linux/mm/swapfile.c
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   1/*
   2 *  linux/mm/swapfile.c
   3 *
   4 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
   5 *  Swap reorganised 29.12.95, Stephen Tweedie
   6 */
   7
   8#include <linux/mm.h>
   9#include <linux/hugetlb.h>
  10#include <linux/mman.h>
  11#include <linux/slab.h>
  12#include <linux/kernel_stat.h>
  13#include <linux/swap.h>
  14#include <linux/vmalloc.h>
  15#include <linux/pagemap.h>
  16#include <linux/namei.h>
  17#include <linux/shmem_fs.h>
  18#include <linux/blkdev.h>
  19#include <linux/random.h>
  20#include <linux/writeback.h>
  21#include <linux/proc_fs.h>
  22#include <linux/seq_file.h>
  23#include <linux/init.h>
  24#include <linux/ksm.h>
  25#include <linux/rmap.h>
  26#include <linux/security.h>
  27#include <linux/backing-dev.h>
  28#include <linux/mutex.h>
  29#include <linux/capability.h>
  30#include <linux/syscalls.h>
  31#include <linux/memcontrol.h>
  32#include <linux/poll.h>
  33#include <linux/oom.h>
  34#include <linux/frontswap.h>
  35#include <linux/swapfile.h>
  36#include <linux/export.h>
  37
  38#include <asm/pgtable.h>
  39#include <asm/tlbflush.h>
  40#include <linux/swapops.h>
  41#include <linux/page_cgroup.h>
  42
  43static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
  44                                 unsigned char);
  45static void free_swap_count_continuations(struct swap_info_struct *);
  46static sector_t map_swap_entry(swp_entry_t, struct block_device**);
  47
  48DEFINE_SPINLOCK(swap_lock);
  49static unsigned int nr_swapfiles;
  50atomic_long_t nr_swap_pages;
  51/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
  52long total_swap_pages;
  53static int least_priority;
  54static atomic_t highest_priority_index = ATOMIC_INIT(-1);
  55
  56static const char Bad_file[] = "Bad swap file entry ";
  57static const char Unused_file[] = "Unused swap file entry ";
  58static const char Bad_offset[] = "Bad swap offset entry ";
  59static const char Unused_offset[] = "Unused swap offset entry ";
  60
  61struct swap_list_t swap_list = {-1, -1};
  62
  63struct swap_info_struct *swap_info[MAX_SWAPFILES];
  64
  65static DEFINE_MUTEX(swapon_mutex);
  66
  67static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
  68/* Activity counter to indicate that a swapon or swapoff has occurred */
  69static atomic_t proc_poll_event = ATOMIC_INIT(0);
  70
  71static inline unsigned char swap_count(unsigned char ent)
  72{
  73        return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
  74}
  75
  76/* returns 1 if swap entry is freed */
  77static int
  78__try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
  79{
  80        swp_entry_t entry = swp_entry(si->type, offset);
  81        struct page *page;
  82        int ret = 0;
  83
  84        page = find_get_page(swap_address_space(entry), entry.val);
  85        if (!page)
  86                return 0;
  87        /*
  88         * This function is called from scan_swap_map() and it's called
  89         * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
  90         * We have to use trylock for avoiding deadlock. This is a special
  91         * case and you should use try_to_free_swap() with explicit lock_page()
  92         * in usual operations.
  93         */
  94        if (trylock_page(page)) {
  95                ret = try_to_free_swap(page);
  96                unlock_page(page);
  97        }
  98        page_cache_release(page);
  99        return ret;
 100}
 101
 102/*
 103 * swapon tell device that all the old swap contents can be discarded,
 104 * to allow the swap device to optimize its wear-levelling.
 105 */
 106static int discard_swap(struct swap_info_struct *si)
 107{
 108        struct swap_extent *se;
 109        sector_t start_block;
 110        sector_t nr_blocks;
 111        int err = 0;
 112
 113        /* Do not discard the swap header page! */
 114        se = &si->first_swap_extent;
 115        start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
 116        nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
 117        if (nr_blocks) {
 118                err = blkdev_issue_discard(si->bdev, start_block,
 119                                nr_blocks, GFP_KERNEL, 0);
 120                if (err)
 121                        return err;
 122                cond_resched();
 123        }
 124
 125        list_for_each_entry(se, &si->first_swap_extent.list, list) {
 126                start_block = se->start_block << (PAGE_SHIFT - 9);
 127                nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
 128
 129                err = blkdev_issue_discard(si->bdev, start_block,
 130                                nr_blocks, GFP_KERNEL, 0);
 131                if (err)
 132                        break;
 133
 134                cond_resched();
 135        }
 136        return err;             /* That will often be -EOPNOTSUPP */
 137}
 138
 139/*
 140 * swap allocation tell device that a cluster of swap can now be discarded,
 141 * to allow the swap device to optimize its wear-levelling.
 142 */
 143static void discard_swap_cluster(struct swap_info_struct *si,
 144                                 pgoff_t start_page, pgoff_t nr_pages)
 145{
 146        struct swap_extent *se = si->curr_swap_extent;
 147        int found_extent = 0;
 148
 149        while (nr_pages) {
 150                struct list_head *lh;
 151
 152                if (se->start_page <= start_page &&
 153                    start_page < se->start_page + se->nr_pages) {
 154                        pgoff_t offset = start_page - se->start_page;
 155                        sector_t start_block = se->start_block + offset;
 156                        sector_t nr_blocks = se->nr_pages - offset;
 157
 158                        if (nr_blocks > nr_pages)
 159                                nr_blocks = nr_pages;
 160                        start_page += nr_blocks;
 161                        nr_pages -= nr_blocks;
 162
 163                        if (!found_extent++)
 164                                si->curr_swap_extent = se;
 165
 166                        start_block <<= PAGE_SHIFT - 9;
 167                        nr_blocks <<= PAGE_SHIFT - 9;
 168                        if (blkdev_issue_discard(si->bdev, start_block,
 169                                    nr_blocks, GFP_NOIO, 0))
 170                                break;
 171                }
 172
 173                lh = se->list.next;
 174                se = list_entry(lh, struct swap_extent, list);
 175        }
 176}
 177
 178static int wait_for_discard(void *word)
 179{
 180        schedule();
 181        return 0;
 182}
 183
 184#define SWAPFILE_CLUSTER        256
 185#define LATENCY_LIMIT           256
 186
 187static unsigned long scan_swap_map(struct swap_info_struct *si,
 188                                   unsigned char usage)
 189{
 190        unsigned long offset;
 191        unsigned long scan_base;
 192        unsigned long last_in_cluster = 0;
 193        int latency_ration = LATENCY_LIMIT;
 194        int found_free_cluster = 0;
 195
 196        /*
 197         * We try to cluster swap pages by allocating them sequentially
 198         * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
 199         * way, however, we resort to first-free allocation, starting
 200         * a new cluster.  This prevents us from scattering swap pages
 201         * all over the entire swap partition, so that we reduce
 202         * overall disk seek times between swap pages.  -- sct
 203         * But we do now try to find an empty cluster.  -Andrea
 204         * And we let swap pages go all over an SSD partition.  Hugh
 205         */
 206
 207        si->flags += SWP_SCANNING;
 208        scan_base = offset = si->cluster_next;
 209
 210        if (unlikely(!si->cluster_nr--)) {
 211                if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
 212                        si->cluster_nr = SWAPFILE_CLUSTER - 1;
 213                        goto checks;
 214                }
 215                if (si->flags & SWP_PAGE_DISCARD) {
 216                        /*
 217                         * Start range check on racing allocations, in case
 218                         * they overlap the cluster we eventually decide on
 219                         * (we scan without swap_lock to allow preemption).
 220                         * It's hardly conceivable that cluster_nr could be
 221                         * wrapped during our scan, but don't depend on it.
 222                         */
 223                        if (si->lowest_alloc)
 224                                goto checks;
 225                        si->lowest_alloc = si->max;
 226                        si->highest_alloc = 0;
 227                }
 228                spin_unlock(&si->lock);
 229
 230                /*
 231                 * If seek is expensive, start searching for new cluster from
 232                 * start of partition, to minimize the span of allocated swap.
 233                 * But if seek is cheap, search from our current position, so
 234                 * that swap is allocated from all over the partition: if the
 235                 * Flash Translation Layer only remaps within limited zones,
 236                 * we don't want to wear out the first zone too quickly.
 237                 */
 238                if (!(si->flags & SWP_SOLIDSTATE))
 239                        scan_base = offset = si->lowest_bit;
 240                last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 241
 242                /* Locate the first empty (unaligned) cluster */
 243                for (; last_in_cluster <= si->highest_bit; offset++) {
 244                        if (si->swap_map[offset])
 245                                last_in_cluster = offset + SWAPFILE_CLUSTER;
 246                        else if (offset == last_in_cluster) {
 247                                spin_lock(&si->lock);
 248                                offset -= SWAPFILE_CLUSTER - 1;
 249                                si->cluster_next = offset;
 250                                si->cluster_nr = SWAPFILE_CLUSTER - 1;
 251                                found_free_cluster = 1;
 252                                goto checks;
 253                        }
 254                        if (unlikely(--latency_ration < 0)) {
 255                                cond_resched();
 256                                latency_ration = LATENCY_LIMIT;
 257                        }
 258                }
 259
 260                offset = si->lowest_bit;
 261                last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 262
 263                /* Locate the first empty (unaligned) cluster */
 264                for (; last_in_cluster < scan_base; offset++) {
 265                        if (si->swap_map[offset])
 266                                last_in_cluster = offset + SWAPFILE_CLUSTER;
 267                        else if (offset == last_in_cluster) {
 268                                spin_lock(&si->lock);
 269                                offset -= SWAPFILE_CLUSTER - 1;
 270                                si->cluster_next = offset;
 271                                si->cluster_nr = SWAPFILE_CLUSTER - 1;
 272                                found_free_cluster = 1;
 273                                goto checks;
 274                        }
 275                        if (unlikely(--latency_ration < 0)) {
 276                                cond_resched();
 277                                latency_ration = LATENCY_LIMIT;
 278                        }
 279                }
 280
 281                offset = scan_base;
 282                spin_lock(&si->lock);
 283                si->cluster_nr = SWAPFILE_CLUSTER - 1;
 284                si->lowest_alloc = 0;
 285        }
 286
 287checks:
 288        if (!(si->flags & SWP_WRITEOK))
 289                goto no_page;
 290        if (!si->highest_bit)
 291                goto no_page;
 292        if (offset > si->highest_bit)
 293                scan_base = offset = si->lowest_bit;
 294
 295        /* reuse swap entry of cache-only swap if not busy. */
 296        if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
 297                int swap_was_freed;
 298                spin_unlock(&si->lock);
 299                swap_was_freed = __try_to_reclaim_swap(si, offset);
 300                spin_lock(&si->lock);
 301                /* entry was freed successfully, try to use this again */
 302                if (swap_was_freed)
 303                        goto checks;
 304                goto scan; /* check next one */
 305        }
 306
 307        if (si->swap_map[offset])
 308                goto scan;
 309
 310        if (offset == si->lowest_bit)
 311                si->lowest_bit++;
 312        if (offset == si->highest_bit)
 313                si->highest_bit--;
 314        si->inuse_pages++;
 315        if (si->inuse_pages == si->pages) {
 316                si->lowest_bit = si->max;
 317                si->highest_bit = 0;
 318        }
 319        si->swap_map[offset] = usage;
 320        si->cluster_next = offset + 1;
 321        si->flags -= SWP_SCANNING;
 322
 323        if (si->lowest_alloc) {
 324                /*
 325                 * Only set when SWP_PAGE_DISCARD, and there's a scan
 326                 * for a free cluster in progress or just completed.
