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Linux/mm/swapfile.c

  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 /*
 52  * Some modules use swappable objects and may try to swap them out under
 53  * memory pressure (via the shrinker). Before doing so, they may wish to
 54  * check to see if any swap space is available.
 55  */
 56 EXPORT_SYMBOL_GPL(nr_swap_pages);
 57 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
 58 long total_swap_pages;
 59 static int least_priority;
 60 
 61 static const char Bad_file[] = "Bad swap file entry ";
 62 static const char Unused_file[] = "Unused swap file entry ";
 63 static const char Bad_offset[] = "Bad swap offset entry ";
 64 static const char Unused_offset[] = "Unused swap offset entry ";
 65 
 66 /*
 67  * all active swap_info_structs
 68  * protected with swap_lock, and ordered by priority.
 69  */
 70 PLIST_HEAD(swap_active_head);
 71 
 72 /*
 73  * all available (active, not full) swap_info_structs
 74  * protected with swap_avail_lock, ordered by priority.
 75  * This is used by get_swap_page() instead of swap_active_head
 76  * because swap_active_head includes all swap_info_structs,
 77  * but get_swap_page() doesn't need to look at full ones.
 78  * This uses its own lock instead of swap_lock because when a
 79  * swap_info_struct changes between not-full/full, it needs to
 80  * add/remove itself to/from this list, but the swap_info_struct->lock
 81  * is held and the locking order requires swap_lock to be taken
 82  * before any swap_info_struct->lock.
 83  */
 84 static PLIST_HEAD(swap_avail_head);
 85 static DEFINE_SPINLOCK(swap_avail_lock);
 86 
 87 struct swap_info_struct *swap_info[MAX_SWAPFILES];
 88 
 89 static DEFINE_MUTEX(swapon_mutex);
 90 
 91 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
 92 /* Activity counter to indicate that a swapon or swapoff has occurred */
 93 static atomic_t proc_poll_event = ATOMIC_INIT(0);
 94 
 95 static inline unsigned char swap_count(unsigned char ent)
 96 {
 97         return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
 98 }
 99 
100 /* returns 1 if swap entry is freed */
101 static int
102 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
103 {
104         swp_entry_t entry = swp_entry(si->type, offset);
105         struct page *page;
106         int ret = 0;
107 
108         page = find_get_page(swap_address_space(entry), swp_offset(entry));
109         if (!page)
110                 return 0;
111         /*
112          * This function is called from scan_swap_map() and it's called
113          * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
114          * We have to use trylock for avoiding deadlock. This is a special
115          * case and you should use try_to_free_swap() with explicit lock_page()
116          * in usual operations.
117          */
118         if (trylock_page(page)) {
119                 ret = try_to_free_swap(page);
120                 unlock_page(page);
121         }
122         put_page(page);
123         return ret;
124 }
125 
126 /*
127  * swapon tell device that all the old swap contents can be discarded,
128  * to allow the swap device to optimize its wear-levelling.
129  */
130 static int discard_swap(struct swap_info_struct *si)
131 {
132         struct swap_extent *se;
133         sector_t start_block;
134         sector_t nr_blocks;
135         int err = 0;
136 
137         /* Do not discard the swap header page! */
138         se = &si->first_swap_extent;
139         start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
140         nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
141         if (nr_blocks) {
142                 err = blkdev_issue_discard(si->bdev, start_block,
143                                 nr_blocks, GFP_KERNEL, 0);
144                 if (err)
145                         return err;
146                 cond_resched();
147         }
148 
149         list_for_each_entry(se, &si->first_swap_extent.list, list) {
150                 start_block = se->start_block << (PAGE_SHIFT - 9);
151                 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
152 
153                 err = blkdev_issue_discard(si->bdev, start_block,
154                                 nr_blocks, GFP_KERNEL, 0);
155                 if (err)
156                         break;
157 
158                 cond_resched();
159         }
160         return err;             /* That will often be -EOPNOTSUPP */
161 }
162 
163 /*
164  * swap allocation tell device that a cluster of swap can now be discarded,
165  * to allow the swap device to optimize its wear-levelling.
166  */
167 static void discard_swap_cluster(struct swap_info_struct *si,
168                                  pgoff_t start_page, pgoff_t nr_pages)
169 {
170         struct swap_extent *se = si->curr_swap_extent;
171         int found_extent = 0;
172 
173         while (nr_pages) {
174                 if (se->start_page <= start_page &&
175                     start_page < se->start_page + se->nr_pages) {
176                         pgoff_t offset = start_page - se->start_page;
177                         sector_t start_block = se->start_block + offset;
178                         sector_t nr_blocks = se->nr_pages - offset;
179 
180                         if (nr_blocks > nr_pages)
181                                 nr_blocks = nr_pages;
182                         start_page += nr_blocks;
183                         nr_pages -= nr_blocks;
184 
185                         if (!found_extent++)
186                                 si->curr_swap_extent = se;
187 
188                         start_block <<= PAGE_SHIFT - 9;
189                         nr_blocks <<= PAGE_SHIFT - 9;
190                         if (blkdev_issue_discard(si->bdev, start_block,
191                                     nr_blocks, GFP_NOIO, 0))
192                                 break;
193                 }
194 
195                 se = list_next_entry(se, list);
196         }
197 }
198 
199 #define SWAPFILE_CLUSTER        256
200 #define LATENCY_LIMIT           256
201 
202 static inline void cluster_set_flag(struct swap_cluster_info *info,
203         unsigned int flag)
204 {
205         info->flags = flag;
206 }
207 
208 static inline unsigned int cluster_count(struct swap_cluster_info *info)
209 {
210         return info->data;
211 }
212 
213 static inline void cluster_set_count(struct swap_cluster_info *info,
214                                      unsigned int c)
215 {
216         info->data = c;
217 }
218 
219 static inline void cluster_set_count_flag(struct swap_cluster_info *info,
220                                          unsigned int c, unsigned int f)
221 {
222         info->flags = f;
223         info->data = c;
224 }
225 
226 static inline unsigned int cluster_next(struct swap_cluster_info *info)
227 {
228         return info->data;
229 }
230 
231 static inline void cluster_set_next(struct swap_cluster_info *info,
232                                     unsigned int n)
233 {
234         info->data = n;
235 }
236 
237 static inline void cluster_set_next_flag(struct swap_cluster_info *info,
238                                          unsigned int n, unsigned int f)
239 {
240         info->flags = f;
241         info->data = n;
242 }
243 
244 static inline bool cluster_is_free(struct swap_cluster_info *info)
245 {
246         return info->flags & CLUSTER_FLAG_FREE;
247 }
248 
249 static inline bool cluster_is_null(struct swap_cluster_info *info)
250 {
251         return info->flags & CLUSTER_FLAG_NEXT_NULL;
252 }
253 
254 static inline void cluster_set_null(struct swap_cluster_info *info)
255 {
256         info->flags = CLUSTER_FLAG_NEXT_NULL;
257         info->data = 0;
258 }
259 
260 static inline bool cluster_list_empty(struct swap_cluster_list *list)
261 {
262         return cluster_is_null(&list->head);
263 }
264 
265 static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
266 {
267         return cluster_next(&list->head);
268 }
269 
270 static void cluster_list_init(struct swap_cluster_list *list)
271 {
272         cluster_set_null(&list->head);
273         cluster_set_null(&list->tail);
274 }
275 
276 static void cluster_list_add_tail(struct swap_cluster_list *list,
277                                   struct swap_cluster_info *ci,
278                                   unsigned int idx)
279 {
280         if (cluster_list_empty(list)) {
281                 cluster_set_next_flag(&list->head, idx, 0);
282                 cluster_set_next_flag(&list->tail, idx, 0);
283         } else {
284                 unsigned int tail = cluster_next(&list->tail);
285 
286                 cluster_set_next(&ci[tail], idx);
287                 cluster_set_next_flag(&list->tail, idx, 0);
288         }
289 }
290 
291 static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
292                                            struct swap_cluster_info *ci)
293 {
294         unsigned int idx;
295 
296         idx = cluster_next(&list->head);
297         if (cluster_next(&list->tail) == idx) {
298                 cluster_set_null(&list->head);
299                 cluster_set_null(&list->tail);
300         } else
301                 cluster_set_next_flag(&list->head,
302                                       cluster_next(&ci[idx]), 0);
303 
304         return idx;
305 }
306 
307 /* Add a cluster to discard list and schedule it to do discard */
308 static void swap_cluster_schedule_discard(struct swap_info_struct *si,
309                 unsigned int idx)
310 {
311         /*
312          * If scan_swap_map() can't find a free cluster, it will check
313          * si->swap_map directly. To make sure the discarding cluster isn't
314          * taken by scan_swap_map(), mark the swap entries bad (occupied). It
315          * will be cleared after discard
316          */
317         memset(si->swap_map + idx * SWAPFILE_CLUSTER,
318                         SWAP_MAP_BAD, SWAPFILE_CLUSTER);
319 
320         cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
321 
322         schedule_work(&si->discard_work);
323 }
324 
325 /*
326  * Doing discard actually. After a cluster discard is finished, the cluster
327  * will be added to free cluster list. caller should hold si->lock.
328 */
329 static void swap_do_scheduled_discard(struct swap_info_struct *si)
330 {
331         struct swap_cluster_info *info;
332         unsigned int idx;
333 
334         info = si->cluster_info;
335 
336         while (!cluster_list_empty(&si->discard_clusters)) {
337                 idx = cluster_list_del_first(&si->discard_clusters, info);
338                 spin_unlock(&si->lock);
339 
340                 discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
341                                 SWAPFILE_CLUSTER);
342 
343                 spin_lock(&si->lock);
344                 cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE);
345                 cluster_list_add_tail(&si->free_clusters, info, idx);
346                 memset(si->swap_map + idx * SWAPFILE_CLUSTER,
347                                 0, SWAPFILE_CLUSTER);
348         }
349 }
350 
351 static void swap_discard_work(struct work_struct *work)
352 {
353         struct swap_info_struct *si;
354 
355         si = container_of(work, struct swap_info_struct, discard_work);
356 
357         spin_lock(&si->lock);
358         swap_do_scheduled_discard(si);
359         spin_unlock(&si->lock);
360 }
361 
362 /*
363  * The cluster corresponding to page_nr will be used. The cluster will be
364  * removed from free cluster list and its usage counter will be increased.
365  */
366 static void inc_cluster_info_page(struct swap_info_struct *p,
367         struct swap_cluster_info *cluster_info, unsigned long page_nr)
368 {
369         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
370 
371         if (!cluster_info)
372                 return;
373         if (cluster_is_free(&cluster_info[idx])) {
374                 VM_BUG_ON(cluster_list_first(&p->free_clusters) != idx);
375                 cluster_list_del_first(&p->free_clusters, cluster_info);
376                 cluster_set_count_flag(&cluster_info[idx], 0, 0);
377         }
378 
379         VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
380         cluster_set_count(&cluster_info[idx],
381                 cluster_count(&cluster_info[idx]) + 1);
382 }
383 
384 /*
385  * The cluster corresponding to page_nr decreases one usage. If the usage
386  * counter becomes 0, which means no page in the cluster is in using, we can
387  * optionally discard the cluster and add it to free cluster list.
388  */
389 static void dec_cluster_info_page(struct swap_info_struct *p,
390         struct swap_cluster_info *cluster_info, unsigned long page_nr)
391 {
392         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
393 
394         if (!cluster_info)
395                 return;
396 
397         VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
398         cluster_set_count(&cluster_info[idx],
399                 cluster_count(&cluster_info[idx]) - 1);
400 
401         if (cluster_count(&cluster_info[idx]) == 0) {
402                 /*
403                  * If the swap is discardable, prepare discard the cluster
404                  * instead of free it immediately. The cluster will be freed
405                  * after discard.
406                  */
407                 if ((p->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
408                                  (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
409                         swap_cluster_schedule_discard(p, idx);
410                         return;
411                 }
412 
413                 cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
414                 cluster_list_add_tail(&p->free_clusters, cluster_info, idx);
415         }
416 }
417 
418 /*
419  * It's possible scan_swap_map() uses a free cluster in the middle of free
420  * cluster list. Avoiding such abuse to avoid list corruption.
