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0001 /*
0002  *  linux/mm/swapfile.c
0003  *
0004  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
0005  *  Swap reorganised 29.12.95, Stephen Tweedie
0006  */
0007 
0008 #include <linux/mm.h>
0009 #include <linux/hugetlb.h>
0010 #include <linux/mman.h>
0011 #include <linux/slab.h>
0012 #include <linux/kernel_stat.h>
0013 #include <linux/swap.h>
0014 #include <linux/vmalloc.h>
0015 #include <linux/pagemap.h>
0016 #include <linux/namei.h>
0017 #include <linux/shmem_fs.h>
0018 #include <linux/blkdev.h>
0019 #include <linux/random.h>
0020 #include <linux/writeback.h>
0021 #include <linux/proc_fs.h>
0022 #include <linux/seq_file.h>
0023 #include <linux/init.h>
0024 #include <linux/ksm.h>
0025 #include <linux/rmap.h>
0026 #include <linux/security.h>
0027 #include <linux/backing-dev.h>
0028 #include <linux/mutex.h>
0029 #include <linux/capability.h>
0030 #include <linux/syscalls.h>
0031 #include <linux/memcontrol.h>
0032 #include <linux/poll.h>
0033 #include <linux/oom.h>
0034 #include <linux/frontswap.h>
0035 #include <linux/swapfile.h>
0036 #include <linux/export.h>
0037 
0038 #include <asm/pgtable.h>
0039 #include <asm/tlbflush.h>
0040 #include <linux/swapops.h>
0041 #include <linux/swap_cgroup.h>
0042 
0043 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
0044                  unsigned char);
0045 static void free_swap_count_continuations(struct swap_info_struct *);
0046 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
0047 
0048 DEFINE_SPINLOCK(swap_lock);
0049 static unsigned int nr_swapfiles;
0050 atomic_long_t nr_swap_pages;
0051 /*
0052  * Some modules use swappable objects and may try to swap them out under
0053  * memory pressure (via the shrinker). Before doing so, they may wish to
0054  * check to see if any swap space is available.
0055  */
0056 EXPORT_SYMBOL_GPL(nr_swap_pages);
0057 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
0058 long total_swap_pages;
0059 static int least_priority;
0060 
0061 static const char Bad_file[] = "Bad swap file entry ";
0062 static const char Unused_file[] = "Unused swap file entry ";
0063 static const char Bad_offset[] = "Bad swap offset entry ";
0064 static const char Unused_offset[] = "Unused swap offset entry ";
0065 
0066 /*
0067  * all active swap_info_structs
0068  * protected with swap_lock, and ordered by priority.
0069  */
0070 PLIST_HEAD(swap_active_head);
0071 
0072 /*
0073  * all available (active, not full) swap_info_structs
0074  * protected with swap_avail_lock, ordered by priority.
0075  * This is used by get_swap_page() instead of swap_active_head
0076  * because swap_active_head includes all swap_info_structs,
0077  * but get_swap_page() doesn't need to look at full ones.
0078  * This uses its own lock instead of swap_lock because when a
0079  * swap_info_struct changes between not-full/full, it needs to
0080  * add/remove itself to/from this list, but the swap_info_struct->lock
0081  * is held and the locking order requires swap_lock to be taken
0082  * before any swap_info_struct->lock.
0083  */
0084 static PLIST_HEAD(swap_avail_head);
0085 static DEFINE_SPINLOCK(swap_avail_lock);
0086 
0087 struct swap_info_struct *swap_info[MAX_SWAPFILES];
0088 
0089 static DEFINE_MUTEX(swapon_mutex);
0090 
0091 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
0092 /* Activity counter to indicate that a swapon or swapoff has occurred */
0093 static atomic_t proc_poll_event = ATOMIC_INIT(0);
0094 
0095 static inline unsigned char swap_count(unsigned char ent)
0096 {
0097     return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
0098 }
0099 
0100 /* returns 1 if swap entry is freed */
0101 static int
0102 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
0103 {
0104     swp_entry_t entry = swp_entry(si->type, offset);
0105     struct page *page;
0106     int ret = 0;
0107 
0108     page = find_get_page(swap_address_space(entry), swp_offset(entry));
0109     if (!page)
0110         return 0;
0111     /*
0112      * This function is called from scan_swap_map() and it's called
0113      * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
0114      * We have to use trylock for avoiding deadlock. This is a special
0115      * case and you should use try_to_free_swap() with explicit lock_page()
0116      * in usual operations.
0117      */
0118     if (trylock_page(page)) {
0119         ret = try_to_free_swap(page);
0120         unlock_page(page);
0121     }
0122     put_page(page);
0123     return ret;
0124 }
0125 
0126 /*
0127  * swapon tell device that all the old swap contents can be discarded,
0128  * to allow the swap device to optimize its wear-levelling.
0129  */
0130 static int discard_swap(struct swap_info_struct *si)
0131 {
0132     struct swap_extent *se;
0133     sector_t start_block;
0134     sector_t nr_blocks;
0135     int err = 0;
0136 
0137     /* Do not discard the swap header page! */
0138     se = &si->first_swap_extent;
0139     start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
0140     nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
0141     if (nr_blocks) {
0142         err = blkdev_issue_discard(si->bdev, start_block,
0143                 nr_blocks, GFP_KERNEL, 0);
0144         if (err)
0145             return err;
0146         cond_resched();
0147     }
0148 
0149     list_for_each_entry(se, &si->first_swap_extent.list, list) {
0150         start_block = se->start_block << (PAGE_SHIFT - 9);
0151         nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
0152 
0153         err = blkdev_issue_discard(si->bdev, start_block,
0154                 nr_blocks, GFP_KERNEL, 0);
0155         if (err)
0156             break;
0157 
0158         cond_resched();
0159     }
0160     return err;     /* That will often be -EOPNOTSUPP */
0161 }
0162 
0163 /*
0164  * swap allocation tell device that a cluster of swap can now be discarded,
0165  * to allow the swap device to optimize its wear-levelling.
0166  */
0167 static void discard_swap_cluster(struct swap_info_struct *si,
0168                  pgoff_t start_page, pgoff_t nr_pages)
0169 {
0170     struct swap_extent *se = si->curr_swap_extent;
0171     int found_extent = 0;
0172 
0173     while (nr_pages) {
0174         if (se->start_page <= start_page &&
0175             start_page < se->start_page + se->nr_pages) {
0176             pgoff_t offset = start_page - se->start_page;
0177             sector_t start_block = se->start_block + offset;
0178             sector_t nr_blocks = se->nr_pages - offset;
0179 
0180             if (nr_blocks > nr_pages)
0181                 nr_blocks = nr_pages;
0182             start_page += nr_blocks;
0183             nr_pages -= nr_blocks;
0184 
0185             if (!found_extent++)
0186                 si->curr_swap_extent = se;
0187 
0188             start_block <<= PAGE_SHIFT - 9;
0189             nr_blocks <<= PAGE_SHIFT - 9;
0190             if (blkdev_issue_discard(si->bdev, start_block,
0191                     nr_blocks, GFP_NOIO, 0))
0192                 break;
0193         }
0194 
0195         se = list_next_entry(se, list);
0196     }
0197 }
0198 
0199 #define SWAPFILE_CLUSTER    256
0200 #define LATENCY_LIMIT       256
0201 
0202 static inline void cluster_set_flag(struct swap_cluster_info *info,
0203     unsigned int flag)
0204 {
0205     info->flags = flag;
0206 }
0207 
0208 static inline unsigned int cluster_count(struct swap_cluster_info *info)
0209 {
0210     return info->data;
0211 }
0212 
0213 static inline void cluster_set_count(struct swap_cluster_info *info,
0214                      unsigned int c)
0215 {
0216     info->data = c;
0217 }
0218 
0219 static inline void cluster_set_count_flag(struct swap_cluster_info *info,
0220                      unsigned int c, unsigned int f)
0221 {
0222     info->flags = f;
0223     info->data = c;
0224 }
0225 
0226 static inline unsigned int cluster_next(struct swap_cluster_info *info)
0227 {
0228     return info->data;
0229 }
0230 
0231 static inline void cluster_set_next(struct swap_cluster_info *info,
0232                     unsigned int n)
0233 {
0234     info->data = n;
0235 }
0236 
0237 static inline void cluster_set_next_flag(struct swap_cluster_info *info,
0238                      unsigned int n, unsigned int f)
0239 {
0240     info->flags = f;
0241     info->data = n;
0242 }
0243 
0244 static inline bool cluster_is_free(struct swap_cluster_info *info)
0245 {
0246     return info->flags & CLUSTER_FLAG_FREE;
0247 }
0248 
0249 static inline bool cluster_is_null(struct swap_cluster_info *info)
0250 {
0251     return info->flags & CLUSTER_FLAG_NEXT_NULL;
0252 }
0253 
0254 static inline void cluster_set_null(struct swap_cluster_info *info)
0255 {
0256     info->flags = CLUSTER_FLAG_NEXT_NULL;
0257     info->data = 0;
0258 }
0259 
0260 static inline bool cluster_list_empty(struct swap_cluster_list *list)
0261 {
0262     return cluster_is_null(&list->head);
0263 }
0264 
0265 static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
0266 {
0267     return cluster_next(&list->head);
0268 }
0269 
0270 static void cluster_list_init(struct swap_cluster_list *list)
0271 {
0272     cluster_set_null(&list->head);
0273     cluster_set_null(&list->tail);
0274 }
0275 
0276 static void cluster_list_add_tail(struct swap_cluster_list *list,
0277                   struct swap_cluster_info *ci,
0278                   unsigned int idx)
0279 {
0280     if (cluster_list_empty(list)) {
0281         cluster_set_next_flag(&list->head, idx, 0);
0282         cluster_set_next_flag(&list->tail, idx, 0);
0283     } else {
0284         unsigned int tail = cluster_next(&list->tail);
0285 
0286         cluster_set_next(&ci[tail], idx);
0287         cluster_set_next_flag(&list->tail, idx, 0);
0288     }
0289 }
0290 
0291 static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
0292                        struct swap_cluster_info *ci)
0293 {
0294     unsigned int idx;
0295 
0296     idx = cluster_next(&list->head);
0297     if (cluster_next(&list->tail) == idx) {
0298         cluster_set_null(&list->head);
0299         cluster_set_null(&list->tail);
0300     } else
0301         cluster_set_next_flag(&list->head,
0302                       cluster_next(&ci[idx]), 0);
0303 
0304     return idx;
0305 }
0306 
0307 /* Add a cluster to discard list and schedule it to do discard */
0308 static void swap_cluster_schedule_discard(struct swap_info_struct *si,
0309         unsigned int idx)
0310 {
0311     /*
0312      * If scan_swap_map() can't find a free cluster, it will check
0313      * si->swap_map directly. To make sure the discarding cluster isn't
0314      * taken by scan_swap_map(), mark the swap entries bad (occupied). It
0315      * will be cleared after discard
0316      */
0317     memset(si->swap_map + idx * SWAPFILE_CLUSTER,
0318             SWAP_MAP_BAD, SWAPFILE_CLUSTER);
0319 
0320     cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
0321 
0322     schedule_work(&si->discard_work);
0323 }
0324 
0325 /*
0326  * Doing discard actually. After a cluster discard is finished, the cluster
0327  * will be added to free cluster list. caller should hold si->lock.
0328 */
0329 static void swap_do_scheduled_discard(struct swap_info_struct *si)
0330 {
0331     struct swap_cluster_info *info;
0332     unsigned int idx;
0333 
0334     info = si->cluster_info;
0335 
0336     while (!cluster_list_empty(&si->discard_clusters)) {
0337         idx = cluster_list_del_first(&si->discard_clusters, info);
0338         spin_unlock(&si->lock);
0339 
0340         discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
0341                 SWAPFILE_CLUSTER);
0342 
0343         spin_lock(&si->lock);
0344         cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE);
0345         cluster_list_add_tail(&si->free_clusters, info, idx);
0346         memset(si->swap_map + idx * SWAPFILE_CLUSTER,
0347                 0, SWAPFILE_CLUSTER);
0348     }
0349 }
0350 
0351 static void swap_discard_work(struct work_struct *work)
0352 {
0353     struct swap_info_struct *si;
0354 
0355     si = container_of(work, struct swap_info_struct, discard_work);
0356 
0357     spin_lock(&si->lock);
0358     swap_do_scheduled_discard(si);
0359     spin_unlock(&si->lock);
0360 }
0361 
0362 /*
0363  * The cluster corresponding to page_nr will be used. The cluster will be
0364  * removed from free cluster list and its usage counter will be increased.