 327                 */
 328                if (found_free_cluster) {
 329                        /*
 330                         * To optimize wear-levelling, discard the
 331                         * old data of the cluster, taking care not to
 332                         * discard any of its pages that have already
 333                         * been allocated by racing tasks (offset has
 334                         * already stepped over any at the beginning).
 335                         */
 336                        if (offset < si->highest_alloc &&
 337                            si->lowest_alloc <= last_in_cluster)
 338                                last_in_cluster = si->lowest_alloc - 1;
 339                        si->flags |= SWP_DISCARDING;
 340                        spin_unlock(&si->lock);
 341
 342                        if (offset < last_in_cluster)
 343                                discard_swap_cluster(si, offset,
 344                                        last_in_cluster - offset + 1);
 345
 346                        spin_lock(&si->lock);
 347                        si->lowest_alloc = 0;
 348                        si->flags &= ~SWP_DISCARDING;
 349
 350                        smp_mb();       /* wake_up_bit advises this */
 351                        wake_up_bit(&si->flags, ilog2(SWP_DISCARDING));
 352
 353                } else if (si->flags & SWP_DISCARDING) {
 354                        /*
 355                         * Delay using pages allocated by racing tasks
 356                         * until the whole discard has been issued. We
 357                         * could defer that delay until swap_writepage,
 358                         * but it's easier to keep this self-contained.
 359                         */
 360                        spin_unlock(&si->lock);
 361                        wait_on_bit(&si->flags, ilog2(SWP_DISCARDING),
 362                                wait_for_discard, TASK_UNINTERRUPTIBLE);
 363                        spin_lock(&si->lock);
 364                } else {
 365                        /*
 366                         * Note pages allocated by racing tasks while
 367                         * scan for a free cluster is in progress, so
 368                         * that its final discard can exclude them.
 369                         */
 370                        if (offset < si->lowest_alloc)
 371                                si->lowest_alloc = offset;
 372                        if (offset > si->highest_alloc)
 373                                si->highest_alloc = offset;
 374                }
 375        }
 376        return offset;
 377
 378scan:
 379        spin_unlock(&si->lock);
 380        while (++offset <= si->highest_bit) {
 381                if (!si->swap_map[offset]) {
 382                        spin_lock(&si->lock);
 383                        goto checks;
 384                }
 385                if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
 386                        spin_lock(&si->lock);
 387                        goto checks;
 388                }
 389                if (unlikely(--latency_ration < 0)) {
 390                        cond_resched();
 391                        latency_ration = LATENCY_LIMIT;
 392                }
 393        }
 394        offset = si->lowest_bit;
 395        while (++offset < scan_base) {
 396                if (!si->swap_map[offset]) {
 397                        spin_lock(&si->lock);
 398                        goto checks;
 399                }
 400                if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
 401                        spin_lock(&si->lock);
 402                        goto checks;
 403                }
 404                if (unlikely(--latency_ration < 0)) {
 405                        cond_resched();
 406                        latency_ration = LATENCY_LIMIT;
 407                }
 408        }
 409        spin_lock(&si->lock);
 410
 411no_page:
 412        si->flags -= SWP_SCANNING;
 413        return 0;
 414}
 415
 416swp_entry_t get_swap_page(void)
 417{
 418        struct swap_info_struct *si;
 419        pgoff_t offset;
 420        int type, next;
 421        int wrapped = 0;
 422        int hp_index;
 423
 424        spin_lock(&swap_lock);
 425        if (atomic_long_read(&nr_swap_pages) <= 0)
 426                goto noswap;
 427        atomic_long_dec(&nr_swap_pages);
 428
 429        for (type = swap_list.next; type >= 0 && wrapped < 2; type = next) {
 430                hp_index = atomic_xchg(&highest_priority_index, -1);
 431                /*
 432                 * highest_priority_index records current highest priority swap
 433                 * type which just frees swap entries. If its priority is
 434                 * higher than that of swap_list.next swap type, we use it.  It
 435                 * isn't protected by swap_lock, so it can be an invalid value
 436                 * if the corresponding swap type is swapoff. We double check
 437                 * the flags here. It's even possible the swap type is swapoff
 438                 * and swapon again and its priority is changed. In such rare
 439                 * case, low prority swap type might be used, but eventually
 440                 * high priority swap will be used after several rounds of
 441                 * swap.
 442                 */
 443                if (hp_index != -1 && hp_index != type &&
 444                    swap_info[type]->prio < swap_info[hp_index]->prio &&
 445                    (swap_info[hp_index]->flags & SWP_WRITEOK)) {
 446                        type = hp_index;
 447                        swap_list.next = type;
 448                }
 449
 450                si = swap_info[type];
 451                next = si->next;
 452                if (next < 0 ||
 453                    (!wrapped && si->prio != swap_info[next]->prio)) {
 454                        next = swap_list.head;
 455                        wrapped++;
 456                }
 457
 458                spin_lock(&si->lock);
 459                if (!si->highest_bit) {
 460                        spin_unlock(&si->lock);
 461                        continue;
 462                }
 463                if (!(si->flags & SWP_WRITEOK)) {
 464                        spin_unlock(&si->lock);
 465                        continue;
 466                }
 467
 468                swap_list.next = next;
 469
 470                spin_unlock(&swap_lock);
 471                /* This is called for allocating swap entry for cache */
 472                offset = scan_swap_map(si, SWAP_HAS_CACHE);
 473                spin_unlock(&si->lock);
 474                if (offset)
 475                        return swp_entry(type, offset);
 476                spin_lock(&swap_lock);
 477                next = swap_list.next;
 478        }
 479
 480        atomic_long_inc(&nr_swap_pages);
 481noswap:
 482        spin_unlock(&swap_lock);
 483        return (swp_entry_t) {0};
 484}
 485
 486/* The only caller of this function is now susupend routine */
 487swp_entry_t get_swap_page_of_type(int type)
 488{
 489        struct swap_info_struct *si;
 490        pgoff_t offset;
 491
 492        si = swap_info[type];
 493        spin_lock(&si->lock);
 494        if (si && (si->flags & SWP_WRITEOK)) {
 495                atomic_long_dec(&nr_swap_pages);
 496                /* This is called for allocating swap entry, not cache */
 497                offset = scan_swap_map(si, 1);
 498                if (offset) {
 499                        spin_unlock(&si->lock);
 500                        return swp_entry(type, offset);
 501                }
 502                atomic_long_inc(&nr_swap_pages);
 503        }
 504        spin_unlock(&si->lock);
 505        return (swp_entry_t) {0};
 506}
 507
 508static struct swap_info_struct *swap_info_get(swp_entry_t entry)
 509{
 510        struct swap_info_struct *p;
 511        unsigned long offset, type;
 512
 513        if (!entry.val)
 514                goto out;
 515        type = swp_type(entry);
 516        if (type >= nr_swapfiles)
 517                goto bad_nofile;
 518        p = swap_info[type];
 519        if (!(p->flags & SWP_USED))
 520                goto bad_device;
 521        offset = swp_offset(entry);
 522        if (offset >= p->max)
 523                goto bad_offset;
 524        if (!p->swap_map[offset])
 525                goto bad_free;
 526        spin_lock(&p->lock);
 527        return p;
 528
 529bad_free:
 530        printk(KERN_ERR "swap_free: %s%08lx\n", Unused_offset, entry.val);
 531        goto out;
 532bad_offset:
 533        printk(KERN_ERR "swap_free: %s%08lx\n", Bad_offset, entry.val);
 534        goto out;
 535bad_device:
 536        printk(KERN_ERR "swap_free: %s%08lx\n", Unused_file, entry.val);
 537        goto out;
 538bad_nofile:
 539        printk(KERN_ERR "swap_free: %s%08lx\n", Bad_file, entry.val);
 540out:
 541        return NULL;
 542}
 543
 544/*
 545 * This swap type frees swap entry, check if it is the highest priority swap
 546 * type which just frees swap entry. get_swap_page() uses
 547 * highest_priority_index to search highest priority swap type. The
 548 * swap_info_struct.lock can't protect us if there are multiple swap types
 549 * active, so we use atomic_cmpxchg.
 550 */
 551static void set_highest_priority_index(int type)
 552{
 553        int old_hp_index, new_hp_index;
 554
 555        do {
 556                old_hp_index = atomic_read(&highest_priority_index);
 557                if (old_hp_index != -1 &&
 558                        swap_info[old_hp_index]->prio >= swap_info[type]->prio)
 559                        break;
 560                new_hp_index = type;
 561        } while (atomic_cmpxchg(&highest_priority_index,
 562                old_hp_index, new_hp_index) != old_hp_index);
 563}
 564
 565static unsigned char swap_entry_free(struct swap_info_struct *p,
 566                                     swp_entry_t entry, unsigned char usage)
 567{
 568        unsigned long offset = swp_offset(entry);
 569        unsigned char count;
 570        unsigned char has_cache;
 571
 572        count = p->swap_map[offset];
 573        has_cache = count & SWAP_HAS_CACHE;
 574        count &= ~SWAP_HAS_CACHE;
 575
 576        if (usage == SWAP_HAS_CACHE) {
 577                VM_BUG_ON(!has_cache);
 578                has_cache = 0;
 579        } else if (count == SWAP_MAP_SHMEM) {
 580                /*
 581                 * Or we could insist on shmem.c using a special
 582                 * swap_shmem_free() and free_shmem_swap_and_cache()...