421  */
422 static bool
423 scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
424         unsigned long offset)
425 {
426         struct percpu_cluster *percpu_cluster;
427         bool conflict;
428 
429         offset /= SWAPFILE_CLUSTER;
430         conflict = !cluster_list_empty(&si->free_clusters) &&
431                 offset != cluster_list_first(&si->free_clusters) &&
432                 cluster_is_free(&si->cluster_info[offset]);
433 
434         if (!conflict)
435                 return false;
436 
437         percpu_cluster = this_cpu_ptr(si->percpu_cluster);
438         cluster_set_null(&percpu_cluster->index);
439         return true;
440 }
441 
442 /*
443  * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
444  * might involve allocating a new cluster for current CPU too.
445  */
446 static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
447         unsigned long *offset, unsigned long *scan_base)
448 {
449         struct percpu_cluster *cluster;
450         bool found_free;
451         unsigned long tmp;
452 
453 new_cluster:
454         cluster = this_cpu_ptr(si->percpu_cluster);
455         if (cluster_is_null(&cluster->index)) {
456                 if (!cluster_list_empty(&si->free_clusters)) {
457                         cluster->index = si->free_clusters.head;
458                         cluster->next = cluster_next(&cluster->index) *
459                                         SWAPFILE_CLUSTER;
460                 } else if (!cluster_list_empty(&si->discard_clusters)) {
461                         /*
462                          * we don't have free cluster but have some clusters in
463                          * discarding, do discard now and reclaim them
464                          */
465                         swap_do_scheduled_discard(si);
466                         *scan_base = *offset = si->cluster_next;
467                         goto new_cluster;
468                 } else
469                         return;
470         }
471 
472         found_free = false;
473 
474         /*
475          * Other CPUs can use our cluster if they can't find a free cluster,
476          * check if there is still free entry in the cluster
477          */
478         tmp = cluster->next;
479         while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) *
480                SWAPFILE_CLUSTER) {
481                 if (!si->swap_map[tmp]) {
482                         found_free = true;
483                         break;
484                 }
485                 tmp++;
486         }
487         if (!found_free) {
488                 cluster_set_null(&cluster->index);
489                 goto new_cluster;
490         }
491         cluster->next = tmp + 1;
492         *offset = tmp;
493         *scan_base = tmp;
494 }
495 
496 static unsigned long scan_swap_map(struct swap_info_struct *si,
497                                    unsigned char usage)
498 {
499         unsigned long offset;
500         unsigned long scan_base;
501         unsigned long last_in_cluster = 0;
502         int latency_ration = LATENCY_LIMIT;
503 
504         /*
505          * We try to cluster swap pages by allocating them sequentially
506          * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
507          * way, however, we resort to first-free allocation, starting
508          * a new cluster.  This prevents us from scattering swap pages
509          * all over the entire swap partition, so that we reduce
510          * overall disk seek times between swap pages.  -- sct
511          * But we do now try to find an empty cluster.  -Andrea
512          * And we let swap pages go all over an SSD partition.  Hugh
513          */
514 
515         si->flags += SWP_SCANNING;
516         scan_base = offset = si->cluster_next;
517 
518         /* SSD algorithm */
519         if (si->cluster_info) {
520                 scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
521                 goto checks;
522         }
523 
524         if (unlikely(!si->cluster_nr--)) {
525                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
526                         si->cluster_nr = SWAPFILE_CLUSTER - 1;
527                         goto checks;
528                 }
529 
530                 spin_unlock(&si->lock);
531 
532                 /*
533                  * If seek is expensive, start searching for new cluster from
534                  * start of partition, to minimize the span of allocated swap.
535                  * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
536                  * case, just handled by scan_swap_map_try_ssd_cluster() above.
537                  */
538                 scan_base = offset = si->lowest_bit;
539                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
540 
541                 /* Locate the first empty (unaligned) cluster */
542                 for (; last_in_cluster <= si->highest_bit; offset++) {
543                         if (si->swap_map[offset])
544                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
545                         else if (offset == last_in_cluster) {
546                                 spin_lock(&si->lock);
547                                 offset -= SWAPFILE_CLUSTER - 1;
548                                 si->cluster_next = offset;
549                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
550                                 goto checks;
551                         }
552                         if (unlikely(--latency_ration < 0)) {
553                                 cond_resched();
554                                 latency_ration = LATENCY_LIMIT;
555                         }
556                 }
557 
558                 offset = scan_base;
559                 spin_lock(&si->lock);
560                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
561         }
562 
563 checks:
564         if (si->cluster_info) {
565                 while (scan_swap_map_ssd_cluster_conflict(si, offset))
566                         scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
567         }
568         if (!(si->flags & SWP_WRITEOK))
569                 goto no_page;
570         if (!si->highest_bit)
571                 goto no_page;
572         if (offset > si->highest_bit)
573                 scan_base = offset = si->lowest_bit;
574 
575         /* reuse swap entry of cache-only swap if not busy. */
576         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
577                 int swap_was_freed;
578                 spin_unlock(&si->lock);
579                 swap_was_freed = __try_to_reclaim_swap(si, offset);
580                 spin_lock(&si->lock);
581                 /* entry was freed successfully, try to use this again */
582                 if (swap_was_freed)
583                         goto checks;
584                 goto scan; /* check next one */
585         }
586 
587         if (si->swap_map[offset])
588                 goto scan;
589 
590         if (offset == si->lowest_bit)
591                 si->lowest_bit++;
592         if (offset == si->highest_bit)
593                 si->highest_bit--;
594         si->inuse_pages++;
595         if (si->inuse_pages == si->pages) {
596                 si->lowest_bit = si->max;
597                 si->highest_bit = 0;
598                 spin_lock(&swap_avail_lock);
599                 plist_del(&si->avail_list, &swap_avail_head);
600                 spin_unlock(&swap_avail_lock);
601         }
602         si->swap_map[offset] = usage;
603         inc_cluster_info_page(si, si->cluster_info, offset);
604         si->cluster_next = offset + 1;
605         si->flags -= SWP_SCANNING;
606 
607         return offset;
608 
609 scan:
610         spin_unlock(&si->lock);
611         while (++offset <= si->highest_bit) {
612                 if (!si->swap_map[offset]) {
613                         spin_lock(&si->lock);
614                         goto checks;
615                 }
616                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
617                         spin_lock(&si->lock);
618                         goto checks;
619                 }
620                 if (unlikely(--latency_ration < 0)) {
621                         cond_resched();
622                         latency_ration = LATENCY_LIMIT;
623                 }
624         }
625         offset = si->lowest_bit;
626         while (offset < scan_base) {
627                 if (!si->swap_map[offset]) {
628                         spin_lock(&si->lock);
629                         goto checks;
630                 }
631                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
632                         spin_lock(&si->lock);
633                         goto checks;
634                 }
635                 if (unlikely(--latency_ration < 0)) {
636                         cond_resched();
637                         latency_ration = LATENCY_LIMIT;
638                 }
639                 offset++;
640         }
641         spin_lock(&si->lock);
642 
643 no_page:
644         si->flags -= SWP_SCANNING;
645         return 0;
646 }
647 
648 swp_entry_t get_swap_page(void)
649 {
650         struct swap_info_struct *si, *next;
651         pgoff_t offset;
652 
653         if (atomic_long_read(&nr_swap_pages) <= 0)
654                 goto noswap;
655         atomic_long_dec(&nr_swap_pages);
656 
657         spin_lock(&swap_avail_lock);
658 
659 start_over:
660         plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
661                 /* requeue si to after same-priority siblings */
662                 plist_requeue(&si->avail_list, &swap_avail_head);
663                 spin_unlock(&swap_avail_lock);
664                 spin_lock(&si->lock);
665                 if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
666                         spin_lock(&swap_avail_lock);
667                         if (plist_node_empty(&si->avail_list)) {
668                                 spin_unlock(&si->lock);
669                                 goto nextsi;
670                         }
671                         WARN(!si->highest_bit,
672                              "swap_info %d in list but !highest_bit\n",
673                              si->type);
674                         WARN(!(si->flags & SWP_WRITEOK),
675                              "swap_info %d in list but !SWP_WRITEOK\n",
676                              si->type);
677                         plist_del(&si->avail_list, &swap_avail_head);
678                         spin_unlock(&si->lock);
679                         goto nextsi;
680                 }
681 
682                 /* This is called for allocating swap entry for cache */
683                 offset = scan_swap_map(si, SWAP_HAS_CACHE);
684                 spin_unlock(&si->lock);
685                 if (offset)
686                         return swp_entry(si->type, offset);
687                 pr_debug("scan_swap_map of si %d failed to find offset\n",
688                        si->type);
689                 spin_lock(&swap_avail_lock);
690 nextsi:
691                 /*
692                  * if we got here, it's likely that si was almost full before,
693                  * and since scan_swap_map() can drop the si->lock, multiple
694                  * callers probably all tried to get a page from the same si
695                  * and it filled up before we could get one; or, the si filled
696                  * up between us dropping swap_avail_lock and taking si->lock.
697                  * Since we dropped the swap_avail_lock, the swap_avail_head
698                  * list may have been modified; so if next is still in the
699                  * swap_avail_head list then try it, otherwise start over.
700                  */
701                 if (plist_node_empty(&next->avail_list))
702                         goto start_over;
703         }
704 
705         spin_unlock(&swap_avail_lock);
706 
707         atomic_long_inc(&nr_swap_pages);
708 noswap:
709         return (swp_entry_t) {0};
710 }
711 
712 /* The only caller of this function is now suspend routine */
713 swp_entry_t get_swap_page_of_type(int type)
714 {
715         struct swap_info_struct *si;
716         pgoff_t offset;
717 
718         si = swap_info[type];
719         spin_lock(&si->lock);
720         if (si && (si->flags & SWP_WRITEOK)) {
721                 atomic_long_dec(&nr_swap_pages);
722                 /* This is called for allocating swap entry, not cache */
723                 offset = scan_swap_map(si, 1);
724                 if (offset) {
725                         spin_unlock(&si->lock);
726                         return swp_entry(type, offset);
727                 }
728                 atomic_long_inc(&nr_swap_pages);
729         }
730         spin_unlock(&si->lock);
731         return (swp_entry_t) {0};
732 }
733 
734 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
735 {
736         struct swap_info_struct *p;
737         unsigned long offset, type;
738 
739         if (!entry.val)
740                 goto out;
741         type = swp_type(entry);
742         if (type >= nr_swapfiles)
743                 goto bad_nofile;
744         p = swap_info[type];
745         if (!(p->flags & SWP_USED))
746                 goto bad_device;
747         offset = swp_offset(entry);
748         if (offset >= p->max)
749                 goto bad_offset;
750         if (!p->swap_map[offset])
751                 goto bad_free;
752         spin_lock(&p->lock);
753         return p;
754 
755 bad_free:
756         pr_err("swap_free: %s%08lx\n", Unused_offset, entry.val);
757         goto out;
758 bad_offset:
759         pr_err("swap_free: %s%08lx\n", Bad_offset, entry.val);
760         goto out;
761 bad_device:
762         pr_err("swap_free: %s%08lx\n", Unused_file, entry.val);
763         goto out;
764 bad_nofile:
765         pr_err("swap_free: %s%08lx\n", Bad_file, entry.val);
766 out:
767         return NULL;
768 }
769 
770 static unsigned char swap_entry_free(struct swap_info_struct *p,
771                                      swp_entry_t entry, unsigned char usage)
772 {
773         unsigned long offset = swp_offset(entry);
774         unsigned char count;
775         unsigned char has_cache;
776 
777         count = p->swap_map[offset];
778         has_cache = count & SWAP_HAS_CACHE;
779         count &= ~SWAP_HAS_CACHE;
780 
781         if (usage == SWAP_HAS_CACHE) {
782                 VM_BUG_ON(!has_cache);
783                 has_cache = 0;
784         } else if (count == SWAP_MAP_SHMEM) {
785                 /*
786                  * Or we could insist on shmem.c using a special
787                  * swap_shmem_free() and free_shmem_swap_and_cache()...
