treewide: refresh kmalloc_obj() conversionsgrafted

This is another run of the Coccinelle script for converting kmalloc()
family of allocations to kmalloc_obj() via the existing rules in
scripts/coccinelle/api/kmalloc_objs.cocci

This catches both the set of kmalloc() uses added since the first
kmalloc_obj() conversions in v7.0 and adds a large group missed in the
first pass due to Coccinelle not interacting well with the cleanup.h
scoped_...() family of macros[1]. I worked around this with spatch's
"--macro-file" argument to a file with all the scoped_...() macros mapped
to Coccinelle's YACFE_ITERATOR[2] as that was the closest viable control
flow indicator I could find.

Build tested allmodconfig on x86, arm64, arm, loongarch, mips, powerpc,
riscv, and s390 with no new warnings.

Link: https://lore.kernel.org/lkml/202609021314.8A9C0B8@keescook/ [1]
Link: https://github.com/coccinelle/coccinelle/blob/master/standard.h [2]
Signed-off-by: Kees Cook <kees+treewide@kernel.org>

1 files changed, 1396 insertions, 0 deletions

diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
new file mode 100644
index 000000000..6ad7b39ae
--- /dev/null
+++ b/fs/btrfs/extent_map.c
@@ -0,0 +1,1396 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include "messages.h"
+#include "ctree.h"
+#include "extent_map.h"
+#include "compression.h"
+#include "btrfs_inode.h"
+#include "disk-io.h"
+
+
+static struct kmem_cache *extent_map_cache;
+
+int __init btrfs_extent_map_init(void)
+{
+	extent_map_cache = kmem_cache_create("btrfs_extent_map",
+					     sizeof(struct extent_map), 0, 0, NULL);
+	if (!extent_map_cache)
+		return -ENOMEM;
+	return 0;
+}
+
+void __cold btrfs_extent_map_exit(void)
+{
+	kmem_cache_destroy(extent_map_cache);
+}
+
+/*
+ * Initialize the extent tree @tree.  Should be called for each new inode or
+ * other user of the extent_map interface.
+ */
+void btrfs_extent_map_tree_init(struct extent_map_tree *tree)
+{
+	tree->root = RB_ROOT;
+	INIT_LIST_HEAD(&tree->modified_extents);
+	rwlock_init(&tree->lock);
+}
+
+/*
+ * Allocate a new extent_map structure.  The new structure is returned with a
+ * reference count of one and needs to be freed using free_extent_map()
+ */
+struct extent_map *btrfs_alloc_extent_map(void)
+{
+	struct extent_map *em;
+	em = kmem_cache_zalloc(extent_map_cache, GFP_NOFS);
+	if (!em)
+		return NULL;
+	RB_CLEAR_NODE(&em->rb_node);
+	refcount_set(&em->refs, 1);
+	INIT_LIST_HEAD(&em->list);
+	return em;
+}
+
+/*
+ * Drop the reference out on @em by one and free the structure if the reference
+ * count hits zero.
+ */
+void btrfs_free_extent_map(struct extent_map *em)
+{
+	if (!em)
+		return;
+	if (refcount_dec_and_test(&em->refs)) {
+		WARN_ON(btrfs_extent_map_in_tree(em));
+		WARN_ON(!list_empty(&em->list));
+		kmem_cache_free(extent_map_cache, em);
+	}
+}
+
+/* Do the math around the end of an extent, handling wrapping. */
+static u64 range_end(u64 start, u64 len)
+{
+	if (start + len < start)
+		return (u64)-1;
+	return start + len;
+}
+
+static void remove_em(struct btrfs_inode *inode, struct extent_map *em)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+
+	rb_erase(&em->rb_node, &inode->extent_tree.root);
+	RB_CLEAR_NODE(&em->rb_node);
+
+	if (!btrfs_is_testing(fs_info) && btrfs_is_fstree(btrfs_root_id(inode->root)))
+		percpu_counter_dec(&fs_info->evictable_extent_maps);
+}
+
+static int tree_insert(struct rb_root *root, struct extent_map *em)
+{
+	struct rb_node **p = &root->rb_node;
+	struct rb_node *parent = NULL;
+	struct extent_map *entry = NULL;
+	struct rb_node *orig_parent = NULL;
+	u64 end = range_end(em->start, em->len);
+
+	while (*p) {
+		parent = *p;
+		entry = rb_entry(parent, struct extent_map, rb_node);
+
+		if (em->start < entry->start)
+			p = &(*p)->rb_left;
+		else if (em->start >= btrfs_extent_map_end(entry))
+			p = &(*p)->rb_right;
+		else
+			return -EEXIST;
+	}
+
+	orig_parent = parent;
+	while (parent && em->start >= btrfs_extent_map_end(entry)) {
+		parent = rb_next(parent);
+		entry = rb_entry(parent, struct extent_map, rb_node);
+	}
+	if (parent)
+		if (end > entry->start && em->start < btrfs_extent_map_end(entry))
+			return -EEXIST;
+
+	parent = orig_parent;
+	entry = rb_entry(parent, struct extent_map, rb_node);
+	while (parent && em->start < entry->start) {
+		parent = rb_prev(parent);
+		entry = rb_entry(parent, struct extent_map, rb_node);
+	}
+	if (parent)
+		if (end > entry->start && em->start < btrfs_extent_map_end(entry))
+			return -EEXIST;
+
+	rb_link_node(&em->rb_node, orig_parent, p);
+	rb_insert_color(&em->rb_node, root);
+	return 0;
+}
+
+/*
+ * Search through the tree for an extent_map with a given offset.  If it can't
+ * be found, try to find some neighboring extents
+ */
+static struct rb_node *tree_search(struct rb_root *root, u64 offset,
+				   struct rb_node **prev_or_next_ret)
+{
+	struct rb_node *n = root->rb_node;
+	struct rb_node *prev = NULL;
+	struct rb_node *orig_prev = NULL;
+	struct extent_map *entry;
+	struct extent_map *prev_entry = NULL;
+
+	ASSERT(prev_or_next_ret);
+
+	while (n) {
+		entry = rb_entry(n, struct extent_map, rb_node);
+		prev = n;
+		prev_entry = entry;
+
+		if (offset < entry->start)
+			n = n->rb_left;
+		else if (offset >= btrfs_extent_map_end(entry))
+			n = n->rb_right;
+		else
+			return n;
+	}
+
+	orig_prev = prev;
+	while (prev && offset >= btrfs_extent_map_end(prev_entry)) {
+		prev = rb_next(prev);
+		prev_entry = rb_entry(prev, struct extent_map, rb_node);
+	}
+
+	/*
+	 * Previous extent map found, return as in this case the caller does not
+	 * care about the next one.