 583                 */
 584                count = 0;
 585        } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
 586                if (count == COUNT_CONTINUED) {
 587                        if (swap_count_continued(p, offset, count))
 588                                count = SWAP_MAP_MAX | COUNT_CONTINUED;
 589                        else
 590                                count = SWAP_MAP_MAX;
 591                } else
 592                        count--;
 593        }
 594
 595        if (!count)
 596                mem_cgroup_uncharge_swap(entry);
 597
 598        usage = count | has_cache;
 599        p->swap_map[offset] = usage;
 600
 601        /* free if no reference */
 602        if (!usage) {
 603                if (offset < p->lowest_bit)
 604                        p->lowest_bit = offset;
 605                if (offset > p->highest_bit)
 606                        p->highest_bit = offset;
 607                set_highest_priority_index(p->type);
 608                atomic_long_inc(&nr_swap_pages);
 609                p->inuse_pages--;
 610                frontswap_invalidate_page(p->type, offset);
 611                if (p->flags & SWP_BLKDEV) {
 612                        struct gendisk *disk = p->bdev->bd_disk;
 613                        if (disk->fops->swap_slot_free_notify)
 614                                disk->fops->swap_slot_free_notify(p->bdev,
 615                                                                  offset);
 616                }
 617        }
 618
 619        return usage;
 620}
 621
 622/*
 623 * Caller has made sure that the swapdevice corresponding to entry
 624 * is still around or has not been recycled.
 625 */
 626void swap_free(swp_entry_t entry)
 627{
 628        struct swap_info_struct *p;
 629
 630        p = swap_info_get(entry);
 631        if (p) {
 632                swap_entry_free(p, entry, 1);
 633                spin_unlock(&p->lock);
 634        }
 635}
 636
 637/*
 638 * Called after dropping swapcache to decrease refcnt to swap entries.
 639 */
 640void swapcache_free(swp_entry_t entry, struct page *page)
 641{
 642        struct swap_info_struct *p;
 643        unsigned char count;
 644
 645        p = swap_info_get(entry);
 646        if (p) {
 647                count = swap_entry_free(p, entry, SWAP_HAS_CACHE);
 648                if (page)
 649                        mem_cgroup_uncharge_swapcache(page, entry, count != 0);
 650                spin_unlock(&p->lock);
 651        }
 652}
 653
 654/*
 655 * How many references to page are currently swapped out?
 656 * This does not give an exact answer when swap count is continued,
 657 * but does include the high COUNT_CONTINUED flag to allow for that.
 658 */
 659int page_swapcount(struct page *page)
 660{
 661        int count = 0;
 662        struct swap_info_struct *p;
 663        swp_entry_t entry;
 664
 665        entry.val = page_private(page);
 666        p = swap_info_get(entry);
 667        if (p) {
 668                count = swap_count(p->swap_map[swp_offset(entry)]);
 669                spin_unlock(&p->lock);
 670        }
 671        return count;
 672}
 673
 674/*
 675 * We can write to an anon page without COW if there are no other references
 676 * to it.  And as a side-effect, free up its swap: because the old content
 677 * on disk will never be read, and seeking back there to write new content
 678 * later would only waste time away from clustering.
 679 */
 680int reuse_swap_page(struct page *page)
 681{
 682        int count;
 683
 684        VM_BUG_ON(!PageLocked(page));
 685        if (unlikely(PageKsm(page)))
 686                return 0;
 687        count = page_mapcount(page);
 688        if (count <= 1 && PageSwapCache(page)) {
 689                count += page_swapcount(page);
 690                if (count == 1 && !PageWriteback(page)) {
 691                        delete_from_swap_cache(page);
 692                        SetPageDirty(page);
 693                }
 694        }
 695        return count <= 1;
 696}
 697
 698/*
 699 * If swap is getting full, or if there are no more mappings of this page,
 700 * then try_to_free_swap is called to free its swap space.
 701 */
 702int try_to_free_swap(struct page *page)
 703{
 704        VM_BUG_ON(!PageLocked(page));
 705
 706        if (!PageSwapCache(page))
 707                return 0;
 708        if (PageWriteback(page))
 709                return 0;
 710        if (page_swapcount(page))
 711                return 0;
 712
 713        /*
 714         * Once hibernation has begun to create its image of memory,
 715         * there's a danger that one of the calls to try_to_free_swap()
 716         * - most probably a call from __try_to_reclaim_swap() while
 717         * hibernation is allocating its own swap pages for the image,
 718         * but conceivably even a call from memory reclaim - will free
 719         * the swap from a page which has already been recorded in the
 720         * image as a clean swapcache page, and then reuse its swap for
 721         * another page of the image.  On waking from hibernation, the
 722         * original page might be freed under memory pressure, then
 723         * later read back in from swap, now with the wrong data.
 724         *
 725         * Hibration suspends storage while it is writing the image
 726         * to disk so check that here.
 727         */
 728        if (pm_suspended_storage())
 729                return 0;
 730
 731        delete_from_swap_cache(page);
 732        SetPageDirty(page);
 733        return 1;
 734}
 735
 736/*
 737 * Free the swap entry like above, but also try to
 738 * free the page cache entry if it is the last user.
 739 */
 740int free_swap_and_cache(swp_entry_t entry)
 741{
 742        struct swap_info_struct *p;
 743        struct page *page = NULL;
 744
 745        if (non_swap_entry(entry))
 746                return 1;
 747
 748        p = swap_info_get(entry);
 749        if (p) {
 750                if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
 751                        page = find_get_page(swap_address_space(entry),
 752                                                entry.val);
 753                        if (page && !trylock_page(page)) {
 754                                page_cache_release(page);
 755                                page = NULL;
 756                        }
 757                }
 758                spin_unlock(&p->lock);
 759        }
 760        if (page) {
 761                /*
 762                 * Not mapped elsewhere, or swap space full? Free it!
 763                 * Also recheck PageSwapCache now page is locked (above).
 764                 */
 765                if (PageSwapCache(page) && !PageWriteback(page) &&
 766                                (!page_mapped(page) || vm_swap_full())) {
 767                        delete_from_swap_cache(page);
 768                        SetPageDirty(page);
 769                }
 770                unlock_page(page);
 771                page_cache_release(page);
 772        }
 773        return p != NULL;
 774}
 775
 776#ifdef CONFIG_HIBERNATION
 777/*
 778 * Find the swap type that corresponds to given device (if any).
 779 *
 780 * @offset - number of the PAGE_SIZE-sized block of the device, starting
 781 * from 0, in which the swap header is expected to be located.
 782 *
 783 * This is needed for the suspend to disk (aka swsusp).
 784 */
 785int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 786{
 787        struct block_device *bdev = NULL;
 788        int type;
 789
 790        if (device)
 791                bdev = bdget(device);
 792
 793        spin_lock(&swap_lock);
 794        for (type = 0; type < nr_swapfiles; type++) {
 795                struct swap_info_struct *sis = swap_info[type];
 796
 797                if (!(sis->flags & SWP_WRITEOK))
 798                        continue;
 799
 800                if (!bdev) {
 801                        if (bdev_p)
 802                                *bdev_p = bdgrab(sis->bdev);
 803
 804                        spin_unlock(&swap_lock);
 805                        return type;
 806                }
 807                if (bdev == sis->bdev) {
 808                        struct swap_extent *se = &sis->first_swap_extent;
 809
 810                        if (se->start_block == offset) {
 811                                if (bdev_p)
 812                                        *bdev_p = bdgrab(sis->bdev);
 813
 814                                spin_unlock(&swap_lock);
 815                                bdput(bdev);
 816                                return type;
 817                        }
 818                }
 819        }
 820        spin_unlock(&swap_lock);
 821        if (bdev)
 822                bdput(bdev);
 823
 824        return -ENODEV;
 825}
 826
 827/*
 828 * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
 829 * corresponding to given index in swap_info (swap type).
 830 */
 831sector_t swapdev_block(int type, pgoff_t offset)
 832{
 833        struct block_device *bdev;
 834
 835        if ((unsigned int)type >= nr_swapfiles)
 836                return 0;
 837        if (!(swap_info[type]->flags & SWP_WRITEOK))
 838                return 0;
 839        return map_swap_entry(swp_entry(type, offset), &bdev);
 840}
 841
 842/*
 843 * Return either the total number of swap pages of given type, or the number
 844 * of free pages of that type (depending on @free)
 845 *
 846 * This is needed for software suspend
 847 */
 848unsigned int count_swap_pages(int type, int free)
 849{
 850        unsigned int n = 0;
 851
 852        spin_lock(&swap_lock);
 853        if ((unsigned int)type < nr_swapfiles) {
 854                struct swap_info_struct *sis = swap_info[type];
 855
 856                spin_lock(&sis->lock);
 857                if (sis->flags & SWP_WRITEOK) {
 858                        n = sis->pages;
 859                        if (free)
 860                                n -= sis->inuse_pages;
 861                }
 862                spin_unlock(&sis->lock);
 863        }
 864        spin_unlock(&swap_lock);
 865        return n;
 866}
 867#endif /* CONFIG_HIBERNATION */
 868
 869static inline int maybe_same_pte(pte_t pte, pte_t swp_pte)
 870{
 871#ifdef CONFIG_MEM_SOFT_DIRTY
 872        /*
 873         * When pte keeps soft dirty bit the pte generated
 874         * from swap entry does not has it, still it's same
 875         * pte from logical point of view.
 876         */
 877        pte_t swp_pte_dirty = pte_swp_mksoft_dirty(swp_pte);
 878        return pte_same(pte, swp_pte) || pte_same(pte, swp_pte_dirty);
 879#else
 880        return pte_same(pte, swp_pte);
 881#endif
 882}
 883
 884/*
 885 * No need to decide whether this PTE shares the swap entry with others,
 886 * just let do_wp_page work it out if a write is requested later - to
 887 * force COW, vm_page_prot omits write permission from any private vma.
 888 */
 889static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 890                unsigned long addr, swp_entry_t entry, struct page *page)
 891{
 892        struct page *swapcache;
 893        struct mem_cgroup *memcg;
 894        spinlock_t *ptl;
 895        pte_t *pte;
 896        int ret = 1;
 897
 898        swapcache = page;
 899        page = ksm_might_need_to_copy(page, vma, addr);
 900        if (unlikely(!page))
 901                return -ENOMEM;
 902
 903        if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
 904                                         GFP_KERNEL, &memcg)) {
 905                ret = -ENOMEM;
 906                goto out_nolock;
 907        }
 908
 909        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 910        if (unlikely(!maybe_same_pte(*pte, swp_entry_to_pte(entry)))) {
 911                mem_cgroup_cancel_charge_swapin(memcg);
 912                ret = 0;
 913                goto out;
 914        }
 915
 916        dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
 917        inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
 918        get_page(page);
 919        set_pte_at(vma->vm_mm, addr, pte,
 920                   pte_mkold(mk_pte(page, vma->vm_page_prot)));
 921        if (page == swapcache)
 922                page_add_anon_rmap(page, vma, addr);
 923        else /* ksm created a completely new copy */
 924                page_add_new_anon_rmap(page, vma, addr);
 925        mem_cgroup_commit_charge_swapin(page, memcg);
 926        swap_free(entry);
 927        /*
 928         * Move the page to the active list so it is not
 929         * immediately swapped out again after swapon.