788                  */
789                 count = 0;
790         } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
791                 if (count == COUNT_CONTINUED) {
792                         if (swap_count_continued(p, offset, count))
793                                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
794                         else
795                                 count = SWAP_MAP_MAX;
796                 } else
797                         count--;
798         }
799 
800         usage = count | has_cache;
801         p->swap_map[offset] = usage;
802 
803         /* free if no reference */
804         if (!usage) {
805                 mem_cgroup_uncharge_swap(entry);
806                 dec_cluster_info_page(p, p->cluster_info, offset);
807                 if (offset < p->lowest_bit)
808                         p->lowest_bit = offset;
809                 if (offset > p->highest_bit) {
810                         bool was_full = !p->highest_bit;
811                         p->highest_bit = offset;
812                         if (was_full && (p->flags & SWP_WRITEOK)) {
813                                 spin_lock(&swap_avail_lock);
814                                 WARN_ON(!plist_node_empty(&p->avail_list));
815                                 if (plist_node_empty(&p->avail_list))
816                                         plist_add(&p->avail_list,
817                                                   &swap_avail_head);
818                                 spin_unlock(&swap_avail_lock);
819                         }
820                 }
821                 atomic_long_inc(&nr_swap_pages);
822                 p->inuse_pages--;
823                 frontswap_invalidate_page(p->type, offset);
824                 if (p->flags & SWP_BLKDEV) {
825                         struct gendisk *disk = p->bdev->bd_disk;
826                         if (disk->fops->swap_slot_free_notify)
827                                 disk->fops->swap_slot_free_notify(p->bdev,
828                                                                   offset);
829                 }
830         }
831 
832         return usage;
833 }
834 
835 /*
836  * Caller has made sure that the swap device corresponding to entry
837  * is still around or has not been recycled.
838  */
839 void swap_free(swp_entry_t entry)
840 {
841         struct swap_info_struct *p;
842 
843         p = swap_info_get(entry);
844         if (p) {
845                 swap_entry_free(p, entry, 1);
846                 spin_unlock(&p->lock);
847         }
848 }
849 
850 /*
851  * Called after dropping swapcache to decrease refcnt to swap entries.
852  */
853 void swapcache_free(swp_entry_t entry)
854 {
855         struct swap_info_struct *p;
856 
857         p = swap_info_get(entry);
858         if (p) {
859                 swap_entry_free(p, entry, SWAP_HAS_CACHE);
860                 spin_unlock(&p->lock);
861         }
862 }
863 
864 /*
865  * How many references to page are currently swapped out?
866  * This does not give an exact answer when swap count is continued,
867  * but does include the high COUNT_CONTINUED flag to allow for that.
868  */
869 int page_swapcount(struct page *page)
870 {
871         int count = 0;
872         struct swap_info_struct *p;
873         swp_entry_t entry;
874 
875         entry.val = page_private(page);
876         p = swap_info_get(entry);
877         if (p) {
878                 count = swap_count(p->swap_map[swp_offset(entry)]);
879                 spin_unlock(&p->lock);
880         }
881         return count;
882 }
883 
884 /*
885  * How many references to @entry are currently swapped out?
886  * This considers COUNT_CONTINUED so it returns exact answer.
887  */
888 int swp_swapcount(swp_entry_t entry)
889 {
890         int count, tmp_count, n;
891         struct swap_info_struct *p;
892         struct page *page;
893         pgoff_t offset;
894         unsigned char *map;
895 
896         p = swap_info_get(entry);
897         if (!p)
898                 return 0;
899 
900         count = swap_count(p->swap_map[swp_offset(entry)]);
901         if (!(count & COUNT_CONTINUED))
902                 goto out;
903 
904         count &= ~COUNT_CONTINUED;
905         n = SWAP_MAP_MAX + 1;
906 
907         offset = swp_offset(entry);
908         page = vmalloc_to_page(p->swap_map + offset);
909         offset &= ~PAGE_MASK;
910         VM_BUG_ON(page_private(page) != SWP_CONTINUED);
911 
912         do {
913                 page = list_next_entry(page, lru);
914                 map = kmap_atomic(page);
915                 tmp_count = map[offset];
916                 kunmap_atomic(map);
917 
918                 count += (tmp_count & ~COUNT_CONTINUED) * n;
919                 n *= (SWAP_CONT_MAX + 1);
920         } while (tmp_count & COUNT_CONTINUED);
921 out:
922         spin_unlock(&p->lock);
923         return count;
924 }
925 
926 /*
927  * We can write to an anon page without COW if there are no other references
928  * to it.  And as a side-effect, free up its swap: because the old content
929  * on disk will never be read, and seeking back there to write new content
930  * later would only waste time away from clustering.
931  *
932  * NOTE: total_mapcount should not be relied upon by the caller if
933  * reuse_swap_page() returns false, but it may be always overwritten
934  * (see the other implementation for CONFIG_SWAP=n).
935  */
936 bool reuse_swap_page(struct page *page, int *total_mapcount)
937 {
938         int count;
939 
940         VM_BUG_ON_PAGE(!PageLocked(page), page);
941         if (unlikely(PageKsm(page)))
942                 return false;
943         count = page_trans_huge_mapcount(page, total_mapcount);
944         if (count <= 1 && PageSwapCache(page)) {
945                 count += page_swapcount(page);
946                 if (count != 1)
947                         goto out;
948                 if (!PageWriteback(page)) {
949                         delete_from_swap_cache(page);
950                         SetPageDirty(page);
951                 } else {
952                         swp_entry_t entry;
953                         struct swap_info_struct *p;
954 
955                         entry.val = page_private(page);
956                         p = swap_info_get(entry);
957                         if (p->flags & SWP_STABLE_WRITES) {
958                                 spin_unlock(&p->lock);
959                                 return false;
960                         }
961                         spin_unlock(&p->lock);
962                 }
963         }
964 out:
965         return count <= 1;
966 }
967 
968 /*
969  * If swap is getting full, or if there are no more mappings of this page,
970  * then try_to_free_swap is called to free its swap space.
971  */
972 int try_to_free_swap(struct page *page)
973 {
974         VM_BUG_ON_PAGE(!PageLocked(page), page);
975 
976         if (!PageSwapCache(page))
977                 return 0;
978         if (PageWriteback(page))
979                 return 0;
980         if (page_swapcount(page))
981                 return 0;
982 
983         /*
984          * Once hibernation has begun to create its image of memory,
985          * there's a danger that one of the calls to try_to_free_swap()
986          * - most probably a call from __try_to_reclaim_swap() while
987          * hibernation is allocating its own swap pages for the image,
988          * but conceivably even a call from memory reclaim - will free
989          * the swap from a page which has already been recorded in the
990          * image as a clean swapcache page, and then reuse its swap for
991          * another page of the image.  On waking from hibernation, the
992          * original page might be freed under memory pressure, then
993          * later read back in from swap, now with the wrong data.
994          *
995          * Hibernation suspends storage while it is writing the image
996          * to disk so check that here.
997          */
998         if (pm_suspended_storage())
999                 return 0;
1000 
1001         delete_from_swap_cache(page);
1002         SetPageDirty(page);
1003         return 1;
1004 }
1005 
1006 /*
1007  * Free the swap entry like above, but also try to
1008  * free the page cache entry if it is the last user.
1009  */
1010 int free_swap_and_cache(swp_entry_t entry)
1011 {
1012         struct swap_info_struct *p;
1013         struct page *page = NULL;
1014 
1015         if (non_swap_entry(entry))
1016                 return 1;
1017 
1018         p = swap_info_get(entry);
1019         if (p) {
1020                 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
1021                         page = find_get_page(swap_address_space(entry),
1022                                              swp_offset(entry));
1023                         if (page && !trylock_page(page)) {
1024                                 put_page(page);
1025                                 page = NULL;
1026                         }
1027                 }
1028                 spin_unlock(&p->lock);
1029         }
1030         if (page) {
1031                 /*
1032                  * Not mapped elsewhere, or swap space full? Free it!
1033                  * Also recheck PageSwapCache now page is locked (above).
1034                  */
1035                 if (PageSwapCache(page) && !PageWriteback(page) &&
1036                     (!page_mapped(page) || mem_cgroup_swap_full(page))) {
1037                         delete_from_swap_cache(page);
1038                         SetPageDirty(page);
1039                 }
1040                 unlock_page(page);
1041                 put_page(page);
1042         }
1043         return p != NULL;
1044 }
1045 
1046 #ifdef CONFIG_HIBERNATION
1047 /*
1048  * Find the swap type that corresponds to given device (if any).
1049  *
1050  * @offset - number of the PAGE_SIZE-sized block of the device, starting
1051  * from 0, in which the swap header is expected to be located.
1052  *
1053  * This is needed for the suspend to disk (aka swsusp).
1054  */
1055 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
1056 {
1057         struct block_device *bdev = NULL;
1058         int type;
1059 
1060         if (device)
1061                 bdev = bdget(device);
1062 
1063         spin_lock(&swap_lock);
1064         for (type = 0; type < nr_swapfiles; type++) {
1065                 struct swap_info_struct *sis = swap_info[type];
1066 
1067                 if (!(sis->flags & SWP_WRITEOK))
1068                         continue;
1069 
1070                 if (!bdev) {
1071                         if (bdev_p)
1072                                 *bdev_p = bdgrab(sis->bdev);
1073 
1074                         spin_unlock(&swap_lock);
1075                         return type;
1076                 }
1077                 if (bdev == sis->bdev) {
1078                         struct swap_extent *se = &sis->first_swap_extent;
1079 
1080                         if (se->start_block == offset) {
1081                                 if (bdev_p)
1082                                         *bdev_p = bdgrab(sis->bdev);
1083 
1084                                 spin_unlock(&swap_lock);
1085                                 bdput(bdev);
1086                                 return type;
1087                         }
1088                 }
1089         }
1090         spin_unlock(&swap_lock);
1091         if (bdev)
1092                 bdput(bdev);
1093 
1094         return -ENODEV;
1095 }
1096 
1097 /*
1098  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
1099  * corresponding to given index in swap_info (swap type).
1100  */
1101 sector_t swapdev_block(int type, pgoff_t offset)
1102 {
1103         struct block_device *bdev;
1104 
1105         if ((unsigned int)type >= nr_swapfiles)
1106                 return 0;
1107         if (!(swap_info[type]->flags & SWP_WRITEOK))
1108                 return 0;
1109         return map_swap_entry(swp_entry(type, offset), &bdev);
1110 }
1111 
1112 /*
1113  * Return either the total number of swap pages of given type, or the number
1114  * of free pages of that type (depending on @free)
1115  *
1116  * This is needed for software suspend
1117  */
1118 unsigned int count_swap_pages(int type, int free)
1119 {
1120         unsigned int n = 0;
1121 
1122         spin_lock(&swap_lock);
1123         if ((unsigned int)type < nr_swapfiles) {
1124                 struct swap_info_struct *sis = swap_info[type];
1125 
1126                 spin_lock(&sis->lock);
1127                 if (sis->flags & SWP_WRITEOK) {
1128                         n = sis->pages;
1129                         if (free)
1130                                 n -= sis->inuse_pages;
1131                 }
1132                 spin_unlock(&sis->lock);
1133         }
1134         spin_unlock(&swap_lock);
1135         return n;
1136 }
1137 #endif /* CONFIG_HIBERNATION */
1138 
1139 static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
1140 {
1141         return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
1142 }
1143 
1144 /*
1145  * No need to decide whether this PTE shares the swap entry with others,
1146  * just let do_wp_page work it out if a write is requested later - to
1147  * force COW, vm_page_prot omits write permission from any private vma.
1148  */
1149 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
1150                 unsigned long addr, swp_entry_t entry, struct page *page)
1151 {
1152         struct page *swapcache;
1153         struct mem_cgroup *memcg;
1154         spinlock_t *ptl;
1155         pte_t *pte;
1156         int ret = 1;
1157 
1158         swapcache = page;
1159         page = ksm_might_need_to_copy(page, vma, addr);
1160         if (unlikely(!page))
1161                 return -ENOMEM;
1162 
1163         if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
1164                                 &memcg, false)) {
1165                 ret = -ENOMEM;
1166                 goto out_nolock;
1167         }
1168 
1169         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
1170         if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
1171                 mem_cgroup_cancel_charge(page, memcg, false);
1172                 ret = 0;
1173                 goto out;
1174         }
1175 
1176         dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
1177         inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
1178         get_page(page);
1179         set_pte_at(vma->vm_mm, addr, pte,
1180                    pte_mkold(mk_pte(page, vma->vm_page_prot)));
1181         if (page == swapcache) {
1182                 page_add_anon_rmap(page, vma, addr, false);
1183                 mem_cgroup_commit_charge(page, memcg, true, false);
1184         } else { /* ksm created a completely new copy */
1185                 page_add_new_anon_rmap(page, vma, addr, false);
1186                 mem_cgroup_commit_charge(page, memcg, false, false);
1187                 lru_cache_add_active_or_unevictable(page, vma);
1188         }
1189         swap_free(entry);
1190         /*
1191          * Move the page to the active list so it is not
1192          * immediately swapped out again after swapon.