+	 */
+	if (prev) {
+		*prev_or_next_ret = prev;
+		return NULL;
+	}
+
+	prev = orig_prev;
+	prev_entry = rb_entry(prev, struct extent_map, rb_node);
+	while (prev && offset < prev_entry->start) {
+		prev = rb_prev(prev);
+		prev_entry = rb_entry(prev, struct extent_map, rb_node);
+	}
+	*prev_or_next_ret = prev;
+
+	return NULL;
+}
+
+static inline u64 extent_map_block_len(const struct extent_map *em)
+{
+	if (btrfs_extent_map_is_compressed(em))
+		return em->disk_num_bytes;
+	return em->len;
+}
+
+static inline u64 extent_map_block_end(const struct extent_map *em)
+{
+	const u64 block_start = btrfs_extent_map_block_start(em);
+	const u64 block_end = block_start + extent_map_block_len(em);
+
+	if (block_end < block_start)
+		return (u64)-1;
+
+	return block_end;
+}
+
+static bool can_merge_extent_map(const struct extent_map *em)
+{
+	if (em->flags & EXTENT_FLAG_PINNED)
+		return false;
+
+	/* Don't merge compressed extents, we need to know their actual size. */
+	if (btrfs_extent_map_is_compressed(em))
+		return false;
+
+	if (em->flags & EXTENT_FLAG_LOGGING)
+		return false;
+
+	/*
+	 * We don't want to merge stuff that hasn't been written to the log yet
+	 * since it may not reflect exactly what is on disk, and that would be
+	 * bad.
+	 */
+	if (!list_empty(&em->list))
+		return false;
+
+	return true;
+}
+
+/* Check to see if two extent_map structs are adjacent and safe to merge. */
+static bool mergeable_maps(const struct extent_map *prev, const struct extent_map *next)
+{
+	if (btrfs_extent_map_end(prev) != next->start)
+		return false;
+
+	/*
+	 * The merged flag is not an on-disk flag, it just indicates we had the
+	 * extent maps of 2 (or more) adjacent extents merged, so factor it out.
+	 */
+	if ((prev->flags & ~EXTENT_FLAG_MERGED) !=
+	    (next->flags & ~EXTENT_FLAG_MERGED))
+		return false;
+
+	if (next->disk_bytenr < EXTENT_MAP_LAST_BYTE - 1)
+		return btrfs_extent_map_block_start(next) == extent_map_block_end(prev);
+
+	/* HOLES and INLINE extents. */
+	return next->disk_bytenr == prev->disk_bytenr;
+}
+
+/*
+ * Handle the on-disk data extents merge for @prev and @next.
+ *
+ * @prev:    left extent to merge
+ * @next:    right extent to merge
+ * @merged:  the extent we will not discard after the merge; updated with new values
+ *
+ * After this, one of the two extents is the new merged extent and the other is
+ * removed from the tree and likely freed. Note that @merged is one of @prev/@next
+ * so there is const/non-const aliasing occurring here.
+ *
+ * Only touches disk_bytenr/disk_num_bytes/offset/ram_bytes.
+ * For now only uncompressed regular extent can be merged.
+ */
+static void merge_ondisk_extents(const struct extent_map *prev, const struct extent_map *next,
+				 struct extent_map *merged)
+{
+	u64 new_disk_bytenr;
+	u64 new_disk_num_bytes;
+	u64 new_offset;
+
+	/* @prev and @next should not be compressed. */
+	ASSERT(!btrfs_extent_map_is_compressed(prev));
+	ASSERT(!btrfs_extent_map_is_compressed(next));
+
+	/*
+	 * There are two different cases where @prev and @next can be merged.
+	 *
+	 * 1) They are referring to the same data extent:
+	 *
+	 * |<----- data extent A ----->|
+	 *    |<- prev ->|<- next ->|
+	 *
+	 * 2) They are referring to different data extents but still adjacent:
+	 *
+	 * |<-- data extent A -->|<-- data extent B -->|
+	 *            |<- prev ->|<- next ->|
+	 *
+	 * The calculation here always merges the data extents first, then updates
+	 * @offset using the new data extents.
+	 *
+	 * For case 1), the merged data extent would be the same.
+	 * For case 2), we just merge the two data extents into one.
+	 */
+	new_disk_bytenr = min(prev->disk_bytenr, next->disk_bytenr);
+	new_disk_num_bytes = max(prev->disk_bytenr + prev->disk_num_bytes,
+				 next->disk_bytenr + next->disk_num_bytes) -
+			     new_disk_bytenr;
+	new_offset = prev->disk_bytenr + prev->offset - new_disk_bytenr;
+
+	merged->disk_bytenr = new_disk_bytenr;
+	merged->disk_num_bytes = new_disk_num_bytes;
+	merged->ram_bytes = new_disk_num_bytes;
+	merged->offset = new_offset;
+}
+
+static void dump_extent_map(struct btrfs_fs_info *fs_info, const char *prefix,
+			    struct extent_map *em)
+{
+	if (!IS_ENABLED(CONFIG_BTRFS_DEBUG))
+		return;
+	btrfs_crit(fs_info,
+"%s, start=%llu len=%llu disk_bytenr=%llu disk_num_bytes=%llu ram_bytes=%llu offset=%llu flags=0x%x",
+		prefix, em->start, em->len, em->disk_bytenr, em->disk_num_bytes,
+		em->ram_bytes, em->offset, em->flags);
+	ASSERT(0);
+}
+
+/* Internal sanity checks for btrfs debug builds. */
+static void validate_extent_map(struct btrfs_fs_info *fs_info, struct extent_map *em)
+{
+	const u32 blocksize = fs_info->sectorsize;
+
+	if (!IS_ENABLED(CONFIG_BTRFS_DEBUG))
+		return;
+
+	if (!IS_ALIGNED(em->start, blocksize) ||
+	    !IS_ALIGNED(em->len, blocksize))
+		dump_extent_map(fs_info, "unaligned start offset or length members", em);
+
+	if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE) {
+		if (em->disk_num_bytes == 0)
+			dump_extent_map(fs_info, "zero disk_num_bytes", em);
+		if (em->offset + em->len > em->ram_bytes)
+			dump_extent_map(fs_info, "ram_bytes too small", em);
+		if (em->offset + em->len > em->disk_num_bytes &&
+		    !btrfs_extent_map_is_compressed(em))
+			dump_extent_map(fs_info, "disk_num_bytes too small", em);
+		if (!btrfs_extent_map_is_compressed(em) &&
+		    em->ram_bytes != em->disk_num_bytes)
+			dump_extent_map(fs_info,
+		"ram_bytes mismatch with disk_num_bytes for non-compressed em",
+					em);
+		if (!IS_ALIGNED(em->disk_bytenr, blocksize) ||
+		    !IS_ALIGNED(em->disk_num_bytes, blocksize) ||
+		    !IS_ALIGNED(em->offset, blocksize) ||
+		    !IS_ALIGNED(em->ram_bytes, blocksize))
+			dump_extent_map(fs_info, "unaligned members", em);
+	} else if (em->offset) {
+		dump_extent_map(fs_info, "non-zero offset for hole/inline", em);
+	}
+}
+
+static void try_merge_map(struct btrfs_inode *inode, struct extent_map *em)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	struct extent_map *merge = NULL;
+	struct rb_node *rb;
+
+	/*
+	 * We can't modify an extent map that is in the tree and that is being
+	 * used by another task, as it can cause that other task to see it in
+	 * inconsistent state during the merging. We always have 1 reference for
+	 * the tree and 1 for this task (which is unpinning the extent map or
+	 * clearing the logging flag), so anything > 2 means it's being used by
+	 * other tasks too.
