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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/swap_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 
 55 static const char Bad_file[] = "Bad swap file entry ";
 56 static const char Unused_file[] = "Unused swap file entry ";
 57 static const char Bad_offset[] = "Bad swap offset entry ";
 58 static const char Unused_offset[] = "Unused swap offset entry ";
 59 
 60 /*
 61  * all active swap_info_structs
 62  * protected with swap_lock, and ordered by priority.
 63  */
 64 PLIST_HEAD(swap_active_head);
 65 
 66 /*
 67  * all available (active, not full) swap_info_structs
 68  * protected with swap_avail_lock, ordered by priority.
 69  * This is used by get_swap_page() instead of swap_active_head
 70  * because swap_active_head includes all swap_info_structs,
 71  * but get_swap_page() doesn't need to look at full ones.
 72  * This uses its own lock instead of swap_lock because when a
 73  * swap_info_struct changes between not-full/full, it needs to
 74  * add/remove itself to/from this list, but the swap_info_struct->lock
 75  * is held and the locking order requires swap_lock to be taken
 76  * before any swap_info_struct->lock.
 77  */
 78 static PLIST_HEAD(swap_avail_head);
 79 static DEFINE_SPINLOCK(swap_avail_lock);
 80 
 81 struct swap_info_struct *swap_info[MAX_SWAPFILES];
 82 
 83 static DEFINE_MUTEX(swapon_mutex);
 84 
 85 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
 86 /* Activity counter to indicate that a swapon or swapoff has occurred */
 87 static atomic_t proc_poll_event = ATOMIC_INIT(0);
 88 
 89 static inline unsigned char swap_count(unsigned char ent)
 90 {
 91         return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
 92 }
 93 
 94 /* returns 1 if swap entry is freed */
 95 static int
 96 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
 97 {
 98         swp_entry_t entry = swp_entry(si->type, offset);
 99         struct page *page;
100         int ret = 0;
101 
102         page = find_get_page(swap_address_space(entry), entry.val);
103         if (!page)
104                 return 0;
105         /*
106          * This function is called from scan_swap_map() and it's called
107          * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
108          * We have to use trylock for avoiding deadlock. This is a special
109          * case and you should use try_to_free_swap() with explicit lock_page()
110          * in usual operations.
111          */
112         if (trylock_page(page)) {
113                 ret = try_to_free_swap(page);
114                 unlock_page(page);
115         }
116         page_cache_release(page);
117         return ret;
118 }
119 
120 /*
121  * swapon tell device that all the old swap contents can be discarded,
122  * to allow the swap device to optimize its wear-levelling.
123  */
124 static int discard_swap(struct swap_info_struct *si)
125 {
126         struct swap_extent *se;
127         sector_t start_block;
128         sector_t nr_blocks;
129         int err = 0;
130 
131         /* Do not discard the swap header page! */
132         se = &si->first_swap_extent;
133         start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
134         nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
135         if (nr_blocks) {
136                 err = blkdev_issue_discard(si->bdev, start_block,
137                                 nr_blocks, GFP_KERNEL, 0);
138                 if (err)
139                         return err;
140                 cond_resched();
141         }
142 
143         list_for_each_entry(se, &si->first_swap_extent.list, list) {
144                 start_block = se->start_block << (PAGE_SHIFT - 9);
145                 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
146 
147                 err = blkdev_issue_discard(si->bdev, start_block,
148                                 nr_blocks, GFP_KERNEL, 0);
149                 if (err)
150                         break;
151 
152                 cond_resched();
153         }
154         return err;             /* That will often be -EOPNOTSUPP */
155 }
156 
157 /*
158  * swap allocation tell device that a cluster of swap can now be discarded,
159  * to allow the swap device to optimize its wear-levelling.
160  */
161 static void discard_swap_cluster(struct swap_info_struct *si,
162                                  pgoff_t start_page, pgoff_t nr_pages)
163 {
164         struct swap_extent *se = si->curr_swap_extent;
165         int found_extent = 0;
166 
167         while (nr_pages) {
168                 struct list_head *lh;
169 
170                 if (se->start_page <= start_page &&
171                     start_page < se->start_page + se->nr_pages) {
172                         pgoff_t offset = start_page - se->start_page;
173                         sector_t start_block = se->start_block + offset;
174                         sector_t nr_blocks = se->nr_pages - offset;
175 
176                         if (nr_blocks > nr_pages)
177                                 nr_blocks = nr_pages;
178                         start_page += nr_blocks;
179                         nr_pages -= nr_blocks;
180 
181                         if (!found_extent++)
182                                 si->curr_swap_extent = se;
183 
184                         start_block <<= PAGE_SHIFT - 9;
185                         nr_blocks <<= PAGE_SHIFT - 9;
186                         if (blkdev_issue_discard(si->bdev, start_block,
187                                     nr_blocks, GFP_NOIO, 0))
188                                 break;
189                 }
190 
191                 lh = se->list.next;
192                 se = list_entry(lh, struct swap_extent, list);
193         }
194 }
195 
196 #define SWAPFILE_CLUSTER        256
197 #define LATENCY_LIMIT           256
198 
199 static inline void cluster_set_flag(struct swap_cluster_info *info,
200         unsigned int flag)
201 {
202         info->flags = flag;
203 }
204 
205 static inline unsigned int cluster_count(struct swap_cluster_info *info)
206 {
207         return info->data;
208 }
209 
210 static inline void cluster_set_count(struct swap_cluster_info *info,
211                                      unsigned int c)
212 {
213         info->data = c;
214 }
215 
216 static inline void cluster_set_count_flag(struct swap_cluster_info *info,
217                                          unsigned int c, unsigned int f)
218 {
219         info->flags = f;
220         info->data = c;
221 }
222 
223 static inline unsigned int cluster_next(struct swap_cluster_info *info)
224 {
225         return info->data;
226 }
227 
228 static inline void cluster_set_next(struct swap_cluster_info *info,
229                                     unsigned int n)
230 {
231         info->data = n;
232 }
233 
234 static inline void cluster_set_next_flag(struct swap_cluster_info *info,
235                                          unsigned int n, unsigned int f)
236 {
237         info->flags = f;
238         info->data = n;
239 }
240 
241 static inline bool cluster_is_free(struct swap_cluster_info *info)
242 {
243         return info->flags & CLUSTER_FLAG_FREE;
244 }
245 
246 static inline bool cluster_is_null(struct swap_cluster_info *info)
247 {
248         return info->flags & CLUSTER_FLAG_NEXT_NULL;
249 }
250 
251 static inline void cluster_set_null(struct swap_cluster_info *info)
252 {
253         info->flags = CLUSTER_FLAG_NEXT_NULL;
254         info->data = 0;
255 }
256 
257 /* Add a cluster to discard list and schedule it to do discard */
258 static void swap_cluster_schedule_discard(struct swap_info_struct *si,
259                 unsigned int idx)
260 {
261         /*
262          * If scan_swap_map() can't find a free cluster, it will check
263          * si->swap_map directly. To make sure the discarding cluster isn't
264          * taken by scan_swap_map(), mark the swap entries bad (occupied). It
265          * will be cleared after discard
266          */
267         memset(si->swap_map + idx * SWAPFILE_CLUSTER,
268                         SWAP_MAP_BAD, SWAPFILE_CLUSTER);
269 
270         if (cluster_is_null(&si->discard_cluster_head)) {
271                 cluster_set_next_flag(&si->discard_cluster_head,
272                                                 idx, 0);
273                 cluster_set_next_flag(&si->discard_cluster_tail,
274                                                 idx, 0);
275         } else {
276                 unsigned int tail = cluster_next(&si->discard_cluster_tail);
277                 cluster_set_next(&si->cluster_info[tail], idx);
278                 cluster_set_next_flag(&si->discard_cluster_tail,
279                                                 idx, 0);
280         }
281 
282         schedule_work(&si->discard_work);
283 }
284 
285 /*
286  * Doing discard actually. After a cluster discard is finished, the cluster
287  * will be added to free cluster list. caller should hold si->lock.
288 */
289 static void swap_do_scheduled_discard(struct swap_info_struct *si)
290 {
291         struct swap_cluster_info *info;
292         unsigned int idx;
293 
294         info = si->cluster_info;
295 
296         while (!cluster_is_null(&si->discard_cluster_head)) {
297                 idx = cluster_next(&si->discard_cluster_head);
298 
299                 cluster_set_next_flag(&si->discard_cluster_head,
300                                                 cluster_next(&info[idx]), 0);
301                 if (cluster_next(&si->discard_cluster_tail) == idx) {
302                         cluster_set_null(&si->discard_cluster_head);
303                         cluster_set_null(&si->discard_cluster_tail);
304                 }
305                 spin_unlock(&si->lock);
306 
307                 discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
308                                 SWAPFILE_CLUSTER);
309 
310                 spin_lock(&si->lock);
311                 cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE);
312                 if (cluster_is_null(&si->free_cluster_head)) {
313                         cluster_set_next_flag(&si->free_cluster_head,
314                                                 idx, 0);
315                         cluster_set_next_flag(&si->free_cluster_tail,
316                                                 idx, 0);
317                 } else {
318                         unsigned int tail;
319 
320                         tail = cluster_next(&si->free_cluster_tail);
321                         cluster_set_next(&info[tail], idx);
322                         cluster_set_next_flag(&si->free_cluster_tail,
323                                                 idx, 0);
324                 }
325                 memset(si->swap_map + idx * SWAPFILE_CLUSTER,
326                                 0, SWAPFILE_CLUSTER);
327         }
328 }
329 
330 static void swap_discard_work(struct work_struct *work)
331 {
332         struct swap_info_struct *si;
333 
334         si = container_of(work, struct swap_info_struct, discard_work);
335 
336         spin_lock(&si->lock);
337         swap_do_scheduled_discard(si);
338         spin_unlock(&si->lock);
339 }
340 
341 /*
342  * The cluster corresponding to page_nr will be used. The cluster will be
343  * removed from free cluster list and its usage counter will be increased.
344  */
345 static void inc_cluster_info_page(struct swap_info_struct *p,
346         struct swap_cluster_info *cluster_info, unsigned long page_nr)
347 {
348         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
349 
350         if (!cluster_info)
351                 return;
352         if (cluster_is_free(&cluster_info[idx])) {
353                 VM_BUG_ON(cluster_next(&p->free_cluster_head) != idx);
354                 cluster_set_next_flag(&p->free_cluster_head,
355                         cluster_next(&cluster_info[idx]), 0);
356                 if (cluster_next(&p->free_cluster_tail) == idx) {
357                         cluster_set_null(&p->free_cluster_tail);
358                         cluster_set_null(&p->free_cluster_head);
359                 }
360                 cluster_set_count_flag(&cluster_info[idx], 0, 0);
361         }
362 
363         VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
364         cluster_set_count(&cluster_info[idx],
365                 cluster_count(&cluster_info[idx]) + 1);
366 }
367 
368 /*
369  * The cluster corresponding to page_nr decreases one usage. If the usage
370  * counter becomes 0, which means no page in the cluster is in using, we can
371  * optionally discard the cluster and add it to free cluster list.
372  */
373 static void dec_cluster_info_page(struct swap_info_struct *p,
374         struct swap_cluster_info *cluster_info, unsigned long page_nr)
375 {
376         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
377 
378         if (!cluster_info)
379                 return;
380 
381         VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
382         cluster_set_count(&cluster_info[idx],
383                 cluster_count(&cluster_info[idx]) - 1);
384 
385         if (cluster_count(&cluster_info[idx]) == 0) {
386                 /*
387                  * If the swap is discardable, prepare discard the cluster
388                  * instead of free it immediately. The cluster will be freed
389                  * after discard.
390                  */
391                 if ((p->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
392                                  (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
393                         swap_cluster_schedule_discard(p, idx);
394                         return;
395                 }
396 
397                 cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
398                 if (cluster_is_null(&p->free_cluster_head)) {
399                         cluster_set_next_flag(&p->free_cluster_head, idx, 0);
400                         cluster_set_next_flag(&p->free_cluster_tail, idx, 0);
401                 } else {
402                         unsigned int tail = cluster_next(&p->free_cluster_tail);
403                         cluster_set_next(&cluster_info[tail], idx);
404                         cluster_set_next_flag(&p->free_cluster_tail, idx, 0);
405                 }
406         }
407 }
408 
409 /*
410  * It's possible scan_swap_map() uses a free cluster in the middle of free
411  * cluster list. Avoiding such abuse to avoid list corruption.