1193          */
1194         activate_page(page);
1195 out:
1196         pte_unmap_unlock(pte, ptl);
1197 out_nolock:
1198         if (page != swapcache) {
1199                 unlock_page(page);
1200                 put_page(page);
1201         }
1202         return ret;
1203 }
1204 
1205 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
1206                                 unsigned long addr, unsigned long end,
1207                                 swp_entry_t entry, struct page *page)
1208 {
1209         pte_t swp_pte = swp_entry_to_pte(entry);
1210         pte_t *pte;
1211         int ret = 0;
1212 
1213         /*
1214          * We don't actually need pte lock while scanning for swp_pte: since
1215          * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
1216          * page table while we're scanning; though it could get zapped, and on
1217          * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
1218          * of unmatched parts which look like swp_pte, so unuse_pte must
1219          * recheck under pte lock.  Scanning without pte lock lets it be
1220          * preemptable whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
1221          */
1222         pte = pte_offset_map(pmd, addr);
1223         do {
1224                 /*
1225                  * swapoff spends a _lot_ of time in this loop!
1226                  * Test inline before going to call unuse_pte.
1227                  */
1228                 if (unlikely(pte_same_as_swp(*pte, swp_pte))) {
1229                         pte_unmap(pte);
1230                         ret = unuse_pte(vma, pmd, addr, entry, page);
1231                         if (ret)
1232                                 goto out;
1233                         pte = pte_offset_map(pmd, addr);
1234                 }
1235         } while (pte++, addr += PAGE_SIZE, addr != end);
1236         pte_unmap(pte - 1);
1237 out:
1238         return ret;
1239 }
1240 
1241 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
1242                                 unsigned long addr, unsigned long end,
1243                                 swp_entry_t entry, struct page *page)
1244 {
1245         pmd_t *pmd;
1246         unsigned long next;
1247         int ret;
1248 
1249         pmd = pmd_offset(pud, addr);
1250         do {
1251                 cond_resched();
1252                 next = pmd_addr_end(addr, end);
1253                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
1254                         continue;
1255                 ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
1256                 if (ret)
1257                         return ret;
1258         } while (pmd++, addr = next, addr != end);
1259         return 0;
1260 }
1261 
1262 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
1263                                 unsigned long addr, unsigned long end,
1264                                 swp_entry_t entry, struct page *page)
1265 {
1266         pud_t *pud;
1267         unsigned long next;
1268         int ret;
1269 
1270         pud = pud_offset(pgd, addr);
1271         do {
1272                 next = pud_addr_end(addr, end);
1273                 if (pud_none_or_clear_bad(pud))
1274                         continue;
1275                 ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
1276                 if (ret)
1277                         return ret;
1278         } while (pud++, addr = next, addr != end);
1279         return 0;
1280 }
1281 
1282 static int unuse_vma(struct vm_area_struct *vma,
1283                                 swp_entry_t entry, struct page *page)
1284 {
1285         pgd_t *pgd;
1286         unsigned long addr, end, next;
1287         int ret;
1288 
1289         if (page_anon_vma(page)) {
1290                 addr = page_address_in_vma(page, vma);
1291                 if (addr == -EFAULT)
1292                         return 0;
1293                 else
1294                         end = addr + PAGE_SIZE;
1295         } else {
1296                 addr = vma->vm_start;
1297                 end = vma->vm_end;
1298         }
1299 
1300         pgd = pgd_offset(vma->vm_mm, addr);
1301         do {
1302                 next = pgd_addr_end(addr, end);
1303                 if (pgd_none_or_clear_bad(pgd))
1304                         continue;
1305                 ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1306                 if (ret)
1307                         return ret;
1308         } while (pgd++, addr = next, addr != end);
1309         return 0;
1310 }
1311 
1312 static int unuse_mm(struct mm_struct *mm,
1313                                 swp_entry_t entry, struct page *page)
1314 {
1315         struct vm_area_struct *vma;
1316         int ret = 0;
1317 
1318         if (!down_read_trylock(&mm->mmap_sem)) {
1319                 /*
1320                  * Activate page so shrink_inactive_list is unlikely to unmap
1321                  * its ptes while lock is dropped, so swapoff can make progress.
1322                  */
1323                 activate_page(page);
1324                 unlock_page(page);
1325                 down_read(&mm->mmap_sem);
1326                 lock_page(page);
1327         }
1328         for (vma = mm->mmap; vma; vma = vma->vm_next) {
1329                 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1330                         break;
1331                 cond_resched();
1332         }
1333         up_read(&mm->mmap_sem);
1334         return (ret < 0)? ret: 0;
1335 }
1336 
1337 /*
1338  * Scan swap_map (or frontswap_map if frontswap parameter is true)
1339  * from current position to next entry still in use.
1340  * Recycle to start on reaching the end, returning 0 when empty.
1341  */
1342 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1343                                         unsigned int prev, bool frontswap)
1344 {
1345         unsigned int max = si->max;
1346         unsigned int i = prev;
1347         unsigned char count;
1348 
1349         /*
1350          * No need for swap_lock here: we're just looking
1351          * for whether an entry is in use, not modifying it; false
1352          * hits are okay, and sys_swapoff() has already prevented new
1353          * allocations from this area (while holding swap_lock).
1354          */
1355         for (;;) {
1356                 if (++i >= max) {
1357                         if (!prev) {
1358                                 i = 0;
1359                                 break;
1360                         }
1361                         /*
1362                          * No entries in use at top of swap_map,
1363                          * loop back to start and recheck there.
1364                          */
1365                         max = prev + 1;
1366                         prev = 0;
1367                         i = 1;
1368                 }
1369                 count = READ_ONCE(si->swap_map[i]);
1370                 if (count && swap_count(count) != SWAP_MAP_BAD)
1371                         if (!frontswap || frontswap_test(si, i))
1372                                 break;
1373                 if ((i % LATENCY_LIMIT) == 0)
1374                         cond_resched();
1375         }
1376         return i;
1377 }
1378 
1379 /*
1380  * We completely avoid races by reading each swap page in advance,
1381  * and then search for the process using it.  All the necessary
1382  * page table adjustments can then be made atomically.
1383  *
1384  * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1385  * pages_to_unuse==0 means all pages; ignored if frontswap is false
1386  */
1387 int try_to_unuse(unsigned int type, bool frontswap,
1388                  unsigned long pages_to_unuse)
1389 {
1390         struct swap_info_struct *si = swap_info[type];
1391         struct mm_struct *start_mm;
1392         volatile unsigned char *swap_map; /* swap_map is accessed without
1393                                            * locking. Mark it as volatile
1394                                            * to prevent compiler doing
1395                                            * something odd.
1396                                            */
1397         unsigned char swcount;
1398         struct page *page;
1399         swp_entry_t entry;
1400         unsigned int i = 0;
1401         int retval = 0;
1402 
1403         /*
1404          * When searching mms for an entry, a good strategy is to
1405          * start at the first mm we freed the previous entry from
1406          * (though actually we don't notice whether we or coincidence
1407          * freed the entry).  Initialize this start_mm with a hold.
1408          *
1409          * A simpler strategy would be to start at the last mm we
1410          * freed the previous entry from; but that would take less
1411          * advantage of mmlist ordering, which clusters forked mms
1412          * together, child after parent.  If we race with dup_mmap(), we
1413          * prefer to resolve parent before child, lest we miss entries
1414          * duplicated after we scanned child: using last mm would invert
1415          * that.
1416          */
1417         start_mm = &init_mm;
1418         atomic_inc(&init_mm.mm_users);
1419 
1420         /*
1421          * Keep on scanning until all entries have gone.  Usually,
1422          * one pass through swap_map is enough, but not necessarily:
1423          * there are races when an instance of an entry might be missed.
1424          */
1425         while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1426                 if (signal_pending(current)) {
1427                         retval = -EINTR;
1428                         break;
1429                 }
1430 
1431                 /*
1432                  * Get a page for the entry, using the existing swap
1433                  * cache page if there is one.  Otherwise, get a clean
1434                  * page and read the swap into it.
1435                  */
1436                 swap_map = &si->swap_map[i];
1437                 entry = swp_entry(type, i);
1438                 page = read_swap_cache_async(entry,
1439                                         GFP_HIGHUSER_MOVABLE, NULL, 0);
1440                 if (!page) {
1441                         /*
1442                          * Either swap_duplicate() failed because entry
1443                          * has been freed independently, and will not be
1444                          * reused since sys_swapoff() already disabled
1445                          * allocation from here, or alloc_page() failed.
1446                          */
1447                         swcount = *swap_map;
1448                         /*
1449                          * We don't hold lock here, so the swap entry could be
1450                          * SWAP_MAP_BAD (when the cluster is discarding).
1451                          * Instead of fail out, We can just skip the swap
1452                          * entry because swapoff will wait for discarding
1453                          * finish anyway.
1454                          */
1455                         if (!swcount || swcount == SWAP_MAP_BAD)
1456                                 continue;
1457                         retval = -ENOMEM;
1458                         break;
1459                 }
1460 
1461                 /*
1462                  * Don't hold on to start_mm if it looks like exiting.
1463                  */
1464                 if (atomic_read(&start_mm->mm_users) == 1) {
1465                         mmput(start_mm);
1466                         start_mm = &init_mm;
1467                         atomic_inc(&init_mm.mm_users);
1468                 }
1469 
1470                 /*
1471                  * Wait for and lock page.  When do_swap_page races with
1472                  * try_to_unuse, do_swap_page can handle the fault much
1473                  * faster than try_to_unuse can locate the entry.  This
1474                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
1475                  * defer to do_swap_page in such a case - in some tests,
1476                  * do_swap_page and try_to_unuse repeatedly compete.
1477                  */
1478                 wait_on_page_locked(page);
1479                 wait_on_page_writeback(page);
1480                 lock_page(page);
1481                 wait_on_page_writeback(page);
1482 
1483                 /*
1484                  * Remove all references to entry.
1485                  */
1486                 swcount = *swap_map;
1487                 if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1488                         retval = shmem_unuse(entry, page);
1489                         /* page has already been unlocked and released */
1490                         if (retval < 0)
1491                                 break;
1492                         continue;
1493                 }
1494                 if (swap_count(swcount) && start_mm != &init_mm)
1495                         retval = unuse_mm(start_mm, entry, page);
1496 
1497                 if (swap_count(*swap_map)) {
1498                         int set_start_mm = (*swap_map >= swcount);
1499                         struct list_head *p = &start_mm->mmlist;
1500                         struct mm_struct *new_start_mm = start_mm;
1501                         struct mm_struct *prev_mm = start_mm;
1502                         struct mm_struct *mm;
1503 
1504                         atomic_inc(&new_start_mm->mm_users);
1505                         atomic_inc(&prev_mm->mm_users);
1506                         spin_lock(&mmlist_lock);
1507                         while (swap_count(*swap_map) && !retval &&
1508                                         (p = p->next) != &start_mm->mmlist) {
1509                                 mm = list_entry(p, struct mm_struct, mmlist);
1510                                 if (!atomic_inc_not_zero(&mm->mm_users))
1511                                         continue;
1512                                 spin_unlock(&mmlist_lock);
1513                                 mmput(prev_mm);
1514                                 prev_mm = mm;
1515 
1516                                 cond_resched();
1517 
1518                                 swcount = *swap_map;
1519                                 if (!swap_count(swcount)) /* any usage ? */
1520                                         ;
1521                                 else if (mm == &init_mm)
1522                                         set_start_mm = 1;
1523                                 else
1524                                         retval = unuse_mm(mm, entry, page);
1525 
1526                                 if (set_start_mm && *swap_map < swcount) {
1527                                         mmput(new_start_mm);
1528                                         atomic_inc(&mm->mm_users);
1529                                         new_start_mm = mm;
1530                                         set_start_mm = 0;
1531                                 }
1532                                 spin_lock(&mmlist_lock);
1533                         }
1534                         spin_unlock(&mmlist_lock);
1535                         mmput(prev_mm);
1536                         mmput(start_mm);
1537                         start_mm = new_start_mm;
1538                 }
1539                 if (retval) {
1540                         unlock_page(page);
1541                         put_page(page);
1542                         break;
1543                 }
1544 
1545                 /*
1546                  * If a reference remains (rare), we would like to leave
1547                  * the page in the swap cache; but try_to_unmap could
1548                  * then re-duplicate the entry once we drop page lock,
1549                  * so we might loop indefinitely; also, that page could
1550                  * not be swapped out to other storage meanwhile.  So:
1551                  * delete from cache even if there's another reference,
1552                  * after ensuring that the data has been saved to disk -
1553                  * since if the reference remains (rarer), it will be
1554                  * read from disk into another page.  Splitting into two
1555                  * pages would be incorrect if swap supported "shared
1556                  * private" pages, but they are handled by tmpfs files.
