse==0 means all pages; ignored if frontswap is false
1109  */
1110 int try_to_unuse(unsigned int type, bool frontswap,
1111                  unsigned long pages_to_unuse)
1112 {
1113         struct swap_info_struct *si = swap_info[type];
1114         struct mm_struct *start_mm;
1115         unsigned char *swap_map;
1116         unsigned char swcount;
1117         struct page *page;
1118         swp_entry_t entry;
1119         unsigned int i = 0;
1120         int retval = 0;
1121 
1122         /*
1123          * When searching mms for an entry, a good strategy is to
1124          * start at the first mm we freed the previous entry from
1125          * (though actually we don't notice whether we or coincidence
1126          * freed the entry).  Initialize this start_mm with a hold.
1127          *
1128          * A simpler strategy would be to start at the last mm we
1129          * freed the previous entry from; but that would take less
1130          * advantage of mmlist ordering, which clusters forked mms
1131          * together, child after parent.  If we race with dup_mmap(), we
1132          * prefer to resolve parent before child, lest we miss entries
1133          * duplicated after we scanned child: using last mm would invert
1134          * that.
1135          */
1136         start_mm = &init_mm;
1137         atomic_inc(&init_mm.mm_users);
1138 
1139         /*
1140          * Keep on scanning until all entries have gone.  Usually,
1141          * one pass through swap_map is enough, but not necessarily:
1142          * there are races when an instance of an entry might be missed.
1143          */
1144         while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1145                 if (signal_pending(current)) {
1146                         retval = -EINTR;
1147                         break;
1148                 }
1149 
1150                 /*
1151                  * Get a page for the entry, using the existing swap
1152                  * cache page if there is one.  Otherwise, get a clean
1153                  * page and read the swap into it.
1154                  */
1155                 swap_map = &si->swap_map[i];
1156                 entry = swp_entry(type, i);
1157                 page = read_swap_cache_async(entry,
1158                                         GFP_HIGHUSER_MOVABLE, NULL, 0);
1159                 if (!page) {
1160                         /*
1161                          * Either swap_duplicate() failed because entry
1162                          * has been freed independently, and will not be
1163                          * reused since sys_swapoff() already disabled
1164                          * allocation from here, or alloc_page() failed.
1165                          */
1166                         if (!*swap_map)
1167                                 continue;
1168                         retval = -ENOMEM;
1169                         break;
1170                 }
1171 
1172                 /*
1173                  * Don't hold on to start_mm if it looks like exiting.
1174                  */
1175                 if (atomic_read(&start_mm->mm_users) == 1) {
1176                         mmput(start_mm);
1177                         start_mm = &init_mm;
1178                         atomic_inc(&init_mm.mm_users);
1179                 }
1180 
1181                 /*
1182                  * Wait for and lock page.  When do_swap_page races with
1183                  * try_to_unuse, do_swap_page can handle the fault much
1184                  * faster than try_to_unuse can locate the entry.  This
1185                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
1186                  * defer to do_swap_page in such a case - in some tests,
1187                  * do_swap_page and try_to_unuse repeatedly compete.
1188                  */
1189                 wait_on_page_locked(page);
1190                 wait_on_page_writeback(page);
1191                 lock_page(page);
1192                 wait_on_page_writeback(page);
1193 
1194                 /*
1195                  * Remove all references to entry.
1196                  */
1197                 swcount = *swap_map;
1198                 if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1199                         retval = shmem_unuse(entry, page);
1200                         /* page has already been unlocked and released */
1201                         if (retval < 0)
1202                                 break;
1203                         continue;
1204                 }
1205                 if (swap_count(swcount) && start_mm != &init_mm)
1206                         retval = unuse_mm(start_mm, entry, page);
1207 
1208                 if (swap_count(*swap_map)) {
1209                         int set_start_mm = (*swap_map >= swcount);
1210                         struct list_head *p = &start_mm->mmlist;
1211                         struct mm_struct *new_start_mm = start_mm;
1212                         struct mm_struct *prev_mm = start_mm;
1213                         struct mm_struct *mm;
1214 
1215                         atomic_inc(&new_start_mm->mm_users);
1216                         atomic_inc(&prev_mm->mm_users);
1217                         spin_lock(&mmlist_lock);
1218                         while (swap_count(*swap_map) && !retval &&
1219                                         (p = p->next) != &start_mm->mmlist) {
1220                                 mm = list_entry(p, struct mm_struct, mmlist);
1221                                 if (!atomic_inc_not_zero(&mm->mm_users))
1222                                         continue;
1223                                 spin_unlock(&mmlist_lock);
1224                                 mmput(prev_mm);
1225                                 prev_mm = mm;
1226 
1227                                 cond_resched();
1228 
1229                                 swcount = *swap_map;
1230                                 if (!swap_count(swcount)) /* any usage ? */
1231                                         ;
1232                                 else if (mm == &init_mm)
1233                                         set_start_mm = 1;
1234                                 else
1235                                         retval = unuse_mm(mm, entry, page);
1236 
1237                                 if (set_start_mm && *swap_map < swcount) {
1238                                         mmput(new_start_mm);
1239                                         atomic_inc(&mm->mm_users);
1240                                         new_start_mm = mm;
1241                                         set_start_mm = 0;
1242                                 }
1243                                 spin_lock(&mmlist_lock);
1244                         }
1245                         spin_unlock(&mmlist_lock);
1246                         mmput(prev_mm);
1247                         mmput(start_mm);
1248                         start_mm = new_start_mm;
1249                 }
1250                 if (retval) {
1251                         unlock_page(page);
1252                         page_cache_release(page);
1253                         break;
1254                 }
1255 
1256                 /*
1257                  * If a reference remains (rare), we would like to leave
1258                  * the page in the swap cache; but try_to_unmap could
1259                  * then re-duplicate the entry once we drop page lock,
1260                  * so we might loop indefinitely; also, that page could
1261                  * not be swapped out to other storage meanwhile.  So:
1262                  * delete from cache even if there's another reference,
1263                  * after ensuring that the data has been saved to disk -
1264                  * since if the reference remains (rarer), it will be
1265                  * read from disk into another page.  Splitting into two
1266                  * pages would be incorrect if swap supported "shared
1267                  * private" pages, but they are handled by tmpfs files.
