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_DISCARDABLE) {
 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_DISCARDABLE, 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
 869/*
 870 * No need to decide whether this PTE shares the swap entry with others,
 871 * just let do_wp_page work it out if a write is requested later - to
 872 * force COW, vm_page_prot omits write permission from any private vma.
 873 */
 874static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 875                unsigned long addr, swp_entry_t entry, struct page *page)
 876{
 877        struct page *swapcache;
 878        struct mem_cgroup *memcg;
 879        spinlock_t *ptl;
 880        pte_t *pte;
 881        int ret = 1;
 882
 883        swapcache = page;
 884        page = ksm_might_need_to_copy(page, vma, addr);
 885        if (unlikely(!page))
 886                return -ENOMEM;
 887
 888        if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
 889                                         GFP_KERNEL, &memcg)) {
 890                ret = -ENOMEM;
 891                goto out_nolock;
 892        }
 893
 894        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 895        if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
 896                mem_cgroup_cancel_charge_swapin(memcg);
 897                ret = 0;
 898                goto out;
 899        }
 900
 901        dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
 902        inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
 903        get_page(page);
 904        set_pte_at(vma->vm_mm, addr, pte,
 905                   pte_mkold(mk_pte(page, vma->vm_page_prot)));
 906        if (page == swapcache)
 907                page_add_anon_rmap(page, vma, addr);
 908        else /* ksm created a completely new copy */
 909                page_add_new_anon_rmap(page, vma, addr);
 910        mem_cgroup_commit_charge_swapin(page, memcg);
 911        swap_free(entry);
 912        /*
 913         * Move the page to the active list so it is not
 914         * immediately swapped out again after swapon.
 915         */
 916        activate_page(page);
 917out:
 918        pte_unmap_unlock(pte, ptl);
 919out_nolock:
 920        if (page != swapcache) {
 921                unlock_page(page);
 922                put_page(page);
 923        }
 924        return ret;
 925}
 926
 927static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 928                                unsigned long addr, unsigned long end,
 929                                swp_entry_t entry, struct page *page)
 930{
 931        pte_t swp_pte = swp_entry_to_pte(entry);
 932        pte_t *pte;
 933        int ret = 0;
 934
 935        /*
 936         * We don't actually need pte lock while scanning for swp_pte: since
 937         * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
 938         * page table while we're scanning; though it could get zapped, and on
 939         * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
 940         * of unmatched parts which look like swp_pte, so unuse_pte must
 941         * recheck under pte lock.  Scanning without pte lock lets it be
 942         * preemptible whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
 943         */
 944        pte = pte_offset_map(pmd, addr);
 945        do {
 946                /*
 947                 * swapoff spends a _lot_ of time in this loop!
 948                 * Test inline before going to call unuse_pte.
 949                 */
 950                if (unlikely(pte_same(*pte, swp_pte))) {
 951                        pte_unmap(pte);
 952                        ret = unuse_pte(vma, pmd, addr, entry, page);
 953                        if (ret)
 954                                goto out;
 955                        pte = pte_offset_map(pmd, addr);
 956                }
 957        } while (pte++, addr += PAGE_SIZE, addr != end);
 958        pte_unmap(pte - 1);
 959out:
 960        return ret;
 961}
 962
 963static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 964                                unsigned long addr, unsigned long end,
 965                                swp_entry_t entry, struct page *page)
 966{
 967        pmd_t *pmd;
 968        unsigned long next;
 969        int ret;
 970
 971        pmd = pmd_offset(pud, addr);
 972        do {
 973                next = pmd_addr_end(addr, end);
 974                if (pmd_none_or_trans_huge_or_clear_bad(pmd))
 975                        continue;
 976                ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
 977                if (ret)
 978                        return ret;
 979        } while (pmd++, addr = next, addr != end);
 980        return 0;
 981}
 982
 983static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 984                                unsigned long addr, unsigned long end,
 985                                swp_entry_t entry, struct page *page)
 986{
 987        pud_t *pud;
 988        unsigned long next;
 989        int ret;
 990
 991        pud = pud_offset(pgd, addr);
 992        do {
 993                next = pud_addr_end(addr, end);
 994                if (pud_none_or_clear_bad(pud))
 995                        continue;
 996                ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
 997                if (ret)
 998                        return ret;
 999        } while (pud++, addr = next, addr != end);
1000        return 0;
1001}
1002
1003static int unuse_vma(struct vm_area_struct *vma,
1004                                swp_entry_t entry, struct page *page)
1005{
1006        pgd_t *pgd;
1007        unsigned long addr, end, next;
1008        int ret;
1009
1010        if (page_anon_vma(page)) {
1011                addr = page_address_in_vma(page, vma);
1012                if (addr == -EFAULT)
1013                        return 0;
1014                else
1015                        end = addr + PAGE_SIZE;
1016        } else {
1017                addr = vma->vm_start;
1018                end = vma->vm_end;
1019        }
1020
1021        pgd = pgd_offset(vma->vm_mm, addr);
1022        do {
1023                next = pgd_addr_end(addr, end);
1024                if (pgd_none_or_clear_bad(pgd))
1025                        continue;
1026                ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1027                if (ret)
1028                        return ret;
1029        } while (pgd++, addr = next, addr != end);
1030        return 0;
1031}
1032
1033static int unuse_mm(struct mm_struct *mm,
1034                                swp_entry_t entry, struct page *page)
1035{
1036        struct vm_area_struct *vma;
1037        int ret = 0;
1038
1039        if (!down_read_trylock(&mm->mmap_sem)) {
1040                /*
1041                 * Activate page so shrink_inactive_list is unlikely to unmap
1042                 * its ptes while lock is dropped, so swapoff can make progress.
1043                 */
1044                activate_page(page);
1045                unlock_page(page);
1046                down_read(&mm->mmap_sem);
1047                lock_page(page);
1048        }
1049        for (vma = mm->mmap; vma; vma = vma->vm_next) {
1050                if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1051                        break;
1052        }
1053        up_read(&mm->mmap_sem);
1054        return (ret < 0)? ret: 0;
1055}
1056
1057/*
1058 * Scan swap_map (or frontswap_map if frontswap parameter is true)
1059 * from current position to next entry still in use.
1060 * Recycle to start on reaching the end, returning 0 when empty.
1061 */
1062static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1063                                        unsigned int prev, bool frontswap)
1064{
1065        unsigned int max = si->max;
1066        unsigned int i = prev;
1067        unsigned char count;
1068
1069        /*
1070         * No need for swap_lock here: we're just looking
1071         * for whether an entry is in use, not modifying it; false
1072         * hits are okay, and sys_swapoff() has already prevented new
1073         * allocations from this area (while holding swap_lock).
1074         */
1075        for (;;) {
1076                if (++i >= max) {
1077                        if (!prev) {
1078                                i = 0;
1079                                break;
1080                        }
1081                        /*
1082                         * No entries in use at top of swap_map,
1083                         * loop back to start and recheck there.