1557                  *
1558                  * Given how unuse_vma() targets one particular offset
1559                  * in an anon_vma, once the anon_vma has been determined,
1560                  * this splitting happens to be just what is needed to
1561                  * handle where KSM pages have been swapped out: re-reading
1562                  * is unnecessarily slow, but we can fix that later on.
1563                  */
1564                 if (swap_count(*swap_map) &&
1565                      PageDirty(page) && PageSwapCache(page)) {
1566                         struct writeback_control wbc = {
1567                                 .sync_mode = WB_SYNC_NONE,
1568                         };
1569 
1570                         swap_writepage(page, &wbc);
1571                         lock_page(page);
1572                         wait_on_page_writeback(page);
1573                 }
1574 
1575                 /*
1576                  * It is conceivable that a racing task removed this page from
1577                  * swap cache just before we acquired the page lock at the top,
1578                  * or while we dropped it in unuse_mm().  The page might even
1579                  * be back in swap cache on another swap area: that we must not
1580                  * delete, since it may not have been written out to swap yet.
1581                  */
1582                 if (PageSwapCache(page) &&
1583                     likely(page_private(page) == entry.val))
1584                         delete_from_swap_cache(page);
1585 
1586                 /*
1587                  * So we could skip searching mms once swap count went
1588                  * to 1, we did not mark any present ptes as dirty: must
1589                  * mark page dirty so shrink_page_list will preserve it.
1590                  */
1591                 SetPageDirty(page);
1592                 unlock_page(page);
1593                 put_page(page);
1594 
1595                 /*
1596                  * Make sure that we aren't completely killing
1597                  * interactive performance.
1598                  */
1599                 cond_resched();
1600                 if (frontswap && pages_to_unuse > 0) {
1601                         if (!--pages_to_unuse)
1602                                 break;
1603                 }
1604         }
1605 
1606         mmput(start_mm);
1607         return retval;
1608 }
1609 
1610 /*
1611  * After a successful try_to_unuse, if no swap is now in use, we know
1612  * we can empty the mmlist.  swap_lock must be held on entry and exit.
1613  * Note that mmlist_lock nests inside swap_lock, and an mm must be
1614  * added to the mmlist just after page_duplicate - before would be racy.
1615  */
1616 static void drain_mmlist(void)
1617 {
1618         struct list_head *p, *next;
1619         unsigned int type;
1620 
1621         for (type = 0; type < nr_swapfiles; type++)
1622                 if (swap_info[type]->inuse_pages)
1623                         return;
1624         spin_lock(&mmlist_lock);
1625         list_for_each_safe(p, next, &init_mm.mmlist)
1626                 list_del_init(p);
1627         spin_unlock(&mmlist_lock);
1628 }
1629 
1630 /*
1631  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1632  * corresponds to page offset for the specified swap entry.
1633  * Note that the type of this function is sector_t, but it returns page offset
1634  * into the bdev, not sector offset.
1635  */
1636 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1637 {
1638         struct swap_info_struct *sis;
1639         struct swap_extent *start_se;
1640         struct swap_extent *se;
1641         pgoff_t offset;
1642 
1643         sis = swap_info[swp_type(entry)];
1644         *bdev = sis->bdev;
1645 
1646         offset = swp_offset(entry);
1647         start_se = sis->curr_swap_extent;
1648         se = start_se;
1649 
1650         for ( ; ; ) {
1651                 if (se->start_page <= offset &&
1652                                 offset < (se->start_page + se->nr_pages)) {
1653                         return se->start_block + (offset - se->start_page);
1654                 }
1655                 se = list_next_entry(se, list);
1656                 sis->curr_swap_extent = se;
1657                 BUG_ON(se == start_se);         /* It *must* be present */
1658         }
1659 }
1660 
1661 /*
1662  * Returns the page offset into bdev for the specified page's swap entry.
1663  */
1664 sector_t map_swap_page(struct page *page, struct block_device **bdev)
1665 {
1666         swp_entry_t entry;
1667         entry.val = page_private(page);
1668         return map_swap_entry(entry, bdev);
1669 }
1670 
1671 /*
1672  * Free all of a swapdev's extent information
1673  */
1674 static void destroy_swap_extents(struct swap_info_struct *sis)
1675 {
1676         while (!list_empty(&sis->first_swap_extent.list)) {
1677                 struct swap_extent *se;
1678 
1679                 se = list_first_entry(&sis->first_swap_extent.list,
1680                                 struct swap_extent, list);
1681                 list_del(&se->list);
1682                 kfree(se);
1683         }
1684 
1685         if (sis->flags & SWP_FILE) {
1686                 struct file *swap_file = sis->swap_file;
1687                 struct address_space *mapping = swap_file->f_mapping;
1688 
1689                 sis->flags &= ~SWP_FILE;
1690                 mapping->a_ops->swap_deactivate(swap_file);
1691         }
1692 }
1693 
1694 /*
1695  * Add a block range (and the corresponding page range) into this swapdev's
1696  * extent list.  The extent list is kept sorted in page order.
1697  *
1698  * This function rather assumes that it is called in ascending page order.
1699  */
1700 int
1701 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1702                 unsigned long nr_pages, sector_t start_block)
1703 {
1704         struct swap_extent *se;
1705         struct swap_extent *new_se;
1706         struct list_head *lh;
1707 
1708         if (start_page == 0) {
1709                 se = &sis->first_swap_extent;
1710                 sis->curr_swap_extent = se;
1711                 se->start_page = 0;
1712                 se->nr_pages = nr_pages;
1713                 se->start_block = start_block;
1714                 return 1;
1715         } else {
1716                 lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1717                 se = list_entry(lh, struct swap_extent, list);
1718                 BUG_ON(se->start_page + se->nr_pages != start_page);
1719                 if (se->start_block + se->nr_pages == start_block) {
1720                         /* Merge it */
1721                         se->nr_pages += nr_pages;
1722                         return 0;
1723                 }
1724         }
1725 
1726         /*
1727          * No merge.  Insert a new extent, preserving ordering.
1728          */
1729         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1730         if (new_se == NULL)
1731                 return -ENOMEM;
1732         new_se->start_page = start_page;
1733         new_se->nr_pages = nr_pages;
1734         new_se->start_block = start_block;
1735 
1736         list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1737         return 1;
1738 }
1739 
1740 /*
1741  * A `swap extent' is a simple thing which maps a contiguous range of pages
1742  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1743  * is built at swapon time and is then used at swap_writepage/swap_readpage
1744  * time for locating where on disk a page belongs.
1745  *
1746  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1747  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1748  * swap files identically.
1749  *
1750  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1751  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1752  * swapfiles are handled *identically* after swapon time.
1753  *
1754  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1755  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1756  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1757  * requirements, they are simply tossed out - we will never use those blocks
1758  * for swapping.
1759  *
1760  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1761  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1762  * which will scribble on the fs.
1763  *
1764  * The amount of disk space which a single swap extent represents varies.
1765  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1766  * extents in the list.  To avoid much list walking, we cache the previous
1767  * search location in `curr_swap_extent', and start new searches from there.
1768  * This is extremely effective.  The average number of iterations in
1769  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1770  */
1771 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1772 {
1773         struct file *swap_file = sis->swap_file;
1774         struct address_space *mapping = swap_file->f_mapping;
1775         struct inode *inode = mapping->host;
1776         int ret;
1777 
1778         if (S_ISBLK(inode->i_mode)) {
1779                 ret = add_swap_extent(sis, 0, sis->max, 0);
1780                 *span = sis->pages;
1781                 return ret;
1782         }
1783 
1784         if (mapping->a_ops->swap_activate) {
1785                 ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1786                 if (!ret) {
1787                         sis->flags |= SWP_FILE;
1788                         ret = add_swap_extent(sis, 0, sis->max, 0);
1789                         *span = sis->pages;
1790                 }
1791                 return ret;
1792         }
1793 
1794         return generic_swapfile_activate(sis, swap_file, span);
1795 }
1796 
1797 static void _enable_swap_info(struct swap_info_struct *p, int prio,
1798                                 unsigned char *swap_map,
1799                                 struct swap_cluster_info *cluster_info)
1800 {
1801         if (prio >= 0)
1802                 p->prio = prio;
1803         else
1804                 p->prio = --least_priority;
1805         /*
1806          * the plist prio is negated because plist ordering is
1807          * low-to-high, while swap ordering is high-to-low
1808          */
1809         p->list.prio = -p->prio;
1810         p->avail_list.prio = -p->prio;
1811         p->swap_map = swap_map;
1812         p->cluster_info = cluster_info;
1813         p->flags |= SWP_WRITEOK;
1814         atomic_long_add(p->pages, &nr_swap_pages);
1815         total_swap_pages += p->pages;
1816 
1817         assert_spin_locked(&swap_lock);
1818         /*
1819          * both lists are plists, and thus priority ordered.
1820          * swap_active_head needs to be priority ordered for swapoff(),
1821          * which on removal of any swap_info_struct with an auto-assigned
1822          * (i.e. negative) priority increments the auto-assigned priority
1823          * of any lower-priority swap_info_structs.
1824          * swap_avail_head needs to be priority ordered for get_swap_page(),
1825          * which allocates swap pages from the highest available priority
1826          * swap_info_struct.