 930         */
 931        activate_page(page);
 932out:
 933        pte_unmap_unlock(pte, ptl);
 934out_nolock:
 935        if (page != swapcache) {
 936                unlock_page(page);
 937                put_page(page);
 938        }
 939        return ret;
 940}
 941
 942static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 943                                unsigned long addr, unsigned long end,
 944                                swp_entry_t entry, struct page *page)
 945{
 946        pte_t swp_pte = swp_entry_to_pte(entry);
 947        pte_t *pte;
 948        int ret = 0;
 949
 950        /*
 951         * We don't actually need pte lock while scanning for swp_pte: since
 952         * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
 953         * page table while we're scanning; though it could get zapped, and on
 954         * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
 955         * of unmatched parts which look like swp_pte, so unuse_pte must
 956         * recheck under pte lock.  Scanning without pte lock lets it be
 957         * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
 958         */
 959        pte = pte_offset_map(pmd, addr);
 960        do {
 961                /*
 962                 * swapoff spends a _lot_ of time in this loop!
 963                 * Test inline before going to call unuse_pte.
 964                 */
 965                if (unlikely(maybe_same_pte(*pte, swp_pte))) {
 966                        pte_unmap(pte);
 967                        ret = unuse_pte(vma, pmd, addr, entry, page);
 968                        if (ret)
 969                                goto out;
 970                        pte = pte_offset_map(pmd, addr);
 971                }
 972        } while (pte++, addr += PAGE_SIZE, addr != end);
 973        pte_unmap(pte - 1);
 974out:
 975        return ret;
 976}
 977
 978static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 979                                unsigned long addr, unsigned long end,
 980                                swp_entry_t entry, struct page *page)
 981{
 982        pmd_t *pmd;
 983        unsigned long next;
 984        int ret;
 985
 986        pmd = pmd_offset(pud, addr);
 987        do {
 988                next = pmd_addr_end(addr, end);
 989                if (pmd_none_or_trans_huge_or_clear_bad(pmd))
 990                        continue;
 991                ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
 992                if (ret)
 993                        return ret;
 994        } while (pmd++, addr = next, addr != end);
 995        return 0;
 996}
 997
 998static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 999                                unsigned long addr, unsigned long end,
1000                                swp_entry_t entry, struct page *page)
1001{
1002        pud_t *pud;
1003        unsigned long next;
1004        int ret;
1005
1006        pud = pud_offset(pgd, addr);
1007        do {
1008                next = pud_addr_end(addr, end);
1009                if (pud_none_or_clear_bad(pud))
1010                        continue;
1011                ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
1012                if (ret)
1013                        return ret;
1014        } while (pud++, addr = next, addr != end);
1015        return 0;
1016}
1017
1018static int unuse_vma(struct vm_area_struct *vma,
1019                                swp_entry_t entry, struct page *page)
1020{
1021        pgd_t *pgd;
1022        unsigned long addr, end, next;
1023        int ret;
1024
1025        if (page_anon_vma(page)) {
1026                addr = page_address_in_vma(page, vma);
1027                if (addr == -EFAULT)
1028                        return 0;
1029                else
1030                        end = addr + PAGE_SIZE;
1031        } else {
1032                addr = vma->vm_start;
1033                end = vma->vm_end;
1034        }
1035
1036        pgd = pgd_offset(vma->vm_mm, addr);
1037        do {
1038                next = pgd_addr_end(addr, end);
1039                if (pgd_none_or_clear_bad(pgd))
1040                        continue;
1041                ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1042                if (ret)
1043                        return ret;
1044        } while (pgd++, addr = next, addr != end);
1045        return 0;
1046}
1047
1048static int unuse_mm(struct mm_struct *mm,
1049                                swp_entry_t entry, struct page *page)
1050{
1051        struct vm_area_struct *vma;
1052        int ret = 0;
1053
1054        if (!down_read_trylock(&mm->mmap_sem)) {
1055                /*
1056                 * Activate page so shrink_inactive_list is unlikely to unmap
1057                 * its ptes while lock is dropped, so swapoff can make progress.
1058                 */
1059                activate_page(page);
1060                unlock_page(page);
1061                down_read(&mm->mmap_sem);
1062                lock_page(page);
1063        }
1064        for (vma = mm->mmap; vma; vma = vma->vm_next) {
1065                if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1066                        break;
1067        }
1068        up_read(&mm->mmap_sem);
1069        return (ret < 0)? ret: 0;
1070}
1071
1072/*
1073 * Scan swap_map (or frontswap_map if frontswap parameter is true)
1074 * from current position to next entry still in use.
1075 * Recycle to start on reaching the end, returning 0 when empty.
1076 */
1077static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1078                                        unsigned int prev, bool frontswap)
1079{
1080        unsigned int max = si->max;
1081        unsigned int i = prev;
1082        unsigned char count;
1083
1084        /*
1085         * No need for swap_lock here: we're just looking
1086         * for whether an entry is in use, not modifying it; false
1087         * hits are okay, and sys_swapoff() has already prevented new
1088         * allocations from this area (while holding swap_lock).
1089         */
1090        for (;;) {
1091                if (++i >= max) {
1092                        if (!prev) {
1093                                i = 0;
1094                                break;
1095                        }
1096                        /*
1097                         * No entries in use at top of swap_map,
1098                         * loop back to start and recheck there.
1099                         */
1100                        max = prev + 1;
1101                        prev = 0;
1102                        i = 1;
1103                }
1104                if (frontswap) {
1105                        if (frontswap_test(si, i))
1106                                break;
1107                        else
1108                                continue;
1109                }
1110                count = si->swap_map[i];
1111                if (count && swap_count(count) != SWAP_MAP_BAD)
1112                        break;
1113        }
1114        return i;
1115}
1116
1117/*
1118 * We completely avoid races by reading each swap page in advance,
1119 * and then search for the process using it.  All the necessary
1120 * page table adjustments can then be made atomically.
1121 *
1122 * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1123 * pages_to_unuse==0 means all pages; ignored if frontswap is false
1124 */
1125int try_to_unuse(unsigned int type, bool frontswap,
1126                 unsigned long pages_to_unuse)
1127{
1128        struct swap_info_struct *si = swap_info[type];
1129        struct mm_struct *start_mm;
1130        unsigned char *swap_map;
1131        unsigned char swcount;
1132        struct page *page;
1133        swp_entry_t entry;
1134        unsigned int i = 0;
1135        int retval = 0;
1136
1137        /*
1138         * When searching mms for an entry, a good strategy is to
1139         * start at the first mm we freed the previous entry from
1140         * (though actually we don't notice whether we or coincidence
1141         * freed the entry).  Initialize this start_mm with a hold.
1142         *
1143         * A simpler strategy would be to start at the last mm we
1144         * freed the previous entry from; but that would take less
1145         * advantage of mmlist ordering, which clusters forked mms
1146         * together, child after parent.  If we race with dup_mmap(), we
1147         * prefer to resolve parent before child, lest we miss entries
1148         * duplicated after we scanned child: using last mm would invert
1149         * that.
1150         */
1151        start_mm = &init_mm;
1152        atomic_inc(&init_mm.mm_users);
1153
1154        /*
1155         * Keep on scanning until all entries have gone.  Usually,
1156         * one pass through swap_map is enough, but not necessarily:
1157         * there are races when an instance of an entry might be missed.
1158         */
1159        while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1160                if (signal_pending(current)) {
1161                        retval = -EINTR;
1162                        break;
1163                }
1164
1165                /*
1166                 * Get a page for the entry, using the existing swap
1167                 * cache page if there is one.  Otherwise, get a clean
1168                 * page and read the swap into it.
1169                 */
1170                swap_map = &si->swap_map[i];
1171                entry = swp_entry(type, i);
1172                page = read_swap_cache_async(entry,
1173                                        GFP_HIGHUSER_MOVABLE, NULL, 0);
1174                if (!page) {
1175                        /*
1176                         * Either swap_duplicate() failed because entry
1177                         * has been freed independently, and will not be
1178                         * reused since sys_swapoff() already disabled
1179                         * allocation from here, or alloc_page() failed.
1180                         */
1181                        if (!*swap_map)
1182                                continue;
1183                        retval = -ENOMEM;
1184                        break;
1185                }
1186
1187                /*
1188                 * Don't hold on to start_mm if it looks like exiting.
1189                 */
1190                if (atomic_read(&start_mm->mm_users) == 1) {
1191                        mmput(start_mm);
1192                        start_mm = &init_mm;
1193                        atomic_inc(&init_mm.mm_users);
1194                }
1195
1196                /*
1197                 * Wait for and lock page.  When do_swap_page races with
1198                 * try_to_unuse, do_swap_page can handle the fault much
1199                 * faster than try_to_unuse can locate the entry.  This
1200                 * apparently redundant "wait_on_page_locked" lets try_to_unuse
1201                 * defer to do_swap_page in such a case - in some tests,
1202                 * do_swap_page and try_to_unuse repeatedly compete.
1203                 */
1204                wait_on_page_locked(page);
1205                wait_on_page_writeback(page);
1206                lock_page(page);
1207                wait_on_page_writeback(page);
1208
1209                /*
1210                 * Remove all references to entry.
1211                 */
1212                swcount = *swap_map;
1213                if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1214                        retval = shmem_unuse(entry, page);
1215                        /* page has already been unlocked and released */
1216                        if (retval < 0)
1217                                break;
1218                        continue;
1219                }
1220                if (swap_count(swcount) && start_mm != &init_mm)
1221                        retval = unuse_mm(start_mm, entry, page);
1222
1223                if (swap_count(*swap_map)) {
1224                        int set_start_mm = (*swap_map >= swcount);
1225                        struct list_head *p = &start_mm->mmlist;
1226                        struct mm_struct *new_start_mm = start_mm;
1227                        struct mm_struct *prev_mm = start_mm;
1228                        struct mm_struct *mm;
1229
1230                        atomic_inc(&new_start_mm->mm_users);
1231                        atomic_inc(&prev_mm->mm_users);
1232                        spin_lock(&mmlist_lock);
1233                        while (swap_count(*swap_map) && !retval &&
1234                                        (p = p->next) != &start_mm->mmlist) {
1235                                mm = list_entry(p, struct mm_struct, mmlist);
1236                                if (!atomic_inc_not_zero(&mm->mm_users))
1237                                        continue;
1238                                spin_unlock(&mmlist_lock);
1239                                mmput(prev_mm);
1240                                prev_mm = mm;
1241
1242                                cond_resched();
1243
1244                                swcount = *swap_map;
1245                                if (!swap_count(swcount)) /* any usage ? */
1246                                        ;
1247                                else if (mm == &init_mm)
1248                                        set_start_mm = 1;
1249                                else
1250                                        retval = unuse_mm(mm, entry, page);
1251
1252                                if (set_start_mm && *swap_map < swcount) {
1253                                        mmput(new_start_mm);
1254                                        atomic_inc(&mm->mm_users);
1255                                        new_start_mm = mm;
1256                                        set_start_mm = 0;
1257                                }
1258                                spin_lock(&mmlist_lock);
1259                        }
1260                        spin_unlock(&mmlist_lock);
1261                        mmput(prev_mm);
1262                        mmput(start_mm);
1263                        start_mm = new_start_mm;
1264                }
1265                if (retval) {
1266                        unlock_page(page);
1267                        page_cache_release(page);
1268                        break;
1269                }
1270
1271                /*
1272                 * If a reference remains (rare), we would like to leave
1273                 * the page in the swap cache; but try_to_unmap could
1274                 * then re-duplicate the entry once we drop page lock,
1275                 * so we might loop indefinitely; also, that page could
1276                 * not be swapped out to other storage meanwhile.  So:
1277                 * delete from cache even if there's another reference,
1278                 * after ensuring that the data has been saved to disk -
1279                 * since if the reference remains (rarer), it will be
1280                 * read from disk into another page.  Splitting into two
1281                 * pages would be incorrect if swap supported "shared
1282                 * private" pages, but they are handled by tmpfs files.