1084                         */
1085                        max = prev + 1;
1086                        prev = 0;
1087                        i = 1;
1088                }
1089                if (frontswap) {
1090                        if (frontswap_test(si, i))
1091                                break;
1092                        else
1093                                continue;
1094                }
1095                count = si->swap_map[i];
1096                if (count && swap_count(count) != SWAP_MAP_BAD)
1097                        break;
1098        }
1099        return i;
1100}
1101
1102/*
1103 * We completely avoid races by reading each swap page in advance,
1104 * and then search for the process using it.  All the necessary
1105 * page table adjustments can then be made atomically.
1106 *
1107 * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1108 * pages_to_unuse==0 means all pages; ignored if frontswap is false
1109 */
1110int try_to_unuse(unsigned int type, bool frontswap,
1111                 unsigned long pages_to_unuse)
1112{
1113        struct swap_info_struct *si = swap_info[type];
1114        struct mm_struct *start_mm;
1115        unsigned char *swap_map;
1116        unsigned char swcount;
1117        struct page *page;
1118        swp_entry_t entry;
1119        unsigned int i = 0;
1120        int retval = 0;
1121
1122        /*
1123         * When searching mms for an entry, a good strategy is to
1124         * start at the first mm we freed the previous entry from
1125         * (though actually we don't notice whether we or coincidence
1126         * freed the entry).  Initialize this start_mm with a hold.
1127         *
1128         * A simpler strategy would be to start at the last mm we
1129         * freed the previous entry from; but that would take less
1130         * advantage of mmlist ordering, which clusters forked mms
1131         * together, child after parent.  If we race with dup_mmap(), we
1132         * prefer to resolve parent before child, lest we miss entries
1133         * duplicated after we scanned child: using last mm would invert
1134         * that.
1135         */
1136        start_mm = &init_mm;
1137        atomic_inc(&init_mm.mm_users);
1138
1139        /*
1140         * Keep on scanning until all entries have gone.  Usually,
1141         * one pass through swap_map is enough, but not necessarily:
1142         * there are races when an instance of an entry might be missed.
1143         */
1144        while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1145                if (signal_pending(current)) {
1146                        retval = -EINTR;
1147                        break;
1148                }
1149
1150                /*
1151                 * Get a page for the entry, using the existing swap
1152                 * cache page if there is one.  Otherwise, get a clean
1153                 * page and read the swap into it.
1154                 */
1155                swap_map = &si->swap_map[i];
1156                entry = swp_entry(type, i);
1157                page = read_swap_cache_async(entry,
1158                                        GFP_HIGHUSER_MOVABLE, NULL, 0);
1159                if (!page) {
1160                        /*
1161                         * Either swap_duplicate() failed because entry
1162                         * has been freed independently, and will not be
1163                         * reused since sys_swapoff() already disabled
1164                         * allocation from here, or alloc_page() failed.
1165                         */
1166                        if (!*swap_map)
1167                                continue;
1168                        retval = -ENOMEM;
1169                        break;
1170                }
1171
1172                /*
1173                 * Don't hold on to start_mm if it looks like exiting.
1174                 */
1175                if (atomic_read(&start_mm->mm_users) == 1) {
1176                        mmput(start_mm);
1177                        start_mm = &init_mm;
1178                        atomic_inc(&init_mm.mm_users);
1179                }
1180
1181                /*
1182                 * Wait for and lock page.  When do_swap_page races with
1183                 * try_to_unuse, do_swap_page can handle the fault much
1184                 * faster than try_to_unuse can locate the entry.  This
1185                 * apparently redundant "wait_on_page_locked" lets try_to_unuse
1186                 * defer to do_swap_page in such a case - in some tests,
1187                 * do_swap_page and try_to_unuse repeatedly compete.
1188                 */
1189                wait_on_page_locked(page);
1190                wait_on_page_writeback(page);
1191                lock_page(page);
1192                wait_on_page_writeback(page);
1193
1194                /*
1195                 * Remove all references to entry.
1196                 */
1197                swcount = *swap_map;
1198                if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1199                        retval = shmem_unuse(entry, page);
1200                        /* page has already been unlocked and released */
1201                        if (retval < 0)
1202                                break;
1203                        continue;
1204                }
1205                if (swap_count(swcount) && start_mm != &init_mm)
1206                        retval = unuse_mm(start_mm, entry, page);
1207
1208                if (swap_count(*swap_map)) {
1209                        int set_start_mm = (*swap_map >= swcount);
1210                        struct list_head *p = &start_mm->mmlist;
1211                        struct mm_struct *new_start_mm = start_mm;
1212                        struct mm_struct *prev_mm = start_mm;
1213                        struct mm_struct *mm;
1214
1215                        atomic_inc(&new_start_mm->mm_users);
1216                        atomic_inc(&prev_mm->mm_users);
1217                        spin_lock(&mmlist_lock);
1218                        while (swap_count(*swap_map) && !retval &&
1219                                        (p = p->next) != &start_mm->mmlist) {
1220                                mm = list_entry(p, struct mm_struct, mmlist);
1221                                if (!atomic_inc_not_zero(&mm->mm_users))
1222                                        continue;
1223                                spin_unlock(&mmlist_lock);
1224                                mmput(prev_mm);
1225                                prev_mm = mm;
1226
1227                                cond_resched();
1228
1229                                swcount = *swap_map;
1230                                if (!swap_count(swcount)) /* any usage ? */
1231                                        ;
1232                                else if (mm == &init_mm)
1233                                        set_start_mm = 1;
1234                                else
1235                                        retval = unuse_mm(mm, entry, page);
1236
1237                                if (set_start_mm && *swap_map < swcount) {
1238                                        mmput(new_start_mm);
1239                                        atomic_inc(&mm->mm_users);
1240                                        new_start_mm = mm;
1241                                        set_start_mm = 0;
1242                                }
1243                                spin_lock(&mmlist_lock);
1244                        }
1245                        spin_unlock(&mmlist_lock);
1246                        mmput(prev_mm);
1247                        mmput(start_mm);
1248                        start_mm = new_start_mm;
1249                }
1250                if (retval) {
1251                        unlock_page(page);
1252                        page_cache_release(page);
1253                        break;
1254                }
1255
1256                /*
1257                 * If a reference remains (rare), we would like to leave
1258                 * the page in the swap cache; but try_to_unmap could
1259                 * then re-duplicate the entry once we drop page lock,
1260                 * so we might loop indefinitely; also, that page could
1261                 * not be swapped out to other storage meanwhile.  So:
1262                 * delete from cache even if there's another reference,
1263                 * after ensuring that the data has been saved to disk -
1264                 * since if the reference remains (rarer), it will be
1265                 * read from disk into another page.  Splitting into two
1266                 * pages would be incorrect if swap supported "shared
1267                 * private" pages, but they are handled by tmpfs files.
1268                 *
1269                 * Given how unuse_vma() targets one particular offset
1270                 * in an anon_vma, once the anon_vma has been determined,
1271                 * this splitting happens to be just what is needed to
1272                 * handle where KSM pages have been swapped out: re-reading
1273                 * is unnecessarily slow, but we can fix that later on.