0365  */
0366 static void inc_cluster_info_page(struct swap_info_struct *p,
0367     struct swap_cluster_info *cluster_info, unsigned long page_nr)
0368 {
0369     unsigned long idx = page_nr / SWAPFILE_CLUSTER;
0370 
0371     if (!cluster_info)
0372         return;
0373     if (cluster_is_free(&cluster_info[idx])) {
0374         VM_BUG_ON(cluster_list_first(&p->free_clusters) != idx);
0375         cluster_list_del_first(&p->free_clusters, cluster_info);
0376         cluster_set_count_flag(&cluster_info[idx], 0, 0);
0377     }
0378 
0379     VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
0380     cluster_set_count(&cluster_info[idx],
0381         cluster_count(&cluster_info[idx]) + 1);
0382 }
0383 
0384 /*
0385  * The cluster corresponding to page_nr decreases one usage. If the usage
0386  * counter becomes 0, which means no page in the cluster is in using, we can
0387  * optionally discard the cluster and add it to free cluster list.
0388  */
0389 static void dec_cluster_info_page(struct swap_info_struct *p,
0390     struct swap_cluster_info *cluster_info, unsigned long page_nr)
0391 {
0392     unsigned long idx = page_nr / SWAPFILE_CLUSTER;
0393 
0394     if (!cluster_info)
0395         return;
0396 
0397     VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
0398     cluster_set_count(&cluster_info[idx],
0399         cluster_count(&cluster_info[idx]) - 1);
0400 
0401     if (cluster_count(&cluster_info[idx]) == 0) {
0402         /*
0403          * If the swap is discardable, prepare discard the cluster
0404          * instead of free it immediately. The cluster will be freed
0405          * after discard.
0406          */
0407         if ((p->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
0408                  (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
0409             swap_cluster_schedule_discard(p, idx);
0410             return;
0411         }
0412 
0413         cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
0414         cluster_list_add_tail(&p->free_clusters, cluster_info, idx);
0415     }
0416 }
0417 
0418 /*
0419  * It's possible scan_swap_map() uses a free cluster in the middle of free
0420  * cluster list. Avoiding such abuse to avoid list corruption.
0421  */
0422 static bool
0423 scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
0424     unsigned long offset)
0425 {
0426     struct percpu_cluster *percpu_cluster;
0427     bool conflict;
0428 
0429     offset /= SWAPFILE_CLUSTER;
0430     conflict = !cluster_list_empty(&si->free_clusters) &&
0431         offset != cluster_list_first(&si->free_clusters) &&
0432         cluster_is_free(&si->cluster_info[offset]);
0433 
0434     if (!conflict)
0435         return false;
0436 
0437     percpu_cluster = this_cpu_ptr(si->percpu_cluster);
0438     cluster_set_null(&percpu_cluster->index);
0439     return true;
0440 }
0441 
0442 /*
0443  * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
0444  * might involve allocating a new cluster for current CPU too.
0445  */
0446 static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
0447     unsigned long *offset, unsigned long *scan_base)
0448 {
0449     struct percpu_cluster *cluster;
0450     bool found_free;
0451     unsigned long tmp;
0452 
0453 new_cluster:
0454     cluster = this_cpu_ptr(si->percpu_cluster);
0455     if (cluster_is_null(&cluster->index)) {
0456         if (!cluster_list_empty(&si->free_clusters)) {
0457             cluster->index = si->free_clusters.head;
0458             cluster->next = cluster_next(&cluster->index) *
0459                     SWAPFILE_CLUSTER;
0460         } else if (!cluster_list_empty(&si->discard_clusters)) {
0461             /*
0462              * we don't have free cluster but have some clusters in
0463              * discarding, do discard now and reclaim them
0464              */
0465             swap_do_scheduled_discard(si);
0466             *scan_base = *offset = si->cluster_next;
0467             goto new_cluster;
0468         } else
0469             return;
0470     }
0471 
0472     found_free = false;
0473 
0474     /*
0475      * Other CPUs can use our cluster if they can't find a free cluster,
0476      * check if there is still free entry in the cluster
0477      */
0478     tmp = cluster->next;
0479     while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) *
0480            SWAPFILE_CLUSTER) {
0481         if (!si->swap_map[tmp]) {
0482             found_free = true;
0483             break;
0484         }
0485         tmp++;
0486     }
0487     if (!found_free) {
0488         cluster_set_null(&cluster->index);
0489         goto new_cluster;
0490     }
0491     cluster->next = tmp + 1;
0492     *offset = tmp;
0493     *scan_base = tmp;
0494 }
0495 
0496 static unsigned long scan_swap_map(struct swap_info_struct *si,
0497                    unsigned char usage)
0498 {
0499     unsigned long offset;
0500     unsigned long scan_base;
0501     unsigned long last_in_cluster = 0;
0502     int latency_ration = LATENCY_LIMIT;
0503 
0504     /*
0505      * We try to cluster swap pages by allocating them sequentially
0506      * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
0507      * way, however, we resort to first-free allocation, starting
0508      * a new cluster.  This prevents us from scattering swap pages
0509      * all over the entire swap partition, so that we reduce
0510      * overall disk seek times between swap pages.  -- sct
0511      * But we do now try to find an empty cluster.  -Andrea
0512      * And we let swap pages go all over an SSD partition.  Hugh
0513      */
0514 
0515     si->flags += SWP_SCANNING;
0516     scan_base = offset = si->cluster_next;
0517 
0518     /* SSD algorithm */
0519     if (si->cluster_info) {
0520         scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
0521         goto checks;
0522     }
0523 
0524     if (unlikely(!si->cluster_nr--)) {
0525         if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
0526             si->cluster_nr = SWAPFILE_CLUSTER - 1;
0527             goto checks;
0528         }
0529 
0530         spin_unlock(&si->lock);
0531 
0532         /*
0533          * If seek is expensive, start searching for new cluster from
0534          * start of partition, to minimize the span of allocated swap.
0535          * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
0536          * case, just handled by scan_swap_map_try_ssd_cluster() above.
0537          */
0538         scan_base = offset = si->lowest_bit;
0539         last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
0540 
0541         /* Locate the first empty (unaligned) cluster */
0542         for (; last_in_cluster <= si->highest_bit; offset++) {
0543             if (si->swap_map[offset])
0544                 last_in_cluster = offset + SWAPFILE_CLUSTER;
0545             else if (offset == last_in_cluster) {
0546                 spin_lock(&si->lock);
0547                 offset -= SWAPFILE_CLUSTER - 1;
0548                 si->cluster_next = offset;
0549                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
0550                 goto checks;
0551             }
0552             if (unlikely(--latency_ration < 0)) {
0553                 cond_resched();
0554                 latency_ration = LATENCY_LIMIT;
0555             }
0556         }
0557 
0558         offset = scan_base;
0559         spin_lock(&si->lock);
0560         si->cluster_nr = SWAPFILE_CLUSTER - 1;
0561     }
0562 
0563 checks:
0564     if (si->cluster_info) {
0565         while (scan_swap_map_ssd_cluster_conflict(si, offset))
0566             scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
0567     }
0568     if (!(si->flags & SWP_WRITEOK))
0569         goto no_page;
0570     if (!si->highest_bit)
0571         goto no_page;
0572     if (offset > si->highest_bit)
0573         scan_base = offset = si->lowest_bit;
0574 
0575     /* reuse swap entry of cache-only swap if not busy. */
0576     if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
0577         int swap_was_freed;
0578         spin_unlock(&si->lock);
0579         swap_was_freed = __try_to_reclaim_swap(si, offset);
0580         spin_lock(&si->lock);
0581         /* entry was freed successfully, try to use this again */
0582         if (swap_was_freed)
0583             goto checks;
0584         goto scan; /* check next one */
0585     }
0586 
0587     if (si->swap_map[offset])
0588         goto scan;
0589 
0590     if (offset == si->lowest_bit)
0591         si->lowest_bit++;
0592     if (offset == si->highest_bit)
0593         si->highest_bit--;
0594     si->inuse_pages++;
0595     if (si->inuse_pages == si->pages) {
0596         si->lowest_bit = si->max;
0597         si->highest_bit = 0;
0598         spin_lock(&swap_avail_lock);
0599         plist_del(&si->avail_list, &swap_avail_head);
0600         spin_unlock(&swap_avail_lock);
0601     }
0602     si->swap_map[offset] = usage;
0603     inc_cluster_info_page(si, si->cluster_info, offset);
0604     si->cluster_next = offset + 1;
0605     si->flags -= SWP_SCANNING;
0606 
0607     return offset;
0608 
0609 scan:
0610     spin_unlock(&si->lock);
0611     while (++offset <= si->highest_bit) {
0612         if (!si->swap_map[offset]) {
0613             spin_lock(&si->lock);
0614             goto checks;
0615         }
0616         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
0617             spin_lock(&si->lock);
0618             goto checks;
0619         }
0620         if (unlikely(--latency_ration < 0)) {
0621             cond_resched();
0622             latency_ration = LATENCY_LIMIT;
0623         }
0624     }
0625     offset = si->lowest_bit;
0626     while (offset < scan_base) {
0627         if (!si->swap_map[offset]) {
0628             spin_lock(&si->lock);
0629             goto checks;
0630         }
0631         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
0632             spin_lock(&si->lock);
0633             goto checks;
0634         }
0635         if (unlikely(--latency_ration < 0)) {
0636             cond_resched();
0637             latency_ration = LATENCY_LIMIT;
0638         }
0639         offset++;
0640     }
0641     spin_lock(&si->lock);
0642 
0643 no_page:
0644     si->flags -= SWP_SCANNING;
0645     return 0;
0646 }
0647 
0648 swp_entry_t get_swap_page(void)
0649 {
0650     struct swap_info_struct *si, *next;
0651     pgoff_t offset;
0652 
0653     if (atomic_long_read(&nr_swap_pages) <= 0)
0654         goto noswap;
0655     atomic_long_dec(&nr_swap_pages);
0656 
0657     spin_lock(&swap_avail_lock);
0658 
0659 start_over:
0660     plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
0661         /* requeue si to after same-priority siblings */
0662         plist_requeue(&si->avail_list, &swap_avail_head);
0663         spin_unlock(&swap_avail_lock);
0664         spin_lock(&si->lock);
0665         if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
0666             spin_lock(&swap_avail_lock);
0667             if (plist_node_empty(&si->avail_list)) {
0668                 spin_unlock(&si->lock);
0669                 goto nextsi;
0670             }
0671             WARN(!si->highest_bit,
0672                  "swap_info %d in list but !highest_bit\n",
0673                  si->type);
0674             WARN(!(si->flags & SWP_WRITEOK),
0675                  "swap_info %d in list but !SWP_WRITEOK\n",
0676                  si->type);
0677             plist_del(&si->avail_list, &swap_avail_head);
0678             spin_unlock(&si->lock);
0679             goto nextsi;
0680         }
0681 
0682         /* This is called for allocating swap entry for cache */
0683         offset = scan_swap_map(si, SWAP_HAS_CACHE);
0684         spin_unlock(&si->lock);
0685         if (offset)
0686             return swp_entry(si->type, offset);
0687         pr_debug("scan_swap_map of si %d failed to find offset\n",
0688                si->type);
0689         spin_lock(&swap_avail_lock);
0690 nextsi:
0691         /*
0692          * if we got here, it's likely that si was almost full before,
0693          * and since scan_swap_map() can drop the si->lock, multiple
0694          * callers probably all tried to get a page from the same si
0695          * and it filled up before we could get one; or, the si filled
0696          * up between us dropping swap_avail_lock and taking si->lock.
0697          * Since we dropped the swap_avail_lock, the swap_avail_head
0698          * list may have been modified; so if next is still in the
0699          * swap_avail_head list then try it, otherwise start over.