+	 */
+	if (refcount_read(&em->refs) > 2)
+		return;
+
+	if (!can_merge_extent_map(em))
+		return;
+
+	if (em->start != 0) {
+		rb = rb_prev(&em->rb_node);
+		merge = rb_entry_safe(rb, struct extent_map, rb_node);
+
+		if (rb && can_merge_extent_map(merge) && mergeable_maps(merge, em)) {
+			em->start = merge->start;
+			em->len += merge->len;
+			em->generation = max(em->generation, merge->generation);
+
+			if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE)
+				merge_ondisk_extents(merge, em, em);
+			em->flags |= EXTENT_FLAG_MERGED;
+
+			validate_extent_map(fs_info, em);
+			remove_em(inode, merge);
+			btrfs_free_extent_map(merge);
+		}
+	}
+
+	rb = rb_next(&em->rb_node);
+	merge = rb_entry_safe(rb, struct extent_map, rb_node);
+
+	if (rb && can_merge_extent_map(merge) && mergeable_maps(em, merge)) {
+		em->len += merge->len;
+		if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE)
+			merge_ondisk_extents(em, merge, em);
+		validate_extent_map(fs_info, em);
+		em->generation = max(em->generation, merge->generation);
+		em->flags |= EXTENT_FLAG_MERGED;
+		remove_em(inode, merge);
+		btrfs_free_extent_map(merge);
+	}
+}
+
+/*
+ * Unpin an extent from the cache.
+ *
+ * @inode:	the inode from which we are unpinning an extent range
+ * @start:	logical offset in the file
+ * @len:	length of the extent
+ * @gen:	generation that this extent has been modified in
+ *
+ * Called after an extent has been written to disk properly.  Set the generation
+ * to the generation that actually added the file item to the inode so we know
+ * we need to sync this extent when we call fsync().
+ *
+ * Returns: 0	     on success
+ * 	    -ENOENT  when the extent is not found in the tree
+ * 	    -EUCLEAN if the found extent does not match the expected start
+ */
+int btrfs_unpin_extent_cache(struct btrfs_inode *inode, u64 start, u64 len, u64 gen)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	struct extent_map_tree *tree = &inode->extent_tree;
+	int ret = 0;
+	struct extent_map *em;
+
+	write_lock(&tree->lock);
+	em = btrfs_lookup_extent_mapping(tree, start, len);
+
+	if (WARN_ON(!em)) {
+		btrfs_warn(fs_info,
+"no extent map found for inode %llu (root %lld) when unpinning extent range [%llu, %llu), generation %llu",
+			   btrfs_ino(inode), btrfs_root_id(inode->root),
+			   start, start + len, gen);
+		ret = -ENOENT;
+		goto out;
+	}
+
+	if (WARN_ON(em->start != start)) {
+		btrfs_warn(fs_info,
+"found extent map for inode %llu (root %lld) with unexpected start offset %llu when unpinning extent range [%llu, %llu), generation %llu",
+			   btrfs_ino(inode), btrfs_root_id(inode->root),
+			   em->start, start, start + len, gen);
+		ret = -EUCLEAN;
+		goto out;
+	}
+
+	em->generation = gen;
+	em->flags &= ~EXTENT_FLAG_PINNED;
+
+	try_merge_map(inode, em);
+
+out:
+	write_unlock(&tree->lock);
+	btrfs_free_extent_map(em);
+	return ret;
+
+}
+
+void btrfs_clear_em_logging(struct btrfs_inode *inode, struct extent_map *em)
+{
+	lockdep_assert_held_write(&inode->extent_tree.lock);
+
+	em->flags &= ~EXTENT_FLAG_LOGGING;
+	if (btrfs_extent_map_in_tree(em))
+		try_merge_map(inode, em);
+}
+
+static inline void setup_extent_mapping(struct btrfs_inode *inode,
+					struct extent_map *em,
+					bool modified)
+{
+	refcount_inc(&em->refs);
+
+	ASSERT(list_empty(&em->list));
+
+	if (modified)
+		list_add(&em->list, &inode->extent_tree.modified_extents);
+	else
+		try_merge_map(inode, em);
+}
+
+/*
+ * Add a new extent map to an inode's extent map tree.
+ *
+ * @inode:	the target inode
+ * @em:		map to insert
+ * @modified:	indicate whether the given @em should be added to the
+ *	        modified list, which indicates the extent needs to be logged
+ *
+ * Insert @em into the @inode's extent map tree or perform a simple
+ * forward/backward merge with existing mappings.  The extent_map struct passed
+ * in will be inserted into the tree directly, with an additional reference
+ * taken, or a reference dropped if the merge attempt was successful.