412  */
413 static bool
414 scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
415         unsigned long offset)
416 {
417         struct percpu_cluster *percpu_cluster;
418         bool conflict;
419 
420         offset /= SWAPFILE_CLUSTER;
421         conflict = !cluster_is_null(&si->free_cluster_head) &&
422                 offset != cluster_next(&si->free_cluster_head) &&
423                 cluster_is_free(&si->cluster_info[offset]);
424 
425         if (!conflict)
426                 return false;
427 
428         percpu_cluster = this_cpu_ptr(si->percpu_cluster);
429         cluster_set_null(&percpu_cluster->index);
430         return true;
431 }
432 
433 /*
434  * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
435  * might involve allocating a new cluster for current CPU too.
436  */
437 static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
438         unsigned long *offset, unsigned long *scan_base)
439 {
440         struct percpu_cluster *cluster;
441         bool found_free;
442         unsigned long tmp;
443 
444 new_cluster:
445         cluster = this_cpu_ptr(si->percpu_cluster);
446         if (cluster_is_null(&cluster->index)) {
447                 if (!cluster_is_null(&si->free_cluster_head)) {
448                         cluster->index = si->free_cluster_head;
449                         cluster->next = cluster_next(&cluster->index) *
450                                         SWAPFILE_CLUSTER;
451                 } else if (!cluster_is_null(&si->discard_cluster_head)) {
452                         /*
453                          * we don't have free cluster but have some clusters in
454                          * discarding, do discard now and reclaim them
455                          */
456                         swap_do_scheduled_discard(si);
457                         *scan_base = *offset = si->cluster_next;
458                         goto new_cluster;
459                 } else
460                         return;
461         }
462 
463         found_free = false;
464 
465         /*
466          * Other CPUs can use our cluster if they can't find a free cluster,
467          * check if there is still free entry in the cluster
468          */
469         tmp = cluster->next;
470         while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) *
471                SWAPFILE_CLUSTER) {
472                 if (!si->swap_map[tmp]) {
473                         found_free = true;
474                         break;
475                 }
476                 tmp++;
477         }
478         if (!found_free) {
479                 cluster_set_null(&cluster->index);
480                 goto new_cluster;
481         }
482         cluster->next = tmp + 1;
483         *offset = tmp;
484         *scan_base = tmp;
485 }
486 
487 static unsigned long scan_swap_map(struct swap_info_struct *si,
488                                    unsigned char usage)
489 {
490         unsigned long offset;
491         unsigned long scan_base;
492         unsigned long last_in_cluster = 0;
493         int latency_ration = LATENCY_LIMIT;
494 
495         /*
496          * We try to cluster swap pages by allocating them sequentially
497          * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
498          * way, however, we resort to first-free allocation, starting
499          * a new cluster.  This prevents us from scattering swap pages
500          * all over the entire swap partition, so that we reduce
501          * overall disk seek times between swap pages.  -- sct
502          * But we do now try to find an empty cluster.  -Andrea
503          * And we let swap pages go all over an SSD partition.  Hugh
504          */
505 
506         si->flags += SWP_SCANNING;
507         scan_base = offset = si->cluster_next;
508 
509         /* SSD algorithm */
510         if (si->cluster_info) {
511                 scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
512                 goto checks;
513         }
514 
515         if (unlikely(!si->cluster_nr--)) {
516                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
517                         si->cluster_nr = SWAPFILE_CLUSTER - 1;
518                         goto checks;
519                 }
520 
521                 spin_unlock(&si->lock);
522 
523                 /*
524                  * If seek is expensive, start searching for new cluster from
525                  * start of partition, to minimize the span of allocated swap.
526                  * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
527                  * case, just handled by scan_swap_map_try_ssd_cluster() above.
528                  */
529                 scan_base = offset = si->lowest_bit;
530                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
531 
532                 /* Locate the first empty (unaligned) cluster */
533                 for (; last_in_cluster <= si->highest_bit; offset++) {
534                         if (si->swap_map[offset])
535                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
536                         else if (offset == last_in_cluster) {
537                                 spin_lock(&si->lock);
538                                 offset -= SWAPFILE_CLUSTER - 1;
539                                 si->cluster_next = offset;
540                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
541                                 goto checks;
542                         }
543                         if (unlikely(--latency_ration < 0)) {
544                                 cond_resched();
545                                 latency_ration = LATENCY_LIMIT;
546                         }
547                 }
548 
549                 offset = scan_base;
550                 spin_lock(&si->lock);
551                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
552         }
553 
554 checks:
555         if (si->cluster_info) {
556                 while (scan_swap_map_ssd_cluster_conflict(si, offset))
557                         scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
558         }
559         if (!(si->flags & SWP_WRITEOK))
560                 goto no_page;
561         if (!si->highest_bit)
562                 goto no_page;
563         if (offset > si->highest_bit)
564                 scan_base = offset = si->lowest_bit;
565 
566         /* reuse swap entry of cache-only swap if not busy. */
567         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
568                 int swap_was_freed;
569                 spin_unlock(&si->lock);
570                 swap_was_freed = __try_to_reclaim_swap(si, offset);
571                 spin_lock(&si->lock);
572                 /* entry was freed successfully, try to use this again */
573                 if (swap_was_freed)
574                         goto checks;
575                 goto scan; /* check next one */
576         }
577 
578         if (si->swap_map[offset])
579                 goto scan;
580 
581         if (offset == si->lowest_bit)
582                 si->lowest_bit++;
583         if (offset == si->highest_bit)
584                 si->highest_bit--;
585         si->inuse_pages++;
586         if (si->inuse_pages == si->pages) {
587                 si->lowest_bit = si->max;
588                 si->highest_bit = 0;
589                 spin_lock(&swap_avail_lock);
590                 plist_del(&si->avail_list, &swap_avail_head);
591                 spin_unlock(&swap_avail_lock);
592         }
593         si->swap_map[offset] = usage;
594         inc_cluster_info_page(si, si->cluster_info, offset);
595         si->cluster_next = offset + 1;
596         si->flags -= SWP_SCANNING;
597 
598         return offset;
599 
600 scan:
601         spin_unlock(&si->lock);
602         while (++offset <= si->highest_bit) {
603                 if (!si->swap_map[offset]) {
604                         spin_lock(&si->lock);
605                         goto checks;
606                 }
607                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
608                         spin_lock(&si->lock);
609                         goto checks;
610                 }
611                 if (unlikely(--latency_ration < 0)) {
612                         cond_resched();
613                         latency_ration = LATENCY_LIMIT;
614                 }
615         }
616         offset = si->lowest_bit;
617         while (offset < scan_base) {
618                 if (!si->swap_map[offset]) {
619                         spin_lock(&si->lock);
620                         goto checks;
621                 }
622                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
623                         spin_lock(&si->lock);
624                         goto checks;
625                 }
626                 if (unlikely(--latency_ration < 0)) {
627                         cond_resched();
628                         latency_ration = LATENCY_LIMIT;
629                 }
630                 offset++;
631         }
632         spin_lock(&si->lock);
633 
634 no_page:
635         si->flags -= SWP_SCANNING;
636         return 0;
637 }
638 
639 swp_entry_t get_swap_page(void)
640 {
641         struct swap_info_struct *si, *next;
642         pgoff_t offset;
643 
644         if (atomic_long_read(&nr_swap_pages) <= 0)
645                 goto noswap;
646         atomic_long_dec(&nr_swap_pages);
647 
648         spin_lock(&swap_avail_lock);
649 
650 start_over:
651         plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
652                 /* requeue si to after same-priority siblings */
653                 plist_requeue(&si->avail_list, &swap_avail_head);
654                 spin_unlock(&swap_avail_lock);
655                 spin_lock(&si->lock);
656                 if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
657                         spin_lock(&swap_avail_lock);
658                         if (plist_node_empty(&si->avail_list)) {
659                                 spin_unlock(&si->lock);
660                                 goto nextsi;
661                         }
662                         WARN(!si->highest_bit,
663                              "swap_info %d in list but !highest_bit\n",
664                              si->type);
665                         WARN(!(si->flags & SWP_WRITEOK),
666                              "swap_info %d in list but !SWP_WRITEOK\n",
667                              si->type);
668                         plist_del(&si->avail_list, &swap_avail_head);
669                         spin_unlock(&si->lock);
670                         goto nextsi;
671                 }
672 
673                 /* This is called for allocating swap entry for cache */
674                 offset = scan_swap_map(si, SWAP_HAS_CACHE);
675                 spin_unlock(&si->lock);
676                 if (offset)
677                         return swp_entry(si->type, offset);
678                 pr_debug("scan_swap_map of si %d failed to find offset\n",
679                        si->type);
680                 spin_lock(&swap_avail_lock);
681 nextsi:
682                 /*
683                  * if we got here, it's likely that si was almost full before,
684                  * and since scan_swap_map() can drop the si->lock, multiple
685                  * callers probably all tried to get a page from the same si
686                  * and it filled up before we could get one; or, the si filled
687                  * up between us dropping swap_avail_lock and taking si->lock.
688                  * Since we dropped the swap_avail_lock, the swap_avail_head
689                  * list may have been modified; so if next is still in the
690                  * swap_avail_head list then try it, otherwise start over.
691                  */
692                 if (plist_node_empty(&next->avail_list))
693                         goto start_over;
694         }
695 
696         spin_unlock(&swap_avail_lock);
697 
698         atomic_long_inc(&nr_swap_pages);
699 noswap:
700         return (swp_entry_t) {0};
701 }
702 
703 /* The only caller of this function is now suspend routine */
704 swp_entry_t get_swap_page_of_type(int type)
705 {
706         struct swap_info_struct *si;
707         pgoff_t offset;
708 
709         si = swap_info[type];
710         spin_lock(&si->lock);
711         if (si && (si->flags & SWP_WRITEOK)) {
712                 atomic_long_dec(&nr_swap_pages);
713                 /* This is called for allocating swap entry, not cache */
714                 offset = scan_swap_map(si, 1);
715                 if (offset) {
716                         spin_unlock(&si->lock);
717                         return swp_entry(type, offset);
718                 }
719                 atomic_long_inc(&nr_swap_pages);
720         }
721         spin_unlock(&si->lock);
722         return (swp_entry_t) {0};
723 }
724 
725 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
726 {
727         struct swap_info_struct *p;
728         unsigned long offset, type;
729 
730         if (!entry.val)
731                 goto out;
732         type = swp_type(entry);
733         if (type >= nr_swapfiles)
734                 goto bad_nofile;
735         p = swap_info[type];
736         if (!(p->flags & SWP_USED))
737                 goto bad_device;
738         offset = swp_offset(entry);
739         if (offset >= p->max)
740                 goto bad_offset;
741         if (!p->swap_map[offset])
742                 goto bad_free;
743         spin_lock(&p->lock);
744         return p;
745 
746 bad_free:
747         pr_err("swap_free: %s%08lx\n", Unused_offset, entry.val);
748         goto out;
749 bad_offset:
750         pr_err("swap_free: %s%08lx\n", Bad_offset, entry.val);
751         goto out;
752 bad_device:
753         pr_err("swap_free: %s%08lx\n", Unused_file, entry.val);
754         goto out;
755 bad_nofile:
756         pr_err("swap_free: %s%08lx\n", Bad_file, entry.val);
757 out:
758         return NULL;
759 }
760 
761 static unsigned char swap_entry_free(struct swap_info_struct *p,
762                                      swp_entry_t entry, unsigned char usage)
763 {
764         unsigned long offset = swp_offset(entry);
765         unsigned char count;
766         unsigned char has_cache;
767 
768         count = p->swap_map[offset];
769         has_cache = count & SWAP_HAS_CACHE;
770         count &= ~SWAP_HAS_CACHE;
771 
772         if (usage == SWAP_HAS_CACHE) {
773                 VM_BUG_ON(!has_cache);
774                 has_cache = 0;
775         } else if (count == SWAP_MAP_SHMEM) {
776                 /*
777                  * Or we could insist on shmem.c using a special
778                  * swap_shmem_free() and free_shmem_swap_and_cache()...