0700          */
0701         if (plist_node_empty(&next->avail_list))
0702             goto start_over;
0703     }
0704 
0705     spin_unlock(&swap_avail_lock);
0706 
0707     atomic_long_inc(&nr_swap_pages);
0708 noswap:
0709     return (swp_entry_t) {0};
0710 }
0711 
0712 /* The only caller of this function is now suspend routine */
0713 swp_entry_t get_swap_page_of_type(int type)
0714 {
0715     struct swap_info_struct *si;
0716     pgoff_t offset;
0717 
0718     si = swap_info[type];
0719     spin_lock(&si->lock);
0720     if (si && (si->flags & SWP_WRITEOK)) {
0721         atomic_long_dec(&nr_swap_pages);
0722         /* This is called for allocating swap entry, not cache */
0723         offset = scan_swap_map(si, 1);
0724         if (offset) {
0725             spin_unlock(&si->lock);
0726             return swp_entry(type, offset);
0727         }
0728         atomic_long_inc(&nr_swap_pages);
0729     }
0730     spin_unlock(&si->lock);
0731     return (swp_entry_t) {0};
0732 }
0733 
0734 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
0735 {
0736     struct swap_info_struct *p;
0737     unsigned long offset, type;
0738 
0739     if (!entry.val)
0740         goto out;
0741     type = swp_type(entry);
0742     if (type >= nr_swapfiles)
0743         goto bad_nofile;
0744     p = swap_info[type];
0745     if (!(p->flags & SWP_USED))
0746         goto bad_device;
0747     offset = swp_offset(entry);
0748     if (offset >= p->max)
0749         goto bad_offset;
0750     if (!p->swap_map[offset])
0751         goto bad_free;
0752     spin_lock(&p->lock);
0753     return p;
0754 
0755 bad_free:
0756     pr_err("swap_free: %s%08lx\n", Unused_offset, entry.val);
0757     goto out;
0758 bad_offset:
0759     pr_err("swap_free: %s%08lx\n", Bad_offset, entry.val);
0760     goto out;
0761 bad_device:
0762     pr_err("swap_free: %s%08lx\n", Unused_file, entry.val);
0763     goto out;
0764 bad_nofile:
0765     pr_err("swap_free: %s%08lx\n", Bad_file, entry.val);
0766 out:
0767     return NULL;
0768 }
0769 
0770 static unsigned char swap_entry_free(struct swap_info_struct *p,
0771                      swp_entry_t entry, unsigned char usage)
0772 {
0773     unsigned long offset = swp_offset(entry);
0774     unsigned char count;
0775     unsigned char has_cache;
0776 
0777     count = p->swap_map[offset];
0778     has_cache = count & SWAP_HAS_CACHE;
0779     count &= ~SWAP_HAS_CACHE;
0780 
0781     if (usage == SWAP_HAS_CACHE) {
0782         VM_BUG_ON(!has_cache);
0783         has_cache = 0;
0784     } else if (count == SWAP_MAP_SHMEM) {
0785         /*
0786          * Or we could insist on shmem.c using a special
0787          * swap_shmem_free() and free_shmem_swap_and_cache()...
0788          */
0789         count = 0;
0790     } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
0791         if (count == COUNT_CONTINUED) {
0792             if (swap_count_continued(p, offset, count))
0793                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
0794             else
0795                 count = SWAP_MAP_MAX;
0796         } else
0797             count--;
0798     }
0799 
0800     usage = count | has_cache;
0801     p->swap_map[offset] = usage;
0802 
0803     /* free if no reference */
0804     if (!usage) {
0805         mem_cgroup_uncharge_swap(entry);
0806         dec_cluster_info_page(p, p->cluster_info, offset);
0807         if (offset < p->lowest_bit)
0808             p->lowest_bit = offset;
0809         if (offset > p->highest_bit) {
0810             bool was_full = !p->highest_bit;
0811             p->highest_bit = offset;
0812             if (was_full && (p->flags & SWP_WRITEOK)) {
0813                 spin_lock(&swap_avail_lock);
0814                 WARN_ON(!plist_node_empty(&p->avail_list));
0815                 if (plist_node_empty(&p->avail_list))
0816                     plist_add(&p->avail_list,
0817                           &swap_avail_head);
0818                 spin_unlock(&swap_avail_lock);
0819             }
0820         }
0821         atomic_long_inc(&nr_swap_pages);
0822         p->inuse_pages--;
0823         frontswap_invalidate_page(p->type, offset);
0824         if (p->flags & SWP_BLKDEV) {
0825             struct gendisk *disk = p->bdev->bd_disk;
0826             if (disk->fops->swap_slot_free_notify)
0827                 disk->fops->swap_slot_free_notify(p->bdev,
0828                                   offset);
0829         }
0830     }
0831 
0832     return usage;
0833 }
0834 
0835 /*
0836  * Caller has made sure that the swap device corresponding to entry
0837  * is still around or has not been recycled.
0838  */
0839 void swap_free(swp_entry_t entry)
0840 {
0841     struct swap_info_struct *p;
0842 
0843     p = swap_info_get(entry);
0844     if (p) {
0845         swap_entry_free(p, entry, 1);
0846         spin_unlock(&p->lock);
0847     }
0848 }
0849 
0850 /*
0851  * Called after dropping swapcache to decrease refcnt to swap entries.
0852  */
0853 void swapcache_free(swp_entry_t entry)
0854 {
0855     struct swap_info_struct *p;
0856 
0857     p = swap_info_get(entry);
0858     if (p) {
0859         swap_entry_free(p, entry, SWAP_HAS_CACHE);
0860         spin_unlock(&p->lock);
0861     }
0862 }
0863 
0864 /*
0865  * How many references to page are currently swapped out?
0866  * This does not give an exact answer when swap count is continued,
0867  * but does include the high COUNT_CONTINUED flag to allow for that.
0868  */
0869 int page_swapcount(struct page *page)
0870 {
0871     int count = 0;
0872     struct swap_info_struct *p;
0873     swp_entry_t entry;
0874 
0875     entry.val = page_private(page);
0876     p = swap_info_get(entry);
0877     if (p) {
0878         count = swap_count(p->swap_map[swp_offset(entry)]);
0879         spin_unlock(&p->lock);
0880     }
0881     return count;
0882 }
0883 
0884 /*
0885  * How many references to @entry are currently swapped out?
0886  * This considers COUNT_CONTINUED so it returns exact answer.
0887  */
0888 int swp_swapcount(swp_entry_t entry)
0889 {
0890     int count, tmp_count, n;
0891     struct swap_info_struct *p;
0892     struct page *page;
0893     pgoff_t offset;
0894     unsigned char *map;
0895 
0896     p = swap_info_get(entry);
0897     if (!p)
0898         return 0;
0899 
0900     count = swap_count(p->swap_map[swp_offset(entry)]);
0901     if (!(count & COUNT_CONTINUED))
0902         goto out;
0903 
0904     count &= ~COUNT_CONTINUED;
0905     n = SWAP_MAP_MAX + 1;
0906 
0907     offset = swp_offset(entry);
0908     page = vmalloc_to_page(p->swap_map + offset);
0909     offset &= ~PAGE_MASK;
0910     VM_BUG_ON(page_private(page) != SWP_CONTINUED);
0911 
0912     do {
0913         page = list_next_entry(page, lru);
0914         map = kmap_atomic(page);
0915         tmp_count = map[offset];
0916         kunmap_atomic(map);
0917 
0918         count += (tmp_count & ~COUNT_CONTINUED) * n;
0919         n *= (SWAP_CONT_MAX + 1);
0920     } while (tmp_count & COUNT_CONTINUED);
0921 out:
0922     spin_unlock(&p->lock);
0923     return count;
0924 }
0925 
0926 /*
0927  * We can write to an anon page without COW if there are no other references
0928  * to it.  And as a side-effect, free up its swap: because the old content
0929  * on disk will never be read, and seeking back there to write new content
0930  * later would only waste time away from clustering.
0931  *
0932  * NOTE: total_mapcount should not be relied upon by the caller if
0933  * reuse_swap_page() returns false, but it may be always overwritten
0934  * (see the other implementation for CONFIG_SWAP=n).
0935  */
0936 bool reuse_swap_page(struct page *page, int *total_mapcount)
0937 {
0938     int count;
0939 
0940     VM_BUG_ON_PAGE(!PageLocked(page), page);
0941     if (unlikely(PageKsm(page)))
0942         return false;
0943     count = page_trans_huge_mapcount(page, total_mapcount);
0944     if (count <= 1 && PageSwapCache(page)) {
0945         count += page_swapcount(page);
0946         if (count != 1)
0947             goto out;
0948         if (!PageWriteback(page)) {
0949             delete_from_swap_cache(page);
0950             SetPageDirty(page);
0951         } else {
0952             swp_entry_t entry;
0953             struct swap_info_struct *p;
0954 
0955             entry.val = page_private(page);
0956             p = swap_info_get(entry);
0957             if (p->flags & SWP_STABLE_WRITES) {
0958                 spin_unlock(&p->lock);
0959                 return false;
0960             }
0961             spin_unlock(&p->lock);
0962         }
0963     }
0964 out:
0965     return count <= 1;
0966 }
0967 
0968 /*
0969  * If swap is getting full, or if there are no more mappings of this page,
0970  * then try_to_free_swap is called to free its swap space.
0971  */
0972 int try_to_free_swap(struct page *page)
0973 {
0974     VM_BUG_ON_PAGE(!PageLocked(page), page);
0975 
0976     if (!PageSwapCache(page))
0977         return 0;
0978     if (PageWriteback(page))
0979         return 0;
0980     if (page_swapcount(page))
0981         return 0;
0982 
0983     /*
0984      * Once hibernation has begun to create its image of memory,
0985      * there's a danger that one of the calls to try_to_free_swap()
0986      * - most probably a call from __try_to_reclaim_swap() while
0987      * hibernation is allocating its own swap pages for the image,
0988      * but conceivably even a call from memory reclaim - will free
0989      * the swap from a page which has already been recorded in the
0990      * image as a clean swapcache page, and then reuse its swap for
0991      * another page of the image.  On waking from hibernation, the
0992      * original page might be freed under memory pressure, then
0993      * later read back in from swap, now with the wrong data.
0994      *
0995      * Hibernation suspends storage while it is writing the image
0996      * to disk so check that here.
0997      */
0998     if (pm_suspended_storage())
0999         return 0;
1000 
1001     delete_from_swap_cache(page);
1002     SetPageDirty(page);
1003     return 1;
1004 }
1005 
1006 /*
1007  * Free the swap entry like above, but also try to
1008  * free the page cache entry if it is the last user.
1009  */
1010 int free_swap_and_cache(swp_entry_t entry)
1011 {
1012     struct swap_info_struct *p;
1013     struct page *page = NULL;
1014 
1015     if (non_swap_entry(entry))
1016         return 1;
1017 
1018     p = swap_info_get(entry);
1019     if (p) {
1020         if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
1021             page = find_get_page(swap_address_space(entry),
1022                          swp_offset(entry));
1023             if (page && !trylock_page(page)) {
1024                 put_page(page);
1025                 page = NULL;
1026             }
1027         }
1028         spin_unlock(&p->lock);
1029     }
1030     if (page) {
1031         /*
1032          * Not mapped elsewhere, or swap space full? Free it!
1033          * Also recheck PageSwapCache now page is locked (above).
1034          */
1035         if (PageSwapCache(page) && !PageWriteback(page) &&
1036             (!page_mapped(page) || mem_cgroup_swap_full(page))) {
1037             delete_from_swap_cache(page);
1038             SetPageDirty(page);
1039         }
1040         unlock_page(page);
1041         put_page(page);
1042     }
1043     return p != NULL;
1044 }
1045 
1046 #ifdef CONFIG_HIBERNATION
1047 /*
1048  * Find the swap type that corresponds to given device (if any).
1049  *
1050  * @offset - number of the PAGE_SIZE-sized block of the device, starting
1051  * from 0, in which the swap header is expected to be located.
1052  *
1053  * This is needed for the suspend to disk (aka swsusp).
1054  */
1055 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
1056 {
1057     struct block_device *bdev = NULL;
1058     int type;
1059 
1060     if (device)
1061         bdev = bdget(device);
1062 
1063     spin_lock(&swap_lock);
1064     for (type = 0; type < nr_swapfiles; type++) {
1065         struct swap_info_struct *sis = swap_info[type];
1066 
1067         if (!(sis->flags & SWP_WRITEOK))
1068             continue;
1069 
1070         if (!bdev) {
1071             if (bdev_p)
1072                 *bdev_p = bdgrab(sis->bdev);
1073 
1074             spin_unlock(&swap_lock);
1075             return type;
1076         }
1077         if (bdev == sis->bdev) {
1078             struct swap_extent *se = &sis->first_swap_extent;
1079 
1080             if (se->start_block == offset) {
1081                 if (bdev_p)
1082                     *bdev_p = bdgrab(sis->bdev);
1083 
1084                 spin_unlock(&swap_lock);
1085                 bdput(bdev);
1086                 return type;
1087             }
1088         }
1089     }
1090     spin_unlock(&swap_lock);
1091     if (bdev)
1092         bdput(bdev);
1093 
1094     return -ENODEV;
1095 }
1096 
1097 /*
1098  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
1099  * corresponding to given index in swap_info (swap type).