1274                 */
1275                if (swap_count(*swap_map) &&
1276                     PageDirty(page) && PageSwapCache(page)) {
1277                        struct writeback_control wbc = {
1278                                .sync_mode = WB_SYNC_NONE,
1279                        };
1280
1281                        swap_writepage(page, &wbc);
1282                        lock_page(page);
1283                        wait_on_page_writeback(page);
1284                }
1285
1286                /*
1287                 * It is conceivable that a racing task removed this page from
1288                 * swap cache just before we acquired the page lock at the top,
1289                 * or while we dropped it in unuse_mm().  The page might even
1290                 * be back in swap cache on another swap area: that we must not
1291                 * delete, since it may not have been written out to swap yet.
1292                 */
1293                if (PageSwapCache(page) &&
1294                    likely(page_private(page) == entry.val))
1295                        delete_from_swap_cache(page);
1296
1297                /*
1298                 * So we could skip searching mms once swap count went
1299                 * to 1, we did not mark any present ptes as dirty: must
1300                 * mark page dirty so shrink_page_list will preserve it.
1301                 */
1302                SetPageDirty(page);
1303                unlock_page(page);
1304                page_cache_release(page);
1305
1306                /*
1307                 * Make sure that we aren't completely killing
1308                 * interactive performance.
1309                 */
1310                cond_resched();
1311                if (frontswap && pages_to_unuse > 0) {
1312                        if (!--pages_to_unuse)
1313                                break;
1314                }
1315        }
1316
1317        mmput(start_mm);
1318        return retval;
1319}
1320
1321/*
1322 * After a successful try_to_unuse, if no swap is now in use, we know
1323 * we can empty the mmlist.  swap_lock must be held on entry and exit.
1324 * Note that mmlist_lock nests inside swap_lock, and an mm must be
1325 * added to the mmlist just after page_duplicate - before would be racy.
1326 */
1327static void drain_mmlist(void)
1328{
1329        struct list_head *p, *next;
1330        unsigned int type;
1331
1332        for (type = 0; type < nr_swapfiles; type++)
1333                if (swap_info[type]->inuse_pages)
1334                        return;
1335        spin_lock(&mmlist_lock);
1336        list_for_each_safe(p, next, &init_mm.mmlist)
1337                list_del_init(p);
1338        spin_unlock(&mmlist_lock);
1339}
1340
1341/*
1342 * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1343 * corresponds to page offset for the specified swap entry.
1344 * Note that the type of this function is sector_t, but it returns page offset
1345 * into the bdev, not sector offset.
1346 */
1347static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1348{
1349        struct swap_info_struct *sis;
1350        struct swap_extent *start_se;
1351        struct swap_extent *se;
1352        pgoff_t offset;
1353
1354        sis = swap_info[swp_type(entry)];
1355        *bdev = sis->bdev;
1356
1357        offset = swp_offset(entry);
1358        start_se = sis->curr_swap_extent;
1359        se = start_se;
1360
1361        for ( ; ; ) {
1362                struct list_head *lh;
1363
1364                if (se->start_page <= offset &&
1365                                offset < (se->start_page + se->nr_pages)) {
1366                        return se->start_block + (offset - se->start_page);
1367                }
1368                lh = se->list.next;
1369                se = list_entry(lh, struct swap_extent, list);
1370                sis->curr_swap_extent = se;
1371                BUG_ON(se == start_se);         /* It *must* be present */
1372        }
1373}
1374
1375/*
1376 * Returns the page offset into bdev for the specified page's swap entry.
1377 */
1378sector_t map_swap_page(struct page *page, struct block_device **bdev)
1379{
1380        swp_entry_t entry;
1381        entry.val = page_private(page);
1382        return map_swap_entry(entry, bdev);
1383}
1384
1385/*
1386 * Free all of a swapdev's extent information
1387 */
1388static void destroy_swap_extents(struct swap_info_struct *sis)
1389{
1390        while (!list_empty(&sis->first_swap_extent.list)) {
1391                struct swap_extent *se;
1392
1393                se = list_entry(sis->first_swap_extent.list.next,
1394                                struct swap_extent, list);
1395                list_del(&se->list);
1396                kfree(se);
1397        }
1398
1399        if (sis->flags & SWP_FILE) {
1400                struct file *swap_file = sis->swap_file;
1401                struct address_space *mapping = swap_file->f_mapping;
1402
1403                sis->flags &= ~SWP_FILE;
1404                mapping->a_ops->swap_deactivate(swap_file);
1405        }
1406}
1407
1408/*
1409 * Add a block range (and the corresponding page range) into this swapdev's
1410 * extent list.  The extent list is kept sorted in page order.
1411 *
1412 * This function rather assumes that it is called in ascending page order.
1413 */
1414int
1415add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1416                unsigned long nr_pages, sector_t start_block)
1417{
1418        struct swap_extent *se;
1419        struct swap_extent *new_se;
1420        struct list_head *lh;
1421
1422        if (start_page == 0) {
1423                se = &sis->first_swap_extent;
1424                sis->curr_swap_extent = se;
1425                se->start_page = 0;
1426                se->nr_pages = nr_pages;
1427                se->start_block = start_block;
1428                return 1;
1429        } else {
1430                lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1431                se = list_entry(lh, struct swap_extent, list);
1432                BUG_ON(se->start_page + se->nr_pages != start_page);
1433                if (se->start_block + se->nr_pages == start_block) {
1434                        /* Merge it */
1435                        se->nr_pages += nr_pages;
1436                        return 0;
1437                }
1438        }
1439
1440        /*
1441         * No merge.  Insert a new extent, preserving ordering.
1442         */
1443        new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1444        if (new_se == NULL)
1445                return -ENOMEM;
1446        new_se->start_page = start_page;
1447        new_se->nr_pages = nr_pages;
1448        new_se->start_block = start_block;
1449
1450        list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1451        return 1;
1452}
1453
1454/*
1455 * A `swap extent' is a simple thing which maps a contiguous range of pages
1456 * onto a contiguous range of disk blocks.  An ordered list of swap extents
1457 * is built at swapon time and is then used at swap_writepage/swap_readpage
1458 * time for locating where on disk a page belongs.
1459 *
1460 * If the swapfile is an S_ISBLK block device, a single extent is installed.
1461 * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1462 * swap files identically.
1463 *
1464 * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1465 * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1466 * swapfiles are handled *identically* after swapon time.
1467 *
1468 * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1469 * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1470 * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1471 * requirements, they are simply tossed out - we will never use those blocks
1472 * for swapping.
1473 *
1474 * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1475 * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1476 * which will scribble on the fs.
1477 *
1478 * The amount of disk space which a single swap extent represents varies.
1479 * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1480 * extents in the list.  To avoid much list walking, we cache the previous
1481 * search location in `curr_swap_extent', and start new searches from there.