779                  */
780                 count = 0;
781         } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
782                 if (count == COUNT_CONTINUED) {
783                         if (swap_count_continued(p, offset, count))
784                                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
785                         else
786                                 count = SWAP_MAP_MAX;
787                 } else
788                         count--;
789         }
790 
791         if (!count)
792                 mem_cgroup_uncharge_swap(entry);
793 
794         usage = count | has_cache;
795         p->swap_map[offset] = usage;
796 
797         /* free if no reference */
798         if (!usage) {
799                 dec_cluster_info_page(p, p->cluster_info, offset);
800                 if (offset < p->lowest_bit)
801                         p->lowest_bit = offset;
802                 if (offset > p->highest_bit) {
803                         bool was_full = !p->highest_bit;
804                         p->highest_bit = offset;
805                         if (was_full && (p->flags & SWP_WRITEOK)) {
806                                 spin_lock(&swap_avail_lock);
807                                 WARN_ON(!plist_node_empty(&p->avail_list));
808                                 if (plist_node_empty(&p->avail_list))
809                                         plist_add(&p->avail_list,
810                                                   &swap_avail_head);
811                                 spin_unlock(&swap_avail_lock);
812                         }
813                 }
814                 atomic_long_inc(&nr_swap_pages);
815                 p->inuse_pages--;
816                 frontswap_invalidate_page(p->type, offset);
817                 if (p->flags & SWP_BLKDEV) {
818                         struct gendisk *disk = p->bdev->bd_disk;
819                         if (disk->fops->swap_slot_free_notify)
820                                 disk->fops->swap_slot_free_notify(p->bdev,
821                                                                   offset);
822                 }
823         }
824 
825         return usage;
826 }
827 
828 /*
829  * Caller has made sure that the swap device corresponding to entry
830  * is still around or has not been recycled.
831  */
832 void swap_free(swp_entry_t entry)
833 {
834         struct swap_info_struct *p;
835 
836         p = swap_info_get(entry);
837         if (p) {
838                 swap_entry_free(p, entry, 1);
839                 spin_unlock(&p->lock);
840         }
841 }
842 
843 /*
844  * Called after dropping swapcache to decrease refcnt to swap entries.
845  */
846 void swapcache_free(swp_entry_t entry)
847 {
848         struct swap_info_struct *p;
849 
850         p = swap_info_get(entry);
851         if (p) {
852                 swap_entry_free(p, entry, SWAP_HAS_CACHE);
853                 spin_unlock(&p->lock);
854         }
855 }
856 
857 /*
858  * How many references to page are currently swapped out?
859  * This does not give an exact answer when swap count is continued,
860  * but does include the high COUNT_CONTINUED flag to allow for that.
861  */
862 int page_swapcount(struct page *page)
863 {
864         int count = 0;
865         struct swap_info_struct *p;
866         swp_entry_t entry;
867 
868         entry.val = page_private(page);
869         p = swap_info_get(entry);
870         if (p) {
871                 count = swap_count(p->swap_map[swp_offset(entry)]);
872                 spin_unlock(&p->lock);
873         }
874         return count;
875 }
876 
877 /*
878  * We can write to an anon page without COW if there are no other references
879  * to it.  And as a side-effect, free up its swap: because the old content
880  * on disk will never be read, and seeking back there to write new content
881  * later would only waste time away from clustering.
882  */
883 int reuse_swap_page(struct page *page)
884 {
885         int count;
886 
887         VM_BUG_ON_PAGE(!PageLocked(page), page);
888         if (unlikely(PageKsm(page)))
889                 return 0;
890         count = page_mapcount(page);
891         if (count <= 1 && PageSwapCache(page)) {
892                 count += page_swapcount(page);
893                 if (count == 1 && !PageWriteback(page)) {
894                         delete_from_swap_cache(page);
895                         SetPageDirty(page);
896                 }
897         }
898         return count <= 1;
899 }
900 
901 /*
902  * If swap is getting full, or if there are no more mappings of this page,
903  * then try_to_free_swap is called to free its swap space.
904  */
905 int try_to_free_swap(struct page *page)
906 {
907         VM_BUG_ON_PAGE(!PageLocked(page), page);
908 
909         if (!PageSwapCache(page))
910                 return 0;
911         if (PageWriteback(page))
912                 return 0;
913         if (page_swapcount(page))
914                 return 0;
915 
916         /*
917          * Once hibernation has begun to create its image of memory,
918          * there's a danger that one of the calls to try_to_free_swap()
919          * - most probably a call from __try_to_reclaim_swap() while
920          * hibernation is allocating its own swap pages for the image,
921          * but conceivably even a call from memory reclaim - will free
922          * the swap from a page which has already been recorded in the
923          * image as a clean swapcache page, and then reuse its swap for
924          * another page of the image.  On waking from hibernation, the
925          * original page might be freed under memory pressure, then
926          * later read back in from swap, now with the wrong data.
927          *
928          * Hibernation suspends storage while it is writing the image
929          * to disk so check that here.
930          */
931         if (pm_suspended_storage())
932                 return 0;
933 
934         delete_from_swap_cache(page);
935         SetPageDirty(page);
936         return 1;
937 }
938 
939 /*
940  * Free the swap entry like above, but also try to
941  * free the page cache entry if it is the last user.
942  */
943 int free_swap_and_cache(swp_entry_t entry)
944 {
945         struct swap_info_struct *p;
946         struct page *page = NULL;
947 
948         if (non_swap_entry(entry))
949                 return 1;
950 
951         p = swap_info_get(entry);
952         if (p) {
953                 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
954                         page = find_get_page(swap_address_space(entry),
955                                                 entry.val);
956                         if (page && !trylock_page(page)) {
957                                 page_cache_release(page);
958                                 page = NULL;
959                         }
960                 }
961                 spin_unlock(&p->lock);
962         }
963         if (page) {
964                 /*
965                  * Not mapped elsewhere, or swap space full? Free it!
966                  * Also recheck PageSwapCache now page is locked (above).
967                  */
968                 if (PageSwapCache(page) && !PageWriteback(page) &&
969                                 (!page_mapped(page) || vm_swap_full())) {
970                         delete_from_swap_cache(page);
971                         SetPageDirty(page);
972                 }
973                 unlock_page(page);
974                 page_cache_release(page);
975         }
976         return p != NULL;
977 }
978 
979 #ifdef CONFIG_HIBERNATION
980 /*
981  * Find the swap type that corresponds to given device (if any).
982  *
983  * @offset - number of the PAGE_SIZE-sized block of the device, starting
984  * from 0, in which the swap header is expected to be located.
985  *
986  * This is needed for the suspend to disk (aka swsusp).
987  */
988 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
989 {
990         struct block_device *bdev = NULL;
991         int type;
992 
993         if (device)
994                 bdev = bdget(device);
995 
996         spin_lock(&swap_lock);
997         for (type = 0; type < nr_swapfiles; type++) {
998                 struct swap_info_struct *sis = swap_info[type];
999 
1000                 if (!(sis->flags & SWP_WRITEOK))
1001                         continue;
1002 
1003                 if (!bdev) {
1004                         if (bdev_p)
1005                                 *bdev_p = bdgrab(sis->bdev);
1006 
1007                         spin_unlock(&swap_lock);
1008                         return type;
1009                 }
1010                 if (bdev == sis->bdev) {
1011                         struct swap_extent *se = &sis->first_swap_extent;
1012 
1013                         if (se->start_block == offset) {
1014                                 if (bdev_p)
1015                                         *bdev_p = bdgrab(sis->bdev);
1016 
1017                                 spin_unlock(&swap_lock);
1018                                 bdput(bdev);
1019                                 return type;
1020                         }
1021                 }
1022         }
1023         spin_unlock(&swap_lock);
1024         if (bdev)
1025                 bdput(bdev);
1026 
1027         return -ENODEV;
1028 }
1029 
1030 /*
1031  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
1032  * corresponding to given index in swap_info (swap type).
1033  */
1034 sector_t swapdev_block(int type, pgoff_t offset)
1035 {
1036         struct block_device *bdev;
1037 
1038         if ((unsigned int)type >= nr_swapfiles)
1039                 return 0;
1040         if (!(swap_info[type]->flags & SWP_WRITEOK))
1041                 return 0;
1042         return map_swap_entry(swp_entry(type, offset), &bdev);
1043 }
1044 
1045 /*
1046  * Return either the total number of swap pages of given type, or the number
1047  * of free pages of that type (depending on @free)
1048  *
1049  * This is needed for software suspend
1050  */
1051 unsigned int count_swap_pages(int type, int free)
1052 {
1053         unsigned int n = 0;
1054 
1055         spin_lock(&swap_lock);
1056         if ((unsigned int)type < nr_swapfiles) {
1057                 struct swap_info_struct *sis = swap_info[type];
1058 
1059                 spin_lock(&sis->lock);
1060                 if (sis->flags & SWP_WRITEOK) {
1061                         n = sis->pages;
1062                         if (free)
1063                                 n -= sis->inuse_pages;
1064                 }
1065                 spin_unlock(&sis->lock);
1066         }
1067         spin_unlock(&swap_lock);
1068         return n;
1069 }
1070 #endif /* CONFIG_HIBERNATION */
1071 
1072 static inline int maybe_same_pte(pte_t pte, pte_t swp_pte)
1073 {
1074 #ifdef CONFIG_MEM_SOFT_DIRTY
1075         /*
1076          * When pte keeps soft dirty bit the pte generated
1077          * from swap entry does not has it, still it's same
1078          * pte from logical point of view.
1079          */
1080         pte_t swp_pte_dirty = pte_swp_mksoft_dirty(swp_pte);
1081         return pte_same(pte, swp_pte) || pte_same(pte, swp_pte_dirty);
1082 #else
1083         return pte_same(pte, swp_pte);
1084 #endif
1085 }
1086 
1087 /*
1088  * No need to decide whether this PTE shares the swap entry with others,
1089  * just let do_wp_page work it out if a write is requested later - to
1090  * force COW, vm_page_prot omits write permission from any private vma.
1091  */
1092 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
1093                 unsigned long addr, swp_entry_t entry, struct page *page)
1094 {
1095         struct page *swapcache;
1096         struct mem_cgroup *memcg;
1097         spinlock_t *ptl;
1098         pte_t *pte;
1099         int ret = 1;
1100 
1101         swapcache = page;
1102         page = ksm_might_need_to_copy(page, vma, addr);
1103         if (unlikely(!page))
1104                 return -ENOMEM;
1105 
1106         if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL, &memcg)) {
1107                 ret = -ENOMEM;
1108                 goto out_nolock;
1109         }
1110 
1111         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
1112         if (unlikely(!maybe_same_pte(*pte, swp_entry_to_pte(entry)))) {
1113                 mem_cgroup_cancel_charge(page, memcg);
1114                 ret = 0;
1115                 goto out;
1116         }
1117 
1118         dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
1119         inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
1120         get_page(page);
1121         set_pte_at(vma->vm_mm, addr, pte,
1122                    pte_mkold(mk_pte(page, vma->vm_page_prot)));
1123         if (page == swapcache) {
1124                 page_add_anon_rmap(page, vma, addr);
1125                 mem_cgroup_commit_charge(page, memcg, true);
1126         } else { /* ksm created a completely new copy */
1127                 page_add_new_anon_rmap(page, vma, addr);
1128                 mem_cgroup_commit_charge(page, memcg, false);
1129                 lru_cache_add_active_or_unevictable(page, vma);
1130         }
1131         swap_free(entry);
1132         /*
1133          * Move the page to the active list so it is not
1134          * immediately swapped out again after swapon.