1827          */
1828         plist_add(&p->list, &swap_active_head);
1829         spin_lock(&swap_avail_lock);
1830         plist_add(&p->avail_list, &swap_avail_head);
1831         spin_unlock(&swap_avail_lock);
1832 }
1833 
1834 static void enable_swap_info(struct swap_info_struct *p, int prio,
1835                                 unsigned char *swap_map,
1836                                 struct swap_cluster_info *cluster_info,
1837                                 unsigned long *frontswap_map)
1838 {
1839         frontswap_init(p->type, frontswap_map);
1840         spin_lock(&swap_lock);
1841         spin_lock(&p->lock);
1842          _enable_swap_info(p, prio, swap_map, cluster_info);
1843         spin_unlock(&p->lock);
1844         spin_unlock(&swap_lock);
1845 }
1846 
1847 static void reinsert_swap_info(struct swap_info_struct *p)
1848 {
1849         spin_lock(&swap_lock);
1850         spin_lock(&p->lock);
1851         _enable_swap_info(p, p->prio, p->swap_map, p->cluster_info);
1852         spin_unlock(&p->lock);
1853         spin_unlock(&swap_lock);
1854 }
1855 
1856 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1857 {
1858         struct swap_info_struct *p = NULL;
1859         unsigned char *swap_map;
1860         struct swap_cluster_info *cluster_info;
1861         unsigned long *frontswap_map;
1862         struct file *swap_file, *victim;
1863         struct address_space *mapping;
1864         struct inode *inode;
1865         struct filename *pathname;
1866         int err, found = 0;
1867         unsigned int old_block_size;
1868 
1869         if (!capable(CAP_SYS_ADMIN))
1870                 return -EPERM;
1871 
1872         BUG_ON(!current->mm);
1873 
1874         pathname = getname(specialfile);
1875         if (IS_ERR(pathname))
1876                 return PTR_ERR(pathname);
1877 
1878         victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1879         err = PTR_ERR(victim);
1880         if (IS_ERR(victim))
1881                 goto out;
1882 
1883         mapping = victim->f_mapping;
1884         spin_lock(&swap_lock);
1885         plist_for_each_entry(p, &swap_active_head, list) {
1886                 if (p->flags & SWP_WRITEOK) {
1887                         if (p->swap_file->f_mapping == mapping) {
1888                                 found = 1;
1889                                 break;
1890                         }
1891                 }
1892         }
1893         if (!found) {
1894                 err = -EINVAL;
1895                 spin_unlock(&swap_lock);
1896                 goto out_dput;
1897         }
1898         if (!security_vm_enough_memory_mm(current->mm, p->pages))
1899                 vm_unacct_memory(p->pages);
1900         else {
1901                 err = -ENOMEM;
1902                 spin_unlock(&swap_lock);
1903                 goto out_dput;
1904         }
1905         spin_lock(&swap_avail_lock);
1906         plist_del(&p->avail_list, &swap_avail_head);
1907         spin_unlock(&swap_avail_lock);
1908         spin_lock(&p->lock);
1909         if (p->prio < 0) {
1910                 struct swap_info_struct *si = p;
1911 
1912                 plist_for_each_entry_continue(si, &swap_active_head, list) {
1913                         si->prio++;
1914                         si->list.prio--;
1915                         si->avail_list.prio--;
1916                 }
1917                 least_priority++;
1918         }
1919         plist_del(&p->list, &swap_active_head);
1920         atomic_long_sub(p->pages, &nr_swap_pages);
1921         total_swap_pages -= p->pages;
1922         p->flags &= ~SWP_WRITEOK;
1923         spin_unlock(&p->lock);
1924         spin_unlock(&swap_lock);
1925 
1926         set_current_oom_origin();
1927         err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
1928         clear_current_oom_origin();
1929 
1930         if (err) {
1931                 /* re-insert swap space back into swap_list */
1932                 reinsert_swap_info(p);
1933                 goto out_dput;
1934         }
1935 
1936         flush_work(&p->discard_work);
1937 
1938         destroy_swap_extents(p);
1939         if (p->flags & SWP_CONTINUED)
1940                 free_swap_count_continuations(p);
1941 
1942         mutex_lock(&swapon_mutex);
1943         spin_lock(&swap_lock);
1944         spin_lock(&p->lock);
1945         drain_mmlist();
1946 
1947         /* wait for anyone still in scan_swap_map */
1948         p->highest_bit = 0;             /* cuts scans short */
1949         while (p->flags >= SWP_SCANNING) {
1950                 spin_unlock(&p->lock);
1951                 spin_unlock(&swap_lock);
1952                 schedule_timeout_uninterruptible(1);
1953                 spin_lock(&swap_lock);
1954                 spin_lock(&p->lock);
1955         }
1956 
1957         swap_file = p->swap_file;
1958         old_block_size = p->old_block_size;
1959         p->swap_file = NULL;
1960         p->max = 0;
1961         swap_map = p->swap_map;
1962         p->swap_map = NULL;
1963         cluster_info = p->cluster_info;
1964         p->cluster_info = NULL;
1965         frontswap_map = frontswap_map_get(p);
1966         spin_unlock(&p->lock);
1967         spin_unlock(&swap_lock);
1968         frontswap_invalidate_area(p->type);
1969         frontswap_map_set(p, NULL);
1970         mutex_unlock(&swapon_mutex);
1971         free_percpu(p->percpu_cluster);
1972         p->percpu_cluster = NULL;
1973         vfree(swap_map);
1974         vfree(cluster_info);
1975         vfree(frontswap_map);
1976         /* Destroy swap account information */
1977         swap_cgroup_swapoff(p->type);
1978 
1979         inode = mapping->host;
1980         if (S_ISBLK(inode->i_mode)) {
1981                 struct block_device *bdev = I_BDEV(inode);
1982                 set_blocksize(bdev, old_block_size);
1983                 blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1984         } else {
1985                 inode_lock(inode);
1986                 inode->i_flags &= ~S_SWAPFILE;
1987                 inode_unlock(inode);
1988         }
1989         filp_close(swap_file, NULL);
1990 
1991         /*
1992          * Clear the SWP_USED flag after all resources are freed so that swapon
1993          * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
1994          * not hold p->lock after we cleared its SWP_WRITEOK.
1995          */
1996         spin_lock(&swap_lock);
1997         p->flags = 0;
1998         spin_unlock(&swap_lock);
1999 
2000         err = 0;
2001         atomic_inc(&proc_poll_event);
2002         wake_up_interruptible(&proc_poll_wait);
2003 
2004 out_dput:
2005         filp_close(victim, NULL);
2006 out:
2007         putname(pathname);
2008         return err;
2009 }
2010 
2011 #ifdef CONFIG_PROC_FS
2012 static unsigned swaps_poll(struct file *file, poll_table *wait)
2013 {
2014         struct seq_file *seq = file->private_data;
2015 
2016         poll_wait(file, &proc_poll_wait, wait);
2017 
2018         if (seq->poll_event != atomic_read(&proc_poll_event)) {
2019                 seq->poll_event = atomic_read(&proc_poll_event);
2020                 return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
2021         }
2022 
2023         return POLLIN | POLLRDNORM;
2024 }
2025 
2026 /* iterator */
2027 static void *swap_start(struct seq_file *swap, loff_t *pos)
2028 {
2029         struct swap_info_struct *si;
2030         int type;
2031         loff_t l = *pos;
2032 
2033         mutex_lock(&swapon_mutex);
2034 
2035         if (!l)
2036                 return SEQ_START_TOKEN;
2037 
2038         for (type = 0; type < nr_swapfiles; type++) {
2039                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
2040                 si = swap_info[type];
2041                 if (!(si->flags & SWP_USED) || !si->swap_map)
2042                         continue;
2043                 if (!--l)
2044                         return si;
2045         }
2046 
2047         return NULL;
2048 }
2049 
2050 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
2051 {
2052         struct swap_info_struct *si = v;
2053         int type;
2054 
2055         if (v == SEQ_START_TOKEN)
2056                 type = 0;
2057         else
2058                 type = si->type + 1;
2059 
2060         for (; type < nr_swapfiles; type++) {
2061                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
2062                 si = swap_info[type];
2063                 if (!(si->flags & SWP_USED) || !si->swap_map)
2064                         continue;
2065                 ++*pos;
2066                 return si;
2067         }
2068 
2069         return NULL;
2070 }
2071 
2072 static void swap_stop(struct seq_file *swap, void *v)
2073 {
2074         mutex_unlock(&swapon_mutex);
2075 }
2076 
2077 static int swap_show(struct seq_file *swap, void *v)
2078 {
2079         struct swap_info_struct *si = v;
2080         struct file *file;
2081         int len;
2082 
2083         if (si == SEQ_START_TOKEN) {
2084                 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
2085                 return 0;
2086         }
2087 
2088         file = si->swap_file;
2089         len = seq_file_path(swap, file, " \t\n\\");
2090         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
2091                         len < 40 ? 40 - len : 1, " ",
2092                         S_ISBLK(file_inode(file)->i_mode) ?
2093                                 "partition" : "file\t",
2094                         si->pages << (PAGE_SHIFT - 10),
2095                         si->inuse_pages << (PAGE_SHIFT - 10),
2096                         si->prio);
2097         return 0;
2098 }
2099 
2100 static const struct seq_operations swaps_op = {
2101         .start =        swap_start,
2102         .next =         swap_next,
2103         .stop =         swap_stop,
2104         .show =         swap_show
2105 };
2106 
2107 static int swaps_open(struct inode *inode, struct file *file)
2108 {
2109         struct seq_file *seq;
2110         int ret;
2111 
2112         ret = seq_open(file, &swaps_op);
2113         if (ret)
2114                 return ret;
2115 
2116         seq = file->private_data;
2117         seq->poll_event = atomic_read(&proc_poll_event);
2118         return 0;
2119 }
2120 
2121 static const struct file_operations proc_swaps_operations = {
2122         .open           = swaps_open,
2123         .read           = seq_read,
2124         .llseek         = seq_lseek,
2125         .release        = seq_release,
2126         .poll           = swaps_poll,
2127 };
2128 
2129 static int __init procswaps_init(void)
2130 {
2131         proc_create("swaps", 0, NULL, &proc_swaps_operations);
2132         return 0;
2133 }
2134 __initcall(procswaps_init);
2135 #endif /* CONFIG_PROC_FS */
2136 
2137 #ifdef MAX_SWAPFILES_CHECK
2138 static int __init max_swapfiles_check(void)
2139 {
2140         MAX_SWAPFILES_CHECK();
2141         return 0;
2142 }
2143 late_initcall(max_swapfiles_check);
2144 #endif
2145 
2146 static struct swap_info_struct *alloc_swap_info(void)
2147 {
2148         struct swap_info_struct *p;
2149         unsigned int type;
2150 
2151         p = kzalloc(sizeof(*p), GFP_KERNEL);
2152         if (!p)
2153                 return ERR_PTR(-ENOMEM);
2154 
2155         spin_lock(&swap_lock);
2156         for (type = 0; type < nr_swapfiles; type++) {
2157                 if (!(swap_info[type]->flags & SWP_USED))
2158                         break;
2159         }
2160         if (type >= MAX_SWAPFILES) {
2161                 spin_unlock(&swap_lock);
2162                 kfree(p);
2163                 return ERR_PTR(-EPERM);
2164         }
2165         if (type >= nr_swapfiles) {
2166                 p->type = type;
2167                 swap_info[type] = p;
2168                 /*
2169                  * Write swap_info[type] before nr_swapfiles, in case a
2170                  * racing procfs swap_start() or swap_next() is reading them.
2171                  * (We never shrink nr_swapfiles, we never free this entry.)
2172                  */
2173                 smp_wmb();
2174                 nr_swapfiles++;
2175         } else {
2176                 kfree(p);
2177                 p = swap_info[type];
2178                 /*
2179                  * Do not memset this entry: a racing procfs swap_next()
2180                  * would be relying on p->type to remain valid.
2181                  */
2182         }
2183         INIT_LIST_HEAD(&p->first_swap_extent.list);
2184         plist_node_init(&p->list, 0);
2185         plist_node_init(&p->avail_list, 0);
2186         p->flags = SWP_USED;
2187         spin_unlock(&swap_lock);
2188         spin_lock_init(&p->lock);
2189 
2190         return p;
2191 }
2192 
2193 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
2194 {
2195         int error;
2196 
2197         if (S_ISBLK(inode->i_mode)) {
2198                 p->bdev = bdgrab(I_BDEV(inode));
2199                 error = blkdev_get(p->bdev,
2200                                    FMODE_READ | FMODE_WRITE | FMODE_EXCL, p);
2201                 if (error < 0) {
2202                         p->bdev = NULL;
2203                         return error;
2204                 }
2205                 p->old_block_size = block_size(p->bdev);
2206                 error = set_blocksize(p->bdev, PAGE_SIZE);
2207                 if (error < 0)
2208                         return error;
2209                 p->flags |= SWP_BLKDEV;
2210         } else if (S_ISREG(inode->i_mode)) {
2211                 p->bdev = inode->i_sb->s_bdev;
2212                 inode_lock(inode);
2213                 if (IS_SWAPFILE(inode))
2214                         return -EBUSY;
2215         } else
2216                 return -EINVAL;
2217 
2218         return 0;
2219 }
2220 
2221 static unsigned long read_swap_header(struct swap_info_struct *p,
2222                                         union swap_header *swap_header,
2223                                         struct inode *inode)
2224 {
2225         int i;
2226         unsigned long maxpages;
2227         unsigned long swapfilepages;
2228         unsigned long last_page;
2229 
2230         if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
2231                 pr_err("Unable to find swap-space signature\n");
2232                 return 0;
2233         }
2234 
2235         /* swap partition endianess hack... */
2236         if (swab32(swap_header->info.version) == 1) {
2237                 swab32s(&swap_header->info.version);
2238                 swab32s(&swap_header->info.last_page);
2239                 swab32s(&swap_header->info.nr_badpages);
2240                 if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2241                         return 0;
2242                 for (i = 0; i < swap_header->info.nr_badpages; i++)
2243                         swab32s(&swap_header->info.badpages[i]);
2244         }
2245         /* Check the swap header's sub-version */
2246         if (swap_header->info.version != 1) {
2247                 pr_warn("Unable to handle swap header version %d\n",
2248                         swap_header->info.version);
2249                 return 0;
2250         }
2251 
2252         p->lowest_bit  = 1;
2253         p->cluster_next = 1;
2254         p->cluster_nr = 0;
2255 
2256         /*
2257          * Find out how many pages are allowed for a single swap
2258          * device. There are two limiting factors: 1) the number
2259          * of bits for the swap offset in the swp_entry_t type, and
2260          * 2) the number of bits in the swap pte as defined by the
2261          * different architectures. In order to find the
2262          * largest possible bit mask, a swap entry with swap type 0
2263          * and swap offset ~0UL is created, encoded to a swap pte,
2264          * decoded to a swp_entry_t again, and finally the swap
2265          * offset is extracted. This will mask all the bits from
2266          * the initial ~0UL mask that can't be encoded in either
2267          * the swp_entry_t or the architecture definition of a
2268          * swap pte.