1283                 *
1284                 * Given how unuse_vma() targets one particular offset
1285                 * in an anon_vma, once the anon_vma has been determined,
1286                 * this splitting happens to be just what is needed to
1287                 * handle where KSM pages have been swapped out: re-reading
1288                 * is unnecessarily slow, but we can fix that later on.
1289                 */
1290                if (swap_count(*swap_map) &&
1291                     PageDirty(page) && PageSwapCache(page)) {
1292                        struct writeback_control wbc = {
1293                                .sync_mode = WB_SYNC_NONE,
1294                        };
1295
1296                        swap_writepage(page, &wbc);
1297                        lock_page(page);
1298                        wait_on_page_writeback(page);
1299                }
1300
1301                /*
1302                 * It is conceivable that a racing task removed this page from
1303                 * swap cache just before we acquired the page lock at the top,
1304                 * or while we dropped it in unuse_mm().  The page might even
1305                 * be back in swap cache on another swap area: that we must not
1306                 * delete, since it may not have been written out to swap yet.
1307                 */
1308                if (PageSwapCache(page) &&
1309                    likely(page_private(page) == entry.val))
1310                        delete_from_swap_cache(page);
1311
1312                /*
1313                 * So we could skip searching mms once swap count went
1314                 * to 1, we did not mark any present ptes as dirty: must
1315                 * mark page dirty so shrink_page_list will preserve it.
1316                 */
1317                SetPageDirty(page);
1318                unlock_page(page);
1319                page_cache_release(page);
1320
1321                /*
1322                 * Make sure that we aren't completely killing
1323                 * interactive performance.
1324                 */
1325                cond_resched();
1326                if (frontswap && pages_to_unuse > 0) {
1327                        if (!--pages_to_unuse)
1328                                break;
1329                }
1330        }
1331
1332        mmput(start_mm);
1333        return retval;
1334}
1335
1336/*
1337 * After a successful try_to_unuse, if no swap is now in use, we know
1338 * we can empty the mmlist.  swap_lock must be held on entry and exit.
1339 * Note that mmlist_lock nests inside swap_lock, and an mm must be
1340 * added to the mmlist just after page_duplicate - before would be racy.
1341 */
1342static void drain_mmlist(void)
1343{
1344        struct list_head *p, *next;
1345        unsigned int type;
1346
1347        for (type = 0; type < nr_swapfiles; type++)
1348                if (swap_info[type]->inuse_pages)
1349                        return;
1350        spin_lock(&mmlist_lock);
1351        list_for_each_safe(p, next, &init_mm.mmlist)
1352                list_del_init(p);
1353        spin_unlock(&mmlist_lock);
1354}
1355
1356/*
1357 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1358 * corresponds to page offset for the specified swap entry.
1359 * Note that the type of this function is sector_t, but it returns page offset
1360 * into the bdev, not sector offset.
1361 */
1362static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1363{
1364        struct swap_info_struct *sis;
1365        struct swap_extent *start_se;
1366        struct swap_extent *se;
1367        pgoff_t offset;
1368
1369        sis = swap_info[swp_type(entry)];
1370        *bdev = sis->bdev;
1371
1372        offset = swp_offset(entry);
1373        start_se = sis->curr_swap_extent;
1374        se = start_se;
1375
1376        for ( ; ; ) {
1377                struct list_head *lh;
1378
1379                if (se->start_page <= offset &&
1380                                offset < (se->start_page + se->nr_pages)) {
1381                        return se->start_block + (offset - se->start_page);
1382                }
1383                lh = se->list.next;
1384                se = list_entry(lh, struct swap_extent, list);
1385                sis->curr_swap_extent = se;
1386                BUG_ON(se == start_se);         /* It *must* be present */
1387        }
1388}
1389
1390/*
1391 * Returns the page offset into bdev for the specified page's swap entry.
1392 */
1393sector_t map_swap_page(struct page *page, struct block_device **bdev)
1394{
1395        swp_entry_t entry;
1396        entry.val = page_private(page);
1397        return map_swap_entry(entry, bdev);
1398}
1399
1400/*
1401 * Free all of a swapdev's extent information
1402 */
1403static void destroy_swap_extents(struct swap_info_struct *sis)
1404{
1405        while (!list_empty(&sis->first_swap_extent.list)) {
1406                struct swap_extent *se;
1407
1408                se = list_entry(sis->first_swap_extent.list.next,
1409                                struct swap_extent, list);
1410                list_del(&se->list);
1411                kfree(se);
1412        }
1413
1414        if (sis->flags & SWP_FILE) {
1415                struct file *swap_file = sis->swap_file;
1416                struct address_space *mapping = swap_file->f_mapping;
1417
1418                sis->flags &= ~SWP_FILE;
1419                mapping->a_ops->swap_deactivate(swap_file);
1420        }
1421}
1422
1423/*
1424 * Add a block range (and the corresponding page range) into this swapdev's
1425 * extent list.  The extent list is kept sorted in page order.
1426 *
1427 * This function rather assumes that it is called in ascending page order.
1428 */
1429int
1430add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1431                unsigned long nr_pages, sector_t start_block)
1432{
1433        struct swap_extent *se;
1434        struct swap_extent *new_se;
1435        struct list_head *lh;
1436
1437        if (start_page == 0) {
1438                se = &sis->first_swap_extent;
1439                sis->curr_swap_extent = se;
1440                se->start_page = 0;
1441                se->nr_pages = nr_pages;
1442                se->start_block = start_block;
1443                return 1;
1444        } else {
1445                lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1446                se = list_entry(lh, struct swap_extent, list);
1447                BUG_ON(se->start_page + se->nr_pages != start_page);
1448                if (se->start_block + se->nr_pages == start_block) {
1449                        /* Merge it */
1450                        se->nr_pages += nr_pages;
1451                        return 0;
1452                }
1453        }
1454
1455        /*
1456         * No merge.  Insert a new extent, preserving ordering.
1457         */
1458        new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1459        if (new_se == NULL)
1460                return -ENOMEM;
1461        new_se->start_page = start_page;
1462        new_se->nr_pages = nr_pages;
1463        new_se->start_block = start_block;
1464
1465        list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1466        return 1;
1467}
1468
1469/*
1470 * A `swap extent' is a simple thing which maps a contiguous range of pages
1471 * onto a contiguous range of disk blocks.  An ordered list of swap extents
1472 * is built at swapon time and is then used at swap_writepage/swap_readpage
1473 * time for locating where on disk a page belongs.
1474 *
1475 * If the swapfile is an S_ISBLK block device, a single extent is installed.
1476 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1477 * swap files identically.
1478 *
1479 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1480 * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1481 * swapfiles are handled *identically* after swapon time.
1482 *
1483 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1484 * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1485 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1486 * requirements, they are simply tossed out - we will never use those blocks
1487 * for swapping.
1488 *
1489 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1490 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1491 * which will scribble on the fs.
1492 *
1493 * The amount of disk space which a single swap extent represents varies.
1494 * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1495 * extents in the list.  To avoid much list walking, we cache the previous
1496 * search location in `curr_swap_extent', and start new searches from there.