1135          */
1136         activate_page(page);
1137 out:
1138         pte_unmap_unlock(pte, ptl);
1139 out_nolock:
1140         if (page != swapcache) {
1141                 unlock_page(page);
1142                 put_page(page);
1143         }
1144         return ret;
1145 }
1146 
1147 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
1148                                 unsigned long addr, unsigned long end,
1149                                 swp_entry_t entry, struct page *page)
1150 {
1151         pte_t swp_pte = swp_entry_to_pte(entry);
1152         pte_t *pte;
1153         int ret = 0;
1154 
1155         /*
1156          * We don't actually need pte lock while scanning for swp_pte: since
1157          * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
1158          * page table while we're scanning; though it could get zapped, and on
1159          * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
1160          * of unmatched parts which look like swp_pte, so unuse_pte must
1161          * recheck under pte lock.  Scanning without pte lock lets it be
1162          * preemptable whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
1163          */
1164         pte = pte_offset_map(pmd, addr);
1165         do {
1166                 /*
1167                  * swapoff spends a _lot_ of time in this loop!
1168                  * Test inline before going to call unuse_pte.
1169                  */
1170                 if (unlikely(maybe_same_pte(*pte, swp_pte))) {
1171                         pte_unmap(pte);
1172                         ret = unuse_pte(vma, pmd, addr, entry, page);
1173                         if (ret)
1174                                 goto out;
1175                         pte = pte_offset_map(pmd, addr);
1176                 }
1177         } while (pte++, addr += PAGE_SIZE, addr != end);
1178         pte_unmap(pte - 1);
1179 out:
1180         return ret;
1181 }
1182 
1183 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
1184                                 unsigned long addr, unsigned long end,
1185                                 swp_entry_t entry, struct page *page)
1186 {
1187         pmd_t *pmd;
1188         unsigned long next;
1189         int ret;
1190 
1191         pmd = pmd_offset(pud, addr);
1192         do {
1193                 next = pmd_addr_end(addr, end);
1194                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
1195                         continue;
1196                 ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
1197                 if (ret)
1198                         return ret;
1199         } while (pmd++, addr = next, addr != end);
1200         return 0;
1201 }
1202 
1203 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
1204                                 unsigned long addr, unsigned long end,
1205                                 swp_entry_t entry, struct page *page)
1206 {
1207         pud_t *pud;
1208         unsigned long next;
1209         int ret;
1210 
1211         pud = pud_offset(pgd, addr);
1212         do {
1213                 next = pud_addr_end(addr, end);
1214                 if (pud_none_or_clear_bad(pud))
1215                         continue;
1216                 ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
1217                 if (ret)
1218                         return ret;
1219         } while (pud++, addr = next, addr != end);
1220         return 0;
1221 }
1222 
1223 static int unuse_vma(struct vm_area_struct *vma,
1224                                 swp_entry_t entry, struct page *page)
1225 {
1226         pgd_t *pgd;
1227         unsigned long addr, end, next;
1228         int ret;
1229 
1230         if (page_anon_vma(page)) {
1231                 addr = page_address_in_vma(page, vma);
1232                 if (addr == -EFAULT)
1233                         return 0;
1234                 else
1235                         end = addr + PAGE_SIZE;
1236         } else {
1237                 addr = vma->vm_start;
1238                 end = vma->vm_end;
1239         }
1240 
1241         pgd = pgd_offset(vma->vm_mm, addr);
1242         do {
1243                 next = pgd_addr_end(addr, end);
1244                 if (pgd_none_or_clear_bad(pgd))
1245                         continue;
1246                 ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1247                 if (ret)
1248                         return ret;
1249         } while (pgd++, addr = next, addr != end);
1250         return 0;
1251 }
1252 
1253 static int unuse_mm(struct mm_struct *mm,
1254                                 swp_entry_t entry, struct page *page)
1255 {
1256         struct vm_area_struct *vma;
1257         int ret = 0;
1258 
1259         if (!down_read_trylock(&mm->mmap_sem)) {
1260                 /*
1261                  * Activate page so shrink_inactive_list is unlikely to unmap
1262                  * its ptes while lock is dropped, so swapoff can make progress.
1263                  */
1264                 activate_page(page);
1265                 unlock_page(page);
1266                 down_read(&mm->mmap_sem);
1267                 lock_page(page);
1268         }
1269         for (vma = mm->mmap; vma; vma = vma->vm_next) {
1270                 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1271                         break;
1272         }
1273         up_read(&mm->mmap_sem);
1274         return (ret < 0)? ret: 0;
1275 }
1276 
1277 /*
1278  * Scan swap_map (or frontswap_map if frontswap parameter is true)
1279  * from current position to next entry still in use.
1280  * Recycle to start on reaching the end, returning 0 when empty.
1281  */
1282 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1283                                         unsigned int prev, bool frontswap)
1284 {
1285         unsigned int max = si->max;
1286         unsigned int i = prev;
1287         unsigned char count;
1288 
1289         /*
1290          * No need for swap_lock here: we're just looking
1291          * for whether an entry is in use, not modifying it; false
1292          * hits are okay, and sys_swapoff() has already prevented new
1293          * allocations from this area (while holding swap_lock).
1294          */
1295         for (;;) {
1296                 if (++i >= max) {
1297                         if (!prev) {
1298                                 i = 0;
1299                                 break;
1300                         }
1301                         /*
1302                          * No entries in use at top of swap_map,
1303                          * loop back to start and recheck there.
1304                          */
1305                         max = prev + 1;
1306                         prev = 0;
1307                         i = 1;
1308                 }
1309                 if (frontswap) {
1310                         if (frontswap_test(si, i))
1311                                 break;
1312                         else
1313                                 continue;
1314                 }
1315                 count = READ_ONCE(si->swap_map[i]);
1316                 if (count && swap_count(count) != SWAP_MAP_BAD)
1317                         break;
1318         }
1319         return i;
1320 }
1321 
1322 /*
1323  * We completely avoid races by reading each swap page in advance,
1324  * and then search for the process using it.  All the necessary
1325  * page table adjustments can then be made atomically.
1326  *
1327  * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1328  * pages_to_unuse==0 means all pages; ignored if frontswap is false
1329  */
1330 int try_to_unuse(unsigned int type, bool frontswap,
1331                  unsigned long pages_to_unuse)
1332 {
1333         struct swap_info_struct *si = swap_info[type];
1334         struct mm_struct *start_mm;
1335         volatile unsigned char *swap_map; /* swap_map is accessed without
1336                                            * locking. Mark it as volatile
1337                                            * to prevent compiler doing
1338                                            * something odd.
1339                                            */
1340         unsigned char swcount;
1341         struct page *page;
1342         swp_entry_t entry;
1343         unsigned int i = 0;
1344         int retval = 0;
1345 
1346         /*
1347          * When searching mms for an entry, a good strategy is to
1348          * start at the first mm we freed the previous entry from
1349          * (though actually we don't notice whether we or coincidence
1350          * freed the entry).  Initialize this start_mm with a hold.
1351          *
1352          * A simpler strategy would be to start at the last mm we
1353          * freed the previous entry from; but that would take less
1354          * advantage of mmlist ordering, which clusters forked mms
1355          * together, child after parent.  If we race with dup_mmap(), we
1356          * prefer to resolve parent before child, lest we miss entries
1357          * duplicated after we scanned child: using last mm would invert
1358          * that.
1359          */
1360         start_mm = &init_mm;
1361         atomic_inc(&init_mm.mm_users);
1362 
1363         /*
1364          * Keep on scanning until all entries have gone.  Usually,
1365          * one pass through swap_map is enough, but not necessarily:
1366          * there are races when an instance of an entry might be missed.
1367          */
1368         while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1369                 if (signal_pending(current)) {
1370                         retval = -EINTR;
1371                         break;
1372                 }
1373 
1374                 /*
1375                  * Get a page for the entry, using the existing swap
1376                  * cache page if there is one.  Otherwise, get a clean
1377                  * page and read the swap into it.
1378                  */
1379                 swap_map = &si->swap_map[i];
1380                 entry = swp_entry(type, i);
1381                 page = read_swap_cache_async(entry,
1382                                         GFP_HIGHUSER_MOVABLE, NULL, 0);
1383                 if (!page) {
1384                         /*
1385                          * Either swap_duplicate() failed because entry
1386                          * has been freed independently, and will not be
1387                          * reused since sys_swapoff() already disabled
1388                          * allocation from here, or alloc_page() failed.
1389                          */
1390                         swcount = *swap_map;
1391                         /*
1392                          * We don't hold lock here, so the swap entry could be
1393                          * SWAP_MAP_BAD (when the cluster is discarding).
1394                          * Instead of fail out, We can just skip the swap
1395                          * entry because swapoff will wait for discarding
1396                          * finish anyway.
1397                          */
1398                         if (!swcount || swcount == SWAP_MAP_BAD)
1399                                 continue;
1400                         retval = -ENOMEM;
1401                         break;
1402                 }
1403 
1404                 /*
1405                  * Don't hold on to start_mm if it looks like exiting.
1406                  */
1407                 if (atomic_read(&start_mm->mm_users) == 1) {
1408                         mmput(start_mm);
1409                         start_mm = &init_mm;
1410                         atomic_inc(&init_mm.mm_users);
1411                 }
1412 
1413                 /*
1414                  * Wait for and lock page.  When do_swap_page races with
1415                  * try_to_unuse, do_swap_page can handle the fault much
1416                  * faster than try_to_unuse can locate the entry.  This
1417                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
1418                  * defer to do_swap_page in such a case - in some tests,
1419                  * do_swap_page and try_to_unuse repeatedly compete.
1420                  */
1421                 wait_on_page_locked(page);
1422                 wait_on_page_writeback(page);
1423                 lock_page(page);
1424                 wait_on_page_writeback(page);
1425 
1426                 /*
1427                  * Remove all references to entry.
1428                  */
1429                 swcount = *swap_map;
1430                 if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1431                         retval = shmem_unuse(entry, page);
1432                         /* page has already been unlocked and released */
1433                         if (retval < 0)
1434                                 break;
1435                         continue;
1436                 }
1437                 if (swap_count(swcount) && start_mm != &init_mm)
1438                         retval = unuse_mm(start_mm, entry, page);
1439 
1440                 if (swap_count(*swap_map)) {
1441                         int set_start_mm = (*swap_map >= swcount);
1442                         struct list_head *p = &start_mm->mmlist;
1443                         struct mm_struct *new_start_mm = start_mm;
1444                         struct mm_struct *prev_mm = start_mm;
1445                         struct mm_struct *mm;
1446 
1447                         atomic_inc(&new_start_mm->mm_users);
1448                         atomic_inc(&prev_mm->mm_users);
1449                         spin_lock(&mmlist_lock);
1450                         while (swap_count(*swap_map) && !retval &&
1451                                         (p = p->next) != &start_mm->mmlist) {
1452                                 mm = list_entry(p, struct mm_struct, mmlist);
1453                                 if (!atomic_inc_not_zero(&mm->mm_users))
1454                                         continue;
1455                                 spin_unlock(&mmlist_lock);
1456                                 mmput(prev_mm);
1457                                 prev_mm = mm;
1458 
1459                                 cond_resched();
1460 
1461                                 swcount = *swap_map;
1462                                 if (!swap_count(swcount)) /* any usage ? */
1463                                         ;
1464                                 else if (mm == &init_mm)
1465                                         set_start_mm = 1;
1466                                 else
1467                                         retval = unuse_mm(mm, entry, page);
1468 
1469                                 if (set_start_mm && *swap_map < swcount) {
1470                                         mmput(new_start_mm);
1471                                         atomic_inc(&mm->mm_users);
1472                                         new_start_mm = mm;
1473                                         set_start_mm = 0;
1474                                 }
1475                                 spin_lock(&mmlist_lock);
1476                         }
1477                         spin_unlock(&mmlist_lock);
1478                         mmput(prev_mm);
1479                         mmput(start_mm);
1480                         start_mm = new_start_mm;
1481                 }
1482                 if (retval) {
1483                         unlock_page(page);
1484                         page_cache_release(page);
1485                         break;
1486                 }
1487 
1488                 /*
1489                  * If a reference remains (rare), we would like to leave
1490                  * the page in the swap cache; but try_to_unmap could
1491                  * then re-duplicate the entry once we drop page lock,
1492                  * so we might loop indefinitely; also, that page could
1493                  * not be swapped out to other storage meanwhile.  So:
1494                  * delete from cache even if there's another reference,
1495                  * after ensuring that the data has been saved to disk -
1496                  * since if the reference remains (rarer), it will be
1497                  * read from disk into another page.  Splitting into two
1498                  * pages would be incorrect if swap supported "shared
1499                  * private" pages, but they are handled by tmpfs files.