1268                  *
1269                  * Given how unuse_vma() targets one particular offset
1270                  * in an anon_vma, once the anon_vma has been determined,
1271                  * this splitting happens to be just what is needed to
1272                  * handle where KSM pages have been swapped out: re-reading
1273                  * is unnecessarily slow, but we can fix that later on.
1274                  */
1275                 if (swap_count(*swap_map) &&
1276                      PageDirty(page) && PageSwapCache(page)) {
1277                         struct writeback_control wbc = {
1278                                 .sync_mode = WB_SYNC_NONE,
1279                         };
1280 
1281                         swap_writepage(page, &wbc);
1282                         lock_page(page);
1283                         wait_on_page_writeback(page);
1284                 }
1285 
1286                 /*
1287                  * It is conceivable that a racing task removed this page from
1288                  * swap cache just before we acquired the page lock at the top,
1289                  * or while we dropped it in unuse_mm().  The page might even
1290                  * be back in swap cache on another swap area: that we must not
1291                  * delete, since it may not have been written out to swap yet.
1292                  */
1293                 if (PageSwapCache(page) &&
1294                     likely(page_private(page) == entry.val))
1295                         delete_from_swap_cache(page);
1296 
1297                 /*
1298                  * So we could skip searching mms once swap count went
1299                  * to 1, we did not mark any present ptes as dirty: must
1300                  * mark page dirty so shrink_page_list will preserve it.
1301                  */
1302                 SetPageDirty(page);
1303                 unlock_page(page);
1304                 page_cache_release(page);
1305 
1306                 /*
1307                  * Make sure that we aren't completely killing
1308                  * interactive performance.
1309                  */
1310                 cond_resched();
1311                 if (frontswap && pages_to_unuse > 0) {
1312                         if (!--pages_to_unuse)
1313                                 break;
1314                 }
1315         }
1316 
1317         mmput(start_mm);
1318         return retval;
1319 }
1320 
1321 /*
1322  * After a successful try_to_unuse, if no swap is now in use, we know
1323  * we can empty the mmlist.  swap_lock must be held on entry and exit.
1324  * Note that mmlist_lock nests inside swap_lock, and an mm must be
1325  * added to the mmlist just after page_duplicate - before would be racy.
1326  */
1327 static void drain_mmlist(void)
1328 {
1329         struct list_head *p, *next;
1330         unsigned int type;
1331 
1332         for (type = 0; type < nr_swapfiles; type++)
1333                 if (swap_info[type]->inuse_pages)
1334                         return;
1335         spin_lock(&mmlist_lock);
1336         list_for_each_safe(p, next, &init_mm.mmlist)
1337                 list_del_init(p);
1338         spin_unlock(&mmlist_lock);
1339 }
1340 
1341 /*
1342  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1343  * corresponds to page offset for the specified swap entry.
1344  * Note that the type of this function is sector_t, but it returns page offset
1345  * into the bdev, not sector offset.
1346  */
1347 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1348 {
1349         struct swap_info_struct *sis;
1350         struct swap_extent *start_se;
1351         struct swap_extent *se;
1352         pgoff_t offset;
1353 
1354         sis = swap_info[swp_type(entry)];
1355         *bdev = sis->bdev;
1356 
1357         offset = swp_offset(entry);
1358         start_se = sis->curr_swap_extent;
1359         se = start_se;
1360 
1361         for ( ; ; ) {
1362                 struct list_head *lh;
1363 
1364                 if (se->start_page <= offset &&
1365                                 offset < (se->start_page + se->nr_pages)) {
1366                         return se->start_block + (offset - se->start_page);
1367                 }
1368                 lh = se->list.next;
1369                 se = list_entry(lh, struct swap_extent, list);
1370                 sis->curr_swap_extent = se;
1371                 BUG_ON(se == start_se);         /* It *must* be present */
1372         }
1373 }
1374 
1375 /*
1376  * Returns the page offset into bdev for the specified page's swap entry.
1377  */
1378 sector_t map_swap_page(struct page *page, struct block_device **bdev)
1379 {
1380         swp_entry_t entry;
1381         entry.val = page_private(page);
1382         return map_swap_entry(entry, bdev);
1383 }
1384 
1385 /*
1386  * Free all of a swapdev's extent information
1387  */
1388 static void destroy_swap_extents(struct swap_info_struct *sis)
1389 {
1390         while (!list_empty(&sis->first_swap_extent.list)) {
1391                 struct swap_extent *se;
1392 
1393                 se = list_entry(sis->first_swap_extent.list.next,
1394                                 struct swap_extent, list);
1395                 list_del(&se->list);
1396                 kfree(se);
1397         }
1398 
1399         if (sis->flags & SWP_FILE) {
1400                 struct file *swap_file = sis->swap_file;
1401                 struct address_space *mapping = swap_file->f_mapping;
1402 
1403                 sis->flags &= ~SWP_FILE;
1404                 mapping->a_ops->swap_deactivate(swap_file);
1405         }
1406 }
1407 
1408 /*
1409  * Add a block range (and the corresponding page range) into this swapdev's
1410  * extent list.  The extent list is kept sorted in page order.
1411  *
1412  * This function rather assumes that it is called in ascending page order.
1413  */
1414 int
1415 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1416                 unsigned long nr_pages, sector_t start_block)
1417 {
1418         struct swap_extent *se;
1419         struct swap_extent *new_se;
1420         struct list_head *lh;
1421 
1422         if (start_page == 0) {
1423                 se = &sis->first_swap_extent;
1424                 sis->curr_swap_extent = se;
1425                 se->start_page = 0;
1426                 se->nr_pages = nr_pages;
1427                 se->start_block = start_block;
1428                 return 1;
1429         } else {
1430                 lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1431                 se = list_entry(lh, struct swap_extent, list);
1432                 BUG_ON(se->start_page + se->nr_pages != start_page);
1433                 if (se->start_block + se->nr_pages == start_block) {
1434                         /* Merge it */
1435                         se->nr_pages += nr_pages;
1436                         return 0;
1437                 }
1438         }
1439 
1440         /*
1441          * No merge.  Insert a new extent, preserving ordering.