1100  */
1101 sector_t swapdev_block(int type, pgoff_t offset)
1102 {
1103     struct block_device *bdev;
1104 
1105     if ((unsigned int)type >= nr_swapfiles)
1106         return 0;
1107     if (!(swap_info[type]->flags & SWP_WRITEOK))
1108         return 0;
1109     return map_swap_entry(swp_entry(type, offset), &bdev);
1110 }
1111 
1112 /*
1113  * Return either the total number of swap pages of given type, or the number
1114  * of free pages of that type (depending on @free)
1115  *
1116  * This is needed for software suspend
1117  */
1118 unsigned int count_swap_pages(int type, int free)
1119 {
1120     unsigned int n = 0;
1121 
1122     spin_lock(&swap_lock);
1123     if ((unsigned int)type < nr_swapfiles) {
1124         struct swap_info_struct *sis = swap_info[type];
1125 
1126         spin_lock(&sis->lock);
1127         if (sis->flags & SWP_WRITEOK) {
1128             n = sis->pages;
1129             if (free)
1130                 n -= sis->inuse_pages;
1131         }
1132         spin_unlock(&sis->lock);
1133     }
1134     spin_unlock(&swap_lock);
1135     return n;
1136 }
1137 #endif /* CONFIG_HIBERNATION */
1138 
1139 static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
1140 {
1141     return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
1142 }
1143 
1144 /*
1145  * No need to decide whether this PTE shares the swap entry with others,
1146  * just let do_wp_page work it out if a write is requested later - to
1147  * force COW, vm_page_prot omits write permission from any private vma.
1148  */
1149 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
1150         unsigned long addr, swp_entry_t entry, struct page *page)
1151 {
1152     struct page *swapcache;
1153     struct mem_cgroup *memcg;
1154     spinlock_t *ptl;
1155     pte_t *pte;
1156     int ret = 1;
1157 
1158     swapcache = page;
1159     page = ksm_might_need_to_copy(page, vma, addr);
1160     if (unlikely(!page))
1161         return -ENOMEM;
1162 
1163     if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
1164                 &memcg, false)) {
1165         ret = -ENOMEM;
1166         goto out_nolock;
1167     }
1168 
1169     pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
1170     if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
1171         mem_cgroup_cancel_charge(page, memcg, false);
1172         ret = 0;
1173         goto out;
1174     }
1175 
1176     dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
1177     inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
1178     get_page(page);
1179     set_pte_at(vma->vm_mm, addr, pte,
1180            pte_mkold(mk_pte(page, vma->vm_page_prot)));
1181     if (page == swapcache) {
1182         page_add_anon_rmap(page, vma, addr, false);
1183         mem_cgroup_commit_charge(page, memcg, true, false);
1184     } else { /* ksm created a completely new copy */
1185         page_add_new_anon_rmap(page, vma, addr, false);
1186         mem_cgroup_commit_charge(page, memcg, false, false);
1187         lru_cache_add_active_or_unevictable(page, vma);
1188     }
1189     swap_free(entry);
1190     /*
1191      * Move the page to the active list so it is not
1192      * immediately swapped out again after swapon.
1193      */
1194     activate_page(page);
1195 out:
1196     pte_unmap_unlock(pte, ptl);
1197 out_nolock:
1198     if (page != swapcache) {
1199         unlock_page(page);
1200         put_page(page);
1201     }
1202     return ret;
1203 }
1204 
1205 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
1206                 unsigned long addr, unsigned long end,
1207                 swp_entry_t entry, struct page *page)
1208 {
1209     pte_t swp_pte = swp_entry_to_pte(entry);
1210     pte_t *pte;
1211     int ret = 0;
1212 
1213     /*
1214      * We don't actually need pte lock while scanning for swp_pte: since
1215      * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
1216      * page table while we're scanning; though it could get zapped, and on
1217      * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
1218      * of unmatched parts which look like swp_pte, so unuse_pte must
1219      * recheck under pte lock.  Scanning without pte lock lets it be
1220      * preemptable whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
1221      */
1222     pte = pte_offset_map(pmd, addr);
1223     do {
1224         /*
1225          * swapoff spends a _lot_ of time in this loop!
1226          * Test inline before going to call unuse_pte.
1227          */
1228         if (unlikely(pte_same_as_swp(*pte, swp_pte))) {
1229             pte_unmap(pte);
1230             ret = unuse_pte(vma, pmd, addr, entry, page);
1231             if (ret)
1232                 goto out;
1233             pte = pte_offset_map(pmd, addr);
1234         }
1235     } while (pte++, addr += PAGE_SIZE, addr != end);
1236     pte_unmap(pte - 1);
1237 out:
1238     return ret;
1239 }
1240 
1241 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
1242                 unsigned long addr, unsigned long end,
1243                 swp_entry_t entry, struct page *page)
1244 {
1245     pmd_t *pmd;
1246     unsigned long next;
1247     int ret;
1248 
1249     pmd = pmd_offset(pud, addr);
1250     do {
1251         cond_resched();
1252         next = pmd_addr_end(addr, end);
1253         if (pmd_none_or_trans_huge_or_clear_bad(pmd))
1254             continue;
1255         ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
1256         if (ret)
1257             return ret;
1258     } while (pmd++, addr = next, addr != end);
1259     return 0;
1260 }
1261 
1262 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
1263                 unsigned long addr, unsigned long end,
1264                 swp_entry_t entry, struct page *page)
1265 {
1266     pud_t *pud;
1267     unsigned long next;
1268     int ret;
1269 
1270     pud = pud_offset(pgd, addr);
1271     do {
1272         next = pud_addr_end(addr, end);
1273         if (pud_none_or_clear_bad(pud))
1274             continue;
1275         ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
1276         if (ret)
1277             return ret;
1278     } while (pud++, addr = next, addr != end);
1279     return 0;
1280 }
1281 
1282 static int unuse_vma(struct vm_area_struct *vma,
1283                 swp_entry_t entry, struct page *page)
1284 {
1285     pgd_t *pgd;
1286     unsigned long addr, end, next;
1287     int ret;
1288 
1289     if (page_anon_vma(page)) {
1290         addr = page_address_in_vma(page, vma);
1291         if (addr == -EFAULT)
1292             return 0;
1293         else
1294             end = addr + PAGE_SIZE;
1295     } else {
1296         addr = vma->vm_start;
1297         end = vma->vm_end;
1298     }
1299 
1300     pgd = pgd_offset(vma->vm_mm, addr);
1301     do {
1302         next = pgd_addr_end(addr, end);
1303         if (pgd_none_or_clear_bad(pgd))
1304             continue;
1305         ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1306         if (ret)
1307             return ret;
1308     } while (pgd++, addr = next, addr != end);
1309     return 0;
1310 }
1311 
1312 static int unuse_mm(struct mm_struct *mm,
1313                 swp_entry_t entry, struct page *page)
1314 {
1315     struct vm_area_struct *vma;
1316     int ret = 0;
1317 
1318     if (!down_read_trylock(&mm->mmap_sem)) {
1319         /*
1320          * Activate page so shrink_inactive_list is unlikely to unmap
1321          * its ptes while lock is dropped, so swapoff can make progress.
1322          */
1323         activate_page(page);
1324         unlock_page(page);
1325         down_read(&mm->mmap_sem);
1326         lock_page(page);
1327     }
1328     for (vma = mm->mmap; vma; vma = vma->vm_next) {
1329         if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1330             break;
1331         cond_resched();
1332     }
1333     up_read(&mm->mmap_sem);
1334     return (ret < 0)? ret: 0;
1335 }
1336 
1337 /*
1338  * Scan swap_map (or frontswap_map if frontswap parameter is true)
1339  * from current position to next entry still in use.
1340  * Recycle to start on reaching the end, returning 0 when empty.
1341  */
1342 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1343                     unsigned int prev, bool frontswap)
1344 {
1345     unsigned int max = si->max;
1346     unsigned int i = prev;
1347     unsigned char count;
1348 
1349     /*
1350      * No need for swap_lock here: we're just looking
1351      * for whether an entry is in use, not modifying it; false
1352      * hits are okay, and sys_swapoff() has already prevented new
1353      * allocations from this area (while holding swap_lock).
1354      */
1355     for (;;) {
1356         if (++i >= max) {
1357             if (!prev) {
1358                 i = 0;
1359                 break;
1360             }
1361             /*
1362              * No entries in use at top of swap_map,
1363              * loop back to start and recheck there.
1364              */
1365             max = prev + 1;
1366             prev = 0;
1367             i = 1;
1368         }
1369         count = READ_ONCE(si->swap_map[i]);
1370         if (count && swap_count(count) != SWAP_MAP_BAD)
1371             if (!frontswap || frontswap_test(si, i))
1372                 break;
1373         if ((i % LATENCY_LIMIT) == 0)
1374             cond_resched();
1375     }
1376     return i;
1377 }
1378 
1379 /*
1380  * We completely avoid races by reading each swap page in advance,
1381  * and then search for the process using it.  All the necessary
1382  * page table adjustments can then be made atomically.
1383  *
1384  * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1385  * pages_to_unuse==0 means all pages; ignored if frontswap is false
1386  */
1387 int try_to_unuse(unsigned int type, bool frontswap,
1388          unsigned long pages_to_unuse)
1389 {
1390     struct swap_info_struct *si = swap_info[type];
1391     struct mm_struct *start_mm;
1392     volatile unsigned char *swap_map; /* swap_map is accessed without
1393                        * locking. Mark it as volatile
1394                        * to prevent compiler doing
1395                        * something odd.
1396                        */
1397     unsigned char swcount;
1398     struct page *page;
1399     swp_entry_t entry;
1400     unsigned int i = 0;
1401     int retval = 0;
1402 
1403     /*
1404      * When searching mms for an entry, a good strategy is to
1405      * start at the first mm we freed the previous entry from
1406      * (though actually we don't notice whether we or coincidence
1407      * freed the entry).  Initialize this start_mm with a hold.
1408      *
1409      * A simpler strategy would be to start at the last mm we
1410      * freed the previous entry from; but that would take less
1411      * advantage of mmlist ordering, which clusters forked mms
1412      * together, child after parent.  If we race with dup_mmap(), we
1413      * prefer to resolve parent before child, lest we miss entries
1414      * duplicated after we scanned child: using last mm would invert
1415      * that.
1416      */
1417     start_mm = &init_mm;
1418     atomic_inc(&init_mm.mm_users);
1419 
1420     /*
1421      * Keep on scanning until all entries have gone.  Usually,
1422      * one pass through swap_map is enough, but not necessarily:
1423      * there are races when an instance of an entry might be missed.
1424      */
1425     while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1426         if (signal_pending(current)) {
1427             retval = -EINTR;
1428             break;
1429         }
1430 
1431         /*
1432          * Get a page for the entry, using the existing swap
1433          * cache page if there is one.  Otherwise, get a clean
1434          * page and read the swap into it.
1435          */
1436         swap_map = &si->swap_map[i];
1437         entry = swp_entry(type, i);
1438         page = read_swap_cache_async(entry,
1439                     GFP_HIGHUSER_MOVABLE, NULL, 0);
1440         if (!page) {
1441             /*
1442              * Either swap_duplicate() failed because entry
1443              * has been freed independently, and will not be
1444              * reused since sys_swapoff() already disabled
1445              * allocation from here, or alloc_page() failed.
1446              */
1447             swcount = *swap_map;
1448             /*
1449              * We don't hold lock here, so the swap entry could be
1450              * SWAP_MAP_BAD (when the cluster is discarding).
1451              * Instead of fail out, We can just skip the swap
1452              * entry because swapoff will wait for discarding
1453              * finish anyway.
1454              */
1455             if (!swcount || swcount == SWAP_MAP_BAD)
1456                 continue;
1457             retval = -ENOMEM;
1458             break;
1459         }
1460 
1461         /*
1462          * Don't hold on to start_mm if it looks like exiting.
1463          */
1464         if (atomic_read(&start_mm->mm_users) == 1) {
1465             mmput(start_mm);
1466             start_mm = &init_mm;
1467             atomic_inc(&init_mm.mm_users);
1468         }
1469 
1470         /*
1471          * Wait for and lock page.  When do_swap_page races with
1472          * try_to_unuse, do_swap_page can handle the fault much
1473          * faster than try_to_unuse can locate the entry.  This
1474          * apparently redundant "wait_on_page_locked" lets try_to_unuse
1475          * defer to do_swap_page in such a case - in some tests,
1476          * do_swap_page and try_to_unuse repeatedly compete.