1482 * This is extremely effective.  The average number of iterations in
1483 * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1484 */
1485static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1486{
1487        struct file *swap_file = sis->swap_file;
1488        struct address_space *mapping = swap_file->f_mapping;
1489        struct inode *inode = mapping->host;
1490        int ret;
1491
1492        if (S_ISBLK(inode->i_mode)) {
1493                ret = add_swap_extent(sis, 0, sis->max, 0);
1494                *span = sis->pages;
1495                return ret;
1496        }
1497
1498        if (mapping->a_ops->swap_activate) {
1499                ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1500                if (!ret) {
1501                        sis->flags |= SWP_FILE;
1502                        ret = add_swap_extent(sis, 0, sis->max, 0);
1503                        *span = sis->pages;
1504                }
1505                return ret;
1506        }
1507
1508        return generic_swapfile_activate(sis, swap_file, span);
1509}
1510
1511static void _enable_swap_info(struct swap_info_struct *p, int prio,
1512                                unsigned char *swap_map)
1513{
1514        int i, prev;
1515
1516        if (prio >= 0)
1517                p->prio = prio;
1518        else
1519                p->prio = --least_priority;
1520        p->swap_map = swap_map;
1521        p->flags |= SWP_WRITEOK;
1522        atomic_long_add(p->pages, &nr_swap_pages);
1523        total_swap_pages += p->pages;
1524
1525        /* insert swap space into swap_list: */
1526        prev = -1;
1527        for (i = swap_list.head; i >= 0; i = swap_info[i]->next) {
1528                if (p->prio >= swap_info[i]->prio)
1529                        break;
1530                prev = i;
1531        }
1532        p->next = i;
1533        if (prev < 0)
1534                swap_list.head = swap_list.next = p->type;
1535        else
1536                swap_info[prev]->next = p->type;
1537}
1538
1539static void enable_swap_info(struct swap_info_struct *p, int prio,
1540                                unsigned char *swap_map,
1541                                unsigned long *frontswap_map)
1542{
1543        frontswap_init(p->type, frontswap_map);
1544        spin_lock(&swap_lock);
1545        spin_lock(&p->lock);
1546         _enable_swap_info(p, prio, swap_map);
1547        spin_unlock(&p->lock);
1548        spin_unlock(&swap_lock);
1549}
1550
1551static void reinsert_swap_info(struct swap_info_struct *p)
1552{
1553        spin_lock(&swap_lock);
1554        spin_lock(&p->lock);
1555        _enable_swap_info(p, p->prio, p->swap_map);
1556        spin_unlock(&p->lock);
1557        spin_unlock(&swap_lock);
1558}
1559
1560SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1561{
1562        struct swap_info_struct *p = NULL;
1563        unsigned char *swap_map;
1564        unsigned long *frontswap_map;
1565        struct file *swap_file, *victim;
1566        struct address_space *mapping;
1567        struct inode *inode;
1568        struct filename *pathname;
1569        int i, type, prev;
1570        int err;
1571
1572        if (!capable(CAP_SYS_ADMIN))
1573                return -EPERM;
1574
1575        BUG_ON(!current->mm);
1576
1577        pathname = getname(specialfile);
1578        if (IS_ERR(pathname))
1579                return PTR_ERR(pathname);
1580
1581        victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1582        err = PTR_ERR(victim);
1583        if (IS_ERR(victim))
1584                goto out;
1585
1586        mapping = victim->f_mapping;
1587        prev = -1;
1588        spin_lock(&swap_lock);
1589        for (type = swap_list.head; type >= 0; type = swap_info[type]->next) {
1590                p = swap_info[type];
1591                if (p->flags & SWP_WRITEOK) {
1592                        if (p->swap_file->f_mapping == mapping)
1593                                break;
1594                }
1595                prev = type;
1596        }
1597        if (type < 0) {
1598                err = -EINVAL;
1599                spin_unlock(&swap_lock);
1600                goto out_dput;
1601        }
1602        if (!security_vm_enough_memory_mm(current->mm, p->pages))
1603                vm_unacct_memory(p->pages);
1604        else {
1605                err = -ENOMEM;
1606                spin_unlock(&swap_lock);
1607                goto out_dput;
1608        }
1609        if (prev < 0)
1610                swap_list.head = p->next;
1611        else
1612                swap_info[prev]->next = p->next;
1613        if (type == swap_list.next) {
1614                /* just pick something that's safe... */
1615                swap_list.next = swap_list.head;
1616        }
1617        spin_lock(&p->lock);
1618        if (p->prio < 0) {
1619                for (i = p->next; i >= 0; i = swap_info[i]->next)
1620                        swap_info[i]->prio = p->prio--;
1621                least_priority++;
1622        }
1623        atomic_long_sub(p->pages, &nr_swap_pages);
1624        total_swap_pages -= p->pages;
1625        p->flags &= ~SWP_WRITEOK;
1626        spin_unlock(&p->lock);
1627        spin_unlock(&swap_lock);
1628
1629        set_current_oom_origin();
1630        err = try_to_unuse(type, false, 0); /* force all pages to be unused */
1631        clear_current_oom_origin();
1632
1633        if (err) {
1634                /* re-insert swap space back into swap_list */
1635                reinsert_swap_info(p);
1636                goto out_dput;
1637        }
1638
1639        destroy_swap_extents(p);
1640        if (p->flags & SWP_CONTINUED)
1641                free_swap_count_continuations(p);
1642
1643        mutex_lock(&swapon_mutex);
1644        spin_lock(&swap_lock);
1645        spin_lock(&p->lock);
1646        drain_mmlist();
1647
1648        /* wait for anyone still in scan_swap_map */
1649        p->highest_bit = 0;             /* cuts scans short */
1650        while (p->flags >= SWP_SCANNING) {
1651                spin_unlock(&p->lock);
1652                spin_unlock(&swap_lock);
1653                schedule_timeout_uninterruptible(1);
1654                spin_lock(&swap_lock);
1655                spin_lock(&p->lock);
1656        }
1657
1658        swap_file = p->swap_file;
1659        p->swap_file = NULL;
1660        p->max = 0;
1661        swap_map = p->swap_map;
1662        p->swap_map = NULL;
1663        p->flags = 0;
1664        frontswap_map = frontswap_map_get(p);
1665        frontswap_map_set(p, NULL);
1666        spin_unlock(&p->lock);
1667        spin_unlock(&swap_lock);
1668        frontswap_invalidate_area(type);
1669        mutex_unlock(&swapon_mutex);
1670        vfree(swap_map);
1671        vfree(frontswap_map);
1672        /* Destroy swap account informatin */
1673        swap_cgroup_swapoff(type);
1674
1675        inode = mapping->host;
1676        if (S_ISBLK(inode->i_mode)) {
1677                struct block_device *bdev = I_BDEV(inode);
1678                set_blocksize(bdev, p->old_block_size);
1679                blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1680        } else {
1681                mutex_lock(&inode->i_mutex);
1682                inode->i_flags &= ~S_SWAPFILE;
1683                mutex_unlock(&inode->i_mutex);
1684        }
1685        filp_close(swap_file, NULL);
1686        err = 0;
1687        atomic_inc(&proc_poll_event);
1688        wake_up_interruptible(&proc_poll_wait);
1689
1690out_dput:
1691        filp_close(victim, NULL);
1692out:
1693        putname(pathname);
1694        return err;
1695}
1696
1697#ifdef CONFIG_PROC_FS
1698static unsigned swaps_poll(struct file *file, poll_table *wait)
1699{
1700        struct seq_file *seq = file->private_data;
1701
1702        poll_wait(file, &proc_poll_wait, wait);
1703
1704        if (seq->poll_event != atomic_read(&proc_poll_event)) {
1705                seq->poll_event = atomic_read(&proc_poll_event);
1706                return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
1707        }
1708
1709        return POLLIN | POLLRDNORM;
1710}
1711
1712/* iterator */
1713static void *swap_start(struct seq_file *swap, loff_t *pos)
1714{
1715        struct swap_info_struct *si;
1716        int type;
1717        loff_t l = *pos;
1718
1719        mutex_lock(&swapon_mutex);