+ */
+static int add_extent_mapping(struct btrfs_inode *inode,
+			      struct extent_map *em, bool modified)
+{
+	struct extent_map_tree *tree = &inode->extent_tree;
+	struct btrfs_root *root = inode->root;
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	int ret;
+
+	lockdep_assert_held_write(&tree->lock);
+
+	validate_extent_map(fs_info, em);
+	ret = tree_insert(&tree->root, em);
+	if (ret)
+		return ret;
+
+	setup_extent_mapping(inode, em, modified);
+
+	if (!btrfs_is_testing(fs_info) && btrfs_is_fstree(btrfs_root_id(root)))
+		percpu_counter_inc(&fs_info->evictable_extent_maps);
+
+	return 0;
+}
+
+static struct extent_map *lookup_extent_mapping(struct extent_map_tree *tree,
+						u64 start, u64 len, bool strict)
+{
+	struct extent_map *em;
+	struct rb_node *rb_node;
+	struct rb_node *prev_or_next = NULL;
+	u64 end = range_end(start, len);
+
+	rb_node = tree_search(&tree->root, start, &prev_or_next);
+	if (!rb_node) {
+		if (prev_or_next)
+			rb_node = prev_or_next;
+		else
+			return NULL;
+	}
+
+	em = rb_entry(rb_node, struct extent_map, rb_node);
+
+	if (strict && !(end > em->start && start < btrfs_extent_map_end(em)))
+		return NULL;
+
+	refcount_inc(&em->refs);
+	return em;
+}
+
+/*
+ * Lookup extent_map that intersects @start + @len range.
+ *
+ * @tree:	tree to lookup in
+ * @start:	byte offset to start the search
+ * @len:	length of the lookup range
+ *
+ * Find and return the first extent_map struct in @tree that intersects the
+ * [start, len] range.  There may be additional objects in the tree that
+ * intersect, so check the object returned carefully to make sure that no
+ * additional lookups are needed.
+ */
+struct extent_map *btrfs_lookup_extent_mapping(struct extent_map_tree *tree,
+					       u64 start, u64 len)
+{
+	return lookup_extent_mapping(tree, start, len, true);
+}
+
+/*
+ * Find a nearby extent map intersecting @start + @len (not an exact search).
+ *
+ * @tree:	tree to lookup in
+ * @start:	byte offset to start the search
+ * @len:	length of the lookup range
+ *
+ * Find and return the first extent_map struct in @tree that intersects the
+ * [start, len] range.
+ *
+ * If one can't be found, any nearby extent may be returned
+ */
+struct extent_map *btrfs_search_extent_mapping(struct extent_map_tree *tree,
+					       u64 start, u64 len)
+{
+	return lookup_extent_mapping(tree, start, len, false);
+}
+
+/*
+ * Remove an extent_map from its inode's extent tree.
+ *
+ * @inode:	the inode the extent map belongs to
+ * @em:		extent map being removed
+ *
+ * Remove @em from the extent tree of @inode.  No reference counts are dropped,
+ * and no checks are done to see if the range is in use.
+ */
+void btrfs_remove_extent_mapping(struct btrfs_inode *inode, struct extent_map *em)
+{
+	struct extent_map_tree *tree = &inode->extent_tree;
+
+	lockdep_assert_held_write(&tree->lock);
+
+	WARN_ON(em->flags & EXTENT_FLAG_PINNED);
+	if (!(em->flags & EXTENT_FLAG_LOGGING))
+		list_del_init(&em->list);
+
+	remove_em(inode, em);
+}
+
+static void replace_extent_mapping(struct btrfs_inode *inode,
+				   struct extent_map *cur,
+				   struct extent_map *new,
+				   bool modified)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	struct extent_map_tree *tree = &inode->extent_tree;
+
+	lockdep_assert_held_write(&tree->lock);
+
+	validate_extent_map(fs_info, new);
+
+	WARN_ON(cur->flags & EXTENT_FLAG_PINNED);
+	ASSERT(btrfs_extent_map_in_tree(cur));
+	if (!(cur->flags & EXTENT_FLAG_LOGGING))
+		list_del_init(&cur->list);
+	rb_replace_node(&cur->rb_node, &new->rb_node, &tree->root);
+	RB_CLEAR_NODE(&cur->rb_node);
+
+	setup_extent_mapping(inode, new, modified);
+}
+
+static struct extent_map *next_extent_map(const struct extent_map *em)
+{
+	struct rb_node *next;
+
+	next = rb_next(&em->rb_node);
+	if (!next)
+		return NULL;
+	return container_of(next, struct extent_map, rb_node);
+}
+
+static struct extent_map *prev_extent_map(struct extent_map *em)
+{
+	struct rb_node *prev;
+
+	prev = rb_prev(&em->rb_node);
+	if (!prev)
+		return NULL;
+	return container_of(prev, struct extent_map, rb_node);
+}
+
+/*
+ * Helper for btrfs_get_extent.  Given an existing extent in the tree,
+ * the existing extent is the nearest extent to map_start,
+ * and an extent that you want to insert, deal with overlap and insert
+ * the best fitted new extent into the tree.
+ */
+static noinline int merge_extent_mapping(struct btrfs_inode *inode,
+					 struct extent_map *existing,
+					 struct extent_map *em,
+					 u64 map_start)
+{
+	struct extent_map *prev;
+	struct extent_map *next;
+	u64 start;
+	u64 end;
+	u64 start_diff;
+
+	if (map_start < em->start || map_start >= btrfs_extent_map_end(em))
+		return -EINVAL;
+
+	if (existing->start > map_start) {
+		next = existing;
+		prev = prev_extent_map(next);
+	} else {
+		prev = existing;
+		next = next_extent_map(prev);
+	}
+
+	start = prev ? btrfs_extent_map_end(prev) : em->start;
+	start = max_t(u64, start, em->start);
+	end = next ? next->start : btrfs_extent_map_end(em);
+	end = min_t(u64, end, btrfs_extent_map_end(em));
+	start_diff = start - em->start;
+	em->start = start;
+	em->len = end - start;
+	if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE)
+		em->offset += start_diff;
+	return add_extent_mapping(inode, em, false);
+}
+
+/*
+ * Add extent mapping into an inode's extent map tree.
