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 /*
  * Copyright (C) 2009-2011 Red Hat, Inc.
  *
  * Author: Mikulas Patocka <mpatocka@redhat.com>
  *
  * This file is released under the GPL.
  */
 
 #include <linux/dm-bufio.h>
 
 #include <linux/device-mapper.h>
 #include <linux/dm-io.h>
 #include <linux/slab.h>
 #include <linux/sched/mm.h>
 #include <linux/jiffies.h>
 #include <linux/vmalloc.h>
 #include <linux/shrinker.h>
 #include <linux/module.h>
 #include <linux/rbtree.h>
 #include <linux/stacktrace.h>
 #include <linux/jump_label.h>
 
 #define DM_MSG_PREFIX "bufio"
 
 /*
  * Memory management policy:
  *  Limit the number of buffers to DM_BUFIO_MEMORY_PERCENT of main memory
  *  or DM_BUFIO_VMALLOC_PERCENT of vmalloc memory (whichever is lower).
  *  Always allocate at least DM_BUFIO_MIN_BUFFERS buffers.
  *  Start background writeback when there are DM_BUFIO_WRITEBACK_PERCENT
  *  dirty buffers.
  */
 #define DM_BUFIO_MIN_BUFFERS        8
 
 #define DM_BUFIO_MEMORY_PERCENT     2
 #define DM_BUFIO_VMALLOC_PERCENT    25
 #define DM_BUFIO_WRITEBACK_RATIO    3
 #define DM_BUFIO_LOW_WATERMARK_RATIO    16
 
 /*
  * Check buffer ages in this interval (seconds)
  */
 #define DM_BUFIO_WORK_TIMER_SECS    30
 
 /*
  * Free buffers when they are older than this (seconds)
  */
 #define DM_BUFIO_DEFAULT_AGE_SECS   300
 
 /*
  * The nr of bytes of cached data to keep around.
  */
 #define DM_BUFIO_DEFAULT_RETAIN_BYTES   (256 * 1024)
 
 /*
  * Align buffer writes to this boundary.
  * Tests show that SSDs have the highest IOPS when using 4k writes.
  */
 #define DM_BUFIO_WRITE_ALIGN        4096
 
 /*
  * dm_buffer->list_mode
  */
 #define LIST_CLEAN  0
 #define LIST_DIRTY  1
 #define LIST_SIZE   2
 
 /*
  * Linking of buffers:
  *  All buffers are linked to buffer_tree with their node field.
  *
  *  Clean buffers that are not being written (B_WRITING not set)
  *  are linked to lru[LIST_CLEAN] with their lru_list field.
  *
  *  Dirty and clean buffers that are being written are linked to
  *  lru[LIST_DIRTY] with their lru_list field. When the write
  *  finishes, the buffer cannot be relinked immediately (because we
  *  are in an interrupt context and relinking requires process
  *  context), so some clean-not-writing buffers can be held on
  *  dirty_lru too.  They are later added to lru in the process
  *  context.
  */
 struct dm_bufio_client {
     struct mutex lock;
     spinlock_t spinlock;
     bool no_sleep;
 
     struct list_head lru[LIST_SIZE];
     unsigned long n_buffers[LIST_SIZE];
 
     struct block_device *bdev;
     unsigned block_size;
     s8 sectors_per_block_bits;
     void (*alloc_callback)(struct dm_buffer *);
     void (*write_callback)(struct dm_buffer *);
     struct kmem_cache *slab_buffer;
     struct kmem_cache *slab_cache;
     struct dm_io_client *dm_io;
 
     struct list_head reserved_buffers;
     unsigned need_reserved_buffers;
 
     unsigned minimum_buffers;
 
     struct rb_root buffer_tree;
     wait_queue_head_t free_buffer_wait;
 
     sector_t start;
 
     int async_write_error;
 
     struct list_head client_list;
 
     struct shrinker shrinker;
     struct work_struct shrink_work;
     atomic_long_t need_shrink;
 };
 
 /*
  * Buffer state bits.
  */
 #define B_READING   0
 #define B_WRITING   1
 #define B_DIRTY     2
 
 /*
  * Describes how the block was allocated:
  * kmem_cache_alloc(), __get_free_pages() or vmalloc().
  * See the comment at alloc_buffer_data.
  */
 enum data_mode {
     DATA_MODE_SLAB = 0,
     DATA_MODE_GET_FREE_PAGES = 1,
     DATA_MODE_VMALLOC = 2,
     DATA_MODE_LIMIT = 3
 };
 
 struct dm_buffer {
     struct rb_node node;
     struct list_head lru_list;
     struct list_head global_list;
     sector_t block;
     void *data;
     unsigned char data_mode;        /* DATA_MODE_* */
     unsigned char list_mode;        /* LIST_* */
     blk_status_t read_error;
     blk_status_t write_error;
     unsigned accessed;
     unsigned hold_count;
     unsigned long state;
     unsigned long last_accessed;
     unsigned dirty_start;
     unsigned dirty_end;
     unsigned write_start;
     unsigned write_end;
     struct dm_bufio_client *c;
     struct list_head write_list;
     void (*end_io)(struct dm_buffer *, blk_status_t);
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
 #define MAX_STACK 10
     unsigned int stack_len;
     unsigned long stack_entries[MAX_STACK];
 #endif
 };
 
 static DEFINE_STATIC_KEY_FALSE(no_sleep_enabled);
 
 /*----------------------------------------------------------------*/
 
 #define dm_bufio_in_request()   (!!current->bio_list)
 
 static void dm_bufio_lock(struct dm_bufio_client *c)
 {
     if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
         spin_lock_bh(&c->spinlock);
     else
         mutex_lock_nested(&c->lock, dm_bufio_in_request());
 }
 
 static int dm_bufio_trylock(struct dm_bufio_client *c)
 {
     if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
         return spin_trylock_bh(&c->spinlock);
     else
         return mutex_trylock(&c->lock);
 }
 
 static void dm_bufio_unlock(struct dm_bufio_client *c)
 {
     if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
         spin_unlock_bh(&c->spinlock);
     else
         mutex_unlock(&c->lock);
 }
 
 /*----------------------------------------------------------------*/
 
 /*
  * Default cache size: available memory divided by the ratio.
  */
 static unsigned long dm_bufio_default_cache_size;
 
 /*
  * Total cache size set by the user.
  */
 static unsigned long dm_bufio_cache_size;
 
 /*
  * A copy of dm_bufio_cache_size because dm_bufio_cache_size can change
  * at any time.  If it disagrees, the user has changed cache size.
  */
 static unsigned long dm_bufio_cache_size_latch;
 
 static DEFINE_SPINLOCK(global_spinlock);
 
 static LIST_HEAD(global_queue);
 
 static unsigned long global_num = 0;
 
 /*
  * Buffers are freed after this timeout
  */
 static unsigned dm_bufio_max_age = DM_BUFIO_DEFAULT_AGE_SECS;
 static unsigned long dm_bufio_retain_bytes = DM_BUFIO_DEFAULT_RETAIN_BYTES;
 
 static unsigned long dm_bufio_peak_allocated;
 static unsigned long dm_bufio_allocated_kmem_cache;
 static unsigned long dm_bufio_allocated_get_free_pages;
 static unsigned long dm_bufio_allocated_vmalloc;
 static unsigned long dm_bufio_current_allocated;
 
 /*----------------------------------------------------------------*/
 
 /*
  * The current number of clients.
  */
 static int dm_bufio_client_count;
 
 /*
  * The list of all clients.
  */
 static LIST_HEAD(dm_bufio_all_clients);
 
 /*
  * This mutex protects dm_bufio_cache_size_latch and dm_bufio_client_count
  */
 static DEFINE_MUTEX(dm_bufio_clients_lock);
 
 static struct workqueue_struct *dm_bufio_wq;
 static struct delayed_work dm_bufio_cleanup_old_work;
 static struct work_struct dm_bufio_replacement_work;
 
 
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
 static void buffer_record_stack(struct dm_buffer *b)
 {
     b->stack_len = stack_trace_save(b->stack_entries, MAX_STACK, 2);
 }
 #endif
 