1442          */
1443         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1444         if (new_se == NULL)
1445                 return -ENOMEM;
1446         new_se->start_page = start_page;
1447         new_se->nr_pages = nr_pages;
1448         new_se->start_block = start_block;
1449 
1450         list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1451         return 1;
1452 }
1453 
1454 /*
1455  * A `swap extent' is a simple thing which maps a contiguous range of pages
1456  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1457  * is built at swapon time and is then used at swap_writepage/swap_readpage
1458  * time for locating where on disk a page belongs.
1459  *
1460  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1461  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1462  * swap files identically.
1463  *
1464  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1465  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1466  * swapfiles are handled *identically* after swapon time.
1467  *
1468  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1469  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1470  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1471  * requirements, they are simply tossed out - we will never use those blocks
1472  * for swapping.
1473  *
1474  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1475  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1476  * which will scribble on the fs.
1477  *
1478  * The amount of disk space which a single swap extent represents varies.
1479  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1480  * extents in the list.  To avoid much list walking, we cache the previous
1481  * search location in `curr_swap_extent', and start new searches from there.
1482  * This is extremely effective.  The average number of iterations in
1483  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1484  */
1485 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1486 {
1487         struct file *swap_file = sis->swap_file;
1488         struct address_space *mapping = swap_file->f_mapping;
1489         struct inode *inode = mapping->host;
1490         int ret;
1491 
1492         if (S_ISBLK(inode->i_mode)) {
1493                 ret = add_swap_extent(sis, 0, sis->max, 0);
1494                 *span = sis->pages;
1495                 return ret;
1496         }
1497 
1498         if (mapping->a_ops->swap_activate) {
1499                 ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1500                 if (!ret) {
1501                         sis->flags |= SWP_FILE;
1502                         ret = add_swap_extent(sis, 0, sis->max, 0);
1503                         *span = sis->pages;
1504                 }
1505                 return ret;
1506         }
1507 
1508         return generic_swapfile_activate(sis, swap_file, span);
1509 }
1510 
1511 static void _enable_swap_info(struct swap_info_struct *p, int prio,
1512                                 unsigned char *swap_map,
1513                                 unsigned long *frontswap_map)
1514 {
1515         int i, prev;
1516 
1517         if (prio >= 0)
1518                 p->prio = prio;
1519         else
1520                 p->prio = --least_priority;
1521         p->swap_map = swap_map;
1522         frontswap_map_set(p, frontswap_map);
1523         p->flags |= SWP_WRITEOK;
1524         atomic_long_add(p->pages, &nr_swap_pages);
1525         total_swap_pages += p->pages;
1526 
1527         /* insert swap space into swap_list: */
1528         prev = -1;
1529         for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1530                 if (p->prio >= swap_info[i]->prio)
1531                         break;
1532                 prev = i;
1533         }
1534         p->next = i;
1535         if (prev < 0)
1536                 swap_list.head = swap_list.next = p->type;
1537         else
1538                 swap_info[prev]->next = p->type;
1539 }
1540 
1541 static void enable_swap_info(struct swap_info_struct *p, int prio,
1542                                 unsigned char *swap_map,
1543                                 unsigned long *frontswap_map)
1544 {
1545         spin_lock(&swap_lock);
1546         spin_lock(&p->lock);
1547         _enable_swap_info(p, prio, swap_map, frontswap_map);
1548         frontswap_init(p->type);
1549         spin_unlock(&p->lock);
1550         spin_unlock(&swap_lock);
1551 }
1552 
1553 static void reinsert_swap_info(struct swap_info_struct *p)
1554 {
1555         spin_lock(&swap_lock);
1556         spin_lock(&p->lock);
1557         _enable_swap_info(p, p->prio, p->swap_map, frontswap_map_get(p));
1558         spin_unlock(&p->lock);
1559         spin_unlock(&swap_lock);
1560 }
1561 
1562 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1563 {
1564         struct swap_info_struct *p = NULL;
1565         unsigned char *swap_map;
1566         struct file *swap_file, *victim;
1567         struct address_space *mapping;
1568         struct inode *inode;
1569         struct filename *pathname;
1570         int i, type, prev;
1571         int err;
1572 
1573         if (!capable(CAP_SYS_ADMIN))
1574                 return -EPERM;
1575 
1576         BUG_ON(!current->mm);
1577 
1578         pathname = getname(specialfile);
1579         if (IS_ERR(pathname))
1580                 return PTR_ERR(pathname);
1581 
1582         victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1583         err = PTR_ERR(victim);
1584         if (IS_ERR(victim))
1585                 goto out;
1586 
1587         mapping = victim->f_mapping;
1588         prev = -1;
1589         spin_lock(&swap_lock);
1590         for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1591                 p = swap_info[type];
1592                 if (p->flags & SWP_WRITEOK) {
1593                         if (p->swap_file->f_mapping == mapping)
1594                                 break;
1595                 }
1596                 prev = type;
1597         }
1598         if (type < 0) {
1599                 err = -EINVAL;
1600                 spin_unlock(&swap_lock);
1601                 goto out_dput;
1602         }
1603         if (!security_vm_enough_memory_mm(current->mm, p->pages))
1604                 vm_unacct_memory(p->pages);
1605         else {
1606                 err = -ENOMEM;
1607                 spin_unlock(&swap_lock);
1608                 goto out_dput;
1609         }
1610         if (prev < 0)
1611                 swap_list.head = p->next;
1612         else
1613                 swap_info[prev]->next = p->next;
1614         if (type == swap_list.next) {
1615                 /* just pick something that's safe... */
1616                 swap_list.next = swap_list.head;
1617         }
1618         spin_lock(&p->lock);
1619         if (p->prio < 0) {
1620                 for (i = p->next; i >= 0; i = swap_info[i]->next)
1621                         swap_info[i]->prio = p->prio--;
1622                 least_priority++;
1623         }
1624         atomic_long_sub(p->pages, &nr_swap_pages);
1625         total_swap_pages -= p->pages;
1626         p->flags &= ~SWP_WRITEOK;
1627         spin_unlock(&p->lock);
1628         spin_unlock(&swap_lock);
1629 
1630         set_current_oom_origin();
1631         err = try_to_unuse(type, false, 0); /* force all pages to be unused */
1632         clear_current_oom_origin();
1633 