1477          */
1478         wait_on_page_locked(page);
1479         wait_on_page_writeback(page);
1480         lock_page(page);
1481         wait_on_page_writeback(page);
1482 
1483         /*
1484          * Remove all references to entry.
1485          */
1486         swcount = *swap_map;
1487         if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1488             retval = shmem_unuse(entry, page);
1489             /* page has already been unlocked and released */
1490             if (retval < 0)
1491                 break;
1492             continue;
1493         }
1494         if (swap_count(swcount) && start_mm != &init_mm)
1495             retval = unuse_mm(start_mm, entry, page);
1496 
1497         if (swap_count(*swap_map)) {
1498             int set_start_mm = (*swap_map >= swcount);
1499             struct list_head *p = &start_mm->mmlist;
1500             struct mm_struct *new_start_mm = start_mm;
1501             struct mm_struct *prev_mm = start_mm;
1502             struct mm_struct *mm;
1503 
1504             atomic_inc(&new_start_mm->mm_users);
1505             atomic_inc(&prev_mm->mm_users);
1506             spin_lock(&mmlist_lock);
1507             while (swap_count(*swap_map) && !retval &&
1508                     (p = p->next) != &start_mm->mmlist) {
1509                 mm = list_entry(p, struct mm_struct, mmlist);
1510                 if (!atomic_inc_not_zero(&mm->mm_users))
1511                     continue;
1512                 spin_unlock(&mmlist_lock);
1513                 mmput(prev_mm);
1514                 prev_mm = mm;
1515 
1516                 cond_resched();
1517 
1518                 swcount = *swap_map;
1519                 if (!swap_count(swcount)) /* any usage ? */
1520                     ;
1521                 else if (mm == &init_mm)
1522                     set_start_mm = 1;
1523                 else
1524                     retval = unuse_mm(mm, entry, page);
1525 
1526                 if (set_start_mm && *swap_map < swcount) {
1527                     mmput(new_start_mm);
1528                     atomic_inc(&mm->mm_users);
1529                     new_start_mm = mm;
1530                     set_start_mm = 0;
1531                 }
1532                 spin_lock(&mmlist_lock);
1533             }
1534             spin_unlock(&mmlist_lock);
1535             mmput(prev_mm);
1536             mmput(start_mm);
1537             start_mm = new_start_mm;
1538         }
1539         if (retval) {
1540             unlock_page(page);
1541             put_page(page);
1542             break;
1543         }
1544 
1545         /*
1546          * If a reference remains (rare), we would like to leave
1547          * the page in the swap cache; but try_to_unmap could
1548          * then re-duplicate the entry once we drop page lock,
1549          * so we might loop indefinitely; also, that page could
1550          * not be swapped out to other storage meanwhile.  So:
1551          * delete from cache even if there's another reference,
1552          * after ensuring that the data has been saved to disk -
1553          * since if the reference remains (rarer), it will be
1554          * read from disk into another page.  Splitting into two
1555          * pages would be incorrect if swap supported "shared
1556          * private" pages, but they are handled by tmpfs files.
1557          *
1558          * Given how unuse_vma() targets one particular offset
1559          * in an anon_vma, once the anon_vma has been determined,
1560          * this splitting happens to be just what is needed to
1561          * handle where KSM pages have been swapped out: re-reading
1562          * is unnecessarily slow, but we can fix that later on.
1563          */
1564         if (swap_count(*swap_map) &&
1565              PageDirty(page) && PageSwapCache(page)) {
1566             struct writeback_control wbc = {
1567                 .sync_mode = WB_SYNC_NONE,
1568             };
1569 
1570             swap_writepage(page, &wbc);
1571             lock_page(page);
1572             wait_on_page_writeback(page);
1573         }
1574 
1575         /*
1576          * It is conceivable that a racing task removed this page from
1577          * swap cache just before we acquired the page lock at the top,
1578          * or while we dropped it in unuse_mm().  The page might even
1579          * be back in swap cache on another swap area: that we must not
1580          * delete, since it may not have been written out to swap yet.
1581          */
1582         if (PageSwapCache(page) &&
1583             likely(page_private(page) == entry.val))
1584             delete_from_swap_cache(page);
1585 
1586         /*
1587          * So we could skip searching mms once swap count went
1588          * to 1, we did not mark any present ptes as dirty: must
1589          * mark page dirty so shrink_page_list will preserve it.
1590          */
1591         SetPageDirty(page);
1592         unlock_page(page);
1593         put_page(page);
1594 
1595         /*
1596          * Make sure that we aren't completely killing
1597          * interactive performance.
1598          */
1599         cond_resched();
1600         if (frontswap && pages_to_unuse > 0) {
1601             if (!--pages_to_unuse)
1602                 break;
1603         }
1604     }
1605 
1606     mmput(start_mm);
1607     return retval;
1608 }
1609 
1610 /*
1611  * After a successful try_to_unuse, if no swap is now in use, we know
1612  * we can empty the mmlist.  swap_lock must be held on entry and exit.
1613  * Note that mmlist_lock nests inside swap_lock, and an mm must be
1614  * added to the mmlist just after page_duplicate - before would be racy.
1615  */
1616 static void drain_mmlist(void)
1617 {
1618     struct list_head *p, *next;
1619     unsigned int type;
1620 
1621     for (type = 0; type < nr_swapfiles; type++)
1622         if (swap_info[type]->inuse_pages)
1623             return;
1624     spin_lock(&mmlist_lock);
1625     list_for_each_safe(p, next, &init_mm.mmlist)
1626         list_del_init(p);
1627     spin_unlock(&mmlist_lock);
1628 }
1629 
1630 /*
1631  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1632  * corresponds to page offset for the specified swap entry.
1633  * Note that the type of this function is sector_t, but it returns page offset
1634  * into the bdev, not sector offset.
1635  */
1636 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1637 {
1638     struct swap_info_struct *sis;
1639     struct swap_extent *start_se;
1640     struct swap_extent *se;
1641     pgoff_t offset;
1642 
1643     sis = swap_info[swp_type(entry)];
1644     *bdev = sis->bdev;
1645 
1646     offset = swp_offset(entry);
1647     start_se = sis->curr_swap_extent;
1648     se = start_se;
1649 
1650     for ( ; ; ) {
1651         if (se->start_page <= offset &&
1652                 offset < (se->start_page + se->nr_pages)) {
1653             return se->start_block + (offset - se->start_page);
1654         }
1655         se = list_next_entry(se, list);
1656         sis->curr_swap_extent = se;
1657         BUG_ON(se == start_se);     /* It *must* be present */
1658     }
1659 }
1660 
1661 /*
1662  * Returns the page offset into bdev for the specified page's swap entry.
1663  */
1664 sector_t map_swap_page(struct page *page, struct block_device **bdev)
1665 {
1666     swp_entry_t entry;
1667     entry.val = page_private(page);
1668     return map_swap_entry(entry, bdev);
1669 }
1670 
1671 /*
1672  * Free all of a swapdev's extent information
1673  */
1674 static void destroy_swap_extents(struct swap_info_struct *sis)
1675 {
1676     while (!list_empty(&sis->first_swap_extent.list)) {
1677         struct swap_extent *se;
1678 
1679         se = list_first_entry(&sis->first_swap_extent.list,
1680                 struct swap_extent, list);
1681         list_del(&se->list);
1682         kfree(se);
1683     }
1684 
1685     if (sis->flags & SWP_FILE) {
1686         struct file *swap_file = sis->swap_file;
1687         struct address_space *mapping = swap_file->f_mapping;
1688 
1689         sis->flags &= ~SWP_FILE;
1690         mapping->a_ops->swap_deactivate(swap_file);
1691     }
1692 }
1693 
1694 /*
1695  * Add a block range (and the corresponding page range) into this swapdev's
1696  * extent list.  The extent list is kept sorted in page order.
1697  *
1698  * This function rather assumes that it is called in ascending page order.
1699  */
1700 int
1701 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1702         unsigned long nr_pages, sector_t start_block)
1703 {
1704     struct swap_extent *se;
1705     struct swap_extent *new_se;
1706     struct list_head *lh;
1707 
1708     if (start_page == 0) {
1709         se = &sis->first_swap_extent;
1710         sis->curr_swap_extent = se;
1711         se->start_page = 0;
1712         se->nr_pages = nr_pages;
1713         se->start_block = start_block;
1714         return 1;
1715     } else {
1716         lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1717         se = list_entry(lh, struct swap_extent, list);
1718         BUG_ON(se->start_page + se->nr_pages != start_page);
1719         if (se->start_block + se->nr_pages == start_block) {
1720             /* Merge it */
1721             se->nr_pages += nr_pages;
1722             return 0;
1723         }
1724     }
1725 
1726     /*
1727      * No merge.  Insert a new extent, preserving ordering.
1728      */
1729     new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1730     if (new_se == NULL)
1731         return -ENOMEM;
1732     new_se->start_page = start_page;
1733     new_se->nr_pages = nr_pages;
1734     new_se->start_block = start_block;
1735 
1736     list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1737     return 1;
1738 }
1739 
1740 /*
1741  * A `swap extent' is a simple thing which maps a contiguous range of pages
1742  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1743  * is built at swapon time and is then used at swap_writepage/swap_readpage
1744  * time for locating where on disk a page belongs.
1745  *
1746  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1747  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1748  * swap files identically.
1749  *
1750  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1751  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1752  * swapfiles are handled *identically* after swapon time.
1753  *
1754  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1755  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1756  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1757  * requirements, they are simply tossed out - we will never use those blocks
1758  * for swapping.
1759  *
1760  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1761  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1762  * which will scribble on the fs.
1763  *
1764  * The amount of disk space which a single swap extent represents varies.
1765  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1766  * extents in the list.  To avoid much list walking, we cache the previous
1767  * search location in `curr_swap_extent', and start new searches from there.
1768  * This is extremely effective.  The average number of iterations in
1769  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1770  */
1771 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1772 {
1773     struct file *swap_file = sis->swap_file;
1774     struct address_space *mapping = swap_file->f_mapping;
1775     struct inode *inode = mapping->host;
1776     int ret;
1777 
1778     if (S_ISBLK(inode->i_mode)) {
1779         ret = add_swap_extent(sis, 0, sis->max, 0);
1780         *span = sis->pages;
1781         return ret;
1782     }
1783 
1784     if (mapping->a_ops->swap_activate) {
1785         ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1786         if (!ret) {
1787             sis->flags |= SWP_FILE;
1788             ret = add_swap_extent(sis, 0, sis->max, 0);
1789             *span = sis->pages;
1790         }
1791         return ret;
1792     }
1793 
1794     return generic_swapfile_activate(sis, swap_file, span);
1795 }
1796 
1797 static void _enable_swap_info(struct swap_info_struct *p, int prio,
1798                 unsigned char *swap_map,
1799                 struct swap_cluster_info *cluster_info)
1800 {
1801     if (prio >= 0)
1802         p->prio = prio;
1803     else
1804         p->prio = --least_priority;
1805     /*
1806      * the plist prio is negated because plist ordering is
1807      * low-to-high, while swap ordering is high-to-low
1808      */
1809     p->list.prio = -p->prio;
1810     p->avail_list.prio = -p->prio;
1811     p->swap_map = swap_map;
1812     p->cluster_info = cluster_info;
1813     p->flags |= SWP_WRITEOK;
1814     atomic_long_add(p->pages, &nr_swap_pages);
1815     total_swap_pages += p->pages;
1816 
1817     assert_spin_locked(&swap_lock);
1818     /*
1819      * both lists are plists, and thus priority ordered.
1820      * swap_active_head needs to be priority ordered for swapoff(),
1821      * which on removal of any swap_info_struct with an auto-assigned
1822      * (i.e. negative) priority increments the auto-assigned priority
1823      * of any lower-priority swap_info_structs.
1824      * swap_avail_head needs to be priority ordered for get_swap_page(),
1825      * which allocates swap pages from the highest available priority
1826      * swap_info_struct.