 /*----------------------------------------------------------------
  * A red/black tree acts as an index for all the buffers.
  *--------------------------------------------------------------*/
 static struct dm_buffer *__find(struct dm_bufio_client *c, sector_t block)
 {
     struct rb_node *n = c->buffer_tree.rb_node;
     struct dm_buffer *b;
 
     while (n) {
         b = container_of(n, struct dm_buffer, node);
 
         if (b->block == block)
             return b;
 
         n = block < b->block ? n->rb_left : n->rb_right;
     }
 
     return NULL;
 }
 
 static struct dm_buffer *__find_next(struct dm_bufio_client *c, sector_t block)
 {
     struct rb_node *n = c->buffer_tree.rb_node;
     struct dm_buffer *b;
     struct dm_buffer *best = NULL;
 
     while (n) {
         b = container_of(n, struct dm_buffer, node);
 
         if (b->block == block)
             return b;
 
         if (block <= b->block) {
             n = n->rb_left;
             best = b;
         } else {
             n = n->rb_right;
         }
     }
 
     return best;
 }
 
 static void __insert(struct dm_bufio_client *c, struct dm_buffer *b)
 {
     struct rb_node **new = &c->buffer_tree.rb_node, *parent = NULL;
     struct dm_buffer *found;
 
     while (*new) {
         found = container_of(*new, struct dm_buffer, node);
 
         if (found->block == b->block) {
             BUG_ON(found != b);
             return;
         }
 
         parent = *new;
         new = b->block < found->block ?
             &found->node.rb_left : &found->node.rb_right;
     }
 
     rb_link_node(&b->node, parent, new);
     rb_insert_color(&b->node, &c->buffer_tree);
 }
 
 static void __remove(struct dm_bufio_client *c, struct dm_buffer *b)
 {
     rb_erase(&b->node, &c->buffer_tree);
 }
 
 /*----------------------------------------------------------------*/
 
 static void adjust_total_allocated(struct dm_buffer *b, bool unlink)
 {
     unsigned char data_mode;
     long diff;
 
     static unsigned long * const class_ptr[DATA_MODE_LIMIT] = {
         &dm_bufio_allocated_kmem_cache,
         &dm_bufio_allocated_get_free_pages,
         &dm_bufio_allocated_vmalloc,
     };
 
     data_mode = b->data_mode;
     diff = (long)b->c->block_size;
     if (unlink)
         diff = -diff;
 
     spin_lock(&global_spinlock);
 
     *class_ptr[data_mode] += diff;
 
     dm_bufio_current_allocated += diff;
 
     if (dm_bufio_current_allocated > dm_bufio_peak_allocated)
         dm_bufio_peak_allocated = dm_bufio_current_allocated;
 
     b->accessed = 1;
 
     if (!unlink) {
         list_add(&b->global_list, &global_queue);
         global_num++;
         if (dm_bufio_current_allocated > dm_bufio_cache_size)
             queue_work(dm_bufio_wq, &dm_bufio_replacement_work);
     } else {
         list_del(&b->global_list);
         global_num--;
     }
 
     spin_unlock(&global_spinlock);
 }
 
 /*
  * Change the number of clients and recalculate per-client limit.
  */
 static void __cache_size_refresh(void)
 {
     BUG_ON(!mutex_is_locked(&dm_bufio_clients_lock));
     BUG_ON(dm_bufio_client_count < 0);
 
     dm_bufio_cache_size_latch = READ_ONCE(dm_bufio_cache_size);
 
     /*
      * Use default if set to 0 and report the actual cache size used.
      */
     if (!dm_bufio_cache_size_latch) {
         (void)cmpxchg(&dm_bufio_cache_size, 0,
                   dm_bufio_default_cache_size);
         dm_bufio_cache_size_latch = dm_bufio_default_cache_size;
     }
 }
 
 /*
  * Allocating buffer data.
  *
  * Small buffers are allocated with kmem_cache, to use space optimally.
  *
  * For large buffers, we choose between get_free_pages and vmalloc.
  * Each has advantages and disadvantages.
  *
  * __get_free_pages can randomly fail if the memory is fragmented.
  * __vmalloc won't randomly fail, but vmalloc space is limited (it may be
  * as low as 128M) so using it for caching is not appropriate.
  *
  * If the allocation may fail we use __get_free_pages. Memory fragmentation
  * won't have a fatal effect here, but it just causes flushes of some other
  * buffers and more I/O will be performed. Don't use __get_free_pages if it
  * always fails (i.e. order >= MAX_ORDER).
  *
  * If the allocation shouldn't fail we use __vmalloc. This is only for the
  * initial reserve allocation, so there's no risk of wasting all vmalloc
  * space.
  */
 static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
                    unsigned char *data_mode)
 {
     if (unlikely(c->slab_cache != NULL)) {
         *data_mode = DATA_MODE_SLAB;
         return kmem_cache_alloc(c->slab_cache, gfp_mask);
     }
 
     if (c->block_size <= KMALLOC_MAX_SIZE &&
         gfp_mask & __GFP_NORETRY) {
         *data_mode = DATA_MODE_GET_FREE_PAGES;
         return (void *)__get_free_pages(gfp_mask,
                         c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
     }
 
     *data_mode = DATA_MODE_VMALLOC;
 
     /*
      * __vmalloc allocates the data pages and auxiliary structures with
      * gfp_flags that were specified, but pagetables are always allocated
      * with GFP_KERNEL, no matter what was specified as gfp_mask.
      *
      * Consequently, we must set per-process flag PF_MEMALLOC_NOIO so that
      * all allocations done by this process (including pagetables) are done
      * as if GFP_NOIO was specified.
      */
     if (gfp_mask & __GFP_NORETRY) {
         unsigned noio_flag = memalloc_noio_save();
         void *ptr = __vmalloc(c->block_size, gfp_mask);
 
         memalloc_noio_restore(noio_flag);
         return ptr;
     }
 
     return __vmalloc(c->block_size, gfp_mask);
 }
 
 /*
  * Free buffer's data.
  */
 static void free_buffer_data(struct dm_bufio_client *c,
                  void *data, unsigned char data_mode)
 {
     switch (data_mode) {
     case DATA_MODE_SLAB:
         kmem_cache_free(c->slab_cache, data);
         break;
 
     case DATA_MODE_GET_FREE_PAGES:
         free_pages((unsigned long)data,
                c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
         break;
 
     case DATA_MODE_VMALLOC:
         vfree(data);
         break;
 
     default:
         DMCRIT("dm_bufio_free_buffer_data: bad data mode: %d",
                data_mode);
         BUG();
     }
 }
 
 /*
  * Allocate buffer and its data.
  */
 static struct dm_buffer *alloc_buffer(struct dm_bufio_client *c, gfp_t gfp_mask)
 {
     struct dm_buffer *b = kmem_cache_alloc(c->slab_buffer, gfp_mask);
 
     if (!b)
         return NULL;
 
     b->c = c;
 
     b->data = alloc_buffer_data(c, gfp_mask, &b->data_mode);
     if (!b->data) {
         kmem_cache_free(c->slab_buffer, b);
         return NULL;
     }
 
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
     b->stack_len = 0;
 #endif
     return b;
 }
 
 /*
  * Free buffer and its data.
  */
 static void free_buffer(struct dm_buffer *b)
 {
     struct dm_bufio_client *c = b->c;
 
     free_buffer_data(c, b->data, b->data_mode);
     kmem_cache_free(c->slab_buffer, b);
 }
 
 /*
  * Link buffer to the buffer tree and clean or dirty queue.
  */
 static void __link_buffer(struct dm_buffer *b, sector_t block, int dirty)
 {
     struct dm_bufio_client *c = b->c;
 
     c->n_buffers[dirty]++;
     b->block = block;
     b->list_mode = dirty;
     list_add(&b->lru_list, &c->lru[dirty]);
     __insert(b->c, b);
     b->last_accessed = jiffies;
 
     adjust_total_allocated(b, false);
 }
 
 /*
  * Unlink buffer from the buffer tree and dirty or clean queue.
  */
 static void __unlink_buffer(struct dm_buffer *b)
 {
     struct dm_bufio_client *c = b->c;
 
