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