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1 /*
2 * linux/mm/swapfile.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 * Swap reorganised 29.12.95, Stephen Tweedie
6 */
7
8 #include <linux/mm.h>
9 #include <linux/hugetlb.h>
10 #include <linux/mman.h>
11 #include <linux/slab.h>
12 #include <linux/kernel_stat.h>
13 #include <linux/swap.h>
14 #include <linux/vmalloc.h>
15 #include <linux/pagemap.h>
16 #include <linux/namei.h>
17 #include <linux/shmem_fs.h>
18 #include <linux/blkdev.h>
19 #include <linux/random.h>
20 #include <linux/writeback.h>
21 #include <linux/proc_fs.h>
22 #include <linux/seq_file.h>
23 #include <linux/init.h>
24 #include <linux/ksm.h>
25 #include <linux/rmap.h>
26 #include <linux/security.h>
27 #include <linux/backing-dev.h>
28 #include <linux/mutex.h>
29 #include <linux/capability.h>
30 #include <linux/syscalls.h>
31 #include <linux/memcontrol.h>
32 #include <linux/poll.h>
33 #include <linux/oom.h>
34 #include <linux/frontswap.h>
35 #include <linux/swapfile.h>
36 #include <linux/export.h>
37
38 #include <asm/pgtable.h>
39 #include <asm/tlbflush.h>
40 #include <linux/swapops.h>
41 #include <linux/swap_cgroup.h>
42
43 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
44 unsigned char);
45 static void free_swap_count_continuations(struct swap_info_struct *);
46 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
47
48 DEFINE_SPINLOCK(swap_lock);
49 static unsigned int nr_swapfiles;
50 atomic_long_t nr_swap_pages;
51 /*
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 }