1 files changed, 30 insertions, 3 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 46851511b661..90e40d5ceccd 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1252,8 +1252,12 @@ static bool lookup_backref_shared_cache(struct btrfs_backref_share_check_ctx *ct
 					struct btrfs_root *root,
 					u64 bytenr, int level, bool *is_shared)
 {
+	const struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_backref_shared_cache_entry *entry;
 
+	if (!current->journal_info)
+		lockdep_assert_held(&fs_info->commit_root_sem);
+
 	if (!ctx->use_path_cache)
 		return false;
 
@@ -1288,7 +1292,7 @@ static bool lookup_backref_shared_cache(struct btrfs_backref_share_check_ctx *ct
 	 * could be a snapshot sharing this extent buffer.
 	 */
 	if (entry->is_shared &&
-	    entry->gen != btrfs_get_last_root_drop_gen(root->fs_info))
+	    entry->gen != btrfs_get_last_root_drop_gen(fs_info))
 		return false;
 
 	*is_shared = entry->is_shared;
@@ -1318,9 +1322,13 @@ static void store_backref_shared_cache(struct btrfs_backref_share_check_ctx *ctx
 				       struct btrfs_root *root,
 				       u64 bytenr, int level, bool is_shared)
 {
+	const struct btrfs_fs_info *fs_info = root->fs_info;
 	struct btrfs_backref_shared_cache_entry *entry;
 	u64 gen;
 
+	if (!current->journal_info)
+		lockdep_assert_held(&fs_info->commit_root_sem);
+
 	if (!ctx->use_path_cache)
 		return;
 
@@ -1336,7 +1344,7 @@ static void store_backref_shared_cache(struct btrfs_backref_share_check_ctx *ctx
 	ASSERT(level >= 0);
 
 	if (is_shared)
-		gen = btrfs_get_last_root_drop_gen(root->fs_info);
+		gen = btrfs_get_last_root_drop_gen(fs_info);
 	else
 		gen = btrfs_root_last_snapshot(&root->root_item);
 
@@ -1864,6 +1872,8 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 		.have_delayed_delete_refs = false,
 	};
 	int level;
+	bool leaf_cached;
+	bool leaf_is_shared;
 
 	for (int i = 0; i < BTRFS_BACKREF_CTX_PREV_EXTENTS_SIZE; i++) {
 		if (ctx->prev_extents_cache[i].bytenr == bytenr)
@@ -1885,6 +1895,23 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 		walk_ctx.time_seq = elem.seq;
 	}
 
+	ctx->use_path_cache = true;
+
+	/*
+	 * We may have previously determined that the current leaf is shared.
+	 * If it is, then we have a data extent that is shared due to a shared
+	 * subtree (caused by snapshotting) and we don't need to check for data
+	 * backrefs. If the leaf is not shared, then we must do backref walking
+	 * to determine if the data extent is shared through reflinks.
+	 */
+	leaf_cached = lookup_backref_shared_cache(ctx, root,
+						  ctx->curr_leaf_bytenr, 0,
+						  &leaf_is_shared);
+	if (leaf_cached && leaf_is_shared) {
+		ret = 1;
+		goto out_trans;
+	}
+
 	walk_ctx.ignore_extent_item_pos = true;
 	walk_ctx.trans = trans;
 	walk_ctx.fs_info = fs_info;
@@ -1893,7 +1920,6 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 	/* -1 means we are in the bytenr of the data extent. */
 	level = -1;
 	ULIST_ITER_INIT(&uiter);
-	ctx->use_path_cache = true;
 	while (1) {
 		bool is_shared;
 		bool cached;
@@ -1964,6 +1990,7 @@ int btrfs_is_data_extent_shared(struct btrfs_inode *inode, u64 bytenr,
 		ctx->prev_extents_cache_slot = slot;
 	}
 
+out_trans:
 	if (trans) {
 		btrfs_put_tree_mod_seq(fs_info, &elem);
 		btrfs_end_transaction(trans);