     BUG_ON(!c->n_buffers[b->list_mode]);
 
     c->n_buffers[b->list_mode]--;
     __remove(b->c, b);
     list_del(&b->lru_list);
 
     adjust_total_allocated(b, true);
 }
 
 /*
  * Place the buffer to the head of dirty or clean LRU queue.
  */
 static void __relink_lru(struct dm_buffer *b, int dirty)
 {
     struct dm_bufio_client *c = b->c;
 
     b->accessed = 1;
 
     BUG_ON(!c->n_buffers[b->list_mode]);
 
     c->n_buffers[b->list_mode]--;
     c->n_buffers[dirty]++;
     b->list_mode = dirty;
     list_move(&b->lru_list, &c->lru[dirty]);
     b->last_accessed = jiffies;
 }
 
 /*----------------------------------------------------------------
  * Submit I/O on the buffer.
  *
  * Bio interface is faster but it has some problems:
  *  the vector list is limited (increasing this limit increases
  *  memory-consumption per buffer, so it is not viable);
  *
  *  the memory must be direct-mapped, not vmalloced;
  *
  * If the buffer is small enough (up to DM_BUFIO_INLINE_VECS pages) and
  * it is not vmalloced, try using the bio interface.
  *
  * If the buffer is big, if it is vmalloced or if the underlying device
  * rejects the bio because it is too large, use dm-io layer to do the I/O.
  * The dm-io layer splits the I/O into multiple requests, avoiding the above
  * shortcomings.
  *--------------------------------------------------------------*/
 
 /*
  * dm-io completion routine. It just calls b->bio.bi_end_io, pretending
  * that the request was handled directly with bio interface.
  */
 static void dmio_complete(unsigned long error, void *context)
 {
     struct dm_buffer *b = context;
 
     b->end_io(b, unlikely(error != 0) ? BLK_STS_IOERR : 0);
 }
 
 static void use_dmio(struct dm_buffer *b, enum req_op op, sector_t sector,
              unsigned n_sectors, unsigned offset)
 {
     int r;
     struct dm_io_request io_req = {
         .bi_opf = op,
         .notify.fn = dmio_complete,
         .notify.context = b,
         .client = b->c->dm_io,
     };
     struct dm_io_region region = {
         .bdev = b->c->bdev,
         .sector = sector,
         .count = n_sectors,
     };
 
     if (b->data_mode != DATA_MODE_VMALLOC) {
         io_req.mem.type = DM_IO_KMEM;
         io_req.mem.ptr.addr = (char *)b->data + offset;
     } else {
         io_req.mem.type = DM_IO_VMA;
         io_req.mem.ptr.vma = (char *)b->data + offset;
     }
 
     r = dm_io(&io_req, 1, &region, NULL);
     if (unlikely(r))
         b->end_io(b, errno_to_blk_status(r));
 }
 
 static void bio_complete(struct bio *bio)
 {
     struct dm_buffer *b = bio->bi_private;
     blk_status_t status = bio->bi_status;
     bio_uninit(bio);
     kfree(bio);
     b->end_io(b, status);
 }
 
 static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
             unsigned n_sectors, unsigned offset)
 {
     struct bio *bio;
     char *ptr;
     unsigned vec_size, len;
 
     vec_size = b->c->block_size >> PAGE_SHIFT;
     if (unlikely(b->c->sectors_per_block_bits < PAGE_SHIFT - SECTOR_SHIFT))
         vec_size += 2;
 
     bio = bio_kmalloc(vec_size, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOWARN);
     if (!bio) {
 dmio:
         use_dmio(b, op, sector, n_sectors, offset);
         return;
     }
     bio_init(bio, b->c->bdev, bio->bi_inline_vecs, vec_size, op);
     bio->bi_iter.bi_sector = sector;
     bio->bi_end_io = bio_complete;
     bio->bi_private = b;
 
     ptr = (char *)b->data + offset;
     len = n_sectors << SECTOR_SHIFT;
 
     do {
         unsigned this_step = min((unsigned)(PAGE_SIZE - offset_in_page(ptr)), len);
         if (!bio_add_page(bio, virt_to_page(ptr), this_step,
                   offset_in_page(ptr))) {
             bio_put(bio);
             goto dmio;
         }
 
         len -= this_step;
         ptr += this_step;
     } while (len > 0);
 
     submit_bio(bio);
 }
 
 static inline sector_t block_to_sector(struct dm_bufio_client *c, sector_t block)
 {
     sector_t sector;
 
     if (likely(c->sectors_per_block_bits >= 0))
         sector = block << c->sectors_per_block_bits;
     else
         sector = block * (c->block_size >> SECTOR_SHIFT);
     sector += c->start;
 
     return sector;
 }
 
 static void submit_io(struct dm_buffer *b, enum req_op op,
               void (*end_io)(struct dm_buffer *, blk_status_t))
 {
     unsigned n_sectors;
     sector_t sector;
     unsigned offset, end;
 
     b->end_io = end_io;
 
     sector = block_to_sector(b->c, b->block);
 
     if (op != REQ_OP_WRITE) {
         n_sectors = b->c->block_size >> SECTOR_SHIFT;
         offset = 0;
     } else {
         if (b->c->write_callback)
             b->c->write_callback(b);
         offset = b->write_start;
         end = b->write_end;
         offset &= -DM_BUFIO_WRITE_ALIGN;
         end += DM_BUFIO_WRITE_ALIGN - 1;
         end &= -DM_BUFIO_WRITE_ALIGN;
         if (unlikely(end > b->c->block_size))
             end = b->c->block_size;
 
         sector += offset >> SECTOR_SHIFT;
         n_sectors = (end - offset) >> SECTOR_SHIFT;
     }
 
     if (b->data_mode != DATA_MODE_VMALLOC)
         use_bio(b, op, sector, n_sectors, offset);
     else
         use_dmio(b, op, sector, n_sectors, offset);
 }
 
 /*----------------------------------------------------------------
  * Writing dirty buffers
  *--------------------------------------------------------------*/
 
 /*
  * The endio routine for write.
  *
  * Set the error, clear B_WRITING bit and wake anyone who was waiting on
  * it.
  */
 static void write_endio(struct dm_buffer *b, blk_status_t status)
 {
     b->write_error = status;
     if (unlikely(status)) {
         struct dm_bufio_client *c = b->c;
 
         (void)cmpxchg(&c->async_write_error, 0,
                 blk_status_to_errno(status));
     }
 
     BUG_ON(!test_bit(B_WRITING, &b->state));
 
     smp_mb__before_atomic();
     clear_bit(B_WRITING, &b->state);
     smp_mb__after_atomic();
 
     wake_up_bit(&b->state, B_WRITING);
 }
 
 /*
  * Initiate a write on a dirty buffer, but don't wait for it.
  *
  * - If the buffer is not dirty, exit.
  * - If there some previous write going on, wait for it to finish (we can't
  *   have two writes on the same buffer simultaneously).
  * - Submit our write and don't wait on it. We set B_WRITING indicating
  *   that there is a write in progress.
  */
 static void __write_dirty_buffer(struct dm_buffer *b,
                  struct list_head *write_list)
 {
     if (!test_bit(B_DIRTY, &b->state))
         return;
 
     clear_bit(B_DIRTY, &b->state);
     wait_on_bit_lock_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
 
     b->write_start = b->dirty_start;
     b->write_end = b->dirty_end;
 
     if (!write_list)
         submit_io(b, REQ_OP_WRITE, write_endio);
     else
         list_add_tail(&b->write_list, write_list);
 }
 
 static void __flush_write_list(struct list_head *write_list)
 {
     struct blk_plug plug;
     blk_start_plug(&plug);
     while (!list_empty(write_list)) {
         struct dm_buffer *b =
             list_entry(write_list->next, struct dm_buffer, write_list);
         list_del(&b->write_list);
         submit_io(b, REQ_OP_WRITE, write_endio);
         cond_resched();
     }
     blk_finish_plug(&plug);
 }
 
 /*
  * Wait until any activity on the buffer finishes.  Possibly write the
  * buffer if it is dirty.  When this function finishes, there is no I/O
  * running on the buffer and the buffer is not dirty.
  */
 static void __make_buffer_clean(struct dm_buffer *b)
 {
     BUG_ON(b->hold_count);
 
     if (!b->state)  /* fast case */
         return;
 
     wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
     __write_dirty_buffer(b, NULL);
     wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
 }
 