1720
1721        if (!l)
1722                return SEQ_START_TOKEN;
1723
1724        for (type = 0; type < nr_swapfiles; type++) {
1725                smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1726                si = swap_info[type];
1727                if (!(si->flags & SWP_USED) || !si->swap_map)
1728                        continue;
1729                if (!--l)
1730                        return si;
1731        }
1732
1733        return NULL;
1734}
1735
1736static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
1737{
1738        struct swap_info_struct *si = v;
1739        int type;
1740
1741        if (v == SEQ_START_TOKEN)
1742                type = 0;
1743        else
1744                type = si->type + 1;
1745
1746        for (; type < nr_swapfiles; type++) {
1747                smp_rmb();      /* read nr_swapfiles before swap_info[type] */
1748                si = swap_info[type];
1749                if (!(si->flags & SWP_USED) || !si->swap_map)
1750                        continue;
1751                ++*pos;
1752                return si;
1753        }
1754
1755        return NULL;
1756}
1757
1758static void swap_stop(struct seq_file *swap, void *v)
1759{
1760        mutex_unlock(&swapon_mutex);
1761}
1762
1763static int swap_show(struct seq_file *swap, void *v)
1764{
1765        struct swap_info_struct *si = v;
1766        struct file *file;
1767        int len;
1768
1769        if (si == SEQ_START_TOKEN) {
1770                seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
1771                return 0;
1772        }
1773
1774        file = si->swap_file;
1775        len = seq_path(swap, &file->f_path, " \t\n\\");
1776        seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
1777                        len < 40 ? 40 - len : 1, " ",
1778                        S_ISBLK(file_inode(file)->i_mode) ?
1779                                "partition" : "file\t",
1780                        si->pages << (PAGE_SHIFT - 10),
1781                        si->inuse_pages << (PAGE_SHIFT - 10),
1782                        si->prio);
1783        return 0;
1784}
1785
1786static const struct seq_operations swaps_op = {
1787        .start =        swap_start,
1788        .next =         swap_next,
1789        .stop =         swap_stop,
1790        .show =         swap_show
1791};
1792
1793static int swaps_open(struct inode *inode, struct file *file)
1794{
1795        struct seq_file *seq;
1796        int ret;
1797
1798        ret = seq_open(file, &swaps_op);
1799        if (ret)
1800                return ret;
1801
1802        seq = file->private_data;
1803        seq->poll_event = atomic_read(&proc_poll_event);
1804        return 0;
1805}
1806
1807static const struct file_operations proc_swaps_operations = {
1808        .open           = swaps_open,
1809        .read           = seq_read,
1810        .llseek         = seq_lseek,
1811        .release        = seq_release,
1812        .poll           = swaps_poll,
1813};
1814
1815static int __init procswaps_init(void)
1816{
1817        proc_create("swaps", 0, NULL, &proc_swaps_operations);
1818        return 0;
1819}
1820__initcall(procswaps_init);
1821#endif /* CONFIG_PROC_FS */
1822
1823#ifdef MAX_SWAPFILES_CHECK
1824static int __init max_swapfiles_check(void)
1825{
1826        MAX_SWAPFILES_CHECK();
1827        return 0;
1828}
1829late_initcall(max_swapfiles_check);
1830#endif
1831
1832static struct swap_info_struct *alloc_swap_info(void)
1833{
1834        struct swap_info_struct *p;
1835        unsigned int type;
1836
1837        p = kzalloc(sizeof(*p), GFP_KERNEL);
1838        if (!p)
1839                return ERR_PTR(-ENOMEM);
1840
1841        spin_lock(&swap_lock);
1842        for (type = 0; type < nr_swapfiles; type++) {
1843                if (!(swap_info[type]->flags & SWP_USED))
1844                        break;
1845        }
1846        if (type >= MAX_SWAPFILES) {
1847                spin_unlock(&swap_lock);
1848                kfree(p);
1849                return ERR_PTR(-EPERM);
1850        }
1851        if (type >= nr_swapfiles) {
1852                p->type = type;
1853                swap_info[type] = p;
1854                /*
1855                 * Write swap_info[type] before nr_swapfiles, in case a
1856                 * racing procfs swap_start() or swap_next() is reading them.
1857                 * (We never shrink nr_swapfiles, we never free this entry.)
1858                 */
1859                smp_wmb();
1860                nr_swapfiles++;
1861        } else {
1862                kfree(p);
1863                p = swap_info[type];
1864                /*
1865                 * Do not memset this entry: a racing procfs swap_next()
1866                 * would be relying on p->type to remain valid.
1867                 */
1868        }
1869        INIT_LIST_HEAD(&p->first_swap_extent.list);
1870        p->flags = SWP_USED;
1871        p->next = -1;
1872        spin_unlock(&swap_lock);
1873        spin_lock_init(&p->lock);
1874
1875        return p;
1876}
1877
1878static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
1879{
1880        int error;
1881
1882        if (S_ISBLK(inode->i_mode)) {
1883                p->bdev = bdgrab(I_BDEV(inode));
1884                error = blkdev_get(p->bdev,
1885                                   FMODE_READ | FMODE_WRITE | FMODE_EXCL,
1886                                   sys_swapon);
1887                if (error < 0) {
1888                        p->bdev = NULL;
1889                        return -EINVAL;
1890                }
1891                p->old_block_size = block_size(p->bdev);
1892                error = set_blocksize(p->bdev, PAGE_SIZE);
1893                if (error < 0)
1894                        return error;
1895                p->flags |= SWP_BLKDEV;
1896        } else if (S_ISREG(inode->i_mode)) {
1897                p->bdev = inode->i_sb->s_bdev;
1898                mutex_lock(&inode->i_mutex);
1899                if (IS_SWAPFILE(inode))
1900                        return -EBUSY;
1901        } else
1902                return -EINVAL;
1903
1904        return 0;
1905}
1906
1907static unsigned long read_swap_header(struct swap_info_struct *p,
1908                                        union swap_header *swap_header,
1909                                        struct inode *inode)
1910{
1911        int i;
1912        unsigned long maxpages;
1913        unsigned long swapfilepages;
1914
1915        if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
1916                printk(KERN_ERR "Unable to find swap-space signature\n");
1917                return 0;
1918        }
1919
1920        /* swap partition endianess hack... */
1921        if (swab32(swap_header->info.version) == 1) {
1922                swab32s(&swap_header->info.version);
1923                swab32s(&swap_header->info.last_page);
1924                swab32s(&swap_header->info.nr_badpages);
1925                for (i = 0; i < swap_header->info.nr_badpages; i++)
1926                        swab32s(&swap_header->info.badpages[i]);
1927        }
1928        /* Check the swap header's sub-version */
1929        if (swap_header->info.version != 1) {
1930                printk(KERN_WARNING
1931                       "Unable to handle swap header version %d\n",
1932                       swap_header->info.version);
1933                return 0;
1934        }
1935
1936        p->lowest_bit  = 1;
1937        p->cluster_next = 1;
1938        p->cluster_nr = 0;
1939
1940        /*
1941         * Find out how many pages are allowed for a single swap
1942         * device. There are two limiting factors: 1) the number
1943         * of bits for the swap offset in the swp_entry_t type, and
1944         * 2) the number of bits in the swap pte as defined by the
1945         * different architectures. In order to find the
1946         * largest possible bit mask, a swap entry with swap type 0
1947         * and swap offset ~0UL is created, encoded to a swap pte,
1948         * decoded to a swp_entry_t again, and finally the swap
1949         * offset is extracted. This will mask all the bits from
1950         * the initial ~0UL mask that can't be encoded in either
1951         * the swp_entry_t or the architecture definition of a
1952         * swap pte.