2269          */
2270         maxpages = swp_offset(pte_to_swp_entry(
2271                         swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
2272         last_page = swap_header->info.last_page;
2273         if (last_page > maxpages) {
2274                 pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
2275                         maxpages << (PAGE_SHIFT - 10),
2276                         last_page << (PAGE_SHIFT - 10));
2277         }
2278         if (maxpages > last_page) {
2279                 maxpages = last_page + 1;
2280                 /* p->max is an unsigned int: don't overflow it */
2281                 if ((unsigned int)maxpages == 0)
2282                         maxpages = UINT_MAX;
2283         }
2284         p->highest_bit = maxpages - 1;
2285 
2286         if (!maxpages)
2287                 return 0;
2288         swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
2289         if (swapfilepages && maxpages > swapfilepages) {
2290                 pr_warn("Swap area shorter than signature indicates\n");
2291                 return 0;
2292         }
2293         if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
2294                 return 0;
2295         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2296                 return 0;
2297 
2298         return maxpages;
2299 }
2300 
2301 static int setup_swap_map_and_extents(struct swap_info_struct *p,
2302                                         union swap_header *swap_header,
2303                                         unsigned char *swap_map,
2304                                         struct swap_cluster_info *cluster_info,
2305                                         unsigned long maxpages,
2306                                         sector_t *span)
2307 {
2308         int i;
2309         unsigned int nr_good_pages;
2310         int nr_extents;
2311         unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
2312         unsigned long idx = p->cluster_next / SWAPFILE_CLUSTER;
2313 
2314         nr_good_pages = maxpages - 1;   /* omit header page */
2315 
2316         cluster_list_init(&p->free_clusters);
2317         cluster_list_init(&p->discard_clusters);
2318 
2319         for (i = 0; i < swap_header->info.nr_badpages; i++) {
2320                 unsigned int page_nr = swap_header->info.badpages[i];
2321                 if (page_nr == 0 || page_nr > swap_header->info.last_page)
2322                         return -EINVAL;
2323                 if (page_nr < maxpages) {
2324                         swap_map[page_nr] = SWAP_MAP_BAD;
2325                         nr_good_pages--;
2326                         /*
2327                          * Haven't marked the cluster free yet, no list
2328                          * operation involved
2329                          */
2330                         inc_cluster_info_page(p, cluster_info, page_nr);
2331                 }
2332         }
2333 
2334         /* Haven't marked the cluster free yet, no list operation involved */
2335         for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
2336                 inc_cluster_info_page(p, cluster_info, i);
2337 
2338         if (nr_good_pages) {
2339                 swap_map[0] = SWAP_MAP_BAD;
2340                 /*
2341                  * Not mark the cluster free yet, no list
2342                  * operation involved
2343                  */
2344                 inc_cluster_info_page(p, cluster_info, 0);
2345                 p->max = maxpages;
2346                 p->pages = nr_good_pages;
2347                 nr_extents = setup_swap_extents(p, span);
2348                 if (nr_extents < 0)
2349                         return nr_extents;
2350                 nr_good_pages = p->pages;
2351         }
2352         if (!nr_good_pages) {
2353                 pr_warn("Empty swap-file\n");
2354                 return -EINVAL;
2355         }
2356 
2357         if (!cluster_info)
2358                 return nr_extents;
2359 
2360         for (i = 0; i < nr_clusters; i++) {
2361                 if (!cluster_count(&cluster_info[idx])) {
2362                         cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
2363                         cluster_list_add_tail(&p->free_clusters, cluster_info,
2364                                               idx);
2365                 }
2366                 idx++;
2367                 if (idx == nr_clusters)
2368                         idx = 0;
2369         }
2370         return nr_extents;
2371 }
2372 
2373 /*
2374  * Helper to sys_swapon determining if a given swap
2375  * backing device queue supports DISCARD operations.
2376  */
2377 static bool swap_discardable(struct swap_info_struct *si)
2378 {
2379         struct request_queue *q = bdev_get_queue(si->bdev);
2380 
2381         if (!q || !blk_queue_discard(q))
2382                 return false;
2383 
2384         return true;
2385 }
2386 
2387 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2388 {
2389         struct swap_info_struct *p;
2390         struct filename *name;
2391         struct file *swap_file = NULL;
2392         struct address_space *mapping;
2393         int prio;
2394         int error;
2395         union swap_header *swap_header;
2396         int nr_extents;
2397         sector_t span;
2398         unsigned long maxpages;
2399         unsigned char *swap_map = NULL;
2400         struct swap_cluster_info *cluster_info = NULL;
2401         unsigned long *frontswap_map = NULL;
2402         struct page *page = NULL;
2403         struct inode *inode = NULL;
2404 
2405         if (swap_flags & ~SWAP_FLAGS_VALID)
2406                 return -EINVAL;
2407 
2408         if (!capable(CAP_SYS_ADMIN))
2409                 return -EPERM;
2410 
2411         p = alloc_swap_info();
2412         if (IS_ERR(p))
2413                 return PTR_ERR(p);
2414 
2415         INIT_WORK(&p->discard_work, swap_discard_work);
2416 
2417         name = getname(specialfile);
2418         if (IS_ERR(name)) {
2419                 error = PTR_ERR(name);
2420                 name = NULL;
2421                 goto bad_swap;
2422         }
2423         swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2424         if (IS_ERR(swap_file)) {
2425                 error = PTR_ERR(swap_file);
2426                 swap_file = NULL;
2427                 goto bad_swap;
2428         }
2429 
2430         p->swap_file = swap_file;
2431         mapping = swap_file->f_mapping;
2432         inode = mapping->host;
2433 
2434         /* If S_ISREG(inode->i_mode) will do inode_lock(inode); */
2435         error = claim_swapfile(p, inode);
2436         if (unlikely(error))
2437                 goto bad_swap;
2438 
2439         /*
2440          * Read the swap header.
2441          */
2442         if (!mapping->a_ops->readpage) {
2443                 error = -EINVAL;
2444                 goto bad_swap;
2445         }
2446         page = read_mapping_page(mapping, 0, swap_file);
2447         if (IS_ERR(page)) {
2448                 error = PTR_ERR(page);
2449                 goto bad_swap;
2450         }
2451         swap_header = kmap(page);
2452 
2453         maxpages = read_swap_header(p, swap_header, inode);
2454         if (unlikely(!maxpages)) {
2455                 error = -EINVAL;
2456                 goto bad_swap;
2457         }
2458 
2459         /* OK, set up the swap map and apply the bad block list */
2460         swap_map = vzalloc(maxpages);
2461         if (!swap_map) {
2462                 error = -ENOMEM;
2463                 goto bad_swap;
2464         }
2465 
2466         if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
2467                 p->flags |= SWP_STABLE_WRITES;
2468 
2469         if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2470                 int cpu;
2471 
2472                 p->flags |= SWP_SOLIDSTATE;
2473                 /*
2474                  * select a random position to start with to help wear leveling
2475                  * SSD
2476                  */
2477                 p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2478 
2479                 cluster_info = vzalloc(DIV_ROUND_UP(maxpages,
2480                         SWAPFILE_CLUSTER) * sizeof(*cluster_info));
2481                 if (!cluster_info) {
2482                         error = -ENOMEM;
2483                         goto bad_swap;
2484                 }
2485                 p->percpu_cluster = alloc_percpu(struct percpu_cluster);
2486                 if (!p->percpu_cluster) {
2487                         error = -ENOMEM;
2488                         goto bad_swap;
2489                 }
2490                 for_each_possible_cpu(cpu) {
2491                         struct percpu_cluster *cluster;
2492                         cluster = per_cpu_ptr(p->percpu_cluster, cpu);
2493                         cluster_set_null(&cluster->index);
2494                 }
2495         }
2496 
2497         error = swap_cgroup_swapon(p->type, maxpages);
2498         if (error)
2499                 goto bad_swap;
2500 
2501         nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2502                 cluster_info, maxpages, &span);
2503         if (unlikely(nr_extents < 0)) {
2504                 error = nr_extents;
2505                 goto bad_swap;
2506         }
2507         /* frontswap enabled? set up bit-per-page map for frontswap */
2508         if (IS_ENABLED(CONFIG_FRONTSWAP))
2509                 frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2510 
2511         if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
2512                 /*
2513                  * When discard is enabled for swap with no particular
2514                  * policy flagged, we set all swap discard flags here in
2515                  * order to sustain backward compatibility with older
2516                  * swapon(8) releases.
2517                  */
2518                 p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
2519                              SWP_PAGE_DISCARD);
2520 
2521                 /*
2522                  * By flagging sys_swapon, a sysadmin can tell us to
2523                  * either do single-time area discards only, or to just
2524                  * perform discards for released swap page-clusters.
2525                  * Now it's time to adjust the p->flags accordingly.
2526                  */
2527                 if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
2528                         p->flags &= ~SWP_PAGE_DISCARD;
2529                 else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
2530                         p->flags &= ~SWP_AREA_DISCARD;
2531 
2532                 /* issue a swapon-time discard if it's still required */
2533                 if (p->flags & SWP_AREA_DISCARD) {
2534                         int err = discard_swap(p);
2535                         if (unlikely(err))
2536                                 pr_err("swapon: discard_swap(%p): %d\n",
2537                                         p, err);
2538                 }
2539         }
2540 
2541         mutex_lock(&swapon_mutex);
2542         prio = -1;
2543         if (swap_flags & SWAP_FLAG_PREFER)
2544                 prio =
2545                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2546         enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
2547 
2548         pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
2549                 p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2550                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2551                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2552                 (p->flags & SWP_DISCARDABLE) ? "D" : "",
2553                 (p->flags & SWP_AREA_DISCARD) ? "s" : "",
2554                 (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
2555                 (frontswap_map) ? "FS" : "");
2556 
2557         mutex_unlock(&swapon_mutex);
2558         atomic_inc(&proc_poll_event);
2559         wake_up_interruptible(&proc_poll_wait);
2560 
2561         if (S_ISREG(inode->i_mode))
2562                 inode->i_flags |= S_SWAPFILE;
2563         error = 0;
2564         goto out;
2565 bad_swap:
2566         free_percpu(p->percpu_cluster);
2567         p->percpu_cluster = NULL;
2568         if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2569                 set_blocksize(p->bdev, p->old_block_size);
2570                 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2571         }
2572         destroy_swap_extents(p);
2573         swap_cgroup_swapoff(p->type);
2574         spin_lock(&swap_lock);
2575         p->swap_file = NULL;
2576         p->flags = 0;
2577         spin_unlock(&swap_lock);
2578         vfree(swap_map);
2579         vfree(cluster_info);
2580         if (swap_file) {
2581                 if (inode && S_ISREG(inode->i_mode)) {
2582                         inode_unlock(inode);
2583                         inode = NULL;
2584                 }
2585                 filp_close(swap_file, NULL);
2586         }
2587 out:
2588         if (page && !IS_ERR(page)) {
2589                 kunmap(page);
2590                 put_page(page);
2591         }
2592         if (name)
2593                 putname(name);
2594         if (inode && S_ISREG(inode->i_mode))
2595                 inode_unlock(inode);
2596         return error;
2597 }
2598 
2599 void si_swapinfo(struct sysinfo *val)
2600 {
2601         unsigned int type;
2602         unsigned long nr_to_be_unused = 0;
2603 
2604         spin_lock(&swap_lock);
2605         for (type = 0; type < nr_swapfiles; type++) {
2606                 struct swap_info_struct *si = swap_info[type];
2607 
2608                 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2609                         nr_to_be_unused += si->inuse_pages;
2610         }
2611         val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2612         val->totalswap = total_swap_pages + nr_to_be_unused;
2613         spin_unlock(&swap_lock);
2614 }
2615 
2616 /*
2617  * Verify that a swap entry is valid and increment its swap map count.