 /*
  * Find some buffer that is not held by anybody, clean it, unlink it and
  * return it.
  */
 static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
 {
     struct dm_buffer *b;
 
     list_for_each_entry_reverse(b, &c->lru[LIST_CLEAN], lru_list) {
         BUG_ON(test_bit(B_WRITING, &b->state));
         BUG_ON(test_bit(B_DIRTY, &b->state));
 
         if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep &&
             unlikely(test_bit(B_READING, &b->state)))
             continue;
 
         if (!b->hold_count) {
             __make_buffer_clean(b);
             __unlink_buffer(b);
             return b;
         }
         cond_resched();
     }
 
     if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
         return NULL;
 
     list_for_each_entry_reverse(b, &c->lru[LIST_DIRTY], lru_list) {
         BUG_ON(test_bit(B_READING, &b->state));
 
         if (!b->hold_count) {
             __make_buffer_clean(b);
             __unlink_buffer(b);
             return b;
         }
         cond_resched();
     }
 
     return NULL;
 }
 
 /*
  * Wait until some other threads free some buffer or release hold count on
  * some buffer.
  *
  * This function is entered with c->lock held, drops it and regains it
  * before exiting.
  */
 static void __wait_for_free_buffer(struct dm_bufio_client *c)
 {
     DECLARE_WAITQUEUE(wait, current);
 
     add_wait_queue(&c->free_buffer_wait, &wait);
     set_current_state(TASK_UNINTERRUPTIBLE);
     dm_bufio_unlock(c);
 
     io_schedule();
 
     remove_wait_queue(&c->free_buffer_wait, &wait);
 
     dm_bufio_lock(c);
 }
 
 enum new_flag {
     NF_FRESH = 0,
     NF_READ = 1,
     NF_GET = 2,
     NF_PREFETCH = 3
 };
 
 /*
  * Allocate a new buffer. If the allocation is not possible, wait until
  * some other thread frees a buffer.
  *
  * May drop the lock and regain it.
  */
 static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
 {
     struct dm_buffer *b;
     bool tried_noio_alloc = false;
 
     /*
      * dm-bufio is resistant to allocation failures (it just keeps
      * one buffer reserved in cases all the allocations fail).
      * So set flags to not try too hard:
      *  GFP_NOWAIT: don't wait; if we need to sleep we'll release our
      *          mutex and wait ourselves.
      *  __GFP_NORETRY: don't retry and rather return failure
      *  __GFP_NOMEMALLOC: don't use emergency reserves
      *  __GFP_NOWARN: don't print a warning in case of failure
      *
      * For debugging, if we set the cache size to 1, no new buffers will
      * be allocated.
      */
     while (1) {
         if (dm_bufio_cache_size_latch != 1) {
             b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
             if (b)
                 return b;
         }
 
         if (nf == NF_PREFETCH)
             return NULL;
 
         if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
             dm_bufio_unlock(c);
             b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
             dm_bufio_lock(c);
             if (b)
                 return b;
             tried_noio_alloc = true;
         }
 
         if (!list_empty(&c->reserved_buffers)) {
             b = list_entry(c->reserved_buffers.next,
                        struct dm_buffer, lru_list);
             list_del(&b->lru_list);
             c->need_reserved_buffers++;
 
             return b;
         }
 
         b = __get_unclaimed_buffer(c);
         if (b)
             return b;
 
         __wait_for_free_buffer(c);
     }
 }
 
 static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c, enum new_flag nf)
 {
     struct dm_buffer *b = __alloc_buffer_wait_no_callback(c, nf);
 
     if (!b)
         return NULL;
 
     if (c->alloc_callback)
         c->alloc_callback(b);
 
     return b;
 }
 
 /*
  * Free a buffer and wake other threads waiting for free buffers.
  */
 static void __free_buffer_wake(struct dm_buffer *b)
 {
     struct dm_bufio_client *c = b->c;
 
     if (!c->need_reserved_buffers)
         free_buffer(b);
     else {
         list_add(&b->lru_list, &c->reserved_buffers);
         c->need_reserved_buffers--;
     }
 
     wake_up(&c->free_buffer_wait);
 }
 
 static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,
                     struct list_head *write_list)
 {
     struct dm_buffer *b, *tmp;
 
     list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_DIRTY], lru_list) {
         BUG_ON(test_bit(B_READING, &b->state));
 
         if (!test_bit(B_DIRTY, &b->state) &&
             !test_bit(B_WRITING, &b->state)) {
             __relink_lru(b, LIST_CLEAN);
             continue;
         }
 
         if (no_wait && test_bit(B_WRITING, &b->state))
             return;
 
         __write_dirty_buffer(b, write_list);
         cond_resched();
     }
 }
 
 /*
  * Check if we're over watermark.
  * If we are over threshold_buffers, start freeing buffers.
  * If we're over "limit_buffers", block until we get under the limit.
  */
 static void __check_watermark(struct dm_bufio_client *c,
                   struct list_head *write_list)
 {
     if (c->n_buffers[LIST_DIRTY] > c->n_buffers[LIST_CLEAN] * DM_BUFIO_WRITEBACK_RATIO)
         __write_dirty_buffers_async(c, 1, write_list);
 }
 
 /*----------------------------------------------------------------
  * Getting a buffer
  *--------------------------------------------------------------*/
 
 static struct dm_buffer *__bufio_new(struct dm_bufio_client *c, sector_t block,
                      enum new_flag nf, int *need_submit,
                      struct list_head *write_list)
 {
     struct dm_buffer *b, *new_b = NULL;
 
     *need_submit = 0;
 
     b = __find(c, block);
     if (b)
         goto found_buffer;
 
     if (nf == NF_GET)
         return NULL;
 
     new_b = __alloc_buffer_wait(c, nf);
     if (!new_b)
         return NULL;
 
     /*
      * We've had a period where the mutex was unlocked, so need to
      * recheck the buffer tree.
      */
     b = __find(c, block);
     if (b) {
         __free_buffer_wake(new_b);
         goto found_buffer;
     }
 
     __check_watermark(c, write_list);
 
     b = new_b;
     b->hold_count = 1;
     b->read_error = 0;
     b->write_error = 0;
     __link_buffer(b, block, LIST_CLEAN);
 
     if (nf == NF_FRESH) {
         b->state = 0;
         return b;
     }
 
     b->state = 1 << B_READING;
     *need_submit = 1;
 
     return b;
 
 found_buffer:
     if (nf == NF_PREFETCH)
         return NULL;
     /*
      * Note: it is essential that we don't wait for the buffer to be
      * read if dm_bufio_get function is used. Both dm_bufio_get and
      * dm_bufio_prefetch can be used in the driver request routine.
      * If the user called both dm_bufio_prefetch and dm_bufio_get on
      * the same buffer, it would deadlock if we waited.
      */
     if (nf == NF_GET && unlikely(test_bit(B_READING, &b->state)))
         return NULL;
 
     b->hold_count++;
     __relink_lru(b, test_bit(B_DIRTY, &b->state) ||
              test_bit(B_WRITING, &b->state));
     return b;
 }
 
 /*
  * The endio routine for reading: set the error, clear the bit and wake up
  * anyone waiting on the buffer.
  */
 static void read_endio(struct dm_buffer *b, blk_status_t status)
 {
     b->read_error = status;
 
     BUG_ON(!test_bit(B_READING, &b->state));
 
     smp_mb__before_atomic();
     clear_bit(B_READING, &b->state);
     smp_mb__after_atomic();
 
     wake_up_bit(&b->state, B_READING);
 }
 
 /*
  * A common routine for dm_bufio_new and dm_bufio_read.  Operation of these
  * functions is similar except that dm_bufio_new doesn't read the
  * buffer from the disk (assuming that the caller overwrites all the data
  * and uses dm_bufio_mark_buffer_dirty to write new data back).
  */
 static void *new_read(struct dm_bufio_client *c, sector_t block,
               enum new_flag nf, struct dm_buffer **bp)
 {
     int need_submit;
     struct dm_buffer *b;
 
     LIST_HEAD(write_list);
 
     dm_bufio_lock(c);
     b = __bufio_new(c, block, nf, &need_submit, &write_list);
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
     if (b && b->hold_count == 1)
         buffer_record_stack(b);
 #endif
     dm_bufio_unlock(c);
 