1953         */
1954        maxpages = swp_offset(pte_to_swp_entry(
1955                        swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
1956        if (maxpages > swap_header->info.last_page) {
1957                maxpages = swap_header->info.last_page + 1;
1958                /* p->max is an unsigned int: don't overflow it */
1959                if ((unsigned int)maxpages == 0)
1960                        maxpages = UINT_MAX;
1961        }
1962        p->highest_bit = maxpages - 1;
1963
1964        if (!maxpages)
1965                return 0;
1966        swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
1967        if (swapfilepages && maxpages > swapfilepages) {
1968                printk(KERN_WARNING
1969                       "Swap area shorter than signature indicates\n");
1970                return 0;
1971        }
1972        if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
1973                return 0;
1974        if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
1975                return 0;
1976
1977        return maxpages;
1978}
1979
1980static int setup_swap_map_and_extents(struct swap_info_struct *p,
1981                                        union swap_header *swap_header,
1982                                        unsigned char *swap_map,
1983                                        unsigned long maxpages,
1984                                        sector_t *span)
1985{
1986        int i;
1987        unsigned int nr_good_pages;
1988        int nr_extents;
1989
1990        nr_good_pages = maxpages - 1;   /* omit header page */
1991
1992        for (i = 0; i < swap_header->info.nr_badpages; i++) {
1993                unsigned int page_nr = swap_header->info.badpages[i];
1994                if (page_nr == 0 || page_nr > swap_header->info.last_page)
1995                        return -EINVAL;
1996                if (page_nr < maxpages) {
1997                        swap_map[page_nr] = SWAP_MAP_BAD;
1998                        nr_good_pages--;
1999                }
2000        }
2001
2002        if (nr_good_pages) {
2003                swap_map[0] = SWAP_MAP_BAD;
2004                p->max = maxpages;
2005                p->pages = nr_good_pages;
2006                nr_extents = setup_swap_extents(p, span);
2007                if (nr_extents < 0)
2008                        return nr_extents;
2009                nr_good_pages = p->pages;
2010        }
2011        if (!nr_good_pages) {
2012                printk(KERN_WARNING "Empty swap-file\n");
2013                return -EINVAL;
2014        }
2015
2016        return nr_extents;
2017}
2018
2019SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2020{
2021        struct swap_info_struct *p;
2022        struct filename *name;
2023        struct file *swap_file = NULL;
2024        struct address_space *mapping;
2025        int i;
2026        int prio;
2027        int error;
2028        union swap_header *swap_header;
2029        int nr_extents;
2030        sector_t span;
2031        unsigned long maxpages;
2032        unsigned char *swap_map = NULL;
2033        unsigned long *frontswap_map = NULL;
2034        struct page *page = NULL;
2035        struct inode *inode = NULL;
2036
2037        if (swap_flags & ~SWAP_FLAGS_VALID)
2038                return -EINVAL;
2039
2040        if (!capable(CAP_SYS_ADMIN))
2041                return -EPERM;
2042
2043        p = alloc_swap_info();
2044        if (IS_ERR(p))
2045                return PTR_ERR(p);
2046
2047        name = getname(specialfile);
2048        if (IS_ERR(name)) {
2049                error = PTR_ERR(name);
2050                name = NULL;
2051                goto bad_swap;
2052        }
2053        swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2054        if (IS_ERR(swap_file)) {
2055                error = PTR_ERR(swap_file);
2056                swap_file = NULL;
2057                goto bad_swap;
2058        }
2059
2060        p->swap_file = swap_file;
2061        mapping = swap_file->f_mapping;
2062
2063        for (i = 0; i < nr_swapfiles; i++) {
2064                struct swap_info_struct *q = swap_info[i];
2065
2066                if (q == p || !q->swap_file)
2067                        continue;
2068                if (mapping == q->swap_file->f_mapping) {
2069                        error = -EBUSY;
2070                        goto bad_swap;
2071                }
2072        }
2073
2074        inode = mapping->host;
2075        /* If S_ISREG(inode->i_mode) will do mutex_lock(&inode->i_mutex); */
2076        error = claim_swapfile(p, inode);
2077        if (unlikely(error))
2078                goto bad_swap;
2079
2080        /*
2081         * Read the swap header.
