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