+ *
+ * @inode:    target inode
+ * @em_in:    extent we are inserting
+ * @start:    start of the logical range btrfs_get_extent() is requesting
+ * @len:      length of the logical range btrfs_get_extent() is requesting
+ *
+ * Note that @em_in's range may be different from [start, start+len),
+ * but they must be overlapped.
+ *
+ * Insert @em_in into the inode's extent map tree. In case there is an
+ * overlapping range, handle the -EEXIST by either:
+ * a) Returning the existing extent in @em_in if @start is within the
+ *    existing em.
+ * b) Merge the existing extent with @em_in passed in.
+ *
+ * Return 0 on success, otherwise -EEXIST.
+ *
+ */
+int btrfs_add_extent_mapping(struct btrfs_inode *inode,
+			     struct extent_map **em_in, u64 start, u64 len)
+{
+	int ret;
+	struct extent_map *em = *em_in;
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+
+	/*
+	 * Tree-checker should have rejected any inline extent with non-zero
+	 * file offset. Here just do a sanity check.
+	 */
+	if (em->disk_bytenr == EXTENT_MAP_INLINE)
+		ASSERT(em->start == 0, "em->start=%llu", em->start);
+
+	ret = add_extent_mapping(inode, em, false);
+	/* it is possible that someone inserted the extent into the tree
+	 * while we had the lock dropped.  It is also possible that
+	 * an overlapping map exists in the tree
+	 */
+	if (ret == -EEXIST) {
+		struct extent_map *existing;
+
+		existing = btrfs_search_extent_mapping(&inode->extent_tree, start, len);
+
+		trace_btrfs_handle_em_exist(fs_info, existing, em, start, len);
+
+		/*
+		 * existing will always be non-NULL, since there must be
+		 * extent causing the -EEXIST.
+		 */
+		if (start >= existing->start &&
+		    start < btrfs_extent_map_end(existing)) {
+			btrfs_free_extent_map(em);
+			*em_in = existing;
+			ret = 0;
+		} else {
+			u64 orig_start = em->start;
+			u64 orig_len = em->len;
+
+			/*
+			 * The existing extent map is the one nearest to
+			 * the [start, start + len) range which overlaps
+			 */
+			ret = merge_extent_mapping(inode, existing, em, start);
+			if (WARN_ON(ret)) {
+				btrfs_free_extent_map(em);
+				*em_in = NULL;
+				btrfs_warn(fs_info,
+"extent map merge error existing [%llu, %llu) with em [%llu, %llu) start %llu",
+					   existing->start, btrfs_extent_map_end(existing),
+					   orig_start, orig_start + orig_len, start);
+			}
+			btrfs_free_extent_map(existing);
+		}
+	}
+
+	ASSERT(ret == 0 || ret == -EEXIST, "ret=%d", ret);
+	return ret;
+}
+
+/*
+ * Drop all extent maps from a tree in the fastest possible way, rescheduling
+ * if needed. This avoids searching the tree, from the root down to the first
+ * extent map, before each deletion.
+ */
+static void drop_all_extent_maps_fast(struct btrfs_inode *inode)
+{
+	struct extent_map_tree *tree = &inode->extent_tree;
+	struct rb_node *node;
+
+	write_lock(&tree->lock);
+	node = rb_first(&tree->root);
+	while (node) {
+		struct extent_map *em;
+		struct rb_node *next = rb_next(node);
+
+		em = rb_entry(node, struct extent_map, rb_node);
+		em->flags &= ~(EXTENT_FLAG_PINNED | EXTENT_FLAG_LOGGING);
+		btrfs_remove_extent_mapping(inode, em);
+		btrfs_free_extent_map(em);
+
+		if (cond_resched_rwlock_write(&tree->lock))
+			node = rb_first(&tree->root);
+		else
+			node = next;
+	}
+	write_unlock(&tree->lock);
+}
+
+/*
+ * Drop all extent maps in a given range.
+ *
+ * @inode:       The target inode.
+ * @start:       Start offset of the range.
+ * @end:         End offset of the range (inclusive value).
+ * @skip_pinned: Indicate if pinned extent maps should be ignored or not.
+ *
+ * This drops all the extent maps that intersect the given range [@start, @end].
+ * Extent maps that partially overlap the range and extend behind or beyond it,
+ * are split.
+ * The caller should have locked an appropriate file range in the inode's io
+ * tree before calling this function.
+ */
+void btrfs_drop_extent_map_range(struct btrfs_inode *inode, u64 start, u64 end,
+				 bool skip_pinned)
+{
+	struct extent_map *split;
+	struct extent_map *split2;
+	struct extent_map *em;
+	struct extent_map_tree *em_tree = &inode->extent_tree;
+	u64 len = end - start + 1;
+
+	WARN_ON(end < start);
+	if (end == (u64)-1) {
+		if (start == 0 && !skip_pinned) {
+			drop_all_extent_maps_fast(inode);
+			return;
+		}
+		len = (u64)-1;
+	} else {
+		/* Make end offset exclusive for use in the loop below. */
+		end++;
+	}
+
+	/*
+	 * It's ok if we fail to allocate the extent maps, see the comment near
+	 * the bottom of the loop below. We only need two spare extent maps in
+	 * the worst case, where the first extent map that intersects our range
+	 * starts before the range and the last extent map that intersects our
+	 * range ends after our range (and they might be the same extent map),
+	 * because we need to split those two extent maps at the boundaries.
+	 */
+	split = btrfs_alloc_extent_map();
+	split2 = btrfs_alloc_extent_map();
+
+	write_lock(&em_tree->lock);
+	em = btrfs_lookup_extent_mapping(em_tree, start, len);
+
+	while (em) {
+		/* extent_map_end() returns exclusive value (last byte + 1). */
+		const u64 em_end = btrfs_extent_map_end(em);
+		struct extent_map *next_em = NULL;
+		u64 gen;
+		unsigned long flags;
+		bool modified;
+
+		if (em_end < end) {
+			next_em = next_extent_map(em);
+			if (next_em) {
+				if (next_em->start < end)
+					refcount_inc(&next_em->refs);
+				else
+					next_em = NULL;
+			}
+		}
+
+		if (skip_pinned && (em->flags & EXTENT_FLAG_PINNED)) {
+			start = em_end;
+			goto next;
+		}
+
+		/*
+		 * In case we split the extent map, we want to preserve the
+		 * EXTENT_FLAG_LOGGING flag on our extent map, but we don't want
+		 * it on the new extent maps.