1500                  *
1501                  * Given how unuse_vma() targets one particular offset
1502                  * in an anon_vma, once the anon_vma has been determined,
1503                  * this splitting happens to be just what is needed to
1504                  * handle where KSM pages have been swapped out: re-reading
1505                  * is unnecessarily slow, but we can fix that later on.
1506                  */
1507                 if (swap_count(*swap_map) &&
1508                      PageDirty(page) && PageSwapCache(page)) {
1509                         struct writeback_control wbc = {
1510                                 .sync_mode = WB_SYNC_NONE,
1511                         };
1512 
1513                         swap_writepage(page, &wbc);
1514                         lock_page(page);
1515                         wait_on_page_writeback(page);
1516                 }
1517 
1518                 /*
1519                  * It is conceivable that a racing task removed this page from
1520                  * swap cache just before we acquired the page lock at the top,
1521                  * or while we dropped it in unuse_mm().  The page might even
1522                  * be back in swap cache on another swap area: that we must not
1523                  * delete, since it may not have been written out to swap yet.
1524                  */
1525                 if (PageSwapCache(page) &&
1526                     likely(page_private(page) == entry.val))
1527                         delete_from_swap_cache(page);
1528 
1529                 /*
1530                  * So we could skip searching mms once swap count went
1531                  * to 1, we did not mark any present ptes as dirty: must
1532                  * mark page dirty so shrink_page_list will preserve it.
1533                  */
1534                 SetPageDirty(page);
1535                 unlock_page(page);
1536                 page_cache_release(page);
1537 
1538                 /*
1539                  * Make sure that we aren't completely killing
1540                  * interactive performance.
1541                  */
1542                 cond_resched();
1543                 if (frontswap && pages_to_unuse > 0) {
1544                         if (!--pages_to_unuse)
1545                                 break;
1546                 }
1547         }
1548 
1549         mmput(start_mm);
1550         return retval;
1551 }
1552 
1553 /*
1554  * After a successful try_to_unuse, if no swap is now in use, we know
1555  * we can empty the mmlist.  swap_lock must be held on entry and exit.
1556  * Note that mmlist_lock nests inside swap_lock, and an mm must be
1557  * added to the mmlist just after page_duplicate - before would be racy.
1558  */
1559 static void drain_mmlist(void)
1560 {
1561         struct list_head *p, *next;
1562         unsigned int type;
1563 
1564         for (type = 0; type < nr_swapfiles; type++)
1565                 if (swap_info[type]->inuse_pages)
1566                         return;
1567         spin_lock(&mmlist_lock);
1568         list_for_each_safe(p, next, &init_mm.mmlist)
1569                 list_del_init(p);
1570         spin_unlock(&mmlist_lock);
1571 }
1572 
1573 /*
1574  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1575  * corresponds to page offset for the specified swap entry.
1576  * Note that the type of this function is sector_t, but it returns page offset
1577  * into the bdev, not sector offset.
1578  */
1579 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1580 {
1581         struct swap_info_struct *sis;
1582         struct swap_extent *start_se;
1583         struct swap_extent *se;
1584         pgoff_t offset;
1585 
1586         sis = swap_info[swp_type(entry)];
1587         *bdev = sis->bdev;
1588 
1589         offset = swp_offset(entry);
1590         start_se = sis->curr_swap_extent;
1591         se = start_se;
1592 
1593         for ( ; ; ) {
1594                 struct list_head *lh;
1595 
1596                 if (se->start_page <= offset &&
1597                                 offset < (se->start_page + se->nr_pages)) {
1598                         return se->start_block + (offset - se->start_page);
1599                 }
1600                 lh = se->list.next;
1601                 se = list_entry(lh, struct swap_extent, list);
1602                 sis->curr_swap_extent = se;
1603                 BUG_ON(se == start_se);         /* It *must* be present */
1604         }
1605 }
1606 
1607 /*
1608  * Returns the page offset into bdev for the specified page's swap entry.
1609  */
1610 sector_t map_swap_page(struct page *page, struct block_device **bdev)
1611 {
1612         swp_entry_t entry;
1613         entry.val = page_private(page);
1614         return map_swap_entry(entry, bdev);
1615 }
1616 
1617 /*
1618  * Free all of a swapdev's extent information
1619  */
1620 static void destroy_swap_extents(struct swap_info_struct *sis)
1621 {
1622         while (!list_empty(&sis->first_swap_extent.list)) {
1623                 struct swap_extent *se;
1624 
1625                 se = list_entry(sis->first_swap_extent.list.next,
1626                                 struct swap_extent, list);
1627                 list_del(&se->list);
1628                 kfree(se);
1629         }
1630 
1631         if (sis->flags & SWP_FILE) {
1632                 struct file *swap_file = sis->swap_file;
1633                 struct address_space *mapping = swap_file->f_mapping;
1634 
1635                 sis->flags &= ~SWP_FILE;
1636                 mapping->a_ops->swap_deactivate(swap_file);
1637         }
1638 }
1639 
1640 /*
1641  * Add a block range (and the corresponding page range) into this swapdev's
1642  * extent list.  The extent list is kept sorted in page order.
1643  *
1644  * This function rather assumes that it is called in ascending page order.
1645  */
1646 int
1647 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1648                 unsigned long nr_pages, sector_t start_block)
1649 {
1650         struct swap_extent *se;
1651         struct swap_extent *new_se;
1652         struct list_head *lh;
1653 
1654         if (start_page == 0) {
1655                 se = &sis->first_swap_extent;
1656                 sis->curr_swap_extent = se;
1657                 se->start_page = 0;
1658                 se->nr_pages = nr_pages;
1659                 se->start_block = start_block;
1660                 return 1;
1661         } else {
1662                 lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1663                 se = list_entry(lh, struct swap_extent, list);
1664                 BUG_ON(se->start_page + se->nr_pages != start_page);
1665                 if (se->start_block + se->nr_pages == start_block) {
1666                         /* Merge it */
1667                         se->nr_pages += nr_pages;
1668                         return 0;
1669                 }
1670         }
1671 
1672         /*
1673          * No merge.  Insert a new extent, preserving ordering.
1674          */
1675         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1676         if (new_se == NULL)
1677                 return -ENOMEM;
1678         new_se->start_page = start_page;
1679         new_se->nr_pages = nr_pages;
1680         new_se->start_block = start_block;
1681 
1682         list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1683         return 1;
1684 }
1685 
1686 /*
1687  * A `swap extent' is a simple thing which maps a contiguous range of pages
1688  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1689  * is built at swapon time and is then used at swap_writepage/swap_readpage
1690  * time for locating where on disk a page belongs.
1691  *
1692  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1693  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1694  * swap files identically.
1695  *
1696  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1697  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1698  * swapfiles are handled *identically* after swapon time.
1699  *
1700  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1701  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1702  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1703  * requirements, they are simply tossed out - we will never use those blocks
1704  * for swapping.
1705  *
1706  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1707  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1708  * which will scribble on the fs.
1709  *
1710  * The amount of disk space which a single swap extent represents varies.
1711  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1712  * extents in the list.  To avoid much list walking, we cache the previous
1713  * search location in `curr_swap_extent', and start new searches from there.
1714  * This is extremely effective.  The average number of iterations in
1715  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1716  */
1717 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1718 {
1719         struct file *swap_file = sis->swap_file;
1720         struct address_space *mapping = swap_file->f_mapping;
1721         struct inode *inode = mapping->host;
1722         int ret;
1723 
1724         if (S_ISBLK(inode->i_mode)) {
1725                 ret = add_swap_extent(sis, 0, sis->max, 0);
1726                 *span = sis->pages;
1727                 return ret;
1728         }
1729 
1730         if (mapping->a_ops->swap_activate) {
1731                 ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1732                 if (!ret) {
1733                         sis->flags |= SWP_FILE;
1734                         ret = add_swap_extent(sis, 0, sis->max, 0);
1735                         *span = sis->pages;
1736                 }
1737                 return ret;
1738         }
1739 
1740         return generic_swapfile_activate(sis, swap_file, span);
1741 }
1742 
1743 static void _enable_swap_info(struct swap_info_struct *p, int prio,
1744                                 unsigned char *swap_map,
1745                                 struct swap_cluster_info *cluster_info)
1746 {
1747         if (prio >= 0)
1748                 p->prio = prio;
1749         else
1750                 p->prio = --least_priority;
1751         /*
1752          * the plist prio is negated because plist ordering is
1753          * low-to-high, while swap ordering is high-to-low
1754          */
1755         p->list.prio = -p->prio;
1756         p->avail_list.prio = -p->prio;
1757         p->swap_map = swap_map;
1758         p->cluster_info = cluster_info;
1759         p->flags |= SWP_WRITEOK;
1760         atomic_long_add(p->pages, &nr_swap_pages);
1761         total_swap_pages += p->pages;
1762 
1763         assert_spin_locked(&swap_lock);
1764         /*
1765          * both lists are plists, and thus priority ordered.
1766          * swap_active_head needs to be priority ordered for swapoff(),
1767          * which on removal of any swap_info_struct with an auto-assigned
1768          * (i.e. negative) priority increments the auto-assigned priority
1769          * of any lower-priority swap_info_structs.
1770          * swap_avail_head needs to be priority ordered for get_swap_page(),
1771          * which allocates swap pages from the highest available priority
1772          * swap_info_struct.