1497 * This is extremely effective.  The average number of iterations in
1498 * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1499 */
1500static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1501{
1502        struct file *swap_file = sis->swap_file;
1503        struct address_space *mapping = swap_file->f_mapping;
1504        struct inode *inode = mapping->host;
1505        int ret;
1506
1507        if (S_ISBLK(inode->i_mode)) {
1508                ret = add_swap_extent(sis, 0, sis->max, 0);
1509                *span = sis->pages;
1510                return ret;
1511        }
1512
1513        if (mapping->a_ops->swap_activate) {
1514                ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1515                if (!ret) {
1516                        sis->flags |= SWP_FILE;
1517                        ret = add_swap_extent(sis, 0, sis->max, 0);
1518                        *span = sis->pages;
1519                }
1520                return ret;
1521        }
1522
1523        return generic_swapfile_activate(sis, swap_file, span);
1524}
1525
1526static void _enable_swap_info(struct swap_info_struct *p, int prio,
1527                                unsigned char *swap_map)
1528{
1529        int i, prev;
1530
1531        if (prio >= 0)
1532                p->prio = prio;
1533        else
1534                p->prio = --least_priority;
1535        p->swap_map = swap_map;
1536        p->flags |= SWP_WRITEOK;
1537        atomic_long_add(p->pages, &nr_swap_pages);
1538        total_swap_pages += p->pages;
1539
1540        /* insert swap space into swap_list: */
1541        prev = -1;
1542        for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1543                if (p->prio >= swap_info[i]->prio)
1544                        break;
1545                prev = i;
1546        }
1547        p->next = i;
1548        if (prev < 0)
1549                swap_list.head = swap_list.next = p->type;
1550        else
1551                swap_info[prev]->next = p->type;
1552}
1553
1554static void enable_swap_info(struct swap_info_struct *p, int prio,
1555                                unsigned char *swap_map,
1556                                unsigned long *frontswap_map)
1557{
1558        frontswap_init(p->type, frontswap_map);
1559        spin_lock(&swap_lock);
1560        spin_lock(&p->lock);
1561         _enable_swap_info(p, prio, swap_map);
1562        spin_unlock(&p->lock);
1563        spin_unlock(&swap_lock);
1564}
1565
1566static void reinsert_swap_info(struct swap_info_struct *p)
1567{
1568        spin_lock(&swap_lock);
1569        spin_lock(&p->lock);
1570        _enable_swap_info(p, p->prio, p->swap_map);
1571        spin_unlock(&p->lock);
1572        spin_unlock(&swap_lock);
1573}
1574
1575SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1576{
1577        struct swap_info_struct *p = NULL;
1578        unsigned char *swap_map;
1579        unsigned long *frontswap_map;
1580        struct file *swap_file, *victim;
1581        struct address_space *mapping;
1582        struct inode *inode;
1583        struct filename *pathname;
1584        int i, type, prev;
1585        int err;
1586
1587        if (!capable(CAP_SYS_ADMIN))
1588                return -EPERM;
1589
1590        BUG_ON(!current->mm);
1591
1592        pathname = getname(specialfile);
1593        if (IS_ERR(pathname))
1594                return PTR_ERR(pathname);
1595
1596        victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1597        err = PTR_ERR(victim);
1598        if (IS_ERR(victim))
1599                goto out;
1600
1601        mapping = victim->f_mapping;
1602        prev = -1;
1603        spin_lock(&swap_lock);
1604        for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1605                p = swap_info[type];
1606                if (p->flags & SWP_WRITEOK) {
1607                        if (p->swap_file->f_mapping == mapping)
1608                                break;
1609                }
1610                prev = type;
1611        }
1612        if (type < 0) {
1613                err = -EINVAL;
1614                spin_unlock(&swap_lock);
1615                goto out_dput;
1616        }
1617        if (!security_vm_enough_memory_mm(current->mm, p->pages))
1618                vm_unacct_memory(p->pages);
1619        else {
1620                err = -ENOMEM;
1621                spin_unlock(&swap_lock);
1622                goto out_dput;
1623        }
1624        if (prev < 0)
1625                swap_list.head = p->next;
1626        else
1627                swap_info[prev]->next = p->next;
1628        if (type == swap_list.next) {
1629                /* just pick something that's safe... */
1630                swap_list.next = swap_list.head;
1631        }
1632        spin_lock(&p->lock);
1633        if (p->prio < 0) {
1634                for (i = p->next; i >= 0; i = swap_info[i]->next)
1635                        swap_info[i]->prio = p->prio--;
1636                least_priority++;
1637        }
1638        atomic_long_sub(p->pages, &nr_swap_pages);
1639        total_swap_pages -= p->pages;
1640        p->flags &= ~SWP_WRITEOK;
1641        spin_unlock(&p->lock);
1642        spin_unlock(&swap_lock);
1643
1644        set_current_oom_origin();
1645        err = try_to_unuse(type, false, 0); /* force all pages to be unused */
1646        clear_current_oom_origin();
1647
1648        if (err) {
1649                /* re-insert swap space back into swap_list */
1650                reinsert_swap_info(p);
1651                goto out_dput;
1652        }
1653
1654        destroy_swap_extents(p);
1655        if (p->flags & SWP_CONTINUED)
1656                free_swap_count_continuations(p);
1657
1658        mutex_lock(&swapon_mutex);
1659        spin_lock(&swap_lock);
1660        spin_lock(&p->lock);
1661        drain_mmlist();
1662
1663        /* wait for anyone still in scan_swap_map */
1664        p->highest_bit = 0;             /* cuts scans short */
1665        while (p->flags >= SWP_SCANNING) {
1666                spin_unlock(&p->lock);
1667                spin_unlock(&swap_lock);
1668                schedule_timeout_uninterruptible(1);
1669                spin_lock(&swap_lock);
1670                spin_lock(&p->lock);
1671        }
1672
1673        swap_file = p->swap_file;
1674        p->swap_file = NULL;
1675        p->max = 0;
1676        swap_map = p->swap_map;
1677        p->swap_map = NULL;
1678        p->flags = 0;
1679        frontswap_map = frontswap_map_get(p);
1680        frontswap_map_set(p, NULL);
1681        spin_unlock(&p->lock);
1682        spin_unlock(&swap_lock);
1683        frontswap_invalidate_area(type);
1684        mutex_unlock(&swapon_mutex);
1685        vfree(swap_map);
1686        vfree(frontswap_map);
1687        /* Destroy swap account informatin */
1688        swap_cgroup_swapoff(type);
1689
1690        inode = mapping->host;
1691        if (S_ISBLK(inode->i_mode)) {
1692                struct block_device *bdev = I_BDEV(inode);
1693                set_blocksize(bdev, p->old_block_size);
1694                blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1695        } else {
1696                mutex_lock(&inode->i_mutex);
1697                inode->i_flags &= ~S_SWAPFILE;
1698                mutex_unlock(&inode->i_mutex);
1699        }
1700        filp_close(swap_file, NULL);
1701        err = 0;
1702        atomic_inc(&proc_poll_event);
1703        wake_up_interruptible(&proc_poll_wait);
1704
1705out_dput:
1706        filp_close(victim, NULL);
1707out:
1708        putname(pathname);
1709        return err;
1710}
1711
1712#ifdef CONFIG_PROC_FS
1713static unsigned swaps_poll(struct file *file, poll_table *wait)
1714{
1715        struct seq_file *seq = file->private_data;
1716
1717        poll_wait(file, &proc_poll_wait, wait);
1718
1719        if (seq->poll_event != atomic_read(&proc_poll_event)) {
1720                seq->poll_event = atomic_read(&proc_poll_event);
1721                return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1722        }
1723
1724        return POLLIN | POLLRDNORM;
1725}
1726
1727/* iterator */
1728static void *swap_start(struct seq_file *swap, loff_t *pos)
1729{
1730        struct swap_info_struct *si;
1731        int type;
1732        loff_t l = *pos;
1733
1734        mutex_lock(&swapon_mutex);
1735
1736        if (!l)
1737                return SEQ_START_TOKEN;
1738
1739        for (type = 0; type < nr_swapfiles; type++) {
1740                smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1741                si = swap_info[type];
1742                if (!(si->flags & SWP_USED) || !si->swap_map)
1743                        continue;
1744                if (!--l)
1745                        return si;
1746        }
1747
1748        return NULL;
1749}
1750
1751static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1752{
1753        struct swap_info_struct *si = v;
1754        int type;
1755
1756        if (v == SEQ_START_TOKEN)
1757                type = 0;
1758        else
1759                type = si->type + 1;
1760
1761        for (; type < nr_swapfiles; type++) {
1762                smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1763                si = swap_info[type];
1764                if (!(si->flags & SWP_USED) || !si->swap_map)
1765                        continue;
1766                ++*pos;
1767                return si;
1768        }
1769
1770        return NULL;
1771}
1772
1773static void swap_stop(struct seq_file *swap, void *v)
1774{
1775        mutex_unlock(&swapon_mutex);
1776}
1777
1778static int swap_show(struct seq_file *swap, void *v)
1779{
1780        struct swap_info_struct *si = v;
1781        struct file *file;
1782        int len;
1783
1784        if (si == SEQ_START_TOKEN) {
1785                seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1786                return 0;
1787        }
1788
1789        file = si->swap_file;
1790        len = seq_path(swap, &file->f_path, " \t\n\\");
1791        seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1792                        len < 40 ? 40 - len : 1, " ",
1793                        S_ISBLK(file_inode(file)->i_mode) ?
1794                                "partition" : "file\t",
1795                        si->pages << (PAGE_SHIFT - 10),
1796                        si->inuse_pages << (PAGE_SHIFT - 10),
1797                        si->prio);
1798        return 0;
1799}
1800
1801static const struct seq_operations swaps_op = {
1802        .start =        swap_start,
1803        .next =         swap_next,
1804        .stop =         swap_stop,
1805        .show =         swap_show
1806};
1807
1808static int swaps_open(struct inode *inode, struct file *file)
1809{
1810        struct seq_file *seq;
1811        int ret;
1812
1813        ret = seq_open(file, &swaps_op);
1814        if (ret)
1815                return ret;
1816
1817        seq = file->private_data;
1818        seq->poll_event = atomic_read(&proc_poll_event);
1819        return 0;
1820}
1821
1822static const struct file_operations proc_swaps_operations = {
1823        .open           = swaps_open,
1824        .read           = seq_read,
1825        .llseek         = seq_lseek,
1826        .release        = seq_release,
1827        .poll           = swaps_poll,
1828};
1829
1830static int __init procswaps_init(void)
1831{
1832        proc_create("swaps", 0, NULL, &proc_swaps_operations);
1833        return 0;
1834}
1835__initcall(procswaps_init);
1836#endif /* CONFIG_PROC_FS */
1837
1838#ifdef MAX_SWAPFILES_CHECK
1839static int __init max_swapfiles_check(void)
1840{
1841        MAX_SWAPFILES_CHECK();
1842        return 0;
1843}
1844late_initcall(max_swapfiles_check);
1845#endif
1846
1847static struct swap_info_struct *alloc_swap_info(void)
1848{
1849        struct swap_info_struct *p;
1850        unsigned int type;
1851
1852        p = kzalloc(sizeof(*p), GFP_KERNEL);
1853        if (!p)
1854                return ERR_PTR(-ENOMEM);
1855
1856        spin_lock(&swap_lock);
1857        for (type = 0; type < nr_swapfiles; type++) {
1858                if (!(swap_info[type]->flags & SWP_USED))
1859                        break;
1860        }
1861        if (type >= MAX_SWAPFILES) {
1862                spin_unlock(&swap_lock);
1863                kfree(p);
1864                return ERR_PTR(-EPERM);
1865        }
1866        if (type >= nr_swapfiles) {
1867                p->type = type;
1868                swap_info[type] = p;
1869                /*
1870                 * Write swap_info[type] before nr_swapfiles, in case a
1871                 * racing procfs swap_start() or swap_next() is reading them.
1872                 * (We never shrink nr_swapfiles, we never free this entry.)
1873                 */
1874                smp_wmb();
1875                nr_swapfiles++;
1876        } else {
1877                kfree(p);
1878                p = swap_info[type];
1879                /*
1880                 * Do not memset this entry: a racing procfs swap_next()
1881                 * would be relying on p->type to remain valid.
1882                 */
1883        }
1884        INIT_LIST_HEAD(&p->first_swap_extent.list);
1885        p->flags = SWP_USED;
1886        p->next = -1;
1887        spin_unlock(&swap_lock);
1888        spin_lock_init(&p->lock);
1889
1890        return p;
1891}
1892
1893static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1894{
1895        int error;
1896
1897        if (S_ISBLK(inode->i_mode)) {
1898                p->bdev = bdgrab(I_BDEV(inode));
1899                error = blkdev_get(p->bdev,
1900                                   FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1901                                   sys_swapon);
1902                if (error < 0) {
1903                        p->bdev = NULL;
1904                        return -EINVAL;
1905                }
1906                p->old_block_size = block_size(p->bdev);
1907                error = set_blocksize(p->bdev, PAGE_SIZE);
1908                if (error < 0)
1909                        return error;
1910                p->flags |= SWP_BLKDEV;
1911        } else if (S_ISREG(inode->i_mode)) {
1912                p->bdev = inode->i_sb->s_bdev;
1913                mutex_lock(&inode->i_mutex);
1914                if (IS_SWAPFILE(inode))
1915                        return -EBUSY;
1916        } else
1917                return -EINVAL;
1918
1919        return 0;
1920}
1921
1922static unsigned long read_swap_header(struct swap_info_struct *p,
1923                                        union swap_header *swap_header,
1924                                        struct inode *inode)
1925{
1926        int i;
1927        unsigned long maxpages;
1928        unsigned long swapfilepages;
1929
1930        if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1931                printk(KERN_ERR "Unable to find swap-space signature\n");
1932                return 0;
1933        }
1934
1935        /* swap partition endianess hack... */
1936        if (swab32(swap_header->info.version) == 1) {
1937                swab32s(&swap_header->info.version);
1938                swab32s(&swap_header->info.last_page);
1939                swab32s(&swap_header->info.nr_badpages);
1940                for (i = 0; i < swap_header->info.nr_badpages; i++)
1941                        swab32s(&swap_header->info.badpages[i]);
1942        }
1943        /* Check the swap header's sub-version */
1944        if (swap_header->info.version != 1) {
1945                printk(KERN_WARNING
1946                       "Unable to handle swap header version %d\n",
1947                       swap_header->info.version);
1948                return 0;
1949        }
1950
1951        p->lowest_bit  = 1;
1952        p->cluster_next = 1;
1953        p->cluster_nr = 0;
1954
1955        /*
1956         * Find out how many pages are allowed for a single swap
1957         * device. There are two limiting factors: 1) the number
1958         * of bits for the swap offset in the swp_entry_t type, and
1959         * 2) the number of bits in the swap pte as defined by the
1960         * different architectures. In order to find the
1961         * largest possible bit mask, a swap entry with swap type 0
1962         * and swap offset ~0UL is created, encoded to a swap pte,
1963         * decoded to a swp_entry_t again, and finally the swap
1964         * offset is extracted. This will mask all the bits from
1965         * the initial ~0UL mask that can't be encoded in either
1966         * the swp_entry_t or the architecture definition of a
1967         * swap pte.