2618  *
2619  * Returns error code in following case.
2620  * - success -> 0
2621  * - swp_entry is invalid -> EINVAL
2622  * - swp_entry is migration entry -> EINVAL
2623  * - swap-cache reference is requested but there is already one. -> EEXIST
2624  * - swap-cache reference is requested but the entry is not used. -> ENOENT
2625  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2626  */
2627 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2628 {
2629         struct swap_info_struct *p;
2630         unsigned long offset, type;
2631         unsigned char count;
2632         unsigned char has_cache;
2633         int err = -EINVAL;
2634 
2635         if (non_swap_entry(entry))
2636                 goto out;
2637 
2638         type = swp_type(entry);
2639         if (type >= nr_swapfiles)
2640                 goto bad_file;
2641         p = swap_info[type];
2642         offset = swp_offset(entry);
2643 
2644         spin_lock(&p->lock);
2645         if (unlikely(offset >= p->max))
2646                 goto unlock_out;
2647 
2648         count = p->swap_map[offset];
2649 
2650         /*
2651          * swapin_readahead() doesn't check if a swap entry is valid, so the
2652          * swap entry could be SWAP_MAP_BAD. Check here with lock held.
2653          */
2654         if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
2655                 err = -ENOENT;
2656                 goto unlock_out;
2657         }
2658 
2659         has_cache = count & SWAP_HAS_CACHE;
2660         count &= ~SWAP_HAS_CACHE;
2661         err = 0;
2662 
2663         if (usage == SWAP_HAS_CACHE) {
2664 
2665                 /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2666                 if (!has_cache && count)
2667                         has_cache = SWAP_HAS_CACHE;
2668                 else if (has_cache)             /* someone else added cache */
2669                         err = -EEXIST;
2670                 else                            /* no users remaining */
2671                         err = -ENOENT;
2672 
2673         } else if (count || has_cache) {
2674 
2675                 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2676                         count += usage;
2677                 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2678                         err = -EINVAL;
2679                 else if (swap_count_continued(p, offset, count))
2680                         count = COUNT_CONTINUED;
2681                 else
2682                         err = -ENOMEM;
2683         } else
2684                 err = -ENOENT;                  /* unused swap entry */
2685 
2686         p->swap_map[offset] = count | has_cache;
2687 
2688 unlock_out:
2689         spin_unlock(&p->lock);
2690 out:
2691         return err;
2692 
2693 bad_file:
2694         pr_err("swap_dup: %s%08lx\n", Bad_file, entry.val);
2695         goto out;
2696 }
2697 
2698 /*
2699  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2700  * (in which case its reference count is never incremented).
2701  */
2702 void swap_shmem_alloc(swp_entry_t entry)
2703 {
2704         __swap_duplicate(entry, SWAP_MAP_SHMEM);
2705 }
2706 
2707 /*
2708  * Increase reference count of swap entry by 1.
2709  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2710  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2711  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2712  * might occur if a page table entry has got corrupted.
2713  */
2714 int swap_duplicate(swp_entry_t entry)
2715 {
2716         int err = 0;
2717 
2718         while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2719                 err = add_swap_count_continuation(entry, GFP_ATOMIC);
2720         return err;
2721 }
2722 
2723 /*
2724  * @entry: swap entry for which we allocate swap cache.
2725  *
2726  * Called when allocating swap cache for existing swap entry,
2727  * This can return error codes. Returns 0 at success.
2728  * -EBUSY means there is a swap cache.
2729  * Note: return code is different from swap_duplicate().
2730  */
2731 int swapcache_prepare(swp_entry_t entry)
2732 {
2733         return __swap_duplicate(entry, SWAP_HAS_CACHE);
2734 }
2735 
2736 struct swap_info_struct *page_swap_info(struct page *page)
2737 {
2738         swp_entry_t swap = { .val = page_private(page) };
2739         return swap_info[swp_type(swap)];
2740 }
2741 
2742 /*
2743  * out-of-line __page_file_ methods to avoid include hell.
2744  */
2745 struct address_space *__page_file_mapping(struct page *page)
2746 {
2747         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2748         return page_swap_info(page)->swap_file->f_mapping;
2749 }
2750 EXPORT_SYMBOL_GPL(__page_file_mapping);
2751 
2752 pgoff_t __page_file_index(struct page *page)
2753 {
2754         swp_entry_t swap = { .val = page_private(page) };
2755         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2756         return swp_offset(swap);
2757 }
2758 EXPORT_SYMBOL_GPL(__page_file_index);
2759 
2760 /*
2761  * add_swap_count_continuation - called when a swap count is duplicated
2762  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2763  * page of the original vmalloc'ed swap_map, to hold the continuation count
2764  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2765  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2766  *
2767  * These continuation pages are seldom referenced: the common paths all work
2768  * on the original swap_map, only referring to a continuation page when the
2769  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2770  *
2771  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2772  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2773  * can be called after dropping locks.
2774  */
2775 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2776 {
2777         struct swap_info_struct *si;
2778         struct page *head;
2779         struct page *page;
2780         struct page *list_page;
2781         pgoff_t offset;
2782         unsigned char count;
2783 
2784         /*
2785          * When debugging, it's easier to use __GFP_ZERO here; but it's better
2786          * for latency not to zero a page while GFP_ATOMIC and holding locks.
2787          */
2788         page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2789 
2790         si = swap_info_get(entry);
2791         if (!si) {
2792                 /*
2793                  * An acceptable race has occurred since the failing
2794                  * __swap_duplicate(): the swap entry has been freed,
2795                  * perhaps even the whole swap_map cleared for swapoff.
2796                  */
2797                 goto outer;
2798         }
2799 
2800         offset = swp_offset(entry);
2801         count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2802 
2803         if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2804                 /*
2805                  * The higher the swap count, the more likely it is that tasks
2806                  * will race to add swap count continuation: we need to avoid
2807                  * over-provisioning.
2808                  */
2809                 goto out;
2810         }
2811 
2812         if (!page) {
2813                 spin_unlock(&si->lock);
2814                 return -ENOMEM;
2815         }
2816 
2817         /*
2818          * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2819          * no architecture is using highmem pages for kernel page tables: so it
2820          * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps.
2821          */
2822         head = vmalloc_to_page(si->swap_map + offset);
2823         offset &= ~PAGE_MASK;
2824 
2825         /*
2826          * Page allocation does not initialize the page's lru field,
2827          * but it does always reset its private field.
2828          */
2829         if (!page_private(head)) {
2830                 BUG_ON(count & COUNT_CONTINUED);
2831                 INIT_LIST_HEAD(&head->lru);
2832                 set_page_private(head, SWP_CONTINUED);
2833                 si->flags |= SWP_CONTINUED;
2834         }
2835 
2836         list_for_each_entry(list_page, &head->lru, lru) {
2837                 unsigned char *map;
2838 
2839                 /*
2840                  * If the previous map said no continuation, but we've found
2841                  * a continuation page, free our allocation and use this one.
2842                  */
2843                 if (!(count & COUNT_CONTINUED))
2844                         goto out;
2845 
2846                 map = kmap_atomic(list_page) + offset;
2847                 count = *map;
2848                 kunmap_atomic(map);
2849 
2850                 /*
2851                  * If this continuation count now has some space in it,
2852                  * free our allocation and use this one.
2853                  */
2854                 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2855                         goto out;
2856         }
2857 
2858         list_add_tail(&page->lru, &head->lru);
2859         page = NULL;                    /* now it's attached, don't free it */
2860 out:
2861         spin_unlock(&si->lock);
2862 outer:
2863         if (page)
2864                 __free_page(page);
2865         return 0;
2866 }
2867 
2868 /*
2869  * swap_count_continued - when the original swap_map count is incremented
2870  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2871  * into, carry if so, or else fail until a new continuation page is allocated;
2872  * when the original swap_map count is decremented from 0 with continuation,
2873  * borrow from the continuation and report whether it still holds more.
2874  * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2875  */
2876 static bool swap_count_continued(struct swap_info_struct *si,
2877                                  pgoff_t offset, unsigned char count)
2878 {
2879         struct page *head;
2880         struct page *page;
2881         unsigned char *map;
2882 
2883         head = vmalloc_to_page(si->swap_map + offset);
2884         if (page_private(head) != SWP_CONTINUED) {
2885                 BUG_ON(count & COUNT_CONTINUED);
2886                 return false;           /* need to add count continuation */
2887         }
2888 
2889         offset &= ~PAGE_MASK;
2890         page = list_entry(head->lru.next, struct page, lru);
2891         map = kmap_atomic(page) + offset;
2892 
2893         if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2894                 goto init_map;          /* jump over SWAP_CONT_MAX checks */
2895 
2896         if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2897                 /*
2898                  * Think of how you add 1 to 999
2899                  */
2900                 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2901                         kunmap_atomic(map);
2902                         page = list_entry(page->lru.next, struct page, lru);
2903                         BUG_ON(page == head);
2904                         map = kmap_atomic(page) + offset;
2905                 }
2906                 if (*map == SWAP_CONT_MAX) {
2907                         kunmap_atomic(map);
2908                         page = list_entry(page->lru.next, struct page, lru);
2909                         if (page == head)
2910                                 return false;   /* add count continuation */
2911                         map = kmap_atomic(page) + offset;
2912 init_map:               *map = 0;               /* we didn't zero the page */
2913                 }
2914                 *map += 1;
2915                 kunmap_atomic(map);
2916                 page = list_entry(page->lru.prev, struct page, lru);
2917                 while (page != head) {
2918                         map = kmap_atomic(page) + offset;
2919                         *map = COUNT_CONTINUED;
2920                         kunmap_atomic(map);
2921                         page = list_entry(page->lru.prev, struct page, lru);
2922                 }
2923                 return true;                    /* incremented */
2924 
2925         } else {                                /* decrementing */
2926                 /*
2927                  * Think of how you subtract 1 from 1000
2928                  */
2929                 BUG_ON(count != COUNT_CONTINUED);
2930                 while (*map == COUNT_CONTINUED) {
2931                         kunmap_atomic(map);
2932                         page = list_entry(page->lru.next, struct page, lru);
2933                         BUG_ON(page == head);
2934                         map = kmap_atomic(page) + offset;
2935                 }
2936                 BUG_ON(*map == 0);
2937                 *map -= 1;
2938                 if (*map == 0)
2939                         count = 0;
2940                 kunmap_atomic(map);
2941                 page = list_entry(page->lru.prev, struct page, lru);
2942                 while (page != head) {
2943                         map = kmap_atomic(page) + offset;
2944                         *map = SWAP_CONT_MAX | count;
2945                         count = COUNT_CONTINUED;
2946                         kunmap_atomic(map);
2947                         page = list_entry(page->lru.prev, struct page, lru);
2948                 }
2949                 return count == COUNT_CONTINUED;
2950         }
2951 }
2952 
2953 /*
2954  * free_swap_count_continuations - swapoff free all the continuation pages
2955  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2956  */
2957 static void free_swap_count_continuations(struct swap_info_struct *si)
2958 {
2959         pgoff_t offset;
2960 
2961         for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2962                 struct page *head;
2963                 head = vmalloc_to_page(si->swap_map + offset);
2964                 if (page_private(head)) {
2965                         struct page *page, *next;
2966 
2967                         list_for_each_entry_safe(page, next, &head->lru, lru) {
2968                                 list_del(&page->lru);
2969                                 __free_page(page);
2970                         }
2971                 }
2972         }
2973 }
2974 

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