1634         if (err) {
1635                 /* re-insert swap space back into swap_list */
1636                 reinsert_swap_info(p);
1637                 goto out_dput;
1638         }
1639 
1640         destroy_swap_extents(p);
1641         if (p->flags & SWP_CONTINUED)
1642                 free_swap_count_continuations(p);
1643 
1644         mutex_lock(&swapon_mutex);
1645         spin_lock(&swap_lock);
1646         spin_lock(&p->lock);
1647         drain_mmlist();
1648 
1649         /* wait for anyone still in scan_swap_map */
1650         p->highest_bit = 0;             /* cuts scans short */
1651         while (p->flags >= SWP_SCANNING) {
1652                 spin_unlock(&p->lock);
1653                 spin_unlock(&swap_lock);
1654                 schedule_timeout_uninterruptible(1);
1655                 spin_lock(&swap_lock);
1656                 spin_lock(&p->lock);
1657         }
1658 
1659         swap_file = p->swap_file;
1660         p->swap_file = NULL;
1661         p->max = 0;
1662         swap_map = p->swap_map;
1663         p->swap_map = NULL;
1664         p->flags = 0;
1665         frontswap_invalidate_area(type);
1666         spin_unlock(&p->lock);
1667         spin_unlock(&swap_lock);
1668         mutex_unlock(&swapon_mutex);
1669         vfree(swap_map);
1670         vfree(frontswap_map_get(p));
1671         /* Destroy swap account informatin */
1672         swap_cgroup_swapoff(type);
1673 
1674         inode = mapping->host;
1675         if (S_ISBLK(inode->i_mode)) {
1676                 struct block_device *bdev = I_BDEV(inode);
1677                 set_blocksize(bdev, p->old_block_size);
1678                 blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1679         } else {
1680                 mutex_lock(&inode->i_mutex);
1681                 inode->i_flags &= ~S_SWAPFILE;
1682                 mutex_unlock(&inode->i_mutex);
1683         }
1684         filp_close(swap_file, NULL);
1685         err = 0;
1686         atomic_inc(&proc_poll_event);
1687         wake_up_interruptible(&proc_poll_wait);
1688 
1689 out_dput:
1690         filp_close(victim, NULL);
1691 out:
1692         putname(pathname);
1693         return err;
1694 }
1695 
1696 #ifdef CONFIG_PROC_FS
1697 static unsigned swaps_poll(struct file *file, poll_table *wait)
1698 {
1699         struct seq_file *seq = file->private_data;
1700 
1701         poll_wait(file, &proc_poll_wait, wait);
1702 
1703         if (seq->poll_event != atomic_read(&proc_poll_event)) {
1704                 seq->poll_event = atomic_read(&proc_poll_event);
1705                 return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1706         }
1707 
1708         return POLLIN | POLLRDNORM;
1709 }
1710 
1711 /* iterator */
1712 static void *swap_start(struct seq_file *swap, loff_t *pos)
1713 {
1714         struct swap_info_struct *si;
1715         int type;
1716         loff_t l = *pos;
1717 
1718         mutex_lock(&swapon_mutex);
1719 
1720         if (!l)
1721                 return SEQ_START_TOKEN;
1722 
1723         for (type = 0; type < nr_swapfiles; type++) {
1724                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1725                 si = swap_info[type];
1726                 if (!(si->flags & SWP_USED) || !si->swap_map)
1727                         continue;
1728                 if (!--l)
1729                         return si;
1730         }
1731 
1732         return NULL;
1733 }
1734 
1735 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1736 {
1737         struct swap_info_struct *si = v;
1738         int type;
1739 
1740         if (v == SEQ_START_TOKEN)
1741                 type = 0;
1742         else
1743                 type = si->type + 1;
1744 
1745         for (; type < nr_swapfiles; type++) {
1746                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1747                 si = swap_info[type];
1748                 if (!(si->flags & SWP_USED) || !si->swap_map)
1749                         continue;
1750                 ++*pos;
1751                 return si;
1752         }
1753 
1754         return NULL;
1755 }
1756 
1757 static void swap_stop(struct seq_file *swap, void *v)
1758 {
1759         mutex_unlock(&swapon_mutex);
1760 }
1761 
1762 static int swap_show(struct seq_file *swap, void *v)
1763 {
1764         struct swap_info_struct *si = v;
1765         struct file *file;
1766         int len;
1767 
1768         if (si == SEQ_START_TOKEN) {
1769                 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1770                 return 0;
1771         }
1772 
1773         file = si->swap_file;
1774         len = seq_path(swap, &file->f_path, " \t\n\\");
1775         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1776                         len < 40 ? 40 - len : 1, " ",
1777                         S_ISBLK(file_inode(file)->i_mode) ?
1778                                 "partition" : "file\t",
1779                         si->pages << (PAGE_SHIFT - 10),
1780                         si->inuse_pages << (PAGE_SHIFT - 10),
1781                         si->prio);
1782         return 0;
1783 }
1784 
1785 static const struct seq_operations swaps_op = {
1786         .start =        swap_start,
1787         .next =         swap_next,
1788         .stop =         swap_stop,
1789         .show =         swap_show
1790 };
1791 
1792 static int swaps_open(struct inode *inode, struct file *file)
1793 {
1794         struct seq_file *seq;
1795         int ret;
1796 
1797         ret = seq_open(file, &swaps_op);
1798         if (ret)
1799                 return ret;
1800 
1801         seq = file->private_data;
1802         seq->poll_event = atomic_read(&proc_poll_event);
1803         return 0;
1804 }
1805 
1806 static const struct file_operations proc_swaps_operations = {
1807         .open           = swaps_open,
1808         .read           = seq_read,
1809         .llseek         = seq_lseek,
1810         .release        = seq_release,
1811         .poll           = swaps_poll,
1812 };
1813 
1814 static int __init procswaps_init(void)
1815 {
1816         proc_create("swaps", 0, NULL, &proc_swaps_operations);
1817         return 0;
1818 }
1819 __initcall(procswaps_init);
1820 #endif /* CONFIG_PROC_FS */
1821 
1822 #ifdef MAX_SWAPFILES_CHECK
1823 static int __init max_swapfiles_check(void)
1824 {
1825         MAX_SWAPFILES_CHECK();
1826         return 0;
1827 }
1828 late_initcall(max_swapfiles_check);
1829 #endif
1830 
1831 static struct swap_info_struct *alloc_swap_info(void)
1832 {
1833         struct swap_info_struct *p;
1834         unsigned int type;
1835 
1836         p = kzalloc(sizeof(*p), GFP_KERNEL);
1837         if (!p)
1838                 return ERR_PTR(-ENOMEM);
1839 
1840         spin_lock(&swap_lock);
1841         for (type = 0; type < nr_swapfiles; type++) {
1842                 if (!(swap_info[type]->flags & SWP_USED))
1843                         break;
1844         }
1845         if (type >= MAX_SWAPFILES) {
1846                 spin_unlock(&swap_lock);
1847                 kfree(p);
1848                 return ERR_PTR(-EPERM);
1849         }
1850         if (type >= nr_swapfiles) {
1851                 p->type = type;
1852                 swap_info[type] = p;
1853                 /*
1854                  * Write swap_info[type] before nr_swapfiles, in case a
1855                  * racing procfs swap_start() or swap_next() is reading them.