1827      */
1828     plist_add(&p->list, &swap_active_head);
1829     spin_lock(&swap_avail_lock);
1830     plist_add(&p->avail_list, &swap_avail_head);
1831     spin_unlock(&swap_avail_lock);
1832 }
1833 
1834 static void enable_swap_info(struct swap_info_struct *p, int prio,
1835                 unsigned char *swap_map,
1836                 struct swap_cluster_info *cluster_info,
1837                 unsigned long *frontswap_map)
1838 {
1839     frontswap_init(p->type, frontswap_map);
1840     spin_lock(&swap_lock);
1841     spin_lock(&p->lock);
1842      _enable_swap_info(p, prio, swap_map, cluster_info);
1843     spin_unlock(&p->lock);
1844     spin_unlock(&swap_lock);
1845 }
1846 
1847 static void reinsert_swap_info(struct swap_info_struct *p)
1848 {
1849     spin_lock(&swap_lock);
1850     spin_lock(&p->lock);
1851     _enable_swap_info(p, p->prio, p->swap_map, p->cluster_info);
1852     spin_unlock(&p->lock);
1853     spin_unlock(&swap_lock);
1854 }
1855 
1856 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1857 {
1858     struct swap_info_struct *p = NULL;
1859     unsigned char *swap_map;
1860     struct swap_cluster_info *cluster_info;
1861     unsigned long *frontswap_map;
1862     struct file *swap_file, *victim;
1863     struct address_space *mapping;
1864     struct inode *inode;
1865     struct filename *pathname;
1866     int err, found = 0;
1867     unsigned int old_block_size;
1868 
1869     if (!capable(CAP_SYS_ADMIN))
1870         return -EPERM;
1871 
1872     BUG_ON(!current->mm);
1873 
1874     pathname = getname(specialfile);
1875     if (IS_ERR(pathname))
1876         return PTR_ERR(pathname);
1877 
1878     victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1879     err = PTR_ERR(victim);
1880     if (IS_ERR(victim))
1881         goto out;
1882 
1883     mapping = victim->f_mapping;
1884     spin_lock(&swap_lock);
1885     plist_for_each_entry(p, &swap_active_head, list) {
1886         if (p->flags & SWP_WRITEOK) {
1887             if (p->swap_file->f_mapping == mapping) {
1888                 found = 1;
1889                 break;
1890             }
1891         }
1892     }
1893     if (!found) {
1894         err = -EINVAL;
1895         spin_unlock(&swap_lock);
1896         goto out_dput;
1897     }
1898     if (!security_vm_enough_memory_mm(current->mm, p->pages))
1899         vm_unacct_memory(p->pages);
1900     else {
1901         err = -ENOMEM;
1902         spin_unlock(&swap_lock);
1903         goto out_dput;
1904     }
1905     spin_lock(&swap_avail_lock);
1906     plist_del(&p->avail_list, &swap_avail_head);
1907     spin_unlock(&swap_avail_lock);
1908     spin_lock(&p->lock);
1909     if (p->prio < 0) {
1910         struct swap_info_struct *si = p;
1911 
1912         plist_for_each_entry_continue(si, &swap_active_head, list) {
1913             si->prio++;
1914             si->list.prio--;
1915             si->avail_list.prio--;
1916         }
1917         least_priority++;
1918     }
1919     plist_del(&p->list, &swap_active_head);
1920     atomic_long_sub(p->pages, &nr_swap_pages);
1921     total_swap_pages -= p->pages;
1922     p->flags &= ~SWP_WRITEOK;
1923     spin_unlock(&p->lock);
1924     spin_unlock(&swap_lock);
1925 
1926     set_current_oom_origin();
1927     err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
1928     clear_current_oom_origin();
1929 
1930     if (err) {
1931         /* re-insert swap space back into swap_list */
1932         reinsert_swap_info(p);
1933         goto out_dput;
1934     }
1935 
1936     flush_work(&p->discard_work);
1937 
1938     destroy_swap_extents(p);
1939     if (p->flags & SWP_CONTINUED)
1940         free_swap_count_continuations(p);
1941 
1942     mutex_lock(&swapon_mutex);
1943     spin_lock(&swap_lock);
1944     spin_lock(&p->lock);
1945     drain_mmlist();
1946 
1947     /* wait for anyone still in scan_swap_map */
1948     p->highest_bit = 0;     /* cuts scans short */
1949     while (p->flags >= SWP_SCANNING) {
1950         spin_unlock(&p->lock);
1951         spin_unlock(&swap_lock);
1952         schedule_timeout_uninterruptible(1);
1953         spin_lock(&swap_lock);
1954         spin_lock(&p->lock);
1955     }
1956 
1957     swap_file = p->swap_file;
1958     old_block_size = p->old_block_size;
1959     p->swap_file = NULL;
1960     p->max = 0;
1961     swap_map = p->swap_map;
1962     p->swap_map = NULL;
1963     cluster_info = p->cluster_info;
1964     p->cluster_info = NULL;
1965     frontswap_map = frontswap_map_get(p);
1966     spin_unlock(&p->lock);
1967     spin_unlock(&swap_lock);
1968     frontswap_invalidate_area(p->type);
1969     frontswap_map_set(p, NULL);
1970     mutex_unlock(&swapon_mutex);
1971     free_percpu(p->percpu_cluster);
1972     p->percpu_cluster = NULL;
1973     vfree(swap_map);
1974     vfree(cluster_info);
1975     vfree(frontswap_map);
1976     /* Destroy swap account information */
1977     swap_cgroup_swapoff(p->type);
1978 
1979     inode = mapping->host;
1980     if (S_ISBLK(inode->i_mode)) {
1981         struct block_device *bdev = I_BDEV(inode);
1982         set_blocksize(bdev, old_block_size);
1983         blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1984     } else {
1985         inode_lock(inode);
1986         inode->i_flags &= ~S_SWAPFILE;
1987         inode_unlock(inode);
1988     }
1989     filp_close(swap_file, NULL);
1990 
1991     /*
1992      * Clear the SWP_USED flag after all resources are freed so that swapon
1993      * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
1994      * not hold p->lock after we cleared its SWP_WRITEOK.
1995      */
1996     spin_lock(&swap_lock);
1997     p->flags = 0;
1998     spin_unlock(&swap_lock);
1999 
2000     err = 0;
2001     atomic_inc(&proc_poll_event);
2002     wake_up_interruptible(&proc_poll_wait);
2003 
2004 out_dput:
2005     filp_close(victim, NULL);
2006 out:
2007     putname(pathname);
2008     return err;
2009 }
2010 
2011 #ifdef CONFIG_PROC_FS
2012 static unsigned swaps_poll(struct file *file, poll_table *wait)
2013 {
2014     struct seq_file *seq = file->private_data;
2015 
2016     poll_wait(file, &proc_poll_wait, wait);
2017 
2018     if (seq->poll_event != atomic_read(&proc_poll_event)) {
2019         seq->poll_event = atomic_read(&proc_poll_event);
2020         return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
2021     }
2022 
2023     return POLLIN | POLLRDNORM;
2024 }
2025 
2026 /* iterator */
2027 static void *swap_start(struct seq_file *swap, loff_t *pos)
2028 {
2029     struct swap_info_struct *si;
2030     int type;
2031     loff_t l = *pos;
2032 
2033     mutex_lock(&swapon_mutex);
2034 
2035     if (!l)
2036         return SEQ_START_TOKEN;
2037 
2038     for (type = 0; type < nr_swapfiles; type++) {
2039         smp_rmb();  /* read nr_swapfiles before swap_info[type] */
2040         si = swap_info[type];
2041         if (!(si->flags & SWP_USED) || !si->swap_map)
2042             continue;
2043         if (!--l)
2044             return si;
2045     }
2046 
2047     return NULL;
2048 }
2049 
2050 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
2051 {
2052     struct swap_info_struct *si = v;
2053     int type;
2054 
2055     if (v == SEQ_START_TOKEN)
2056         type = 0;
2057     else
2058         type = si->type + 1;
2059 
2060     for (; type < nr_swapfiles; type++) {
2061         smp_rmb();  /* read nr_swapfiles before swap_info[type] */
2062         si = swap_info[type];
2063         if (!(si->flags & SWP_USED) || !si->swap_map)
2064             continue;
2065         ++*pos;
2066         return si;
2067     }
2068 
2069     return NULL;
2070 }
2071 
2072 static void swap_stop(struct seq_file *swap, void *v)
2073 {
2074     mutex_unlock(&swapon_mutex);
2075 }
2076 
2077 static int swap_show(struct seq_file *swap, void *v)
2078 {
2079     struct swap_info_struct *si = v;
2080     struct file *file;
2081     int len;
2082 
2083     if (si == SEQ_START_TOKEN) {
2084         seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
2085         return 0;
2086     }
2087 
2088     file = si->swap_file;
2089     len = seq_file_path(swap, file, " \t\n\\");
2090     seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
2091             len < 40 ? 40 - len : 1, " ",
2092             S_ISBLK(file_inode(file)->i_mode) ?
2093                 "partition" : "file\t",
2094             si->pages << (PAGE_SHIFT - 10),
2095             si->inuse_pages << (PAGE_SHIFT - 10),
2096             si->prio);
2097     return 0;
2098 }
2099 
2100 static const struct seq_operations swaps_op = {
2101     .start =    swap_start,
2102     .next =     swap_next,
2103     .stop =     swap_stop,
2104     .show =     swap_show
2105 };
2106 
2107 static int swaps_open(struct inode *inode, struct file *file)
2108 {
2109     struct seq_file *seq;
2110     int ret;
2111 
2112     ret = seq_open(file, &swaps_op);
2113     if (ret)
2114         return ret;
2115 
2116     seq = file->private_data;
2117     seq->poll_event = atomic_read(&proc_poll_event);
2118     return 0;
2119 }
2120 
2121 static const struct file_operations proc_swaps_operations = {
2122     .open       = swaps_open,
2123     .read       = seq_read,
2124     .llseek     = seq_lseek,
2125     .release    = seq_release,
2126     .poll       = swaps_poll,
2127 };
2128 
2129 static int __init procswaps_init(void)
2130 {
2131     proc_create("swaps", 0, NULL, &proc_swaps_operations);
2132     return 0;
2133 }
2134 __initcall(procswaps_init);
2135 #endif /* CONFIG_PROC_FS */
2136 
2137 #ifdef MAX_SWAPFILES_CHECK
2138 static int __init max_swapfiles_check(void)
2139 {
2140     MAX_SWAPFILES_CHECK();
2141     return 0;
2142 }
2143 late_initcall(max_swapfiles_check);
2144 #endif
2145 
2146 static struct swap_info_struct *alloc_swap_info(void)
2147 {
2148     struct swap_info_struct *p;
2149     unsigned int type;
2150 
2151     p = kzalloc(sizeof(*p), GFP_KERNEL);
2152     if (!p)
2153         return ERR_PTR(-ENOMEM);
2154 
2155     spin_lock(&swap_lock);
2156     for (type = 0; type < nr_swapfiles; type++) {
2157         if (!(swap_info[type]->flags & SWP_USED))
2158             break;
2159     }
2160     if (type >= MAX_SWAPFILES) {
2161         spin_unlock(&swap_lock);
2162         kfree(p);
2163         return ERR_PTR(-EPERM);
2164     }
2165     if (type >= nr_swapfiles) {
2166         p->type = type;
2167         swap_info[type] = p;
2168         /*
2169          * Write swap_info[type] before nr_swapfiles, in case a
2170          * racing procfs swap_start() or swap_next() is reading them.
2171          * (We never shrink nr_swapfiles, we never free this entry.)
2172          */
2173         smp_wmb();
2174         nr_swapfiles++;
2175     } else {
2176         kfree(p);
2177         p = swap_info[type];
2178         /*
2179          * Do not memset this entry: a racing procfs swap_next()
2180          * would be relying on p->type to remain valid.