+		 */
+		flags = em->flags & ~EXTENT_FLAG_LOGGING;
+		em->flags &= ~EXTENT_FLAG_PINNED;
+		modified = !list_empty(&em->list);
+
+		/*
+		 * The extent map does not cross our target range, so no need to
+		 * split it, we can remove it directly.
+		 */
+		if (em->start >= start && em_end <= end)
+			goto remove_em;
+
+		gen = em->generation;
+
+		if (em->start < start) {
+			if (!split) {
+				split = split2;
+				split2 = NULL;
+				if (!split)
+					goto remove_em;
+			}
+			split->start = em->start;
+			split->len = start - em->start;
+
+			if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE) {
+				split->disk_bytenr = em->disk_bytenr;
+				split->disk_num_bytes = em->disk_num_bytes;
+				split->offset = em->offset;
+				split->ram_bytes = em->ram_bytes;
+			} else {
+				split->disk_bytenr = em->disk_bytenr;
+				split->disk_num_bytes = 0;
+				split->offset = 0;
+				split->ram_bytes = split->len;
+			}
+
+			split->generation = gen;
+			split->flags = flags;
+			replace_extent_mapping(inode, em, split, modified);
+			btrfs_free_extent_map(split);
+			split = split2;
+			split2 = NULL;
+		}
+		if (em_end > end) {
+			if (!split) {
+				split = split2;
+				split2 = NULL;
+				if (!split)
+					goto remove_em;
+			}
+			split->start = end;
+			split->len = em_end - end;
+			split->disk_bytenr = em->disk_bytenr;
+			split->flags = flags;
+			split->generation = gen;
+
+			if (em->disk_bytenr < EXTENT_MAP_LAST_BYTE) {
+				split->disk_num_bytes = em->disk_num_bytes;
+				split->offset = em->offset + end - em->start;
+				split->ram_bytes = em->ram_bytes;
+			} else {
+				split->disk_num_bytes = 0;
+				split->offset = 0;
+				split->ram_bytes = split->len;
+			}
+
+			if (btrfs_extent_map_in_tree(em)) {
+				replace_extent_mapping(inode, em, split, modified);
+			} else {
+				int ret;
+
+				ret = add_extent_mapping(inode, split, modified);
+				/* Logic error, shouldn't happen. */
+				ASSERT(ret == 0, "ret=%d", ret);
+				if (WARN_ON(ret != 0) && modified)
+					btrfs_set_inode_full_sync(inode);
+			}
+			btrfs_free_extent_map(split);
+			split = NULL;
+		}
+remove_em:
+		if (btrfs_extent_map_in_tree(em)) {
+			/*
+			 * If the extent map is still in the tree it means that
+			 * either of the following is true:
+			 *
+			 * 1) It fits entirely in our range (doesn't end beyond
+			 *    it or starts before it);
+			 *
+			 * 2) It starts before our range and/or ends after our
+			 *    range, and we were not able to allocate the extent
+			 *    maps for split operations, @split and @split2.
+			 *
+			 * If we are at case 2) then we just remove the entire
+			 * extent map - this is fine since if anyone needs it to
+			 * access the subranges outside our range, will just
+			 * load it again from the subvolume tree's file extent
+			 * item. However if the extent map was in the list of
+			 * modified extents, then we must mark the inode for a
+			 * full fsync, otherwise a fast fsync will miss this
+			 * extent if it's new and needs to be logged.
+			 */
+			if ((em->start < start || em_end > end) && modified) {
+				ASSERT(!split);
+				btrfs_set_inode_full_sync(inode);
+			}
+			btrfs_remove_extent_mapping(inode, em);
+		}
+
+		/*
+		 * Once for the tree reference (we replaced or removed the
+		 * extent map from the tree).
+		 */
+		btrfs_free_extent_map(em);
+next:
+		/* Once for us (for our lookup reference). */
+		btrfs_free_extent_map(em);
+
+		em = next_em;
+	}
+
+	write_unlock(&em_tree->lock);
+
+	btrfs_free_extent_map(split);
+	btrfs_free_extent_map(split2);
+}
+
+/*
+ * Replace a range in the inode's extent map tree with a new extent map.
+ *
+ * @inode:      The target inode.
+ * @new_em:     The new extent map to add to the inode's extent map tree.
+ * @modified:   Indicate if the new extent map should be added to the list of
+ *              modified extents (for fast fsync tracking).
+ *
+ * Drops all the extent maps in the inode's extent map tree that intersect the
+ * range of the new extent map and adds the new extent map to the tree.
+ * The caller should have locked an appropriate file range in the inode's io
+ * tree before calling this function.
+ */
+int btrfs_replace_extent_map_range(struct btrfs_inode *inode,
+				   struct extent_map *new_em,
+				   bool modified)
+{
+	const u64 end = new_em->start + new_em->len - 1;
+	struct extent_map_tree *tree = &inode->extent_tree;
+	int ret;
+
+	ASSERT(!btrfs_extent_map_in_tree(new_em));
+
+	/*
+	 * The caller has locked an appropriate file range in the inode's io
+	 * tree, but getting -EEXIST when adding the new extent map can still
+	 * happen in case there are extents that partially cover the range, and
+	 * this is due to two tasks operating on different parts of the extent.
+	 * See commit 18e83ac75bfe67 ("Btrfs: fix unexpected EEXIST from
+	 * btrfs_get_extent") for an example and details.
+	 */
+	do {
+		btrfs_drop_extent_map_range(inode, new_em->start, end, false);
+		write_lock(&tree->lock);
+		ret = add_extent_mapping(inode, new_em, modified);
+		write_unlock(&tree->lock);
+	} while (ret == -EEXIST);
+
+	return ret;
+}
+
+/*
+ * Split off the first pre bytes from the extent_map at [start, start + len],
+ * and set the block_start for it to new_logical.
+ *
+ * This function is used when an ordered_extent needs to be split.