1856                  * (We never shrink nr_swapfiles, we never free this entry.)
1857                  */
1858                 smp_wmb();
1859                 nr_swapfiles++;
1860         } else {
1861                 kfree(p);
1862                 p = swap_info[type];
1863                 /*
1864                  * Do not memset this entry: a racing procfs swap_next()
1865                  * would be relying on p->type to remain valid.
1866                  */
1867         }
1868         INIT_LIST_HEAD(&p->first_swap_extent.list);
1869         p->flags = SWP_USED;
1870         p->next = -1;
1871         spin_unlock(&swap_lock);
1872         spin_lock_init(&p->lock);
1873 
1874         return p;
1875 }
1876 
1877 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1878 {
1879         int error;
1880 
1881         if (S_ISBLK(inode->i_mode)) {
1882                 p->bdev = bdgrab(I_BDEV(inode));
1883                 error = blkdev_get(p->bdev,
1884                                    FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1885                                    sys_swapon);
1886                 if (error < 0) {
1887                         p->bdev = NULL;
1888                         return -EINVAL;
1889                 }
1890                 p->old_block_size = block_size(p->bdev);
1891                 error = set_blocksize(p->bdev, PAGE_SIZE);
1892                 if (error < 0)
1893                         return error;
1894                 p->flags |= SWP_BLKDEV;
1895         } else if (S_ISREG(inode->i_mode)) {
1896                 p->bdev = inode->i_sb->s_bdev;
1897                 mutex_lock(&inode->i_mutex);
1898                 if (IS_SWAPFILE(inode))
1899                         return -EBUSY;
1900         } else
1901                 return -EINVAL;
1902 
1903         return 0;
1904 }
1905 
1906 static unsigned long read_swap_header(struct swap_info_struct *p,
1907                                         union swap_header *swap_header,
1908                                         struct inode *inode)
1909 {
1910         int i;
1911         unsigned long maxpages;
1912         unsigned long swapfilepages;
1913 
1914         if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1915                 printk(KERN_ERR "Unable to find swap-space signature\n");
1916                 return 0;
1917         }
1918 
1919         /* swap partition endianess hack... */
1920         if (swab32(swap_header->info.version) == 1) {
1921                 swab32s(&swap_header->info.version);
1922                 swab32s(&swap_header->info.last_page);
1923                 swab32s(&swap_header->info.nr_badpages);
1924                 for (i = 0; i < swap_header->info.nr_badpages; i++)
1925                         swab32s(&swap_header->info.badpages[i]);
1926         }
1927         /* Check the swap header's sub-version */
1928         if (swap_header->info.version != 1) {
1929                 printk(KERN_WARNING
1930                        "Unable to handle swap header version %d\n",
1931                        swap_header->info.version);
1932                 return 0;
1933         }
1934 
1935         p->lowest_bit  = 1;
1936         p->cluster_next = 1;
1937         p->cluster_nr = 0;
1938 
1939         /*
1940          * Find out how many pages are allowed for a single swap
1941          * device. There are two limiting factors: 1) the number
1942          * of bits for the swap offset in the swp_entry_t type, and
1943          * 2) the number of bits in the swap pte as defined by the
1944          * different architectures. In order to find the
1945          * largest possible bit mask, a swap entry with swap type 0
1946          * and swap offset ~0UL is created, encoded to a swap pte,
1947          * decoded to a swp_entry_t again, and finally the swap
1948          * offset is extracted. This will mask all the bits from
1949          * the initial ~0UL mask that can't be encoded in either
1950          * the swp_entry_t or the architecture definition of a
1951          * swap pte.