1968         */
1969        maxpages = swp_offset(pte_to_swp_entry(
1970                        swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
1971        if (maxpages > swap_header->info.last_page) {
1972                maxpages = swap_header->info.last_page + 1;
1973                /* p->max is an unsigned int: don't overflow it */
1974                if ((unsigned int)maxpages == 0)
1975                        maxpages = UINT_MAX;
1976        }
1977        p->highest_bit = maxpages - 1;
1978
1979        if (!maxpages)
1980                return 0;
1981        swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1982        if (swapfilepages && maxpages > swapfilepages) {
1983                printk(KERN_WARNING
1984                       "Swap area shorter than signature indicates\n");
1985                return 0;
1986        }
1987        if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1988                return 0;
1989        if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1990                return 0;
1991
1992        return maxpages;
1993}
1994
1995static int setup_swap_map_and_extents(struct swap_info_struct *p,
1996                                        union swap_header *swap_header,
1997                                        unsigned char *swap_map,
1998                                        unsigned long maxpages,
1999                                        sector_t *span)
2000{
2001        int i;
2002        unsigned int nr_good_pages;
2003        int nr_extents;
2004
2005        nr_good_pages = maxpages - 1;   /* omit header page */
2006
2007        for (i = 0; i < swap_header->info.nr_badpages; i++) {
2008                unsigned int page_nr = swap_header->info.badpages[i];
2009                if (page_nr == 0 || page_nr > swap_header->info.last_page)
2010                        return -EINVAL;
2011                if (page_nr < maxpages) {
2012                        swap_map[page_nr] = SWAP_MAP_BAD;
2013                        nr_good_pages--;
2014                }
2015        }
2016
2017        if (nr_good_pages) {
2018                swap_map[0] = SWAP_MAP_BAD;
2019                p->max = maxpages;
2020                p->pages = nr_good_pages;
2021                nr_extents = setup_swap_extents(p, span);
2022                if (nr_extents < 0)
2023                        return nr_extents;
2024                nr_good_pages = p->pages;
2025        }
2026        if (!nr_good_pages) {
2027                printk(KERN_WARNING "Empty swap-file\n");
2028                return -EINVAL;
2029        }
2030
2031        return nr_extents;
2032}
2033
2034/*
2035 * Helper to sys_swapon determining if a given swap
2036 * backing device queue supports DISCARD operations.
2037 */
2038static bool swap_discardable(struct swap_info_struct *si)
2039{
2040        struct request_queue *q = bdev_get_queue(si->bdev);
2041
2042        if (!q || !blk_queue_discard(q))
2043                return false;
2044
2045        return true;
2046}
2047
2048SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2049{
2050        struct swap_info_struct *p;
2051        struct filename *name;
2052        struct file *swap_file = NULL;
2053        struct address_space *mapping;
2054        int i;
2055        int prio;
2056        int error;
2057        union swap_header *swap_header;
2058        int nr_extents;
2059        sector_t span;
2060        unsigned long maxpages;
2061        unsigned char *swap_map = NULL;
2062        unsigned long *frontswap_map = NULL;
2063        struct page *page = NULL;
2064        struct inode *inode = NULL;
2065
2066        if (swap_flags & ~SWAP_FLAGS_VALID)
2067                return -EINVAL;
2068
2069        if (!capable(CAP_SYS_ADMIN))
2070                return -EPERM;
2071
2072        p = alloc_swap_info();
2073        if (IS_ERR(p))
2074                return PTR_ERR(p);
2075
2076        name = getname(specialfile);
2077        if (IS_ERR(name)) {
2078                error = PTR_ERR(name);
2079                name = NULL;
2080                goto bad_swap;
2081        }
2082        swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2083        if (IS_ERR(swap_file)) {
2084                error = PTR_ERR(swap_file);
2085                swap_file = NULL;
2086                goto bad_swap;
2087        }
2088
2089        p->swap_file = swap_file;
2090        mapping = swap_file->f_mapping;
2091
2092        for (i = 0; i < nr_swapfiles; i++) {
2093                struct swap_info_struct *q = swap_info[i];
2094
2095                if (q == p || !q->swap_file)
2096                        continue;
2097                if (mapping == q->swap_file->f_mapping) {
2098                        error = -EBUSY;
2099                        goto bad_swap;
2100                }
2101        }
2102
2103        inode = mapping->host;
2104        /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2105        error = claim_swapfile(p, inode);
2106        if (unlikely(error))
2107                goto bad_swap;
2108
2109        /*
2110         * Read the swap header.
2111         */
2112        if (!mapping->a_ops->readpage) {
2113                error = -EINVAL;
2114                goto bad_swap;
2115        }
2116        page = read_mapping_page(mapping, 0, swap_file);
2117        if (IS_ERR(page)) {
2118                error = PTR_ERR(page);
2119                goto bad_swap;
2120        }
2121        swap_header = kmap(page);
2122
2123        maxpages = read_swap_header(p, swap_header, inode);
2124        if (unlikely(!maxpages)) {
2125                error = -EINVAL;
2126                goto bad_swap;
2127        }
2128
2129        /* OK, set up the swap map and apply the bad block list */
2130        swap_map = vzalloc(maxpages);
2131        if (!swap_map) {
2132                error = -ENOMEM;
2133                goto bad_swap;
2134        }
2135
2136        error = swap_cgroup_swapon(p->type, maxpages);
2137        if (error)
2138                goto bad_swap;
2139
2140        nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2141                maxpages, &span);
2142        if (unlikely(nr_extents < 0)) {
2143                error = nr_extents;
2144                goto bad_swap;
2145        }
2146        /* frontswap enabled? set up bit-per-page map for frontswap */
2147        if (frontswap_enabled)
2148                frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2149
2150        if (p->bdev) {
2151                if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2152                        p->flags |= SWP_SOLIDSTATE;
2153                        p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2154                }
2155
2156                if ((swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
2157                        /*
2158                         * When discard is enabled for swap with no particular
2159                         * policy flagged, we set all swap discard flags here in
2160                         * order to sustain backward compatibility with older
2161                         * swapon(8) releases.
2162                         */
2163                        p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
2164                                     SWP_PAGE_DISCARD);
2165
2166                        /*
2167                         * By flagging sys_swapon, a sysadmin can tell us to
2168                         * either do single-time area discards only, or to just
2169                         * perform discards for released swap page-clusters.
2170                         * Now it's time to adjust the p->flags accordingly.
2171                         */
2172                        if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
2173                                p->flags &= ~SWP_PAGE_DISCARD;
2174                        else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
2175                                p->flags &= ~SWP_AREA_DISCARD;
2176
2177                        /* issue a swapon-time discard if it's still required */
2178                        if (p->flags & SWP_AREA_DISCARD) {
2179                                int err = discard_swap(p);
2180                                if (unlikely(err))
2181                                        printk(KERN_ERR
2182                                               "swapon: discard_swap(%p): %d\n",
2183                                                p, err);
2184                        }
2185                }
2186        }
2187
2188        mutex_lock(&swapon_mutex);
2189        prio = -1;
2190        if (swap_flags & SWAP_FLAG_PREFER)
2191                prio =
2192                  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2193        enable_swap_info(p, prio, swap_map, frontswap_map);
2194
2195        printk(KERN_INFO "Adding %uk swap on %s.  "
2196                        "Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
2197                p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2198                nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2199                (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2200                (p->flags & SWP_DISCARDABLE) ? "D" : "",
2201                (p->flags & SWP_AREA_DISCARD) ? "s" : "",
2202                (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
2203                (frontswap_map) ? "FS" : "");
2204
2205        mutex_unlock(&swapon_mutex);
2206        atomic_inc(&proc_poll_event);
2207        wake_up_interruptible(&proc_poll_wait);
2208
2209        if (S_ISREG(inode->i_mode))
2210                inode->i_flags |= S_SWAPFILE;
2211        error = 0;
2212        goto out;
2213bad_swap:
2214        if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2215                set_blocksize(p->bdev, p->old_block_size);
2216                blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2217        }
2218        destroy_swap_extents(p);
2219        swap_cgroup_swapoff(p->type);
2220        spin_lock(&swap_lock);
2221        p->swap_file = NULL;
2222        p->flags = 0;
2223        spin_unlock(&swap_lock);
2224        vfree(swap_map);
2225        if (swap_file) {
2226                if (inode && S_ISREG(inode->i_mode)) {
2227                        mutex_unlock(&inode->i_mutex);
2228                        inode = NULL;
2229                }
2230                filp_close(swap_file, NULL);
2231        }
2232out:
2233        if (page && !IS_ERR(page)) {
2234                kunmap(page);
2235                page_cache_release(page);
2236        }
2237        if (name)
2238                putname(name);
2239        if (inode && S_ISREG(inode->i_mode))
2240                mutex_unlock(&inode->i_mutex);
2241        return error;
2242}
2243
2244void si_swapinfo(struct sysinfo *val)
2245{
2246        unsigned int type;
2247        unsigned long nr_to_be_unused = 0;
2248
2249        spin_lock(&swap_lock);
2250        for (type = 0; type < nr_swapfiles; type++) {
2251                struct swap_info_struct *si = swap_info[type];
2252
2253                if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2254                        nr_to_be_unused += si->inuse_pages;
2255        }
2256        val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2257        val->totalswap = total_swap_pages + nr_to_be_unused;
2258        spin_unlock(&swap_lock);
2259}
2260
2261/*
2262 * Verify that a swap entry is valid and increment its swap map count.
2263 *
2264 * Returns error code in following case.