1773          */
1774         plist_add(&p->list, &swap_active_head);
1775         spin_lock(&swap_avail_lock);
1776         plist_add(&p->avail_list, &swap_avail_head);
1777         spin_unlock(&swap_avail_lock);
1778 }
1779 
1780 static void enable_swap_info(struct swap_info_struct *p, int prio,
1781                                 unsigned char *swap_map,
1782                                 struct swap_cluster_info *cluster_info,
1783                                 unsigned long *frontswap_map)
1784 {
1785         frontswap_init(p->type, frontswap_map);
1786         spin_lock(&swap_lock);
1787         spin_lock(&p->lock);
1788          _enable_swap_info(p, prio, swap_map, cluster_info);
1789         spin_unlock(&p->lock);
1790         spin_unlock(&swap_lock);
1791 }
1792 
1793 static void reinsert_swap_info(struct swap_info_struct *p)
1794 {
1795         spin_lock(&swap_lock);
1796         spin_lock(&p->lock);
1797         _enable_swap_info(p, p->prio, p->swap_map, p->cluster_info);
1798         spin_unlock(&p->lock);
1799         spin_unlock(&swap_lock);
1800 }
1801 
1802 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1803 {
1804         struct swap_info_struct *p = NULL;
1805         unsigned char *swap_map;
1806         struct swap_cluster_info *cluster_info;
1807         unsigned long *frontswap_map;
1808         struct file *swap_file, *victim;
1809         struct address_space *mapping;
1810         struct inode *inode;
1811         struct filename *pathname;
1812         int err, found = 0;
1813         unsigned int old_block_size;
1814 
1815         if (!capable(CAP_SYS_ADMIN))
1816                 return -EPERM;
1817 
1818         BUG_ON(!current->mm);
1819 
1820         pathname = getname(specialfile);
1821         if (IS_ERR(pathname))
1822                 return PTR_ERR(pathname);
1823 
1824         victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1825         err = PTR_ERR(victim);
1826         if (IS_ERR(victim))
1827                 goto out;
1828 
1829         mapping = victim->f_mapping;
1830         spin_lock(&swap_lock);
1831         plist_for_each_entry(p, &swap_active_head, list) {
1832                 if (p->flags & SWP_WRITEOK) {
1833                         if (p->swap_file->f_mapping == mapping) {
1834                                 found = 1;
1835                                 break;
1836                         }
1837                 }
1838         }
1839         if (!found) {
1840                 err = -EINVAL;
1841                 spin_unlock(&swap_lock);
1842                 goto out_dput;
1843         }
1844         if (!security_vm_enough_memory_mm(current->mm, p->pages))
1845                 vm_unacct_memory(p->pages);
1846         else {
1847                 err = -ENOMEM;
1848                 spin_unlock(&swap_lock);
1849                 goto out_dput;
1850         }
1851         spin_lock(&swap_avail_lock);
1852         plist_del(&p->avail_list, &swap_avail_head);
1853         spin_unlock(&swap_avail_lock);
1854         spin_lock(&p->lock);
1855         if (p->prio < 0) {
1856                 struct swap_info_struct *si = p;
1857 
1858                 plist_for_each_entry_continue(si, &swap_active_head, list) {
1859                         si->prio++;
1860                         si->list.prio--;
1861                         si->avail_list.prio--;
1862                 }
1863                 least_priority++;
1864         }
1865         plist_del(&p->list, &swap_active_head);
1866         atomic_long_sub(p->pages, &nr_swap_pages);
1867         total_swap_pages -= p->pages;
1868         p->flags &= ~SWP_WRITEOK;
1869         spin_unlock(&p->lock);
1870         spin_unlock(&swap_lock);
1871 
1872         set_current_oom_origin();
1873         err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
1874         clear_current_oom_origin();
1875 
1876         if (err) {
1877                 /* re-insert swap space back into swap_list */
1878                 reinsert_swap_info(p);
1879                 goto out_dput;
1880         }
1881 
1882         flush_work(&p->discard_work);
1883 
1884         destroy_swap_extents(p);
1885         if (p->flags & SWP_CONTINUED)
1886                 free_swap_count_continuations(p);
1887 
1888         mutex_lock(&swapon_mutex);
1889         spin_lock(&swap_lock);
1890         spin_lock(&p->lock);
1891         drain_mmlist();
1892 
1893         /* wait for anyone still in scan_swap_map */
1894         p->highest_bit = 0;             /* cuts scans short */
1895         while (p->flags >= SWP_SCANNING) {
1896                 spin_unlock(&p->lock);
1897                 spin_unlock(&swap_lock);
1898                 schedule_timeout_uninterruptible(1);
1899                 spin_lock(&swap_lock);
1900                 spin_lock(&p->lock);
1901         }
1902 
1903         swap_file = p->swap_file;
1904         old_block_size = p->old_block_size;
1905         p->swap_file = NULL;
1906         p->max = 0;
1907         swap_map = p->swap_map;
1908         p->swap_map = NULL;
1909         cluster_info = p->cluster_info;
1910         p->cluster_info = NULL;
1911         frontswap_map = frontswap_map_get(p);
1912         spin_unlock(&p->lock);
1913         spin_unlock(&swap_lock);
1914         frontswap_invalidate_area(p->type);
1915         frontswap_map_set(p, NULL);
1916         mutex_unlock(&swapon_mutex);
1917         free_percpu(p->percpu_cluster);
1918         p->percpu_cluster = NULL;
1919         vfree(swap_map);
1920         vfree(cluster_info);
1921         vfree(frontswap_map);
1922         /* Destroy swap account information */
1923         swap_cgroup_swapoff(p->type);
1924 
1925         inode = mapping->host;
1926         if (S_ISBLK(inode->i_mode)) {
1927                 struct block_device *bdev = I_BDEV(inode);
1928                 set_blocksize(bdev, old_block_size);
1929                 blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1930         } else {
1931                 mutex_lock(&inode->i_mutex);
1932                 inode->i_flags &= ~S_SWAPFILE;
1933                 mutex_unlock(&inode->i_mutex);
1934         }
1935         filp_close(swap_file, NULL);
1936 
1937         /*
1938          * Clear the SWP_USED flag after all resources are freed so that swapon
1939          * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
1940          * not hold p->lock after we cleared its SWP_WRITEOK.
1941          */
1942         spin_lock(&swap_lock);
1943         p->flags = 0;
1944         spin_unlock(&swap_lock);
1945 
1946         err = 0;
1947         atomic_inc(&proc_poll_event);
1948         wake_up_interruptible(&proc_poll_wait);
1949 
1950 out_dput:
1951         filp_close(victim, NULL);
1952 out:
1953         putname(pathname);
1954         return err;
1955 }
1956 
1957 #ifdef CONFIG_PROC_FS
1958 static unsigned swaps_poll(struct file *file, poll_table *wait)
1959 {
1960         struct seq_file *seq = file->private_data;
1961 
1962         poll_wait(file, &proc_poll_wait, wait);
1963 
1964         if (seq->poll_event != atomic_read(&proc_poll_event)) {
1965                 seq->poll_event = atomic_read(&proc_poll_event);
1966                 return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1967         }
1968 
1969         return POLLIN | POLLRDNORM;
1970 }
1971 
1972 /* iterator */
1973 static void *swap_start(struct seq_file *swap, loff_t *pos)
1974 {
1975         struct swap_info_struct *si;
1976         int type;
1977         loff_t l = *pos;
1978 
1979         mutex_lock(&swapon_mutex);
1980 
1981         if (!l)
1982                 return SEQ_START_TOKEN;
1983 
1984         for (type = 0; type < nr_swapfiles; type++) {
1985                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1986                 si = swap_info[type];
1987                 if (!(si->flags & SWP_USED) || !si->swap_map)
1988                         continue;
1989                 if (!--l)
1990                         return si;
1991         }
1992 
1993         return NULL;
1994 }
1995 
1996 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1997 {
1998         struct swap_info_struct *si = v;
1999         int type;
2000 
2001         if (v == SEQ_START_TOKEN)
2002                 type = 0;
2003         else
2004                 type = si->type + 1;
2005 
2006         for (; type < nr_swapfiles; type++) {
2007                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
2008                 si = swap_info[type];
2009                 if (!(si->flags & SWP_USED) || !si->swap_map)
2010                         continue;
2011                 ++*pos;
2012                 return si;
2013         }
2014 
2015         return NULL;
2016 }
2017 
2018 static void swap_stop(struct seq_file *swap, void *v)
2019 {
2020         mutex_unlock(&swapon_mutex);
2021 }
2022 
2023 static int swap_show(struct seq_file *swap, void *v)
2024 {
2025         struct swap_info_struct *si = v;
2026         struct file *file;
2027         int len;
2028 
2029         if (si == SEQ_START_TOKEN) {
2030                 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
2031                 return 0;
2032         }
2033 
2034         file = si->swap_file;
2035         len = seq_path(swap, &file->f_path, " \t\n\\");
2036         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
2037                         len < 40 ? 40 - len : 1, " ",
2038                         S_ISBLK(file_inode(file)->i_mode) ?
2039                                 "partition" : "file\t",
2040                         si->pages << (PAGE_SHIFT - 10),
2041                         si->inuse_pages << (PAGE_SHIFT - 10),
2042                         si->prio);
2043         return 0;
2044 }
2045 
2046 static const struct seq_operations swaps_op = {
2047         .start =        swap_start,
2048         .next =         swap_next,
2049         .stop =         swap_stop,
2050         .show =         swap_show
2051 };
2052 
2053 static int swaps_open(struct inode *inode, struct file *file)
2054 {
2055         struct seq_file *seq;
2056         int ret;
2057 
2058         ret = seq_open(file, &swaps_op);
2059         if (ret)
2060                 return ret;
2061 
2062         seq = file->private_data;
2063         seq->poll_event = atomic_read(&proc_poll_event);
2064         return 0;
2065 }
2066 
2067 static const struct file_operations proc_swaps_operations = {
2068         .open           = swaps_open,
2069         .read           = seq_read,
2070         .llseek         = seq_lseek,
2071         .release        = seq_release,
2072         .poll           = swaps_poll,
2073 };
2074 
2075 static int __init procswaps_init(void)
2076 {
2077         proc_create("swaps", 0, NULL, &proc_swaps_operations);
2078         return 0;
2079 }
2080 __initcall(procswaps_init);
2081 #endif /* CONFIG_PROC_FS */
2082 
2083 #ifdef MAX_SWAPFILES_CHECK
2084 static int __init max_swapfiles_check(void)
2085 {
2086         MAX_SWAPFILES_CHECK();
2087         return 0;
2088 }
2089 late_initcall(max_swapfiles_check);
2090 #endif
2091 
2092 static struct swap_info_struct *alloc_swap_info(void)
2093 {
2094         struct swap_info_struct *p;
2095         unsigned int type;
2096 
2097         p = kzalloc(sizeof(*p), GFP_KERNEL);
2098         if (!p)
2099                 return ERR_PTR(-ENOMEM);
2100 
2101         spin_lock(&swap_lock);
2102         for (type = 0; type < nr_swapfiles; type++) {
2103                 if (!(swap_info[type]->flags & SWP_USED))
2104                         break;
2105         }
2106         if (type >= MAX_SWAPFILES) {
2107                 spin_unlock(&swap_lock);
2108                 kfree(p);
2109                 return ERR_PTR(-EPERM);
2110         }
2111         if (type >= nr_swapfiles) {
2112                 p->type = type;
2113                 swap_info[type] = p;
2114                 /*
2115                  * Write swap_info[type] before nr_swapfiles, in case a
2116                  * racing procfs swap_start() or swap_next() is reading them.
2117                  * (We never shrink nr_swapfiles, we never free this entry.)
2118                  */
2119                 smp_wmb();
2120                 nr_swapfiles++;
2121         } else {
2122                 kfree(p);
2123                 p = swap_info[type];
2124                 /*
2125                  * Do not memset this entry: a racing procfs swap_next()
2126                  * would be relying on p->type to remain valid.
2127                  */
2128         }
2129         INIT_LIST_HEAD(&p->first_swap_extent.list);
2130         plist_node_init(&p->list, 0);
2131         plist_node_init(&p->avail_list, 0);
2132         p->flags = SWP_USED;
2133         spin_unlock(&swap_lock);
2134         spin_lock_init(&p->lock);
2135 
2136         return p;
2137 }
2138 
2139 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
2140 {
2141         int error;
2142 
2143         if (S_ISBLK(inode->i_mode)) {
2144                 p->bdev = bdgrab(I_BDEV(inode));
2145                 error = blkdev_get(p->bdev,
2146                                    FMODE_READ | FMODE_WRITE | FMODE_EXCL,
2147                                    sys_swapon);
2148                 if (error < 0) {
2149                         p->bdev = NULL;
2150                         return -EINVAL;
2151                 }
2152                 p->old_block_size = block_size(p->bdev);
2153                 error = set_blocksize(p->bdev, PAGE_SIZE);
2154                 if (error < 0)
2155                         return error;
2156                 p->flags |= SWP_BLKDEV;
2157         } else if (S_ISREG(inode->i_mode)) {
2158                 p->bdev = inode->i_sb->s_bdev;
2159                 mutex_lock(&inode->i_mutex);
2160                 if (IS_SWAPFILE(inode))
2161                         return -EBUSY;
2162         } else
2163                 return -EINVAL;
2164 
2165         return 0;
2166 }
2167 
2168 static unsigned long read_swap_header(struct swap_info_struct *p,
2169                                         union swap_header *swap_header,
2170                                         struct inode *inode)
2171 {
2172         int i;
2173         unsigned long maxpages;
2174         unsigned long swapfilepages;
2175         unsigned long last_page;
2176 
2177         if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
2178                 pr_err("Unable to find swap-space signature\n");
2179                 return 0;
2180         }
2181 
2182         /* swap partition endianess hack... */
2183         if (swab32(swap_header->info.version) == 1) {
2184                 swab32s(&swap_header->info.version);
2185                 swab32s(&swap_header->info.last_page);
2186                 swab32s(&swap_header->info.nr_badpages);
2187                 for (i = 0; i < swap_header->info.nr_badpages; i++)
2188                         swab32s(&swap_header->info.badpages[i]);
2189         }
2190         /* Check the swap header's sub-version */
2191         if (swap_header->info.version != 1) {
2192                 pr_warn("Unable to handle swap header version %d\n",
2193                         swap_header->info.version);
2194                 return 0;
2195         }
2196 
2197         p->lowest_bit  = 1;
2198         p->cluster_next = 1;
2199         p->cluster_nr = 0;
2200 
2201         /*
2202          * Find out how many pages are allowed for a single swap
2203          * device. There are two limiting factors: 1) the number
2204          * of bits for the swap offset in the swp_entry_t type, and
2205          * 2) the number of bits in the swap pte as defined by the
2206          * different architectures. In order to find the
2207          * largest possible bit mask, a swap entry with swap type 0
2208          * and swap offset ~0UL is created, encoded to a swap pte,
2209          * decoded to a swp_entry_t again, and finally the swap
2210          * offset is extracted. This will mask all the bits from
2211          * the initial ~0UL mask that can't be encoded in either
2212          * the swp_entry_t or the architecture definition of a
2213          * swap pte.