1952          */
1953         maxpages = swp_offset(pte_to_swp_entry(
1954                         swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
1955         if (maxpages > swap_header->info.last_page) {
1956                 maxpages = swap_header->info.last_page + 1;
1957                 /* p->max is an unsigned int: don't overflow it */
1958                 if ((unsigned int)maxpages == 0)
1959                         maxpages = UINT_MAX;
1960         }
1961         p->highest_bit = maxpages - 1;
1962 
1963         if (!maxpages)
1964                 return 0;
1965         swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1966         if (swapfilepages && maxpages > swapfilepages) {
1967                 printk(KERN_WARNING
1968                        "Swap area shorter than signature indicates\n");
1969                 return 0;
1970         }
1971         if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1972                 return 0;
1973         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1974                 return 0;
1975 
1976         return maxpages;
1977 }
1978 
1979 static int setup_swap_map_and_extents(struct swap_info_struct *p,
1980                                         union swap_header *swap_header,
1981                                         unsigned char *swap_map,
1982                                         unsigned long maxpages,
1983                                         sector_t *span)
1984 {
1985         int i;
1986         unsigned int nr_good_pages;
1987         int nr_extents;
1988 
1989         nr_good_pages = maxpages - 1;   /* omit header page */
1990 
1991         for (i = 0; i < swap_header->info.nr_badpages; i++) {
1992                 unsigned int page_nr = swap_header->info.badpages[i];
1993                 if (page_nr == 0 || page_nr > swap_header->info.last_page)
1994                         return -EINVAL;
1995                 if (page_nr < maxpages) {
1996                         swap_map[page_nr] = SWAP_MAP_BAD;
1997                         nr_good_pages--;
1998                 }
1999         }
2000 
2001         if (nr_good_pages) {
2002                 swap_map[0] = SWAP_MAP_BAD;
2003                 p->max = maxpages;
2004                 p->pages = nr_good_pages;
2005                 nr_extents = setup_swap_extents(p, span);
2006                 if (nr_extents < 0)
2007                         return nr_extents;
2008                 nr_good_pages = p->pages;
2009         }
2010         if (!nr_good_pages) {
2011                 printk(KERN_WARNING "Empty swap-file\n");
2012                 return -EINVAL;
2013         }
2014 
2015         return nr_extents;
2016 }
2017 
2018 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2019 {
2020         struct swap_info_struct *p;
2021         struct filename *name;
2022         struct file *swap_file = NULL;
2023         struct address_space *mapping;
2024         int i;
2025         int prio;
2026         int error;
2027         union swap_header *swap_header;
2028         int nr_extents;
2029         sector_t span;
2030         unsigned long maxpages;
2031         unsigned char *swap_map = NULL;
2032         unsigned long *frontswap_map = NULL;
2033         struct page *page = NULL;
2034         struct inode *inode = NULL;
2035 
2036         if (swap_flags & ~SWAP_FLAGS_VALID)
2037                 return -EINVAL;
2038 
2039         if (!capable(CAP_SYS_ADMIN))
2040                 return -EPERM;
2041 
2042         p = alloc_swap_info();
2043         if (IS_ERR(p))
2044                 return PTR_ERR(p);
2045 
2046         name = getname(specialfile);
2047         if (IS_ERR(name)) {
2048                 error = PTR_ERR(name);
2049                 name = NULL;
2050                 goto bad_swap;
2051         }
2052         swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2053         if (IS_ERR(swap_file)) {
2054                 error = PTR_ERR(swap_file);
2055                 swap_file = NULL;
2056                 goto bad_swap;
2057         }
2058 
2059         p->swap_file = swap_file;
2060         mapping = swap_file->f_mapping;
2061 
2062         for (i = 0; i < nr_swapfiles; i++) {
2063                 struct swap_info_struct *q = swap_info[i];
2064 
2065                 if (q == p || !q->swap_file)
2066                         continue;
2067                 if (mapping == q->swap_file->f_mapping) {
2068                         error = -EBUSY;
2069                         goto bad_swap;
2070                 }
2071         }
2072 
2073         inode = mapping->host;
2074         /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2075         error = claim_swapfile(p, inode);
2076         if (unlikely(error))
2077                 goto bad_swap;
2078 
2079         /*
2080          * Read the swap header.
2081          */
2082         if (!mapping->a_ops->readpage) {
2083                 error = -EINVAL;
2084                 goto bad_swap;
2085         }
2086         page = read_mapping_page(mapping, 0, swap_file);
2087         if (IS_ERR(page)) {
2088                 error = PTR_ERR(page);
2089                 goto bad_swap;
2090         }
2091         swap_header = kmap(page);
2092 
2093         maxpages = read_swap_header(p, swap_header, inode);
2094         if (unlikely(!maxpages)) {
2095                 error = -EINVAL;
2096                 goto bad_swap;
2097         }
2098 
2099         /* OK, set up the swap map and apply the bad block list */
2100         swap_map = vzalloc(maxpages);
2101         if (!swap_map) {
2102                 error = -ENOMEM;
2103                 goto bad_swap;
2104         }
2105 
2106         error = swap_cgroup_swapon(p->type, maxpages);
2107         if (error)
2108                 goto bad_swap;
2109 
2110         nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2111                 maxpages, &span);
2112         if (unlikely(nr_extents < 0)) {
2113                 error = nr_extents;
2114                 goto bad_swap;
2115         }
2116         /* frontswap enabled? set up bit-per-page map for frontswap */
2117         if (frontswap_enabled)
2118                 frontswap_map = vzalloc(maxpages / sizeof(long));
2119 
2120         if (p->bdev) {
2121                 if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2122                         p->flags |= SWP_SOLIDSTATE;
2123                         p->cluster_next = 1 + (random32() % p->highest_bit);
2124                 }
2125                 if ((swap_flags & SWAP_FLAG_DISCARD) && discard_swap(p) == 0)
2126                         p->flags |= SWP_DISCARDABLE;
2127         }
2128 
2129         mutex_lock(&swapon_mutex);
2130         prio = -1;
2131         if (swap_flags & SWAP_FLAG_PREFER)
2132                 prio =
2133                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2134         enable_swap_info(p, prio, swap_map, frontswap_map);
2135 
2136         printk(KERN_INFO "Adding %uk swap on %s.  "
2137                         "Priority:%d extents:%d across:%lluk %s%s%s\n",
2138                 p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2139                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2140                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2141                 (p->flags & SWP_DISCARDABLE) ? "D" : "",
2142                 (frontswap_map) ? "FS" : "");
2143 
2144         mutex_unlock(&swapon_mutex);
2145         atomic_inc(&proc_poll_event);
2146         wake_up_interruptible(&proc_poll_wait);
2147 
2148         if (S_ISREG(inode->i_mode))
2149                 inode->i_flags |= S_SWAPFILE;
2150         error = 0;
2151         goto out;
2152 bad_swap:
2153         if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2154                 set_blocksize(p->bdev, p->old_block_size);
2155                 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2156         }
2157         destroy_swap_extents(p);
2158         swap_cgroup_swapoff(p->type);
2159         spin_lock(&swap_lock);
2160         p->swap_file = NULL;
2161         p->flags = 0;
2162         spin_unlock(&swap_lock);
2163         vfree(swap_map);
2164         if (swap_file) {
2165                 if (inode && S_ISREG(inode->i_mode)) {
2166                         mutex_unlock(&inode->i_mutex);
2167                         inode = NULL;
2168                 }
2169                 filp_close(swap_file, NULL);
2170         }
2171 out:
2172         if (page && !IS_ERR(page)) {
2173                 kunmap(page);
2174                 page_cache_release(page);
2175         }
2176         if (name)
2177                 putname(name);
2178         if (inode && S_ISREG(inode->i_mode))
2179                 mutex_unlock(&inode->i_mutex);
2180         return error;
2181 }
2182 
2183 void si_swapinfo(struct sysinfo *val)
2184 {
2185         unsigned int type;
2186         unsigned long nr_to_be_unused = 0;
2187 
2188         spin_lock(&swap_lock);
2189         for (type = 0; type < nr_swapfiles; type++) {
2190                 struct swap_info_struct *si = swap_info[type];
2191 
2192                 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2193                         nr_to_be_unused += si->inuse_pages;
2194         }
2195         val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2196         val->totalswap = total_swap_pages + nr_to_be_unused;
2197         spin_unlock(&swap_lock);
2198 }
2199 
2200 /*
2201  * Verify that a swap entry is valid and increment its swap map count.