2181          */
2182     }
2183     INIT_LIST_HEAD(&p->first_swap_extent.list);
2184     plist_node_init(&p->list, 0);
2185     plist_node_init(&p->avail_list, 0);
2186     p->flags = SWP_USED;
2187     spin_unlock(&swap_lock);
2188     spin_lock_init(&p->lock);
2189 
2190     return p;
2191 }
2192 
2193 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
2194 {
2195     int error;
2196 
2197     if (S_ISBLK(inode->i_mode)) {
2198         p->bdev = bdgrab(I_BDEV(inode));
2199         error = blkdev_get(p->bdev,
2200                    FMODE_READ | FMODE_WRITE | FMODE_EXCL, p);
2201         if (error < 0) {
2202             p->bdev = NULL;
2203             return error;
2204         }
2205         p->old_block_size = block_size(p->bdev);
2206         error = set_blocksize(p->bdev, PAGE_SIZE);
2207         if (error < 0)
2208             return error;
2209         p->flags |= SWP_BLKDEV;
2210     } else if (S_ISREG(inode->i_mode)) {
2211         p->bdev = inode->i_sb->s_bdev;
2212         inode_lock(inode);
2213         if (IS_SWAPFILE(inode))
2214             return -EBUSY;
2215     } else
2216         return -EINVAL;
2217 
2218     return 0;
2219 }
2220 
2221 static unsigned long read_swap_header(struct swap_info_struct *p,
2222                     union swap_header *swap_header,
2223                     struct inode *inode)
2224 {
2225     int i;
2226     unsigned long maxpages;
2227     unsigned long swapfilepages;
2228     unsigned long last_page;
2229 
2230     if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
2231         pr_err("Unable to find swap-space signature\n");
2232         return 0;
2233     }
2234 
2235     /* swap partition endianess hack... */
2236     if (swab32(swap_header->info.version) == 1) {
2237         swab32s(&swap_header->info.version);
2238         swab32s(&swap_header->info.last_page);
2239         swab32s(&swap_header->info.nr_badpages);
2240         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2241             return 0;
2242         for (i = 0; i < swap_header->info.nr_badpages; i++)
2243             swab32s(&swap_header->info.badpages[i]);
2244     }
2245     /* Check the swap header's sub-version */
2246     if (swap_header->info.version != 1) {
2247         pr_warn("Unable to handle swap header version %d\n",
2248             swap_header->info.version);
2249         return 0;
2250     }
2251 
2252     p->lowest_bit  = 1;
2253     p->cluster_next = 1;
2254     p->cluster_nr = 0;
2255 
2256     /*
2257      * Find out how many pages are allowed for a single swap
2258      * device. There are two limiting factors: 1) the number
2259      * of bits for the swap offset in the swp_entry_t type, and
2260      * 2) the number of bits in the swap pte as defined by the
2261      * different architectures. In order to find the
2262      * largest possible bit mask, a swap entry with swap type 0
2263      * and swap offset ~0UL is created, encoded to a swap pte,
2264      * decoded to a swp_entry_t again, and finally the swap
2265      * offset is extracted. This will mask all the bits from
2266      * the initial ~0UL mask that can't be encoded in either
2267      * the swp_entry_t or the architecture definition of a
2268      * swap pte.
2269      */
2270     maxpages = swp_offset(pte_to_swp_entry(
2271             swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
2272     last_page = swap_header->info.last_page;
2273     if (last_page > maxpages) {
2274         pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
2275             maxpages << (PAGE_SHIFT - 10),
2276             last_page << (PAGE_SHIFT - 10));
2277     }
2278     if (maxpages > last_page) {
2279         maxpages = last_page + 1;
2280         /* p->max is an unsigned int: don't overflow it */
2281         if ((unsigned int)maxpages == 0)
2282             maxpages = UINT_MAX;
2283     }
2284     p->highest_bit = maxpages - 1;
2285 
2286     if (!maxpages)
2287         return 0;
2288     swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
2289     if (swapfilepages && maxpages > swapfilepages) {
2290         pr_warn("Swap area shorter than signature indicates\n");
2291         return 0;
2292     }
2293     if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
2294         return 0;
2295     if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2296         return 0;
2297 
2298     return maxpages;
2299 }
2300 
2301 static int setup_swap_map_and_extents(struct swap_info_struct *p,
2302                     union swap_header *swap_header,
2303                     unsigned char *swap_map,
2304                     struct swap_cluster_info *cluster_info,
2305                     unsigned long maxpages,
2306                     sector_t *span)
2307 {
2308     int i;
2309     unsigned int nr_good_pages;
2310     int nr_extents;
2311     unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
2312     unsigned long idx = p->cluster_next / SWAPFILE_CLUSTER;
2313 
2314     nr_good_pages = maxpages - 1;   /* omit header page */
2315 
2316     cluster_list_init(&p->free_clusters);
2317     cluster_list_init(&p->discard_clusters);
2318 
2319     for (i = 0; i < swap_header->info.nr_badpages; i++) {
2320         unsigned int page_nr = swap_header->info.badpages[i];
2321         if (page_nr == 0 || page_nr > swap_header->info.last_page)
2322             return -EINVAL;
2323         if (page_nr < maxpages) {
2324             swap_map[page_nr] = SWAP_MAP_BAD;
2325             nr_good_pages--;
2326             /*
2327              * Haven't marked the cluster free yet, no list
2328              * operation involved
2329              */
2330             inc_cluster_info_page(p, cluster_info, page_nr);
2331         }
2332     }
2333 
2334     /* Haven't marked the cluster free yet, no list operation involved */
2335     for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
2336         inc_cluster_info_page(p, cluster_info, i);
2337 
2338     if (nr_good_pages) {
2339         swap_map[0] = SWAP_MAP_BAD;
2340         /*
2341          * Not mark the cluster free yet, no list
2342          * operation involved
2343          */
2344         inc_cluster_info_page(p, cluster_info, 0);
2345         p->max = maxpages;
2346         p->pages = nr_good_pages;
2347         nr_extents = setup_swap_extents(p, span);
2348         if (nr_extents < 0)
2349             return nr_extents;
2350         nr_good_pages = p->pages;
2351     }
2352     if (!nr_good_pages) {
2353         pr_warn("Empty swap-file\n");
2354         return -EINVAL;
2355     }
2356 
2357     if (!cluster_info)
2358         return nr_extents;
2359 
2360     for (i = 0; i < nr_clusters; i++) {
2361         if (!cluster_count(&cluster_info[idx])) {
2362             cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
2363             cluster_list_add_tail(&p->free_clusters, cluster_info,
2364                           idx);
2365         }
2366         idx++;
2367         if (idx == nr_clusters)
2368             idx = 0;
2369     }
2370     return nr_extents;
2371 }
2372 
2373 /*
2374  * Helper to sys_swapon determining if a given swap
2375  * backing device queue supports DISCARD operations.
2376  */
2377 static bool swap_discardable(struct swap_info_struct *si)
2378 {
2379     struct request_queue *q = bdev_get_queue(si->bdev);
2380 
2381     if (!q || !blk_queue_discard(q))
2382         return false;
2383 
2384     return true;
2385 }
2386 
2387 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2388 {
2389     struct swap_info_struct *p;
2390     struct filename *name;
2391     struct file *swap_file = NULL;
2392     struct address_space *mapping;
2393     int prio;
2394     int error;
2395     union swap_header *swap_header;
2396     int nr_extents;
2397     sector_t span;
2398     unsigned long maxpages;
2399     unsigned char *swap_map = NULL;
2400     struct swap_cluster_info *cluster_info = NULL;
2401     unsigned long *frontswap_map = NULL;
2402     struct page *page = NULL;
2403     struct inode *inode = NULL;
2404 
2405     if (swap_flags & ~SWAP_FLAGS_VALID)
2406         return -EINVAL;
2407 
2408     if (!capable(CAP_SYS_ADMIN))
2409         return -EPERM;
2410 
2411     p = alloc_swap_info();
2412     if (IS_ERR(p))
2413         return PTR_ERR(p);
2414 
2415     INIT_WORK(&p->discard_work, swap_discard_work);
2416 
2417     name = getname(specialfile);
2418     if (IS_ERR(name)) {
2419         error = PTR_ERR(name);
2420         name = NULL;
2421         goto bad_swap;
2422     }
2423     swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2424     if (IS_ERR(swap_file)) {
2425         error = PTR_ERR(swap_file);
2426         swap_file = NULL;
2427         goto bad_swap;
2428     }
2429 
2430     p->swap_file = swap_file;
2431     mapping = swap_file->f_mapping;
2432     inode = mapping->host;
2433 
2434     /* If S_ISREG(inode->i_mode) will do inode_lock(inode); */
2435     error = claim_swapfile(p, inode);
2436     if (unlikely(error))
2437         goto bad_swap;
2438 
2439     /*
2440      * Read the swap header.
2441      */
2442     if (!mapping->a_ops->readpage) {
2443         error = -EINVAL;
2444         goto bad_swap;
2445     }
2446     page = read_mapping_page(mapping, 0, swap_file);
2447     if (IS_ERR(page)) {
2448         error = PTR_ERR(page);
2449         goto bad_swap;
2450     }
2451     swap_header = kmap(page);
2452 
2453     maxpages = read_swap_header(p, swap_header, inode);
2454     if (unlikely(!maxpages)) {
2455         error = -EINVAL;
2456         goto bad_swap;
2457     }
2458 
2459     /* OK, set up the swap map and apply the bad block list */
2460     swap_map = vzalloc(maxpages);
2461     if (!swap_map) {
2462         error = -ENOMEM;
2463         goto bad_swap;
2464     }
2465 
2466     if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
2467         p->flags |= SWP_STABLE_WRITES;
2468 
2469     if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2470         int cpu;
2471 
2472         p->flags |= SWP_SOLIDSTATE;
2473         /*
2474          * select a random position to start with to help wear leveling
2475          * SSD
2476          */
2477         p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2478 
2479         cluster_info = vzalloc(DIV_ROUND_UP(maxpages,
2480             SWAPFILE_CLUSTER) * sizeof(*cluster_info));
2481         if (!cluster_info) {
2482             error = -ENOMEM;
2483             goto bad_swap;
2484         }
2485         p->percpu_cluster = alloc_percpu(struct percpu_cluster);
2486         if (!p->percpu_cluster) {
2487             error = -ENOMEM;
2488             goto bad_swap;
2489         }
2490         for_each_possible_cpu(cpu) {
2491             struct percpu_cluster *cluster;
2492             cluster = per_cpu_ptr(p->percpu_cluster, cpu);
2493             cluster_set_null(&cluster->index);
2494         }
2495     }
2496 
2497     error = swap_cgroup_swapon(p->type, maxpages);
2498     if (error)
2499         goto bad_swap;
2500 
2501     nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2502         cluster_info, maxpages, &span);
2503     if (unlikely(nr_extents < 0)) {
2504         error = nr_extents;
2505         goto bad_swap;
2506     }
2507     /* frontswap enabled? set up bit-per-page map for frontswap */
2508     if (IS_ENABLED(CONFIG_FRONTSWAP))
2509         frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2510 
2511     if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
2512         /*
2513          * When discard is enabled for swap with no particular
2514          * policy flagged, we set all swap discard flags here in
2515          * order to sustain backward compatibility with older
2516          * swapon(8) releases.
2517          */
2518         p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
2519                  SWP_PAGE_DISCARD);
2520 
2521         /*
2522          * By flagging sys_swapon, a sysadmin can tell us to
2523          * either do single-time area discards only, or to just
2524          * perform discards for released swap page-clusters.
2525          * Now it's time to adjust the p->flags accordingly.
2526          */
2527         if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
2528             p->flags &= ~SWP_PAGE_DISCARD;
2529         else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
2530             p->flags &= ~SWP_AREA_DISCARD;
2531 
2532         /* issue a swapon-time discard if it's still required */
2533         if (p->flags & SWP_AREA_DISCARD) {
2534             int err = discard_swap(p);
2535             if (unlikely(err))
2536                 pr_err("swapon: discard_swap(%p): %d\n",
2537                     p, err);
2538         }
2539     }
2540 
2541     mutex_lock(&swapon_mutex);
2542     prio = -1;
2543     if (swap_flags & SWAP_FLAG_PREFER)
2544         prio =
2545           (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2546     enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
2547 
2548     pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
2549         p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2550         nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2551         (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2552         (p->flags & SWP_DISCARDABLE) ? "D" : "",
2553         (p->flags & SWP_AREA_DISCARD) ? "s" : "",
2554         (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
2555         (frontswap_map) ? "FS" : "");
2556 
2557     mutex_unlock(&swapon_mutex);
2558     atomic_inc(&proc_poll_event);
2559     wake_up_interruptible(&proc_poll_wait);
2560 
2561     if (S_ISREG(inode->i_mode))
2562         inode->i_flags |= S_SWAPFILE;
2563     error = 0;
2564     goto out;
2565 bad_swap:
2566     free_percpu(p->percpu_cluster);
2567     p->percpu_cluster = NULL;
2568     if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2569         set_blocksize(p->bdev, p->old_block_size);
2570         blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2571     }
2572     destroy_swap_extents(p);
2573     swap_cgroup_swapoff(p->type);
2574     spin_lock(&swap_lock);
2575     p->swap_file = NULL;
2576     p->flags = 0;
2577     spin_unlock(&swap_lock);
2578     vfree(swap_map);
2579     vfree(cluster_info);
2580     if (swap_file) {
2581         if (inode && S_ISREG(inode->i_mode)) {
2582             inode_unlock(inode);
2583             inode = NULL;
2584         }
2585         filp_close(swap_file, NULL);
2586     }
2587 out:
2588     if (page && !IS_ERR(page)) {
2589         kunmap(page);
2590         put_page(page);
2591     }
2592     if (name)
2593         putname(name);
2594     if (inode && S_ISREG(inode->i_mode))
2595         inode_unlock(inode);
2596     return error;
2597 }
2598 
2599 void si_swapinfo(struct sysinfo *val)
2600 {
2601     unsigned int type;
2602     unsigned long nr_to_be_unused = 0;
2603 
2604     spin_lock(&swap_lock);
2605     for (type = 0; type < nr_swapfiles; type++) {
2606         struct swap_info_struct *si = swap_info[type];
2607 
2608         if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2609             nr_to_be_unused += si->inuse_pages;
2610     }
2611     val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2612     val->totalswap = total_swap_pages + nr_to_be_unused;
2613     spin_unlock(&swap_lock);
2614 }
2615 
2616 /*
2617  * Verify that a swap entry is valid and increment its swap map count.