+ */
+int btrfs_split_extent_map(struct btrfs_inode *inode, u64 start, u64 len, u64 pre,
+			   u64 new_logical)
+{
+	struct extent_map_tree *em_tree = &inode->extent_tree;
+	struct extent_map *em;
+	struct extent_map *split_pre = NULL;
+	struct extent_map *split_mid = NULL;
+	int ret = 0;
+	unsigned long flags;
+
+	ASSERT(pre != 0);
+	ASSERT(pre < len);
+
+	split_pre = btrfs_alloc_extent_map();
+	if (!split_pre)
+		return -ENOMEM;
+	split_mid = btrfs_alloc_extent_map();
+	if (!split_mid) {
+		ret = -ENOMEM;
+		goto out_free_pre;
+	}
+
+	btrfs_lock_extent(&inode->io_tree, start, start + len - 1, NULL);
+	write_lock(&em_tree->lock);
+	em = btrfs_lookup_extent_mapping(em_tree, start, len);
+	if (unlikely(!em)) {
+		ret = -EIO;
+		goto out_unlock;
+	}
+
+	ASSERT(em->len == len);
+	ASSERT(!btrfs_extent_map_is_compressed(em));
+	ASSERT(em->disk_bytenr < EXTENT_MAP_LAST_BYTE);
+	ASSERT(em->flags & EXTENT_FLAG_PINNED);
+	ASSERT(!(em->flags & EXTENT_FLAG_LOGGING));
+	ASSERT(!list_empty(&em->list));
+
+	flags = em->flags;
+	em->flags &= ~EXTENT_FLAG_PINNED;
+
+	/* First, replace the em with a new extent_map starting from * em->start */
+	split_pre->start = em->start;
+	split_pre->len = pre;
+	split_pre->disk_bytenr = new_logical;
+	split_pre->disk_num_bytes = split_pre->len;
+	split_pre->offset = 0;
+	split_pre->ram_bytes = split_pre->len;
+	split_pre->flags = flags;
+	split_pre->generation = em->generation;
+
+	replace_extent_mapping(inode, em, split_pre, true);
+
+	/*
+	 * Now we only have an extent_map at:
+	 *     [em->start, em->start + pre]
+	 */
+
+	/* Insert the middle extent_map. */
+	split_mid->start = em->start + pre;
+	split_mid->len = em->len - pre;
+	split_mid->disk_bytenr = btrfs_extent_map_block_start(em) + pre;
+	split_mid->disk_num_bytes = split_mid->len;
+	split_mid->offset = 0;
+	split_mid->ram_bytes = split_mid->len;
+	split_mid->flags = flags;
+	split_mid->generation = em->generation;
+	add_extent_mapping(inode, split_mid, true);
+
+	/* Once for us */
+	btrfs_free_extent_map(em);
+	/* Once for the tree */
+	btrfs_free_extent_map(em);
+
+out_unlock:
+	write_unlock(&em_tree->lock);
+	btrfs_unlock_extent(&inode->io_tree, start, start + len - 1, NULL);
+	btrfs_free_extent_map(split_mid);
+out_free_pre:
+	btrfs_free_extent_map(split_pre);
+	return ret;
+}
+
+struct btrfs_em_shrink_ctx {
+	long nr_to_scan;
+	long scanned;
+};
+
+static long btrfs_scan_inode(struct btrfs_inode *inode, struct btrfs_em_shrink_ctx *ctx)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	const u64 cur_fs_gen = btrfs_get_fs_generation(fs_info);
+	struct extent_map_tree *tree = &inode->extent_tree;
+	long nr_dropped = 0;
+	struct rb_node *node;
+
+	lockdep_assert_held_write(&tree->lock);
+
+	/*
+	 * Take the mmap lock so that we serialize with the inode logging phase
+	 * of fsync because we may need to set the full sync flag on the inode,
+	 * in case we have to remove extent maps in the tree's list of modified
+	 * extents. If we set the full sync flag in the inode while an fsync is
+	 * in progress, we may risk missing new extents because before the flag
+	 * is set, fsync decides to only wait for writeback to complete and then
+	 * during inode logging it sees the flag set and uses the subvolume tree
+	 * to find new extents, which may not be there yet because ordered
+	 * extents haven't completed yet.
+	 *
+	 * We also do a try lock because we don't want to block for too long and
+	 * we are holding the extent map tree's lock in write mode.
+	 */
+	if (!down_read_trylock(&inode->i_mmap_lock))
+		return 0;
+
+	node = rb_first(&tree->root);
+	while (node) {
+		struct rb_node *next = rb_next(node);
+		struct extent_map *em;
+
+		em = rb_entry(node, struct extent_map, rb_node);
+		ctx->scanned++;
+
+		if (em->flags & EXTENT_FLAG_PINNED)
+			goto next;
+
+		/*
+		 * If the inode is in the list of modified extents (new) and its
+		 * generation is the same (or is greater than) the current fs
+		 * generation, it means it was not yet persisted so we have to
+		 * set the full sync flag so that the next fsync will not miss
+		 * it.
+		 */
+		if (!list_empty(&em->list) && em->generation >= cur_fs_gen)
+			btrfs_set_inode_full_sync(inode);
+
+		btrfs_remove_extent_mapping(inode, em);
+		trace_btrfs_extent_map_shrinker_remove_em(inode, em);
+		/* Drop the reference for the tree. */
+		btrfs_free_extent_map(em);
+		nr_dropped++;
+next:
+		if (ctx->scanned >= ctx->nr_to_scan)
+			break;
+
+		/*
+		 * Stop if we need to reschedule or there's contention on the
+		 * lock. This is to avoid slowing other tasks trying to take the
+		 * lock.
+		 */
+		if (need_resched() || rwlock_needbreak(&tree->lock) ||
+		    btrfs_fs_closing(fs_info))
+			break;
+		node = next;
+	}
+	up_read(&inode->i_mmap_lock);
+
+	return nr_dropped;
+}
+
+static struct btrfs_inode *find_first_inode_to_shrink(struct btrfs_root *root,
+						      u64 min_ino)
+{
+	struct btrfs_inode *inode;
+	unsigned long from = min_ino;
+
+	xa_lock(&root->inodes);
+	while (true) {
+		struct extent_map_tree *tree;
+
+		inode = xa_find(&root->inodes, &from, ULONG_MAX, XA_PRESENT);
+		if (!inode)
+			break;
+
+		tree = &inode->extent_tree;
+
+		/*
+		 * We want to be fast so if the lock is busy we don't want to
+		 * spend time waiting for it (some task is about to do IO for
+		 * the inode).
+		 */
+		if (!write_trylock(&tree->lock))
+			goto next;
+
+		/*
+		 * Skip inode if it doesn't have loaded extent maps, so we avoid
+		 * getting a reference and doing an iput later. This includes
+		 * cases like files that were opened for things like stat(2), or
+		 * files with all extent maps previously released through the
+		 * release folio callback (btrfs_release_folio()) or released in
+		 * a previous run, or directories which never have extent maps.