2202  *
2203  * Returns error code in following case.
2204  * - success -> 0
2205  * - swp_entry is invalid -> EINVAL
2206  * - swp_entry is migration entry -> EINVAL
2207  * - swap-cache reference is requested but there is already one. -> EEXIST
2208  * - swap-cache reference is requested but the entry is not used. -> ENOENT
2209  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2210  */
2211 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2212 {
2213         struct swap_info_struct *p;
2214         unsigned long offset, type;
2215         unsigned char count;
2216         unsigned char has_cache;
2217         int err = -EINVAL;
2218 
2219         if (non_swap_entry(entry))
2220                 goto out;
2221 
2222         type = swp_type(entry);
2223         if (type >= nr_swapfiles)
2224                 goto bad_file;
2225         p = swap_info[type];
2226         offset = swp_offset(entry);
2227 
2228         spin_lock(&p->lock);
2229         if (unlikely(offset >= p->max))
2230                 goto unlock_out;
2231 
2232         count = p->swap_map[offset];
2233         has_cache = count & SWAP_HAS_CACHE;
2234         count &= ~SWAP_HAS_CACHE;
2235         err = 0;
2236 
2237         if (usage == SWAP_HAS_CACHE) {
2238 
2239                 /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2240                 if (!has_cache && count)
2241                         has_cache = SWAP_HAS_CACHE;
2242                 else if (has_cache)             /* someone else added cache */
2243                         err = -EEXIST;
2244                 else                            /* no users remaining */
2245                         err = -ENOENT;
2246 
2247         } else if (count || has_cache) {
2248 
2249                 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2250                         count += usage;
2251                 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2252                         err = -EINVAL;
2253                 else if (swap_count_continued(p, offset, count))
2254                         count = COUNT_CONTINUED;
2255                 else
2256                         err = -ENOMEM;
2257         } else
2258                 err = -ENOENT;                  /* unused swap entry */
2259 
2260         p->swap_map[offset] = count | has_cache;
2261 
2262 unlock_out:
2263         spin_unlock(&p->lock);
2264 out:
2265         return err;
2266 
2267 bad_file:
2268         printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2269         goto out;
2270 }
2271 
2272 /*
2273  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2274  * (in which case its reference count is never incremented).
2275  */
2276 void swap_shmem_alloc(swp_entry_t entry)
2277 {
2278         __swap_duplicate(entry, SWAP_MAP_SHMEM);
2279 }
2280 
2281 /*
2282  * Increase reference count of swap entry by 1.
2283  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2284  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2285  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2286  * might occur if a page table entry has got corrupted.
2287  */
2288 int swap_duplicate(swp_entry_t entry)
2289 {
2290         int err = 0;
2291 
2292         while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2293                 err = add_swap_count_continuation(entry, GFP_ATOMIC);
2294         return err;
2295 }
2296 
2297 /*
2298  * @entry: swap entry for which we allocate swap cache.
2299  *
2300  * Called when allocating swap cache for existing swap entry,
2301  * This can return error codes. Returns 0 at success.
2302  * -EBUSY means there is a swap cache.
2303  * Note: return code is different from swap_duplicate().
2304  */
2305 int swapcache_prepare(swp_entry_t entry)
2306 {
2307         return __swap_duplicate(entry, SWAP_HAS_CACHE);
2308 }
2309 
2310 struct swap_info_struct *page_swap_info(struct page *page)
2311 {
2312         swp_entry_t swap = { .val = page_private(page) };
2313         BUG_ON(!PageSwapCache(page));
2314         return swap_info[swp_type(swap)];
2315 }
2316 
2317 /*
2318  * out-of-line __page_file_ methods to avoid include hell.
2319  */
2320 struct address_space *__page_file_mapping(struct page *page)
2321 {
2322         VM_BUG_ON(!PageSwapCache(page));
2323         return page_swap_info(page)->swap_file->f_mapping;
2324 }
2325 EXPORT_SYMBOL_GPL(__page_file_mapping);
2326 
2327 pgoff_t __page_file_index(struct page *page)
2328 {
2329         swp_entry_t swap = { .val = page_private(page) };
2330         VM_BUG_ON(!PageSwapCache(page));
2331         return swp_offset(swap);
2332 }
2333 EXPORT_SYMBOL_GPL(__page_file_index);
2334 
2335 /*
2336  * add_swap_count_continuation - called when a swap count is duplicated
2337  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2338  * page of the original vmalloc'ed swap_map, to hold the continuation count
2339  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2340  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2341  *
2342  * These continuation pages are seldom referenced: the common paths all work
2343  * on the original swap_map, only referring to a continuation page when the
2344  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2345  *
2346  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2347  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2348  * can be called after dropping locks.
2349  */
2350 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2351 {
2352         struct swap_info_struct *si;
2353         struct page *head;
2354         struct page *page;
2355         struct page *list_page;
2356         pgoff_t offset;
2357         unsigned char count;
2358 
2359         /*
2360          * When debugging, it's easier to use __GFP_ZERO here; but it's better
2361          * for latency not to zero a page while GFP_ATOMIC and holding locks.
2362          */
2363         page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2364 
2365         si = swap_info_get(entry);
2366         if (!si) {
2367                 /*
2368                  * An acceptable race has occurred since the failing
2369                  * __swap_duplicate(): the swap entry has been freed,
2370                  * perhaps even the whole swap_map cleared for swapoff.