2618  *
2619  * Returns error code in following case.
2620  * - success -> 0
2621  * - swp_entry is invalid -> EINVAL
2622  * - swp_entry is migration entry -> EINVAL
2623  * - swap-cache reference is requested but there is already one. -> EEXIST
2624  * - swap-cache reference is requested but the entry is not used. -> ENOENT
2625  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2626  */
2627 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2628 {
2629     struct swap_info_struct *p;
2630     unsigned long offset, type;
2631     unsigned char count;
2632     unsigned char has_cache;
2633     int err = -EINVAL;
2634 
2635     if (non_swap_entry(entry))
2636         goto out;
2637 
2638     type = swp_type(entry);
2639     if (type >= nr_swapfiles)
2640         goto bad_file;
2641     p = swap_info[type];
2642     offset = swp_offset(entry);
2643 
2644     spin_lock(&p->lock);
2645     if (unlikely(offset >= p->max))
2646         goto unlock_out;
2647 
2648     count = p->swap_map[offset];
2649 
2650     /*
2651      * swapin_readahead() doesn't check if a swap entry is valid, so the
2652      * swap entry could be SWAP_MAP_BAD. Check here with lock held.
2653      */
2654     if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
2655         err = -ENOENT;
2656         goto unlock_out;
2657     }
2658 
2659     has_cache = count & SWAP_HAS_CACHE;
2660     count &= ~SWAP_HAS_CACHE;
2661     err = 0;
2662 
2663     if (usage == SWAP_HAS_CACHE) {
2664 
2665         /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2666         if (!has_cache && count)
2667             has_cache = SWAP_HAS_CACHE;
2668         else if (has_cache)     /* someone else added cache */
2669             err = -EEXIST;
2670         else                /* no users remaining */
2671             err = -ENOENT;
2672 
2673     } else if (count || has_cache) {
2674 
2675         if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2676             count += usage;
2677         else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2678             err = -EINVAL;
2679         else if (swap_count_continued(p, offset, count))
2680             count = COUNT_CONTINUED;
2681         else
2682             err = -ENOMEM;
2683     } else
2684         err = -ENOENT;          /* unused swap entry */
2685 
2686     p->swap_map[offset] = count | has_cache;
2687 
2688 unlock_out:
2689     spin_unlock(&p->lock);
2690 out:
2691     return err;
2692 
2693 bad_file:
2694     pr_err("swap_dup: %s%08lx\n", Bad_file, entry.val);
2695     goto out;
2696 }
2697 
2698 /*
2699  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2700  * (in which case its reference count is never incremented).
2701  */
2702 void swap_shmem_alloc(swp_entry_t entry)
2703 {
2704     __swap_duplicate(entry, SWAP_MAP_SHMEM);
2705 }
2706 
2707 /*
2708  * Increase reference count of swap entry by 1.
2709  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2710  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2711  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2712  * might occur if a page table entry has got corrupted.
2713  */
2714 int swap_duplicate(swp_entry_t entry)
2715 {
2716     int err = 0;
2717 
2718     while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2719         err = add_swap_count_continuation(entry, GFP_ATOMIC);
2720     return err;
2721 }
2722 
2723 /*
2724  * @entry: swap entry for which we allocate swap cache.
2725  *
2726  * Called when allocating swap cache for existing swap entry,
2727  * This can return error codes. Returns 0 at success.
2728  * -EBUSY means there is a swap cache.
2729  * Note: return code is different from swap_duplicate().
2730  */
2731 int swapcache_prepare(swp_entry_t entry)
2732 {
2733     return __swap_duplicate(entry, SWAP_HAS_CACHE);
2734 }
2735 
2736 struct swap_info_struct *page_swap_info(struct page *page)
2737 {
2738     swp_entry_t swap = { .val = page_private(page) };
2739     return swap_info[swp_type(swap)];
2740 }
2741 
2742 /*
2743  * out-of-line __page_file_ methods to avoid include hell.
2744  */
2745 struct address_space *__page_file_mapping(struct page *page)
2746 {
2747     VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2748     return page_swap_info(page)->swap_file->f_mapping;
2749 }
2750 EXPORT_SYMBOL_GPL(__page_file_mapping);
2751 
2752 pgoff_t __page_file_index(struct page *page)
2753 {
2754     swp_entry_t swap = { .val = page_private(page) };
2755     VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2756     return swp_offset(swap);
2757 }
2758 EXPORT_SYMBOL_GPL(__page_file_index);
2759 
2760 /*
2761  * add_swap_count_continuation - called when a swap count is duplicated
2762  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2763  * page of the original vmalloc'ed swap_map, to hold the continuation count
2764  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2765  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2766  *
2767  * These continuation pages are seldom referenced: the common paths all work
2768  * on the original swap_map, only referring to a continuation page when the
2769  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2770  *
2771  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2772  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2773  * can be called after dropping locks.
2774  */
2775 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2776 {
2777     struct swap_info_struct *si;
2778     struct page *head;
2779     struct page *page;
2780     struct page *list_page;
2781     pgoff_t offset;
2782     unsigned char count;
2783 
2784     /*
2785      * When debugging, it's easier to use __GFP_ZERO here; but it's better
2786      * for latency not to zero a page while GFP_ATOMIC and holding locks.
2787      */
2788     page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2789 
2790     si = swap_info_get(entry);
2791     if (!si) {
2792         /*
2793          * An acceptable race has occurred since the failing
2794          * __swap_duplicate(): the swap entry has been freed,
2795          * perhaps even the whole swap_map cleared for swapoff.
2796          */
2797         goto outer;
2798     }
2799 
2800     offset = swp_offset(entry);
2801     count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2802 
2803     if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2804         /*
2805          * The higher the swap count, the more likely it is that tasks
2806          * will race to add swap count continuation: we need to avoid
2807          * over-provisioning.
2808          */
2809         goto out;
2810     }
2811 
2812     if (!page) {
2813         spin_unlock(&si->lock);
2814         return -ENOMEM;
2815     }
2816 
2817     /*
2818      * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2819      * no architecture is using highmem pages for kernel page tables: so it
2820      * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps.
2821      */
2822     head = vmalloc_to_page(si->swap_map + offset);
2823     offset &= ~PAGE_MASK;
2824 
2825     /*
2826      * Page allocation does not initialize the page's lru field,
2827      * but it does always reset its private field.
2828      */
2829     if (!page_private(head)) {
2830         BUG_ON(count & COUNT_CONTINUED);
2831         INIT_LIST_HEAD(&head->lru);
2832         set_page_private(head, SWP_CONTINUED);
2833         si->flags |= SWP_CONTINUED;
2834     }
2835 
2836     list_for_each_entry(list_page, &head->lru, lru) {
2837         unsigned char *map;
2838 
2839         /*
2840          * If the previous map said no continuation, but we've found
2841          * a continuation page, free our allocation and use this one.
2842          */
2843         if (!(count & COUNT_CONTINUED))
2844             goto out;
2845 
2846         map = kmap_atomic(list_page) + offset;
2847         count = *map;
2848         kunmap_atomic(map);
2849 
2850         /*
2851          * If this continuation count now has some space in it,
2852          * free our allocation and use this one.
2853          */
2854         if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2855             goto out;
2856     }
2857 
2858     list_add_tail(&page->lru, &head->lru);
2859     page = NULL;            /* now it's attached, don't free it */
2860 out:
2861     spin_unlock(&si->lock);
2862 outer:
2863     if (page)
2864         __free_page(page);
2865     return 0;
2866 }
2867 
2868 /*
2869  * swap_count_continued - when the original swap_map count is incremented
2870  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2871  * into, carry if so, or else fail until a new continuation page is allocated;
2872  * when the original swap_map count is decremented from 0 with continuation,
2873  * borrow from the continuation and report whether it still holds more.
2874  * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2875  */
2876 static bool swap_count_continued(struct swap_info_struct *si,
2877                  pgoff_t offset, unsigned char count)
2878 {
2879     struct page *head;
2880     struct page *page;
2881     unsigned char *map;
2882 
2883     head = vmalloc_to_page(si->swap_map + offset);
2884     if (page_private(head) != SWP_CONTINUED) {
2885         BUG_ON(count & COUNT_CONTINUED);
2886         return false;       /* need to add count continuation */
2887     }
2888 
2889     offset &= ~PAGE_MASK;
2890     page = list_entry(head->lru.next, struct page, lru);
2891     map = kmap_atomic(page) + offset;
2892 
2893     if (count == SWAP_MAP_MAX)  /* initial increment from swap_map */
2894         goto init_map;      /* jump over SWAP_CONT_MAX checks */
2895 
2896     if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2897         /*
2898          * Think of how you add 1 to 999
2899          */
2900         while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2901             kunmap_atomic(map);
2902             page = list_entry(page->lru.next, struct page, lru);
2903             BUG_ON(page == head);
2904             map = kmap_atomic(page) + offset;
2905         }
2906         if (*map == SWAP_CONT_MAX) {
2907             kunmap_atomic(map);
2908             page = list_entry(page->lru.next, struct page, lru);
2909             if (page == head)
2910                 return false;   /* add count continuation */
2911             map = kmap_atomic(page) + offset;
2912 init_map:       *map = 0;       /* we didn't zero the page */
2913         }
2914         *map += 1;
2915         kunmap_atomic(map);
2916         page = list_entry(page->lru.prev, struct page, lru);
2917         while (page != head) {
2918             map = kmap_atomic(page) + offset;
2919             *map = COUNT_CONTINUED;
2920             kunmap_atomic(map);
2921             page = list_entry(page->lru.prev, struct page, lru);
2922         }
2923         return true;            /* incremented */
2924 
2925     } else {                /* decrementing */
2926         /*
2927          * Think of how you subtract 1 from 1000
2928          */
2929         BUG_ON(count != COUNT_CONTINUED);
2930         while (*map == COUNT_CONTINUED) {
2931             kunmap_atomic(map);
2932             page = list_entry(page->lru.next, struct page, lru);
2933             BUG_ON(page == head);
2934             map = kmap_atomic(page) + offset;
2935         }
2936         BUG_ON(*map == 0);
2937         *map -= 1;
2938         if (*map == 0)
2939             count = 0;
2940         kunmap_atomic(map);
2941         page = list_entry(page->lru.prev, struct page, lru);
2942         while (page != head) {
2943             map = kmap_atomic(page) + offset;
2944             *map = SWAP_CONT_MAX | count;
2945             count = COUNT_CONTINUED;
2946             kunmap_atomic(map);
2947             page = list_entry(page->lru.prev, struct page, lru);
2948         }
2949         return count == COUNT_CONTINUED;
2950     }
2951 }
2952 
2953 /*
2954  * free_swap_count_continuations - swapoff free all the continuation pages
2955  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2956  */
2957 static void free_swap_count_continuations(struct swap_info_struct *si)
2958 {
2959     pgoff_t offset;
2960 
2961     for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2962         struct page *head;
2963         head = vmalloc_to_page(si->swap_map + offset);
2964         if (page_private(head)) {
2965             struct page *page, *next;
2966 
2967             list_for_each_entry_safe(page, next, &head->lru, lru) {
2968                 list_del(&page->lru);
2969                 __free_page(page);
2970             }
2971         }
2972     }
2973 }