2214          */
2215         maxpages = swp_offset(pte_to_swp_entry(
2216                         swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
2217         last_page = swap_header->info.last_page;
2218         if (last_page > maxpages) {
2219                 pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
2220                         maxpages << (PAGE_SHIFT - 10),
2221                         last_page << (PAGE_SHIFT - 10));
2222         }
2223         if (maxpages > last_page) {
2224                 maxpages = last_page + 1;
2225                 /* p->max is an unsigned int: don't overflow it */
2226                 if ((unsigned int)maxpages == 0)
2227                         maxpages = UINT_MAX;
2228         }
2229         p->highest_bit = maxpages - 1;
2230 
2231         if (!maxpages)
2232                 return 0;
2233         swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
2234         if (swapfilepages && maxpages > swapfilepages) {
2235                 pr_warn("Swap area shorter than signature indicates\n");
2236                 return 0;
2237         }
2238         if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
2239                 return 0;
2240         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2241                 return 0;
2242 
2243         return maxpages;
2244 }
2245 
2246 static int setup_swap_map_and_extents(struct swap_info_struct *p,
2247                                         union swap_header *swap_header,
2248                                         unsigned char *swap_map,
2249                                         struct swap_cluster_info *cluster_info,
2250                                         unsigned long maxpages,
2251                                         sector_t *span)
2252 {
2253         int i;
2254         unsigned int nr_good_pages;
2255         int nr_extents;
2256         unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
2257         unsigned long idx = p->cluster_next / SWAPFILE_CLUSTER;
2258 
2259         nr_good_pages = maxpages - 1;   /* omit header page */
2260 
2261         cluster_set_null(&p->free_cluster_head);
2262         cluster_set_null(&p->free_cluster_tail);
2263         cluster_set_null(&p->discard_cluster_head);
2264         cluster_set_null(&p->discard_cluster_tail);
2265 
2266         for (i = 0; i < swap_header->info.nr_badpages; i++) {
2267                 unsigned int page_nr = swap_header->info.badpages[i];
2268                 if (page_nr == 0 || page_nr > swap_header->info.last_page)
2269                         return -EINVAL;
2270                 if (page_nr < maxpages) {
2271                         swap_map[page_nr] = SWAP_MAP_BAD;
2272                         nr_good_pages--;
2273                         /*
2274                          * Haven't marked the cluster free yet, no list
2275                          * operation involved
2276                          */
2277                         inc_cluster_info_page(p, cluster_info, page_nr);
2278                 }
2279         }
2280 
2281         /* Haven't marked the cluster free yet, no list operation involved */
2282         for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
2283                 inc_cluster_info_page(p, cluster_info, i);
2284 
2285         if (nr_good_pages) {
2286                 swap_map[0] = SWAP_MAP_BAD;
2287                 /*
2288                  * Not mark the cluster free yet, no list
2289                  * operation involved
2290                  */
2291                 inc_cluster_info_page(p, cluster_info, 0);
2292                 p->max = maxpages;
2293                 p->pages = nr_good_pages;
2294                 nr_extents = setup_swap_extents(p, span);
2295                 if (nr_extents < 0)
2296                         return nr_extents;
2297                 nr_good_pages = p->pages;
2298         }
2299         if (!nr_good_pages) {
2300                 pr_warn("Empty swap-file\n");
2301                 return -EINVAL;
2302         }
2303 
2304         if (!cluster_info)
2305                 return nr_extents;
2306 
2307         for (i = 0; i < nr_clusters; i++) {
2308                 if (!cluster_count(&cluster_info[idx])) {
2309                         cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
2310                         if (cluster_is_null(&p->free_cluster_head)) {
2311                                 cluster_set_next_flag(&p->free_cluster_head,
2312                                                                 idx, 0);
2313                                 cluster_set_next_flag(&p->free_cluster_tail,
2314                                                                 idx, 0);
2315                         } else {
2316                                 unsigned int tail;
2317 
2318                                 tail = cluster_next(&p->free_cluster_tail);
2319                                 cluster_set_next(&cluster_info[tail], idx);
2320                                 cluster_set_next_flag(&p->free_cluster_tail,
2321                                                                 idx, 0);
2322                         }
2323                 }
2324                 idx++;
2325                 if (idx == nr_clusters)
2326                         idx = 0;
2327         }
2328         return nr_extents;
2329 }
2330 
2331 /*
2332  * Helper to sys_swapon determining if a given swap
2333  * backing device queue supports DISCARD operations.
2334  */
2335 static bool swap_discardable(struct swap_info_struct *si)
2336 {
2337         struct request_queue *q = bdev_get_queue(si->bdev);
2338 
2339         if (!q || !blk_queue_discard(q))
2340                 return false;
2341 
2342         return true;
2343 }
2344 
2345 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2346 {
2347         struct swap_info_struct *p;
2348         struct filename *name;
2349         struct file *swap_file = NULL;
2350         struct address_space *mapping;
2351         int i;
2352         int prio;
2353         int error;
2354         union swap_header *swap_header;
2355         int nr_extents;
2356         sector_t span;
2357         unsigned long maxpages;
2358         unsigned char *swap_map = NULL;
2359         struct swap_cluster_info *cluster_info = NULL;
2360         unsigned long *frontswap_map = NULL;
2361         struct page *page = NULL;
2362         struct inode *inode = NULL;
2363 
2364         if (swap_flags & ~SWAP_FLAGS_VALID)
2365                 return -EINVAL;
2366 
2367         if (!capable(CAP_SYS_ADMIN))
2368                 return -EPERM;
2369 
2370         p = alloc_swap_info();
2371         if (IS_ERR(p))
2372                 return PTR_ERR(p);
2373 
2374         INIT_WORK(&p->discard_work, swap_discard_work);
2375 
2376         name = getname(specialfile);
2377         if (IS_ERR(name)) {
2378                 error = PTR_ERR(name);
2379                 name = NULL;
2380                 goto bad_swap;
2381         }
2382         swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2383         if (IS_ERR(swap_file)) {
2384                 error = PTR_ERR(swap_file);
2385                 swap_file = NULL;
2386                 goto bad_swap;
2387         }
2388 
2389         p->swap_file = swap_file;
2390         mapping = swap_file->f_mapping;
2391 
2392         for (i = 0; i < nr_swapfiles; i++) {
2393                 struct swap_info_struct *q = swap_info[i];
2394 
2395                 if (q == p || !q->swap_file)
2396                         continue;
2397                 if (mapping == q->swap_file->f_mapping) {
2398                         error = -EBUSY;
2399                         goto bad_swap;
2400                 }
2401         }
2402 
2403         inode = mapping->host;
2404         /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2405         error = claim_swapfile(p, inode);
2406         if (unlikely(error))
2407                 goto bad_swap;
2408 
2409         /*
2410          * Read the swap header.
2411          */
2412         if (!mapping->a_ops->readpage) {
2413                 error = -EINVAL;
2414                 goto bad_swap;
2415         }
2416         page = read_mapping_page(mapping, 0, swap_file);
2417         if (IS_ERR(page)) {
2418                 error = PTR_ERR(page);
2419                 goto bad_swap;
2420         }
2421         swap_header = kmap(page);
2422 
2423         maxpages = read_swap_header(p, swap_header, inode);
2424         if (unlikely(!maxpages)) {
2425                 error = -EINVAL;
2426                 goto bad_swap;
2427         }
2428 
2429         /* OK, set up the swap map and apply the bad block list */
2430         swap_map = vzalloc(maxpages);
2431         if (!swap_map) {
2432                 error = -ENOMEM;
2433                 goto bad_swap;
2434         }
2435         if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2436                 p->flags |= SWP_SOLIDSTATE;
2437                 /*
2438                  * select a random position to start with to help wear leveling
2439                  * SSD
2440                  */
2441                 p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2442 
2443                 cluster_info = vzalloc(DIV_ROUND_UP(maxpages,
2444                         SWAPFILE_CLUSTER) * sizeof(*cluster_info));
2445                 if (!cluster_info) {
2446                         error = -ENOMEM;
2447                         goto bad_swap;
2448                 }
2449                 p->percpu_cluster = alloc_percpu(struct percpu_cluster);
2450                 if (!p->percpu_cluster) {
2451                         error = -ENOMEM;
2452                         goto bad_swap;
2453                 }
2454                 for_each_possible_cpu(i) {
2455                         struct percpu_cluster *cluster;
2456                         cluster = per_cpu_ptr(p->percpu_cluster, i);
2457                         cluster_set_null(&cluster->index);
2458                 }
2459         }
2460 
2461         error = swap_cgroup_swapon(p->type, maxpages);
2462         if (error)
2463                 goto bad_swap;
2464 
2465         nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2466                 cluster_info, maxpages, &span);
2467         if (unlikely(nr_extents < 0)) {
2468                 error = nr_extents;
2469                 goto bad_swap;
2470         }
2471         /* frontswap enabled? set up bit-per-page map for frontswap */
2472         if (frontswap_enabled)
2473                 frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2474 
2475         if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
2476                 /*
2477                  * When discard is enabled for swap with no particular
2478                  * policy flagged, we set all swap discard flags here in
2479                  * order to sustain backward compatibility with older
2480                  * swapon(8) releases.
2481                  */
2482                 p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
2483                              SWP_PAGE_DISCARD);
2484 
2485                 /*
2486                  * By flagging sys_swapon, a sysadmin can tell us to
2487                  * either do single-time area discards only, or to just
2488                  * perform discards for released swap page-clusters.
2489                  * Now it's time to adjust the p->flags accordingly.
2490                  */
2491                 if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
2492                         p->flags &= ~SWP_PAGE_DISCARD;
2493                 else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
2494                         p->flags &= ~SWP_AREA_DISCARD;
2495 
2496                 /* issue a swapon-time discard if it's still required */
2497                 if (p->flags & SWP_AREA_DISCARD) {
2498                         int err = discard_swap(p);
2499                         if (unlikely(err))
2500                                 pr_err("swapon: discard_swap(%p): %d\n",
2501                                         p, err);
2502                 }
2503         }
2504 
2505         mutex_lock(&swapon_mutex);
2506         prio = -1;
2507         if (swap_flags & SWAP_FLAG_PREFER)
2508                 prio =
2509                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2510         enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
2511 
2512         pr_info("Adding %uk swap on %s.  "
2513                         "Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
2514                 p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2515                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2516                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2517                 (p->flags & SWP_DISCARDABLE) ? "D" : "",
2518                 (p->flags & SWP_AREA_DISCARD) ? "s" : "",
2519                 (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
2520                 (frontswap_map) ? "FS" : "");
2521 
2522         mutex_unlock(&swapon_mutex);
2523         atomic_inc(&proc_poll_event);
2524         wake_up_interruptible(&proc_poll_wait);
2525 
2526         if (S_ISREG(inode->i_mode))
2527                 inode->i_flags |= S_SWAPFILE;
2528         error = 0;
2529         goto out;
2530 bad_swap:
2531         free_percpu(p->percpu_cluster);
2532         p->percpu_cluster = NULL;
2533         if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2534                 set_blocksize(p->bdev, p->old_block_size);
2535                 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2536         }
2537         destroy_swap_extents(p);
2538         swap_cgroup_swapoff(p->type);
2539         spin_lock(&swap_lock);
2540         p->swap_file = NULL;
2541         p->flags = 0;
2542         spin_unlock(&swap_lock);
2543         vfree(swap_map);
2544         vfree(cluster_info);
2545         if (swap_file) {
2546                 if (inode && S_ISREG(inode->i_mode)) {
2547                         mutex_unlock(&inode->i_mutex);
2548                         inode = NULL;
2549                 }
2550                 filp_close(swap_file, NULL);
2551         }
2552 out:
2553         if (page && !IS_ERR(page)) {
2554                 kunmap(page);
2555                 page_cache_release(page);
2556         }
2557         if (name)
2558                 putname(name);
2559         if (inode && S_ISREG(inode->i_mode))
2560                 mutex_unlock(&inode->i_mutex);
2561         return error;
2562 }
2563 
2564 void si_swapinfo(struct sysinfo *val)
2565 {
2566         unsigned int type;
2567         unsigned long nr_to_be_unused = 0;
2568 
2569         spin_lock(&swap_lock);
2570         for (type = 0; type < nr_swapfiles; type++) {
2571                 struct swap_info_struct *si = swap_info[type];
2572 
2573                 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2574                         nr_to_be_unused += si->inuse_pages;
2575         }
2576         val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2577         val->totalswap = total_swap_pages + nr_to_be_unused;
2578         spin_unlock(&swap_lock);
2579 }
2580 
2581 /*
2582  * Verify that a swap entry is valid and increment its swap map count.