2371                  */
2372                 goto outer;
2373         }
2374 
2375         offset = swp_offset(entry);
2376         count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2377 
2378         if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2379                 /*
2380                  * The higher the swap count, the more likely it is that tasks
2381                  * will race to add swap count continuation: we need to avoid
2382                  * over-provisioning.
2383                  */
2384                 goto out;
2385         }
2386 
2387         if (!page) {
2388                 spin_unlock(&si->lock);
2389                 return -ENOMEM;
2390         }
2391 
2392         /*
2393          * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2394          * no architecture is using highmem pages for kernel pagetables: so it
2395          * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2396          */
2397         head = vmalloc_to_page(si->swap_map + offset);
2398         offset &= ~PAGE_MASK;
2399 
2400         /*
2401          * Page allocation does not initialize the page's lru field,
2402          * but it does always reset its private field.
2403          */
2404         if (!page_private(head)) {
2405                 BUG_ON(count & COUNT_CONTINUED);
2406                 INIT_LIST_HEAD(&head->lru);
2407                 set_page_private(head, SWP_CONTINUED);
2408                 si->flags |= SWP_CONTINUED;
2409         }
2410 
2411         list_for_each_entry(list_page, &head->lru, lru) {
2412                 unsigned char *map;
2413 
2414                 /*
2415                  * If the previous map said no continuation, but we've found
2416                  * a continuation page, free our allocation and use this one.
2417                  */
2418                 if (!(count & COUNT_CONTINUED))
2419                         goto out;
2420 
2421                 map = kmap_atomic(list_page) + offset;
2422                 count = *map;
2423                 kunmap_atomic(map);
2424 
2425                 /*
2426                  * If this continuation count now has some space in it,
2427                  * free our allocation and use this one.
2428                  */
2429                 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2430                         goto out;
2431         }
2432 
2433         list_add_tail(&page->lru, &head->lru);
2434         page = NULL;                    /* now it's attached, don't free it */
2435 out:
2436         spin_unlock(&si->lock);
2437 outer:
2438         if (page)
2439                 __free_page(page);
2440         return 0;
2441 }
2442 
2443 /*
2444  * swap_count_continued - when the original swap_map count is incremented
2445  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2446  * into, carry if so, or else fail until a new continuation page is allocated;
2447  * when the original swap_map count is decremented from 0 with continuation,
2448  * borrow from the continuation and report whether it still holds more.
2449  * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2450  */
2451 static bool swap_count_continued(struct swap_info_struct *si,
2452                                  pgoff_t offset, unsigned char count)
2453 {
2454         struct page *head;
2455         struct page *page;
2456         unsigned char *map;
2457 
2458         head = vmalloc_to_page(si->swap_map + offset);
2459         if (page_private(head) != SWP_CONTINUED) {
2460                 BUG_ON(count & COUNT_CONTINUED);
2461                 return false;           /* need to add count continuation */
2462         }
2463 
2464         offset &= ~PAGE_MASK;
2465         page = list_entry(head->lru.next, struct page, lru);
2466         map = kmap_atomic(page) + offset;
2467 
2468         if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2469                 goto init_map;          /* jump over SWAP_CONT_MAX checks */
2470 
2471         if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2472                 /*
2473                  * Think of how you add 1 to 999
2474                  */
2475                 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2476                         kunmap_atomic(map);
2477                         page = list_entry(page->lru.next, struct page, lru);
2478                         BUG_ON(page == head);
2479                         map = kmap_atomic(page) + offset;
2480                 }
2481                 if (*map == SWAP_CONT_MAX) {
2482                         kunmap_atomic(map);
2483                         page = list_entry(page->lru.next, struct page, lru);
2484                         if (page == head)
2485                                 return false;   /* add count continuation */
2486                         map = kmap_atomic(page) + offset;
2487 init_map:               *map = 0;               /* we didn't zero the page */
2488                 }
2489                 *map += 1;
2490                 kunmap_atomic(map);
2491                 page = list_entry(page->lru.prev, struct page, lru);
2492                 while (page != head) {
2493                         map = kmap_atomic(page) + offset;
2494                         *map = COUNT_CONTINUED;
2495                         kunmap_atomic(map);
2496                         page = list_entry(page->lru.prev, struct page, lru);
2497                 }
2498                 return true;                    /* incremented */
2499 
2500         } else {                                /* decrementing */
2501                 /*
2502                  * Think of how you subtract 1 from 1000
2503                  */
2504                 BUG_ON(count != COUNT_CONTINUED);
2505                 while (*map == COUNT_CONTINUED) {
2506                         kunmap_atomic(map);
2507                         page = list_entry(page->lru.next, struct page, lru);
2508                         BUG_ON(page == head);
2509                         map = kmap_atomic(page) + offset;
2510                 }
2511                 BUG_ON(*map == 0);
2512                 *map -= 1;
2513                 if (*map == 0)
2514                         count = 0;
2515                 kunmap_atomic(map);
2516                 page = list_entry(page->lru.prev, struct page, lru);
2517                 while (page != head) {
2518                         map = kmap_atomic(page) + offset;
2519                         *map = SWAP_CONT_MAX | count;
2520                         count = COUNT_CONTINUED;
2521                         kunmap_atomic(map);
2522                         page = list_entry(page->lru.prev, struct page, lru);
2523                 }
2524                 return count == COUNT_CONTINUED;
2525         }
2526 }
2527 
2528 /*
2529  * free_swap_count_continuations - swapoff free all the continuation pages
2530  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2531  */
2532 static void free_swap_count_continuations(struct swap_info_struct *si)
2533 {
2534         pgoff_t offset;
2535 
2536         for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2537                 struct page *head;
2538                 head = vmalloc_to_page(si->swap_map + offset);
2539                 if (page_private(head)) {
2540                         struct list_head *this, *next;
2541                         list_for_each_safe(this, next, &head->lru) {
2542                                 struct page *page;
2543                                 page = list_entry(this, struct page, lru);
2544                                 list_del(this);
2545                                 __free_page(page);
2546                         }
2547                 }
2548         }
2549 }
2550 

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