Commit 4e4488d4 authored by Filipe Manana's avatar Filipe Manana Committed by David Sterba
Browse files

btrfs: assert commit root semaphore is held when accessing backref cache 



During fiemap, when accessing the cache that stores the sharedness of an
extent, we need to either be holding a transaction handle or the commit
root semaphore. I left comments about this in the comment that precedes
store_backref_shared_cache() and lookup_backref_shared_cache(), but have
actually not enforced it through assertions. So assert that the commit
root semaphore is held if we are not holding a transaction handle.

Reviewed-by: default avatarJohannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 2b5463fc

fs/btrfs/backref.c

+10 −2
Original line number Diff line number Diff line
@@ -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);