     __flush_write_list(&write_list);
 
     if (!b)
         return NULL;
 
     if (need_submit)
         submit_io(b, REQ_OP_READ, read_endio);
 
     wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
 
     if (b->read_error) {
         int error = blk_status_to_errno(b->read_error);
 
         dm_bufio_release(b);
 
         return ERR_PTR(error);
     }
 
     *bp = b;
 
     return b->data;
 }
 
 void *dm_bufio_get(struct dm_bufio_client *c, sector_t block,
            struct dm_buffer **bp)
 {
     return new_read(c, block, NF_GET, bp);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get);
 
 void *dm_bufio_read(struct dm_bufio_client *c, sector_t block,
             struct dm_buffer **bp)
 {
     BUG_ON(dm_bufio_in_request());
 
     return new_read(c, block, NF_READ, bp);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_read);
 
 void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,
            struct dm_buffer **bp)
 {
     BUG_ON(dm_bufio_in_request());
 
     return new_read(c, block, NF_FRESH, bp);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_new);
 
 void dm_bufio_prefetch(struct dm_bufio_client *c,
                sector_t block, unsigned n_blocks)
 {
     struct blk_plug plug;
 
     LIST_HEAD(write_list);
 
     BUG_ON(dm_bufio_in_request());
 
     blk_start_plug(&plug);
     dm_bufio_lock(c);
 
     for (; n_blocks--; block++) {
         int need_submit;
         struct dm_buffer *b;
         b = __bufio_new(c, block, NF_PREFETCH, &need_submit,
                 &write_list);
         if (unlikely(!list_empty(&write_list))) {
             dm_bufio_unlock(c);
             blk_finish_plug(&plug);
             __flush_write_list(&write_list);
             blk_start_plug(&plug);
             dm_bufio_lock(c);
         }
         if (unlikely(b != NULL)) {
             dm_bufio_unlock(c);
 
             if (need_submit)
                 submit_io(b, REQ_OP_READ, read_endio);
             dm_bufio_release(b);
 
             cond_resched();
 
             if (!n_blocks)
                 goto flush_plug;
             dm_bufio_lock(c);
         }
     }
 
     dm_bufio_unlock(c);
 
 flush_plug:
     blk_finish_plug(&plug);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_prefetch);
 
 void dm_bufio_release(struct dm_buffer *b)
 {
     struct dm_bufio_client *c = b->c;
 
     dm_bufio_lock(c);
 
     BUG_ON(!b->hold_count);
 
     b->hold_count--;
     if (!b->hold_count) {
         wake_up(&c->free_buffer_wait);
 
         /*
          * If there were errors on the buffer, and the buffer is not
          * to be written, free the buffer. There is no point in caching
          * invalid buffer.
          */
         if ((b->read_error || b->write_error) &&
             !test_bit(B_READING, &b->state) &&
             !test_bit(B_WRITING, &b->state) &&
             !test_bit(B_DIRTY, &b->state)) {
             __unlink_buffer(b);
             __free_buffer_wake(b);
         }
     }
 
     dm_bufio_unlock(c);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_release);
 
 void dm_bufio_mark_partial_buffer_dirty(struct dm_buffer *b,
                     unsigned start, unsigned end)
 {
     struct dm_bufio_client *c = b->c;
 
     BUG_ON(start >= end);
     BUG_ON(end > b->c->block_size);
 
     dm_bufio_lock(c);
 
     BUG_ON(test_bit(B_READING, &b->state));
 
     if (!test_and_set_bit(B_DIRTY, &b->state)) {
         b->dirty_start = start;
         b->dirty_end = end;
         __relink_lru(b, LIST_DIRTY);
     } else {
         if (start < b->dirty_start)
             b->dirty_start = start;
         if (end > b->dirty_end)
             b->dirty_end = end;
     }
 
     dm_bufio_unlock(c);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_mark_partial_buffer_dirty);
 
 void dm_bufio_mark_buffer_dirty(struct dm_buffer *b)
 {
     dm_bufio_mark_partial_buffer_dirty(b, 0, b->c->block_size);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_mark_buffer_dirty);
 
 void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c)
 {
     LIST_HEAD(write_list);
 
     BUG_ON(dm_bufio_in_request());
 
     dm_bufio_lock(c);
     __write_dirty_buffers_async(c, 0, &write_list);
     dm_bufio_unlock(c);
     __flush_write_list(&write_list);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers_async);
 
 /*
  * For performance, it is essential that the buffers are written asynchronously
  * and simultaneously (so that the block layer can merge the writes) and then
  * waited upon.
  *
  * Finally, we flush hardware disk cache.
  */
 int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
 {
     int a, f;
     unsigned long buffers_processed = 0;
     struct dm_buffer *b, *tmp;
 
     LIST_HEAD(write_list);
 
     dm_bufio_lock(c);
     __write_dirty_buffers_async(c, 0, &write_list);
     dm_bufio_unlock(c);
     __flush_write_list(&write_list);
     dm_bufio_lock(c);
 
 again:
     list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_DIRTY], lru_list) {
         int dropped_lock = 0;
 
         if (buffers_processed < c->n_buffers[LIST_DIRTY])
             buffers_processed++;
 
         BUG_ON(test_bit(B_READING, &b->state));
 
         if (test_bit(B_WRITING, &b->state)) {
             if (buffers_processed < c->n_buffers[LIST_DIRTY]) {
                 dropped_lock = 1;
                 b->hold_count++;
                 dm_bufio_unlock(c);
                 wait_on_bit_io(&b->state, B_WRITING,
                            TASK_UNINTERRUPTIBLE);
                 dm_bufio_lock(c);
                 b->hold_count--;
             } else
                 wait_on_bit_io(&b->state, B_WRITING,
                            TASK_UNINTERRUPTIBLE);
         }
 
         if (!test_bit(B_DIRTY, &b->state) &&
             !test_bit(B_WRITING, &b->state))
             __relink_lru(b, LIST_CLEAN);
 
         cond_resched();
 
         /*
          * If we dropped the lock, the list is no longer consistent,
          * so we must restart the search.
          *
          * In the most common case, the buffer just processed is
          * relinked to the clean list, so we won't loop scanning the
          * same buffer again and again.
          *
          * This may livelock if there is another thread simultaneously
          * dirtying buffers, so we count the number of buffers walked
          * and if it exceeds the total number of buffers, it means that
          * someone is doing some writes simultaneously with us.  In
          * this case, stop, dropping the lock.
          */
         if (dropped_lock)
             goto again;
     }
     wake_up(&c->free_buffer_wait);
     dm_bufio_unlock(c);
 
     a = xchg(&c->async_write_error, 0);
     f = dm_bufio_issue_flush(c);
     if (a)
         return a;
 
     return f;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers);
 
 /*
  * Use dm-io to send an empty barrier to flush the device.
  */
 int dm_bufio_issue_flush(struct dm_bufio_client *c)
 {
     struct dm_io_request io_req = {
         .bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC,
         .mem.type = DM_IO_KMEM,
         .mem.ptr.addr = NULL,
         .client = c->dm_io,
     };
     struct dm_io_region io_reg = {
         .bdev = c->bdev,
         .sector = 0,
         .count = 0,
     };
 
     BUG_ON(dm_bufio_in_request());
 
     return dm_io(&io_req, 1, &io_reg, NULL);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_issue_flush);
 
 /*
  * Use dm-io to send a discard request to flush the device.
  */
 int dm_bufio_issue_discard(struct dm_bufio_client *c, sector_t block, sector_t count)
 {
     struct dm_io_request io_req = {
         .bi_opf = REQ_OP_DISCARD | REQ_SYNC,
         .mem.type = DM_IO_KMEM,
         .mem.ptr.addr = NULL,
         .client = c->dm_io,
     };
     struct dm_io_region io_reg = {
         .bdev = c->bdev,
         .sector = block_to_sector(c, block),
         .count = block_to_sector(c, count),
     };
 
     BUG_ON(dm_bufio_in_request());
 
     return dm_io(&io_req, 1, &io_reg, NULL);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_issue_discard);
 