2265 * - success -> 0
2266 * - swp_entry is invalid -> EINVAL
2267 * - swp_entry is migration entry -> EINVAL
2268 * - swap-cache reference is requested but there is already one. -> EEXIST
2269 * - swap-cache reference is requested but the entry is not used. -> ENOENT
2270 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2271 */
2272static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2273{
2274        struct swap_info_struct *p;
2275        unsigned long offset, type;
2276        unsigned char count;
2277        unsigned char has_cache;
2278        int err = -EINVAL;
2279
2280        if (non_swap_entry(entry))
2281                goto out;
2282
2283        type = swp_type(entry);
2284        if (type >= nr_swapfiles)
2285                goto bad_file;
2286        p = swap_info[type];
2287        offset = swp_offset(entry);
2288
2289        spin_lock(&p->lock);
2290        if (unlikely(offset >= p->max))
2291                goto unlock_out;
2292
2293        count = p->swap_map[offset];
2294        has_cache = count & SWAP_HAS_CACHE;
2295        count &= ~SWAP_HAS_CACHE;
2296        err = 0;
2297
2298        if (usage == SWAP_HAS_CACHE) {
2299
2300                /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2301                if (!has_cache && count)
2302                        has_cache = SWAP_HAS_CACHE;
2303                else if (has_cache)             /* someone else added cache */
2304                        err = -EEXIST;
2305                else                            /* no users remaining */
2306                        err = -ENOENT;
2307
2308        } else if (count || has_cache) {
2309
2310                if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2311                        count += usage;
2312                else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2313                        err = -EINVAL;
2314                else if (swap_count_continued(p, offset, count))
2315                        count = COUNT_CONTINUED;
2316                else
2317                        err = -ENOMEM;
2318        } else
2319                err = -ENOENT;                  /* unused swap entry */
2320
2321        p->swap_map[offset] = count | has_cache;
2322
2323unlock_out:
2324        spin_unlock(&p->lock);
2325out:
2326        return err;
2327
2328bad_file:
2329        printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2330        goto out;
2331}
2332
2333/*
2334 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2335 * (in which case its reference count is never incremented).
2336 */
2337void swap_shmem_alloc(swp_entry_t entry)
2338{
2339        __swap_duplicate(entry, SWAP_MAP_SHMEM);
2340}
2341
2342/*
2343 * Increase reference count of swap entry by 1.
2344 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2345 * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2346 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2347 * might occur if a page table entry has got corrupted.
2348 */
2349int swap_duplicate(swp_entry_t entry)
2350{
2351        int err = 0;
2352
2353        while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2354                err = add_swap_count_continuation(entry, GFP_ATOMIC);
2355        return err;
2356}
2357
2358/*
2359 * @entry: swap entry for which we allocate swap cache.
2360 *
2361 * Called when allocating swap cache for existing swap entry,
2362 * This can return error codes. Returns 0 at success.
2363 * -EBUSY means there is a swap cache.
2364 * Note: return code is different from swap_duplicate().
2365 */
2366int swapcache_prepare(swp_entry_t entry)
2367{
2368        return __swap_duplicate(entry, SWAP_HAS_CACHE);
2369}
2370
2371struct swap_info_struct *page_swap_info(struct page *page)
2372{
2373        swp_entry_t swap = { .val = page_private(page) };
2374        BUG_ON(!PageSwapCache(page));
2375        return swap_info[swp_type(swap)];
2376}
2377
2378/*
2379 * out-of-line __page_file_ methods to avoid include hell.
2380 */
2381struct address_space *__page_file_mapping(struct page *page)
2382{
2383        VM_BUG_ON(!PageSwapCache(page));
2384        return page_swap_info(page)->swap_file->f_mapping;
2385}
2386EXPORT_SYMBOL_GPL(__page_file_mapping);
2387
2388pgoff_t __page_file_index(struct page *page)
2389{
2390        swp_entry_t swap = { .val = page_private(page) };
2391        VM_BUG_ON(!PageSwapCache(page));
2392        return swp_offset(swap);
2393}
2394EXPORT_SYMBOL_GPL(__page_file_index);
2395
2396/*
2397 * add_swap_count_continuation - called when a swap count is duplicated
2398 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2399 * page of the original vmalloc'ed swap_map, to hold the continuation count
2400 * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2401 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2402 *
2403 * These continuation pages are seldom referenced: the common paths all work
2404 * on the original swap_map, only referring to a continuation page when the
2405 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2406 *
2407 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2408 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2409 * can be called after dropping locks.
2410 */
2411int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2412{
2413        struct swap_info_struct *si;
2414        struct page *head;
2415        struct page *page;
2416        struct page *list_page;
2417        pgoff_t offset;
2418        unsigned char count;
2419
2420        /*
2421         * When debugging, it's easier to use __GFP_ZERO here; but it's better
2422         * for latency not to zero a page while GFP_ATOMIC and holding locks.
2423         */
2424        page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2425
2426        si = swap_info_get(entry);
2427        if (!si) {
2428                /*
2429                 * An acceptable race has occurred since the failing
2430                 * __swap_duplicate(): the swap entry has been freed,
2431                 * perhaps even the whole swap_map cleared for swapoff.
2432                 */
2433                goto outer;
2434        }
2435
2436        offset = swp_offset(entry);
2437        count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2438
2439        if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2440                /*
2441                 * The higher the swap count, the more likely it is that tasks
2442                 * will race to add swap count continuation: we need to avoid
2443                 * over-provisioning.
2444                 */
2445                goto out;
2446        }
2447
2448        if (!page) {
2449                spin_unlock(&si->lock);
2450                return -ENOMEM;
2451        }
2452
2453        /*
2454         * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2455         * no architecture is using highmem pages for kernel pagetables: so it
2456         * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2457         */
2458        head = vmalloc_to_page(si->swap_map + offset);
2459        offset &= ~PAGE_MASK;
2460
2461        /*
2462         * Page allocation does not initialize the page's lru field,
2463         * but it does always reset its private field.
2464         */
2465        if (!page_private(head)) {
2466                BUG_ON(count & COUNT_CONTINUED);
2467                INIT_LIST_HEAD(&head->lru);
2468                set_page_private(head, SWP_CONTINUED);
2469                si->flags |= SWP_CONTINUED;
2470        }
2471
2472        list_for_each_entry(list_page, &head->lru, lru) {
2473                unsigned char *map;
2474
2475                /*
2476                 * If the previous map said no continuation, but we've found
2477                 * a continuation page, free our allocation and use this one.
2478                 */
2479                if (!(count & COUNT_CONTINUED))
2480                        goto out;
2481
2482                map = kmap_atomic(list_page) + offset;
2483                count = *map;
2484                kunmap_atomic(map);
2485
2486                /*
2487                 * If this continuation count now has some space in it,
2488                 * free our allocation and use this one.
2489                 */
2490                if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2491                        goto out;
2492        }
2493
2494        list_add_tail(&page->lru, &head->lru);
2495        page = NULL;                    /* now it's attached, don't free it */
2496out:
2497        spin_unlock(&si->lock);
2498outer:
2499        if (page)
2500                __free_page(page);
2501        return 0;
2502}
2503
2504/*
2505 * swap_count_continued - when the original swap_map count is incremented
2506 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2507 * into, carry if so, or else fail until a new continuation page is allocated;
2508 * when the original swap_map count is decremented from 0 with continuation,
2509 * borrow from the continuation and report whether it still holds more.
2510 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2511 */
2512static bool swap_count_continued(struct swap_info_struct *si,
2513                                 pgoff_t offset, unsigned char count)
2514{
2515        struct page *head;
2516        struct page *page;
2517        unsigned char *map;
2518
2519        head = vmalloc_to_page(si->swap_map + offset);
2520        if (page_private(head) != SWP_CONTINUED) {
2521                BUG_ON(count & COUNT_CONTINUED);
2522                return false;           /* need to add count continuation */
2523        }
2524
2525        offset &= ~PAGE_MASK;
2526        page = list_entry(head->lru.next, struct page, lru);
2527        map = kmap_atomic(page) + offset;
2528
2529        if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2530                goto init_map;          /* jump over SWAP_CONT_MAX checks */
2531
2532        if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2533                /*
2534                 * Think of how you add 1 to 999
2535                 */
2536                while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2537                        kunmap_atomic(map);
2538                        page = list_entry(page->lru.next, struct page, lru);
2539                        BUG_ON(page == head);
2540                        map = kmap_atomic(page) + offset;
2541                }
2542                if (*map == SWAP_CONT_MAX) {
2543                        kunmap_atomic(map);
2544                        page = list_entry(page->lru.next, struct page, lru);
2545                        if (page == head)
2546                                return false;   /* add count continuation */
2547                        map = kmap_atomic(page) + offset;
2548init_map:               *map = 0;               /* we didn't zero the page */
2549                }
2550                *map += 1;
2551                kunmap_atomic(map);
2552                page = list_entry(page->lru.prev, struct page, lru);
2553                while (page != head) {
2554                        map = kmap_atomic(page) + offset;
2555                        *map = COUNT_CONTINUED;
2556                        kunmap_atomic(map);
2557                        page = list_entry(page->lru.prev, struct page, lru);
2558                }
2559                return true;                    /* incremented */
2560
2561        } else {                                /* decrementing */
2562                /*
2563                 * Think of how you subtract 1 from 1000
2564                 */
2565                BUG_ON(count != COUNT_CONTINUED);
2566                while (*map == COUNT_CONTINUED) {
2567                        kunmap_atomic(map);
2568                        page = list_entry(page->lru.next, struct page, lru);
2569                        BUG_ON(page == head);
2570                        map = kmap_atomic(page) + offset;
2571                }
2572                BUG_ON(*map == 0);
2573                *map -= 1;
2574                if (*map == 0)
2575                        count = 0;
2576                kunmap_atomic(map);
2577                page = list_entry(page->lru.prev, struct page, lru);
2578                while (page != head) {
2579                        map = kmap_atomic(page) + offset;
2580                        *map = SWAP_CONT_MAX | count;
2581                        count = COUNT_CONTINUED;
2582                        kunmap_atomic(map);
2583                        page = list_entry(page->lru.prev, struct page, lru);
2584                }
2585                return count == COUNT_CONTINUED;
2586        }
2587}
2588
2589/*
2590 * free_swap_count_continuations - swapoff free all the continuation pages
2591 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2592 */
2593static void free_swap_count_continuations(struct swap_info_struct *si)
2594{
2595        pgoff_t offset;
2596
2597        for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2598                struct page *head;
2599                head = vmalloc_to_page(si->swap_map + offset);
2600                if (page_private(head)) {
2601                        struct list_head *this, *next;
2602                        list_for_each_safe(this, next, &head->lru) {
2603                                struct page *page;
2604                                page = list_entry(this, struct page, lru);
2605                                list_del(this);
2606                                __free_page(page);
2607                        }
2608                }
2609        }
2610}
2611
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