2082         */
2083        if (!mapping->a_ops->readpage) {
2084                error = -EINVAL;
2085                goto bad_swap;
2086        }
2087        page = read_mapping_page(mapping, 0, swap_file);
2088        if (IS_ERR(page)) {
2089                error = PTR_ERR(page);
2090                goto bad_swap;
2091        }
2092        swap_header = kmap(page);
2093
2094        maxpages = read_swap_header(p, swap_header, inode);
2095        if (unlikely(!maxpages)) {
2096                error = -EINVAL;
2097                goto bad_swap;
2098        }
2099
2100        /* OK, set up the swap map and apply the bad block list */
2101        swap_map = vzalloc(maxpages);
2102        if (!swap_map) {
2103                error = -ENOMEM;
2104                goto bad_swap;
2105        }
2106
2107        error = swap_cgroup_swapon(p->type, maxpages);
2108        if (error)
2109                goto bad_swap;
2110
2111        nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2112                maxpages, &span);
2113        if (unlikely(nr_extents < 0)) {
2114                error = nr_extents;
2115                goto bad_swap;
2116        }
2117        /* frontswap enabled? set up bit-per-page map for frontswap */
2118        if (frontswap_enabled)
2119                frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2120
2121        if (p->bdev) {
2122                if (blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2123                        p->flags |= SWP_SOLIDSTATE;
2124                        p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2125                }
2126                if ((swap_flags & SWAP_FLAG_DISCARD) && discard_swap(p) == 0)
2127                        p->flags |= SWP_DISCARDABLE;
2128        }
2129
2130        mutex_lock(&swapon_mutex);
2131        prio = -1;
2132        if (swap_flags & SWAP_FLAG_PREFER)
2133                prio =
2134                  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2135        enable_swap_info(p, prio, swap_map, frontswap_map);
2136
2137        printk(KERN_INFO "Adding %uk swap on %s.  "
2138                        "Priority:%d extents:%d across:%lluk %s%s%s\n",
2139                p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2140                nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2141                (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2142                (p->flags & SWP_DISCARDABLE) ? "D" : "",
2143                (frontswap_map) ? "FS" : "");
2144
2145        mutex_unlock(&swapon_mutex);
2146        atomic_inc(&proc_poll_event);
2147        wake_up_interruptible(&proc_poll_wait);
2148
2149        if (S_ISREG(inode->i_mode))
2150                inode->i_flags |= S_SWAPFILE;
2151        error = 0;
2152        goto out;
2153bad_swap:
2154        if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2155                set_blocksize(p->bdev, p->old_block_size);
2156                blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2157        }
2158        destroy_swap_extents(p);
2159        swap_cgroup_swapoff(p->type);
2160        spin_lock(&swap_lock);
2161        p->swap_file = NULL;
2162        p->flags = 0;
2163        spin_unlock(&swap_lock);
2164        vfree(swap_map);
2165        if (swap_file) {
2166                if (inode && S_ISREG(inode->i_mode)) {
2167                        mutex_unlock(&inode->i_mutex);
2168                        inode = NULL;
2169                }
2170                filp_close(swap_file, NULL);
2171        }
2172out:
2173        if (page && !IS_ERR(page)) {
2174                kunmap(page);
2175                page_cache_release(page);
2176        }
2177        if (name)
2178                putname(name);
2179        if (inode && S_ISREG(inode->i_mode))
2180                mutex_unlock(&inode->i_mutex);
2181        return error;
2182}
2183
2184void si_swapinfo(struct sysinfo *val)
2185{
2186        unsigned int type;
2187        unsigned long nr_to_be_unused = 0;
2188
2189        spin_lock(&swap_lock);
2190        for (type = 0; type < nr_swapfiles; type++) {
2191                struct swap_info_struct *si = swap_info[type];
2192
2193                if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2194                        nr_to_be_unused += si->inuse_pages;
2195        }
2196        val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2197        val->totalswap = total_swap_pages + nr_to_be_unused;
2198        spin_unlock(&swap_lock);
2199}
2200
2201/*
2202 * Verify that a swap entry is valid and increment its swap map count.
2203 *
2204 * Returns error code in following case.
2205 * - success -> 0
2206 * - swp_entry is invalid -> EINVAL
2207 * - swp_entry is migration entry -> EINVAL
2208 * - swap-cache reference is requested but there is already one. -> EEXIST
2209 * - swap-cache reference is requested but the entry is not used. -> ENOENT
2210 * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2211 */
2212static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2213{
2214        struct swap_info_struct *p;
2215        unsigned long offset, type;
2216        unsigned char count;
2217        unsigned char has_cache;
2218        int err = -EINVAL;
2219
2220        if (non_swap_entry(entry))
2221                goto out;
2222
2223        type = swp_type(entry);
2224        if (type >= nr_swapfiles)
2225                goto bad_file;
2226        p = swap_info[type];
2227        offset = swp_offset(entry);
2228
2229        spin_lock(&p->lock);
2230        if (unlikely(offset >= p->max))
2231                goto unlock_out;
2232
2233        count = p->swap_map[offset];
2234        has_cache = count & SWAP_HAS_CACHE;
2235        count &= ~SWAP_HAS_CACHE;
2236        err = 0;
2237
2238        if (usage == SWAP_HAS_CACHE) {
2239
2240                /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2241                if (!has_cache && count)
2242                        has_cache = SWAP_HAS_CACHE;
2243                else if (has_cache)             /* someone else added cache */
2244                        err = -EEXIST;
2245                else                            /* no users remaining */
2246                        err = -ENOENT;
2247
2248        } else if (count || has_cache) {
2249
2250                if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2251                        count += usage;
2252                else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2253                        err = -EINVAL;
2254                else if (swap_count_continued(p, offset, count))
2255                        count = COUNT_CONTINUED;
2256                else
2257                        err = -ENOMEM;
2258        } else
2259                err = -ENOENT;                  /* unused swap entry */
2260
2261        p->swap_map[offset] = count | has_cache;
2262
2263unlock_out:
2264        spin_unlock(&p->lock);
2265out:
2266        return err;
2267
2268bad_file:
2269        printk(KERN_ERR "swap_dup: %s%08lx\n", Bad_file, entry.val);
2270        goto out;
2271}
2272
2273/*
2274 * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2275 * (in which case its reference count is never incremented).
2276 */
2277void swap_shmem_alloc(swp_entry_t entry)
2278{
2279        __swap_duplicate(entry, SWAP_MAP_SHMEM);
2280}
2281
2282/*
2283 * Increase reference count of swap entry by 1.
2284 * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2285 * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2286 * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2287 * might occur if a page table entry has got corrupted.
2288 */
2289int swap_duplicate(swp_entry_t entry)
2290{
2291        int err = 0;
2292
2293        while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2294                err = add_swap_count_continuation(entry, GFP_ATOMIC);
2295        return err;
2296}
2297
2298/*
2299 * @entry: swap entry for which we allocate swap cache.
2300 *
2301 * Called when allocating swap cache for existing swap entry,
2302 * This can return error codes. Returns 0 at success.
2303 * -EBUSY means there is a swap cache.
2304 * Note: return code is different from swap_duplicate().
2305 */
2306int swapcache_prepare(swp_entry_t entry)
2307{
2308        return __swap_duplicate(entry, SWAP_HAS_CACHE);
2309}
2310
2311struct swap_info_struct *page_swap_info(struct page *page)
2312{
2313        swp_entry_t swap = { .val = page_private(page) };
2314        BUG_ON(!PageSwapCache(page));
2315        return swap_info[swp_type(swap)];
2316}
2317
2318/*
2319 * out-of-line __page_file_ methods to avoid include hell.
2320 */
2321struct address_space *__page_file_mapping(struct page *page)
2322{
2323        VM_BUG_ON(!PageSwapCache(page));
2324        return page_swap_info(page)->swap_file->f_mapping;
2325}
2326EXPORT_SYMBOL_GPL(__page_file_mapping);
2327
2328pgoff_t __page_file_index(struct page *page)
2329{
2330        swp_entry_t swap = { .val = page_private(page) };
2331        VM_BUG_ON(!PageSwapCache(page));
2332        return swp_offset(swap);
2333}
2334EXPORT_SYMBOL_GPL(__page_file_index);
2335
2336/*
2337 * add_swap_count_continuation - called when a swap count is duplicated
2338 * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2339 * page of the original vmalloc'ed swap_map, to hold the continuation count
2340 * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2341 * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2342 *
2343 * These continuation pages are seldom referenced: the common paths all work
2344 * on the original swap_map, only referring to a continuation page when the
2345 * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2346 *
2347 * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2348 * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2349 * can be called after dropping locks.