+		 */
+		if (RB_EMPTY_ROOT(&tree->root)) {
+			write_unlock(&tree->lock);
+			goto next;
+		}
+
+		if (igrab(&inode->vfs_inode))
+			break;
+
+		write_unlock(&tree->lock);
+next:
+		from = btrfs_ino(inode) + 1;
+		xa_unlock(&root->inodes);
+		cond_resched();
+		xa_lock(&root->inodes);
+	}
+	xa_unlock(&root->inodes);
+
+	return inode;
+}
+
+static long btrfs_scan_root(struct btrfs_root *root, struct btrfs_em_shrink_ctx *ctx)
+{
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct btrfs_inode *inode;
+	long nr_dropped = 0;
+	u64 min_ino = fs_info->em_shrinker_last_ino + 1;
+
+	inode = find_first_inode_to_shrink(root, min_ino);
+	while (inode) {
+		nr_dropped += btrfs_scan_inode(inode, ctx);
+		write_unlock(&inode->extent_tree.lock);
+
+		min_ino = btrfs_ino(inode) + 1;
+		fs_info->em_shrinker_last_ino = btrfs_ino(inode);
+		iput(&inode->vfs_inode);
+
+		if (ctx->scanned >= ctx->nr_to_scan || btrfs_fs_closing(fs_info))
+			break;
+
+		cond_resched();
+
+		inode = find_first_inode_to_shrink(root, min_ino);
+	}
+
+	if (inode) {
+		/*
+		 * There are still inodes in this root or we happened to process
+		 * the last one and reached the scan limit. In either case set
+		 * the current root to this one, so we'll resume from the next
+		 * inode if there is one or we will find out this was the last
+		 * one and move to the next root.
+		 */
+		fs_info->em_shrinker_last_root = btrfs_root_id(root);
+	} else {
+		/*
+		 * No more inodes in this root, set extent_map_shrinker_last_ino to 0 so
+		 * that when processing the next root we start from its first inode.
+		 */
+		fs_info->em_shrinker_last_ino = 0;
+		fs_info->em_shrinker_last_root = btrfs_root_id(root) + 1;
+	}
+
+	return nr_dropped;
+}
+
+static void btrfs_extent_map_shrinker_worker(struct work_struct *work)
+{
+	struct btrfs_fs_info *fs_info;
+	struct btrfs_em_shrink_ctx ctx;
+	u64 start_root_id;
+	u64 next_root_id;
+	bool cycled = false;
+	long nr_dropped = 0;
+
+	fs_info = container_of(work, struct btrfs_fs_info, em_shrinker_work);
+
+	ctx.scanned = 0;
+	ctx.nr_to_scan = atomic64_read(&fs_info->em_shrinker_nr_to_scan);
+
+	start_root_id = fs_info->em_shrinker_last_root;
+	next_root_id = fs_info->em_shrinker_last_root;
+
+	if (trace_btrfs_extent_map_shrinker_scan_enter_enabled()) {
+		s64 nr = percpu_counter_sum_positive(&fs_info->evictable_extent_maps);
+
+		trace_call__btrfs_extent_map_shrinker_scan_enter(fs_info, nr);
+	}
+
+	while (ctx.scanned < ctx.nr_to_scan && !btrfs_fs_closing(fs_info)) {
+		struct btrfs_root *root;
+		unsigned long count;
+
+		cond_resched();
+
+		spin_lock(&fs_info->fs_roots_radix_lock);
+		count = radix_tree_gang_lookup(&fs_info->fs_roots_radix,
+					       (void **)&root,
+					       (unsigned long)next_root_id, 1);
+		if (count == 0) {
+			spin_unlock(&fs_info->fs_roots_radix_lock);
+			if (start_root_id > 0 && !cycled) {
+				next_root_id = 0;
+				fs_info->em_shrinker_last_root = 0;
+				fs_info->em_shrinker_last_ino = 0;
+				cycled = true;
+				continue;
+			}
+			break;
+		}
+		next_root_id = btrfs_root_id(root) + 1;
+		root = btrfs_grab_root(root);
+		spin_unlock(&fs_info->fs_roots_radix_lock);
+
+		if (!root)
+			continue;
+
+		if (btrfs_is_fstree(btrfs_root_id(root)))
+			nr_dropped += btrfs_scan_root(root, &ctx);
+
+		btrfs_put_root(root);
+	}
+
+	if (trace_btrfs_extent_map_shrinker_scan_exit_enabled()) {
+		s64 nr = percpu_counter_sum_positive(&fs_info->evictable_extent_maps);
+
+		trace_call__btrfs_extent_map_shrinker_scan_exit(fs_info, nr_dropped, nr);
+	}
+
+	atomic64_set(&fs_info->em_shrinker_nr_to_scan, 0);
+}
+
+void btrfs_free_extent_maps(struct btrfs_fs_info *fs_info, long nr_to_scan)
+{
+	/*
+	 * Do nothing if the shrinker is already running. In case of high memory
+	 * pressure we can have a lot of tasks calling us and all passing the
+	 * same nr_to_scan value, but in reality we may need only to free
+	 * nr_to_scan extent maps (or less). In case we need to free more than
+	 * that, we will be called again by the fs shrinker, so no worries about
+	 * not doing enough work to reclaim memory from extent maps.
+	 * We can also be repeatedly called with the same nr_to_scan value
+	 * simply because the shrinker runs asynchronously and multiple calls
+	 * to this function are made before the shrinker does enough progress.
+	 *
+	 * That's why we set the atomic counter to nr_to_scan only if its
+	 * current value is zero, instead of incrementing the counter by
+	 * nr_to_scan.
+	 */
+	if (atomic64_cmpxchg(&fs_info->em_shrinker_nr_to_scan, 0, nr_to_scan) != 0)
+		return;
+
+	queue_work(system_dfl_wq, &fs_info->em_shrinker_work);
+}
+
+void btrfs_init_extent_map_shrinker_work(struct btrfs_fs_info *fs_info)
+{
+	atomic64_set(&fs_info->em_shrinker_nr_to_scan, 0);
+	INIT_WORK(&fs_info->em_shrinker_work, btrfs_extent_map_shrinker_worker);
+}