 /*
  * We first delete any other buffer that may be at that new location.
  *
  * Then, we write the buffer to the original location if it was dirty.
  *
  * Then, if we are the only one who is holding the buffer, relink the buffer
  * in the buffer tree for the new location.
  *
  * If there was someone else holding the buffer, we write it to the new
  * location but not relink it, because that other user needs to have the buffer
  * at the same place.
  */
 void dm_bufio_release_move(struct dm_buffer *b, sector_t new_block)
 {
     struct dm_bufio_client *c = b->c;
     struct dm_buffer *new;
 
     BUG_ON(dm_bufio_in_request());
 
     dm_bufio_lock(c);
 
 retry:
     new = __find(c, new_block);
     if (new) {
         if (new->hold_count) {
             __wait_for_free_buffer(c);
             goto retry;
         }
 
         /*
          * FIXME: Is there any point waiting for a write that's going
          * to be overwritten in a bit?
          */
         __make_buffer_clean(new);
         __unlink_buffer(new);
         __free_buffer_wake(new);
     }
 
     BUG_ON(!b->hold_count);
     BUG_ON(test_bit(B_READING, &b->state));
 
     __write_dirty_buffer(b, NULL);
     if (b->hold_count == 1) {
         wait_on_bit_io(&b->state, B_WRITING,
                    TASK_UNINTERRUPTIBLE);
         set_bit(B_DIRTY, &b->state);
         b->dirty_start = 0;
         b->dirty_end = c->block_size;
         __unlink_buffer(b);
         __link_buffer(b, new_block, LIST_DIRTY);
     } else {
         sector_t old_block;
         wait_on_bit_lock_io(&b->state, B_WRITING,
                     TASK_UNINTERRUPTIBLE);
         /*
          * Relink buffer to "new_block" so that write_callback
          * sees "new_block" as a block number.
          * After the write, link the buffer back to old_block.
          * All this must be done in bufio lock, so that block number
          * change isn't visible to other threads.
          */
         old_block = b->block;
         __unlink_buffer(b);
         __link_buffer(b, new_block, b->list_mode);
         submit_io(b, REQ_OP_WRITE, write_endio);
         wait_on_bit_io(&b->state, B_WRITING,
                    TASK_UNINTERRUPTIBLE);
         __unlink_buffer(b);
         __link_buffer(b, old_block, b->list_mode);
     }
 
     dm_bufio_unlock(c);
     dm_bufio_release(b);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_release_move);
 
 static void forget_buffer_locked(struct dm_buffer *b)
 {
     if (likely(!b->hold_count) && likely(!b->state)) {
         __unlink_buffer(b);
         __free_buffer_wake(b);
     }
 }
 
 /*
  * Free the given buffer.
  *
  * This is just a hint, if the buffer is in use or dirty, this function
  * does nothing.
  */
 void dm_bufio_forget(struct dm_bufio_client *c, sector_t block)
 {
     struct dm_buffer *b;
 
     dm_bufio_lock(c);
 
     b = __find(c, block);
     if (b)
         forget_buffer_locked(b);
 
     dm_bufio_unlock(c);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_forget);
 
 void dm_bufio_forget_buffers(struct dm_bufio_client *c, sector_t block, sector_t n_blocks)
 {
     struct dm_buffer *b;
     sector_t end_block = block + n_blocks;
 
     while (block < end_block) {
         dm_bufio_lock(c);
 
         b = __find_next(c, block);
         if (b) {
             block = b->block + 1;
             forget_buffer_locked(b);
         }
 
         dm_bufio_unlock(c);
 
         if (!b)
             break;
     }
 
 }
 EXPORT_SYMBOL_GPL(dm_bufio_forget_buffers);
 
 void dm_bufio_set_minimum_buffers(struct dm_bufio_client *c, unsigned n)
 {
     c->minimum_buffers = n;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_set_minimum_buffers);
 
 unsigned dm_bufio_get_block_size(struct dm_bufio_client *c)
 {
     return c->block_size;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_block_size);
 
 sector_t dm_bufio_get_device_size(struct dm_bufio_client *c)
 {
     sector_t s = bdev_nr_sectors(c->bdev);
     if (s >= c->start)
         s -= c->start;
     else
         s = 0;
     if (likely(c->sectors_per_block_bits >= 0))
         s >>= c->sectors_per_block_bits;
     else
         sector_div(s, c->block_size >> SECTOR_SHIFT);
     return s;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_device_size);
 
 struct dm_io_client *dm_bufio_get_dm_io_client(struct dm_bufio_client *c)
 {
     return c->dm_io;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_dm_io_client);
 
 sector_t dm_bufio_get_block_number(struct dm_buffer *b)
 {
     return b->block;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_block_number);
 
 void *dm_bufio_get_block_data(struct dm_buffer *b)
 {
     return b->data;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_block_data);
 
 void *dm_bufio_get_aux_data(struct dm_buffer *b)
 {
     return b + 1;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_aux_data);
 
 struct dm_bufio_client *dm_bufio_get_client(struct dm_buffer *b)
 {
     return b->c;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_get_client);
 
 static void drop_buffers(struct dm_bufio_client *c)
 {
     struct dm_buffer *b;
     int i;
     bool warned = false;
 
     BUG_ON(dm_bufio_in_request());
 
     /*
      * An optimization so that the buffers are not written one-by-one.
      */
     dm_bufio_write_dirty_buffers_async(c);
 
     dm_bufio_lock(c);
 
     while ((b = __get_unclaimed_buffer(c)))
         __free_buffer_wake(b);
 
     for (i = 0; i < LIST_SIZE; i++)
         list_for_each_entry(b, &c->lru[i], lru_list) {
             WARN_ON(!warned);
             warned = true;
             DMERR("leaked buffer %llx, hold count %u, list %d",
                   (unsigned long long)b->block, b->hold_count, i);
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
             stack_trace_print(b->stack_entries, b->stack_len, 1);
             /* mark unclaimed to avoid BUG_ON below */
             b->hold_count = 0;
 #endif
         }
 
 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
     while ((b = __get_unclaimed_buffer(c)))
         __free_buffer_wake(b);
 #endif
 
     for (i = 0; i < LIST_SIZE; i++)
         BUG_ON(!list_empty(&c->lru[i]));
 
     dm_bufio_unlock(c);
 }
 
 /*
  * We may not be able to evict this buffer if IO pending or the client
  * is still using it.  Caller is expected to know buffer is too old.
  *
  * And if GFP_NOFS is used, we must not do any I/O because we hold
  * dm_bufio_clients_lock and we would risk deadlock if the I/O gets
  * rerouted to different bufio client.
  */
 static bool __try_evict_buffer(struct dm_buffer *b, gfp_t gfp)
 {
     if (!(gfp & __GFP_FS) ||
         (static_branch_unlikely(&no_sleep_enabled) && b->c->no_sleep)) {
         if (test_bit(B_READING, &b->state) ||
             test_bit(B_WRITING, &b->state) ||
             test_bit(B_DIRTY, &b->state))
             return false;
     }
 
     if (b->hold_count)
         return false;
 