2583  *
2584  * Returns error code in following case.
2585  * - success -> 0
2586  * - swp_entry is invalid -> EINVAL
2587  * - swp_entry is migration entry -> EINVAL
2588  * - swap-cache reference is requested but there is already one. -> EEXIST
2589  * - swap-cache reference is requested but the entry is not used. -> ENOENT
2590  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2591  */
2592 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2593 {
2594         struct swap_info_struct *p;
2595         unsigned long offset, type;
2596         unsigned char count;
2597         unsigned char has_cache;
2598         int err = -EINVAL;
2599 
2600         if (non_swap_entry(entry))
2601                 goto out;
2602 
2603         type = swp_type(entry);
2604         if (type >= nr_swapfiles)
2605                 goto bad_file;
2606         p = swap_info[type];
2607         offset = swp_offset(entry);
2608 
2609         spin_lock(&p->lock);
2610         if (unlikely(offset >= p->max))
2611                 goto unlock_out;
2612 
2613         count = p->swap_map[offset];
2614 
2615         /*
2616          * swapin_readahead() doesn't check if a swap entry is valid, so the
2617          * swap entry could be SWAP_MAP_BAD. Check here with lock held.
2618          */
2619         if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
2620                 err = -ENOENT;
2621                 goto unlock_out;
2622         }
2623 
2624         has_cache = count & SWAP_HAS_CACHE;
2625         count &= ~SWAP_HAS_CACHE;
2626         err = 0;
2627 
2628         if (usage == SWAP_HAS_CACHE) {
2629 
2630                 /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2631                 if (!has_cache && count)
2632                         has_cache = SWAP_HAS_CACHE;
2633                 else if (has_cache)             /* someone else added cache */
2634                         err = -EEXIST;
2635                 else                            /* no users remaining */
2636                         err = -ENOENT;
2637 
2638         } else if (count || has_cache) {
2639 
2640                 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2641                         count += usage;
2642                 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2643                         err = -EINVAL;
2644                 else if (swap_count_continued(p, offset, count))
2645                         count = COUNT_CONTINUED;
2646                 else
2647                         err = -ENOMEM;
2648         } else
2649                 err = -ENOENT;                  /* unused swap entry */
2650 
2651         p->swap_map[offset] = count | has_cache;
2652 
2653 unlock_out:
2654         spin_unlock(&p->lock);
2655 out:
2656         return err;
2657 
2658 bad_file:
2659         pr_err("swap_dup: %s%08lx\n", Bad_file, entry.val);
2660         goto out;
2661 }
2662 
2663 /*
2664  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2665  * (in which case its reference count is never incremented).
2666  */
2667 void swap_shmem_alloc(swp_entry_t entry)
2668 {
2669         __swap_duplicate(entry, SWAP_MAP_SHMEM);
2670 }
2671 
2672 /*
2673  * Increase reference count of swap entry by 1.
2674  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2675  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2676  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2677  * might occur if a page table entry has got corrupted.
2678  */
2679 int swap_duplicate(swp_entry_t entry)
2680 {
2681         int err = 0;
2682 
2683         while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2684                 err = add_swap_count_continuation(entry, GFP_ATOMIC);
2685         return err;
2686 }
2687 
2688 /*
2689  * @entry: swap entry for which we allocate swap cache.
2690  *
2691  * Called when allocating swap cache for existing swap entry,
2692  * This can return error codes. Returns 0 at success.
2693  * -EBUSY means there is a swap cache.
2694  * Note: return code is different from swap_duplicate().
2695  */
2696 int swapcache_prepare(swp_entry_t entry)
2697 {
2698         return __swap_duplicate(entry, SWAP_HAS_CACHE);
2699 }
2700 
2701 struct swap_info_struct *page_swap_info(struct page *page)
2702 {
2703         swp_entry_t swap = { .val = page_private(page) };
2704         BUG_ON(!PageSwapCache(page));
2705         return swap_info[swp_type(swap)];
2706 }
2707 
2708 /*
2709  * out-of-line __page_file_ methods to avoid include hell.
2710  */
2711 struct address_space *__page_file_mapping(struct page *page)
2712 {
2713         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2714         return page_swap_info(page)->swap_file->f_mapping;
2715 }
2716 EXPORT_SYMBOL_GPL(__page_file_mapping);
2717 
2718 pgoff_t __page_file_index(struct page *page)
2719 {
2720         swp_entry_t swap = { .val = page_private(page) };
2721         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2722         return swp_offset(swap);
2723 }
2724 EXPORT_SYMBOL_GPL(__page_file_index);
2725 
2726 /*
2727  * add_swap_count_continuation - called when a swap count is duplicated
2728  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2729  * page of the original vmalloc'ed swap_map, to hold the continuation count
2730  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2731  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2732  *
2733  * These continuation pages are seldom referenced: the common paths all work
2734  * on the original swap_map, only referring to a continuation page when the
2735  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2736  *
2737  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2738  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2739  * can be called after dropping locks.
2740  */
2741 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2742 {
2743         struct swap_info_struct *si;
2744         struct page *head;
2745         struct page *page;
2746         struct page *list_page;
2747         pgoff_t offset;
2748         unsigned char count;
2749 
2750         /*
2751          * When debugging, it's easier to use __GFP_ZERO here; but it's better
2752          * for latency not to zero a page while GFP_ATOMIC and holding locks.
2753          */
2754         page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2755 
2756         si = swap_info_get(entry);
2757         if (!si) {
2758                 /*
2759                  * An acceptable race has occurred since the failing
2760                  * __swap_duplicate(): the swap entry has been freed,
2761                  * perhaps even the whole swap_map cleared for swapoff.
2762                  */
2763                 goto outer;
2764         }
2765 
2766         offset = swp_offset(entry);
2767         count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2768 
2769         if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2770                 /*
2771                  * The higher the swap count, the more likely it is that tasks
2772                  * will race to add swap count continuation: we need to avoid
2773                  * over-provisioning.
2774                  */
2775                 goto out;
2776         }
2777 
2778         if (!page) {
2779                 spin_unlock(&si->lock);
2780                 return -ENOMEM;
2781         }
2782 
2783         /*
2784          * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2785          * no architecture is using highmem pages for kernel page tables: so it
2786          * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps.
2787          */
2788         head = vmalloc_to_page(si->swap_map + offset);
2789         offset &= ~PAGE_MASK;
2790 
2791         /*
2792          * Page allocation does not initialize the page's lru field,
2793          * but it does always reset its private field.
2794          */
2795         if (!page_private(head)) {
2796                 BUG_ON(count & COUNT_CONTINUED);
2797                 INIT_LIST_HEAD(&head->lru);
2798                 set_page_private(head, SWP_CONTINUED);
2799                 si->flags |= SWP_CONTINUED;
2800         }
2801 
2802         list_for_each_entry(list_page, &head->lru, lru) {
2803                 unsigned char *map;
2804 
2805                 /*
2806                  * If the previous map said no continuation, but we've found
2807                  * a continuation page, free our allocation and use this one.
2808                  */
2809                 if (!(count & COUNT_CONTINUED))
2810                         goto out;
2811 
2812                 map = kmap_atomic(list_page) + offset;
2813                 count = *map;
2814                 kunmap_atomic(map);
2815 
2816                 /*
2817                  * If this continuation count now has some space in it,
2818                  * free our allocation and use this one.
2819                  */
2820                 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2821                         goto out;
2822         }
2823 
2824         list_add_tail(&page->lru, &head->lru);
2825         page = NULL;                    /* now it's attached, don't free it */
2826 out:
2827         spin_unlock(&si->lock);
2828 outer:
2829         if (page)
2830                 __free_page(page);
2831         return 0;
2832 }
2833 
2834 /*
2835  * swap_count_continued - when the original swap_map count is incremented
2836  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2837  * into, carry if so, or else fail until a new continuation page is allocated;
2838  * when the original swap_map count is decremented from 0 with continuation,
2839  * borrow from the continuation and report whether it still holds more.
2840  * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2841  */
2842 static bool swap_count_continued(struct swap_info_struct *si,
2843                                  pgoff_t offset, unsigned char count)
2844 {
2845         struct page *head;
2846         struct page *page;
2847         unsigned char *map;
2848 
2849         head = vmalloc_to_page(si->swap_map + offset);
2850         if (page_private(head) != SWP_CONTINUED) {
2851                 BUG_ON(count & COUNT_CONTINUED);
2852                 return false;           /* need to add count continuation */
2853         }
2854 
2855         offset &= ~PAGE_MASK;
2856         page = list_entry(head->lru.next, struct page, lru);
2857         map = kmap_atomic(page) + offset;
2858 
2859         if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2860                 goto init_map;          /* jump over SWAP_CONT_MAX checks */
2861 
2862         if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2863                 /*
2864                  * Think of how you add 1 to 999
2865                  */
2866                 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2867                         kunmap_atomic(map);
2868                         page = list_entry(page->lru.next, struct page, lru);
2869                         BUG_ON(page == head);
2870                         map = kmap_atomic(page) + offset;
2871                 }
2872                 if (*map == SWAP_CONT_MAX) {
2873                         kunmap_atomic(map);
2874                         page = list_entry(page->lru.next, struct page, lru);
2875                         if (page == head)
2876                                 return false;   /* add count continuation */
2877                         map = kmap_atomic(page) + offset;
2878 init_map:               *map = 0;               /* we didn't zero the page */
2879                 }
2880                 *map += 1;
2881                 kunmap_atomic(map);
2882                 page = list_entry(page->lru.prev, struct page, lru);
2883                 while (page != head) {
2884                         map = kmap_atomic(page) + offset;
2885                         *map = COUNT_CONTINUED;
2886                         kunmap_atomic(map);
2887                         page = list_entry(page->lru.prev, struct page, lru);
2888                 }
2889                 return true;                    /* incremented */
2890 
2891         } else {                                /* decrementing */
2892                 /*
2893                  * Think of how you subtract 1 from 1000
2894                  */
2895                 BUG_ON(count != COUNT_CONTINUED);
2896                 while (*map == COUNT_CONTINUED) {
2897                         kunmap_atomic(map);
2898                         page = list_entry(page->lru.next, struct page, lru);
2899                         BUG_ON(page == head);
2900                         map = kmap_atomic(page) + offset;
2901                 }
2902                 BUG_ON(*map == 0);
2903                 *map -= 1;
2904                 if (*map == 0)
2905                         count = 0;
2906                 kunmap_atomic(map);
2907                 page = list_entry(page->lru.prev, struct page, lru);
2908                 while (page != head) {
2909                         map = kmap_atomic(page) + offset;
2910                         *map = SWAP_CONT_MAX | count;
2911                         count = COUNT_CONTINUED;
2912                         kunmap_atomic(map);
2913                         page = list_entry(page->lru.prev, struct page, lru);
2914                 }
2915                 return count == COUNT_CONTINUED;
2916         }
2917 }
2918 
2919 /*
2920  * free_swap_count_continuations - swapoff free all the continuation pages
2921  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2922  */
2923 static void free_swap_count_continuations(struct swap_info_struct *si)
2924 {
2925         pgoff_t offset;
2926 
2927         for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2928                 struct page *head;
2929                 head = vmalloc_to_page(si->swap_map + offset);
2930                 if (page_private(head)) {
2931                         struct list_head *this, *next;
2932                         list_for_each_safe(this, next, &head->lru) {
2933                                 struct page *page;
2934                                 page = list_entry(this, struct page, lru);
2935                                 list_del(this);
2936                                 __free_page(page);
2937                         }
2938                 }
2939         }
2940 }
2941 

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