2350 */
2351int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2352{
2353        struct swap_info_struct *si;
2354        struct page *head;
2355        struct page *page;
2356        struct page *list_page;
2357        pgoff_t offset;
2358        unsigned char count;
2359
2360        /*
2361         * When debugging, it's easier to use __GFP_ZERO here; but it's better
2362         * for latency not to zero a page while GFP_ATOMIC and holding locks.
2363         */
2364        page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2365
2366        si = swap_info_get(entry);
2367        if (!si) {
2368                /*
2369                 * An acceptable race has occurred since the failing
2370                 * __swap_duplicate(): the swap entry has been freed,
2371                 * perhaps even the whole swap_map cleared for swapoff.
2372                 */
2373                goto outer;
2374        }
2375
2376        offset = swp_offset(entry);
2377        count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2378
2379        if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2380                /*
2381                 * The higher the swap count, the more likely it is that tasks
2382                 * will race to add swap count continuation: we need to avoid
2383                 * over-provisioning.
2384                 */
2385                goto out;
2386        }
2387
2388        if (!page) {
2389                spin_unlock(&si->lock);
2390                return -ENOMEM;
2391        }
2392
2393        /*
2394         * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2395         * no architecture is using highmem pages for kernel pagetables: so it
2396         * will not corrupt the GFP_ATOMIC caller's atomic pagetable kmaps.
2397         */
2398        head = vmalloc_to_page(si->swap_map + offset);
2399        offset &= ~PAGE_MASK;
2400
2401        /*
2402         * Page allocation does not initialize the page's lru field,
2403         * but it does always reset its private field.
2404         */
2405        if (!page_private(head)) {
2406                BUG_ON(count & COUNT_CONTINUED);
2407                INIT_LIST_HEAD(&head->lru);
2408                set_page_private(head, SWP_CONTINUED);
2409                si->flags |= SWP_CONTINUED;
2410        }
2411
2412        list_for_each_entry(list_page, &head->lru, lru) {
2413                unsigned char *map;
2414
2415                /*
2416                 * If the previous map said no continuation, but we've found
2417                 * a continuation page, free our allocation and use this one.
2418                 */
2419                if (!(count & COUNT_CONTINUED))
2420                        goto out;
2421
2422                map = kmap_atomic(list_page) + offset;
2423                count = *map;
2424                kunmap_atomic(map);
2425
2426                /*
2427                 * If this continuation count now has some space in it,
2428                 * free our allocation and use this one.
2429                 */
2430                if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2431                        goto out;
2432        }
2433
2434        list_add_tail(&page->lru, &head->lru);
2435        page = NULL;                    /* now it's attached, don't free it */
2436out:
2437        spin_unlock(&si->lock);
2438outer:
2439        if (page)
2440                __free_page(page);
2441        return 0;
2442}
2443
2444/*
2445 * swap_count_continued - when the original swap_map count is incremented
2446 * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2447 * into, carry if so, or else fail until a new continuation page is allocated;
2448 * when the original swap_map count is decremented from 0 with continuation,
2449 * borrow from the continuation and report whether it still holds more.
2450 * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2451 */
2452static bool swap_count_continued(struct swap_info_struct *si,
2453                                 pgoff_t offset, unsigned char count)
2454{
2455        struct page *head;
2456        struct page *page;
2457        unsigned char *map;
2458
2459        head = vmalloc_to_page(si->swap_map + offset);
2460        if (page_private(head) != SWP_CONTINUED) {
2461                BUG_ON(count & COUNT_CONTINUED);
2462                return false;           /* need to add count continuation */
2463        }
2464
2465        offset &= ~PAGE_MASK;
2466        page = list_entry(head->lru.next, struct page, lru);
2467        map = kmap_atomic(page) + offset;
2468
2469        if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2470                goto init_map;          /* jump over SWAP_CONT_MAX checks */
2471
2472        if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2473                /*
2474                 * Think of how you add 1 to 999
2475                 */
2476                while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2477                        kunmap_atomic(map);
2478                        page = list_entry(page->lru.next, struct page, lru);
2479                        BUG_ON(page == head);
2480                        map = kmap_atomic(page) + offset;
2481                }
2482                if (*map == SWAP_CONT_MAX) {
2483                        kunmap_atomic(map);
2484                        page = list_entry(page->lru.next, struct page, lru);
2485                        if (page == head)
2486                                return false;   /* add count continuation */
2487                        map = kmap_atomic(page) + offset;
2488init_map:               *map = 0;               /* we didn't zero the page */
2489                }
2490                *map += 1;
2491                kunmap_atomic(map);
2492                page = list_entry(page->lru.prev, struct page, lru);
2493                while (page != head) {
2494                        map = kmap_atomic(page) + offset;
2495                        *map = COUNT_CONTINUED;
2496                        kunmap_atomic(map);
2497                        page = list_entry(page->lru.prev, struct page, lru);
2498                }
2499                return true;                    /* incremented */
2500
2501        } else {                                /* decrementing */
2502                /*
2503                 * Think of how you subtract 1 from 1000
2504                 */
2505                BUG_ON(count != COUNT_CONTINUED);
2506                while (*map == COUNT_CONTINUED) {
2507                        kunmap_atomic(map);
2508                        page = list_entry(page->lru.next, struct page, lru);
2509                        BUG_ON(page == head);
2510                        map = kmap_atomic(page) + offset;
2511                }
2512                BUG_ON(*map == 0);
2513                *map -= 1;
2514                if (*map == 0)
2515                        count = 0;
2516                kunmap_atomic(map);
2517                page = list_entry(page->lru.prev, struct page, lru);
2518                while (page != head) {
2519                        map = kmap_atomic(page) + offset;
2520                        *map = SWAP_CONT_MAX | count;
2521                        count = COUNT_CONTINUED;
2522                        kunmap_atomic(map);
2523                        page = list_entry(page->lru.prev, struct page, lru);
2524                }
2525                return count == COUNT_CONTINUED;
2526        }
2527}
2528
2529/*
2530 * free_swap_count_continuations - swapoff free all the continuation pages
2531 * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2532 */
2533static void free_swap_count_continuations(struct swap_info_struct *si)
2534{
2535        pgoff_t offset;
2536
2537        for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2538                struct page *head;
2539                head = vmalloc_to_page(si->swap_map + offset);
2540                if (page_private(head)) {
2541                        struct list_head *this, *next;
2542                        list_for_each_safe(this, next, &head->lru) {
2543                                struct page *page;
2544                                page = list_entry(this, struct page, lru);
2545                                list_del(this);
2546                                __free_page(page);
2547                        }
2548                }
2549        }
2550}
2551
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