     __make_buffer_clean(b);
     __unlink_buffer(b);
     __free_buffer_wake(b);
 
     return true;
 }
 
 static unsigned long get_retain_buffers(struct dm_bufio_client *c)
 {
     unsigned long retain_bytes = READ_ONCE(dm_bufio_retain_bytes);
     if (likely(c->sectors_per_block_bits >= 0))
         retain_bytes >>= c->sectors_per_block_bits + SECTOR_SHIFT;
     else
         retain_bytes /= c->block_size;
     return retain_bytes;
 }
 
 static void __scan(struct dm_bufio_client *c)
 {
     int l;
     struct dm_buffer *b, *tmp;
     unsigned long freed = 0;
     unsigned long count = c->n_buffers[LIST_CLEAN] +
                   c->n_buffers[LIST_DIRTY];
     unsigned long retain_target = get_retain_buffers(c);
 
     for (l = 0; l < LIST_SIZE; l++) {
         list_for_each_entry_safe_reverse(b, tmp, &c->lru[l], lru_list) {
             if (count - freed <= retain_target)
                 atomic_long_set(&c->need_shrink, 0);
             if (!atomic_long_read(&c->need_shrink))
                 return;
             if (__try_evict_buffer(b, GFP_KERNEL)) {
                 atomic_long_dec(&c->need_shrink);
                 freed++;
             }
             cond_resched();
         }
     }
 }
 
 static void shrink_work(struct work_struct *w)
 {
     struct dm_bufio_client *c = container_of(w, struct dm_bufio_client, shrink_work);
 
     dm_bufio_lock(c);
     __scan(c);
     dm_bufio_unlock(c);
 }
 
 static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 {
     struct dm_bufio_client *c;
 
     c = container_of(shrink, struct dm_bufio_client, shrinker);
     atomic_long_add(sc->nr_to_scan, &c->need_shrink);
     queue_work(dm_bufio_wq, &c->shrink_work);
 
     return sc->nr_to_scan;
 }
 
 static unsigned long dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
 {
     struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
     unsigned long count = READ_ONCE(c->n_buffers[LIST_CLEAN]) +
                   READ_ONCE(c->n_buffers[LIST_DIRTY]);
     unsigned long retain_target = get_retain_buffers(c);
     unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);
 
     if (unlikely(count < retain_target))
         count = 0;
     else
         count -= retain_target;
 
     if (unlikely(count < queued_for_cleanup))
         count = 0;
     else
         count -= queued_for_cleanup;
 
     return count;
 }
 
 /*
  * Create the buffering interface
  */
 struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsigned block_size,
                            unsigned reserved_buffers, unsigned aux_size,
                            void (*alloc_callback)(struct dm_buffer *),
                            void (*write_callback)(struct dm_buffer *),
                            unsigned int flags)
 {
     int r;
     struct dm_bufio_client *c;
     unsigned i;
     char slab_name[27];
 
     if (!block_size || block_size & ((1 << SECTOR_SHIFT) - 1)) {
         DMERR("%s: block size not specified or is not multiple of 512b", __func__);
         r = -EINVAL;
         goto bad_client;
     }
 
     c = kzalloc(sizeof(*c), GFP_KERNEL);
     if (!c) {
         r = -ENOMEM;
         goto bad_client;
     }
     c->buffer_tree = RB_ROOT;
 
     c->bdev = bdev;
     c->block_size = block_size;
     if (is_power_of_2(block_size))
         c->sectors_per_block_bits = __ffs(block_size) - SECTOR_SHIFT;
     else
         c->sectors_per_block_bits = -1;
 
     c->alloc_callback = alloc_callback;
     c->write_callback = write_callback;
 
     if (flags & DM_BUFIO_CLIENT_NO_SLEEP) {
         c->no_sleep = true;
         static_branch_inc(&no_sleep_enabled);
     }
 
     for (i = 0; i < LIST_SIZE; i++) {
         INIT_LIST_HEAD(&c->lru[i]);
         c->n_buffers[i] = 0;
     }
 
     mutex_init(&c->lock);
     spin_lock_init(&c->spinlock);
     INIT_LIST_HEAD(&c->reserved_buffers);
     c->need_reserved_buffers = reserved_buffers;
 
     dm_bufio_set_minimum_buffers(c, DM_BUFIO_MIN_BUFFERS);
 
     init_waitqueue_head(&c->free_buffer_wait);
     c->async_write_error = 0;
 
     c->dm_io = dm_io_client_create();
     if (IS_ERR(c->dm_io)) {
         r = PTR_ERR(c->dm_io);
         goto bad_dm_io;
     }
 
     if (block_size <= KMALLOC_MAX_SIZE &&
         (block_size < PAGE_SIZE || !is_power_of_2(block_size))) {
         unsigned align = min(1U << __ffs(block_size), (unsigned)PAGE_SIZE);
         snprintf(slab_name, sizeof slab_name, "dm_bufio_cache-%u", block_size);
         c->slab_cache = kmem_cache_create(slab_name, block_size, align,
                           SLAB_RECLAIM_ACCOUNT, NULL);
         if (!c->slab_cache) {
             r = -ENOMEM;
             goto bad;
         }
     }
     if (aux_size)
         snprintf(slab_name, sizeof slab_name, "dm_bufio_buffer-%u", aux_size);
     else
         snprintf(slab_name, sizeof slab_name, "dm_bufio_buffer");
     c->slab_buffer = kmem_cache_create(slab_name, sizeof(struct dm_buffer) + aux_size,
                        0, SLAB_RECLAIM_ACCOUNT, NULL);
     if (!c->slab_buffer) {
         r = -ENOMEM;
         goto bad;
     }
 
     while (c->need_reserved_buffers) {
         struct dm_buffer *b = alloc_buffer(c, GFP_KERNEL);
 
         if (!b) {
             r = -ENOMEM;
             goto bad;
         }
         __free_buffer_wake(b);
     }
 
     INIT_WORK(&c->shrink_work, shrink_work);
     atomic_long_set(&c->need_shrink, 0);
 
     c->shrinker.count_objects = dm_bufio_shrink_count;
     c->shrinker.scan_objects = dm_bufio_shrink_scan;
     c->shrinker.seeks = 1;
     c->shrinker.batch = 0;
     r = register_shrinker(&c->shrinker, "md-%s:(%u:%u)", slab_name,
                   MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
     if (r)
         goto bad;
 
     mutex_lock(&dm_bufio_clients_lock);
     dm_bufio_client_count++;
     list_add(&c->client_list, &dm_bufio_all_clients);
     __cache_size_refresh();
     mutex_unlock(&dm_bufio_clients_lock);
 
     return c;
 
 bad:
     while (!list_empty(&c->reserved_buffers)) {
         struct dm_buffer *b = list_entry(c->reserved_buffers.next,
                          struct dm_buffer, lru_list);
         list_del(&b->lru_list);
         free_buffer(b);
     }
     kmem_cache_destroy(c->slab_cache);
     kmem_cache_destroy(c->slab_buffer);
     dm_io_client_destroy(c->dm_io);
 bad_dm_io:
     mutex_destroy(&c->lock);
     kfree(c);
 bad_client:
     return ERR_PTR(r);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_client_create);
 
 /*
  * Free the buffering interface.
  * It is required that there are no references on any buffers.
  */
 void dm_bufio_client_destroy(struct dm_bufio_client *c)
 {
     unsigned i;
 
     drop_buffers(c);
 
     unregister_shrinker(&c->shrinker);
     flush_work(&c->shrink_work);
 
     mutex_lock(&dm_bufio_clients_lock);
 
     list_del(&c->client_list);
     dm_bufio_client_count--;
     __cache_size_refresh();
 
     mutex_unlock(&dm_bufio_clients_lock);
 
     BUG_ON(!RB_EMPTY_ROOT(&c->buffer_tree));
     BUG_ON(c->need_reserved_buffers);
 
     while (!list_empty(&c->reserved_buffers)) {
         struct dm_buffer *b = list_entry(c->reserved_buffers.next,
                          struct dm_buffer, lru_list);
         list_del(&b->lru_list);
         free_buffer(b);
     }
 
     for (i = 0; i < LIST_SIZE; i++)
         if (c->n_buffers[i])
             DMERR("leaked buffer count %d: %ld", i, c->n_buffers[i]);
 
     for (i = 0; i < LIST_SIZE; i++)
         BUG_ON(c->n_buffers[i]);
 
     kmem_cache_destroy(c->slab_cache);
     kmem_cache_destroy(c->slab_buffer);
     dm_io_client_destroy(c->dm_io);
     mutex_destroy(&c->lock);
     if (c->no_sleep)
         static_branch_dec(&no_sleep_enabled);
     kfree(c);
 }
 EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);
 
 void dm_bufio_set_sector_offset(struct dm_bufio_client *c, sector_t start)
 {
     c->start = start;
 }
 EXPORT_SYMBOL_GPL(dm_bufio_set_sector_offset);
 
 static unsigned get_max_age_hz(void)
 {
     unsigned max_age = READ_ONCE(dm_bufio_max_age);
 
     if (max_age > UINT_MAX / HZ)
         max_age = UINT_MAX / HZ;
 
     return max_age * HZ;
 }
 
 static bool older_than(struct dm_buffer *b, unsigned long age_hz)
 {
     return time_after_eq(jiffies, b->last_accessed + age_hz);
 }
 
 static void __evict_old_buffers(struct dm_bufio_client *c, unsigned long age_hz)
 {
     struct dm_buffer *b, *tmp;
     unsigned long retain_target = get_retain_buffers(c);
     unsigned long count;
     LIST_HEAD(write_list);
 
     dm_bufio_lock(c);
 
     __check_watermark(c, &write_list);
     if (unlikely(!list_empty(&write_list))) {
         dm_bufio_unlock(c);
         __flush_write_list(&write_list);
         dm_bufio_lock(c);
     }
 
     count = c->n_buffers[LIST_CLEAN] + c->n_buffers[LIST_DIRTY];
     list_for_each_entry_safe_reverse(b, tmp, &c->lru[LIST_CLEAN], lru_list) {
         if (count <= retain_target)
             break;
 
         if (!older_than(b, age_hz))
             break;
 
         if (__try_evict_buffer(b, 0))
             count--;
 
         cond_resched();
     }
 
     dm_bufio_unlock(c);
 }
 
 static void do_global_cleanup(struct work_struct *w)
 {
     struct dm_bufio_client *locked_client = NULL;
     struct dm_bufio_client *current_client;
     struct dm_buffer *b;
     unsigned spinlock_hold_count;
     unsigned long threshold = dm_bufio_cache_size -
         dm_bufio_cache_size / DM_BUFIO_LOW_WATERMARK_RATIO;
     unsigned long loops = global_num * 2;
 
     mutex_lock(&dm_bufio_clients_lock);
 
     while (1) {
         cond_resched();
 
         spin_lock(&global_spinlock);
         if (unlikely(dm_bufio_current_allocated <= threshold))
             break;
 
         spinlock_hold_count = 0;
 get_next:
         if (!loops--)
             break;
         if (unlikely(list_empty(&global_queue)))
             break;
         b = list_entry(global_queue.prev, struct dm_buffer, global_list);
 
         if (b->accessed) {
             b->accessed = 0;
             list_move(&b->global_list, &global_queue);
             if (likely(++spinlock_hold_count < 16))
                 goto get_next;
             spin_unlock(&global_spinlock);
             continue;
         }
 
         current_client = b->c;
         if (unlikely(current_client != locked_client)) {
             if (locked_client)
                 dm_bufio_unlock(locked_client);
 
             if (!dm_bufio_trylock(current_client)) {
                 spin_unlock(&global_spinlock);
                 dm_bufio_lock(current_client);
                 locked_client = current_client;
                 continue;
             }
 
             locked_client = current_client;
         }
 
         spin_unlock(&global_spinlock);
 
         if (unlikely(!__try_evict_buffer(b, GFP_KERNEL))) {
             spin_lock(&global_spinlock);
             list_move(&b->global_list, &global_queue);
             spin_unlock(&global_spinlock);
         }
     }
 
     spin_unlock(&global_spinlock);
 
     if (locked_client)
         dm_bufio_unlock(locked_client);
 
     mutex_unlock(&dm_bufio_clients_lock);
 }
 
 static void cleanup_old_buffers(void)
 {
     unsigned long max_age_hz = get_max_age_hz();
     struct dm_bufio_client *c;
 
     mutex_lock(&dm_bufio_clients_lock);
 
     __cache_size_refresh();
 
     list_for_each_entry(c, &dm_bufio_all_clients, client_list)
         __evict_old_buffers(c, max_age_hz);
 
     mutex_unlock(&dm_bufio_clients_lock);
 }
 
 static void work_fn(struct work_struct *w)
 {
     cleanup_old_buffers();
 
     queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
                DM_BUFIO_WORK_TIMER_SECS * HZ);
 }
 
 /*----------------------------------------------------------------
  * Module setup
  *--------------------------------------------------------------*/
 
 /*
  * This is called only once for the whole dm_bufio module.
  * It initializes memory limit.
  */
 static int __init dm_bufio_init(void)
 {
     __u64 mem;
 
     dm_bufio_allocated_kmem_cache = 0;
     dm_bufio_allocated_get_free_pages = 0;
     dm_bufio_allocated_vmalloc = 0;
     dm_bufio_current_allocated = 0;
 
     mem = (__u64)mult_frac(totalram_pages() - totalhigh_pages(),
                    DM_BUFIO_MEMORY_PERCENT, 100) << PAGE_SHIFT;
 
     if (mem > ULONG_MAX)
         mem = ULONG_MAX;
 
 #ifdef CONFIG_MMU
     if (mem > mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100))
         mem = mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100);
 #endif
 
     dm_bufio_default_cache_size = mem;
 
     mutex_lock(&dm_bufio_clients_lock);
     __cache_size_refresh();
     mutex_unlock(&dm_bufio_clients_lock);
 
     dm_bufio_wq = alloc_workqueue("dm_bufio_cache", WQ_MEM_RECLAIM, 0);
     if (!dm_bufio_wq)
         return -ENOMEM;
 
     INIT_DELAYED_WORK(&dm_bufio_cleanup_old_work, work_fn);
     INIT_WORK(&dm_bufio_replacement_work, do_global_cleanup);
     queue_delayed_work(dm_bufio_wq, &dm_bufio_cleanup_old_work,
                DM_BUFIO_WORK_TIMER_SECS * HZ);
 
     return 0;
 }
 
 /*
  * This is called once when unloading the dm_bufio module.
  */
 static void __exit dm_bufio_exit(void)
 {
     int bug = 0;
 
     cancel_delayed_work_sync(&dm_bufio_cleanup_old_work);
     destroy_workqueue(dm_bufio_wq);
 
     if (dm_bufio_client_count) {
         DMCRIT("%s: dm_bufio_client_count leaked: %d",
             __func__, dm_bufio_client_count);
         bug = 1;
     }
 
     if (dm_bufio_current_allocated) {
         DMCRIT("%s: dm_bufio_current_allocated leaked: %lu",
             __func__, dm_bufio_current_allocated);
         bug = 1;
     }
 
     if (dm_bufio_allocated_get_free_pages) {
         DMCRIT("%s: dm_bufio_allocated_get_free_pages leaked: %lu",
                __func__, dm_bufio_allocated_get_free_pages);
         bug = 1;
     }
 
     if (dm_bufio_allocated_vmalloc) {
         DMCRIT("%s: dm_bufio_vmalloc leaked: %lu",
                __func__, dm_bufio_allocated_vmalloc);
         bug = 1;
     }
 
     BUG_ON(bug);
 }
 
 module_init(dm_bufio_init)
 module_exit(dm_bufio_exit)
 
 module_param_named(max_cache_size_bytes, dm_bufio_cache_size, ulong, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(max_cache_size_bytes, "Size of metadata cache");
 
 module_param_named(max_age_seconds, dm_bufio_max_age, uint, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(max_age_seconds, "Max age of a buffer in seconds");
 
 module_param_named(retain_bytes, dm_bufio_retain_bytes, ulong, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(retain_bytes, "Try to keep at least this many bytes cached in memory");
 
 module_param_named(peak_allocated_bytes, dm_bufio_peak_allocated, ulong, S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(peak_allocated_bytes, "Tracks the maximum allocated memory");
 
 module_param_named(allocated_kmem_cache_bytes, dm_bufio_allocated_kmem_cache, ulong, S_IRUGO);
 MODULE_PARM_DESC(allocated_kmem_cache_bytes, "Memory allocated with kmem_cache_alloc");
 
 module_param_named(allocated_get_free_pages_bytes, dm_bufio_allocated_get_free_pages, ulong, S_IRUGO);
 MODULE_PARM_DESC(allocated_get_free_pages_bytes, "Memory allocated with get_free_pages");
 
 module_param_named(allocated_vmalloc_bytes, dm_bufio_allocated_vmalloc, ulong, S_IRUGO);
 MODULE_PARM_DESC(allocated_vmalloc_bytes, "Memory allocated with vmalloc");
 
 module_param_named(current_allocated_bytes, dm_bufio_current_allocated, ulong, S_IRUGO);
 MODULE_PARM_DESC(current_allocated_bytes, "Memory currently used by the cache");
 
 MODULE_AUTHOR("Mikulas Patocka <dm-devel@redhat.com>");
 MODULE_DESCRIPTION(DM_NAME " buffered I/O library");
 MODULE_LICENSE("GPL");

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