[PATCH 4/4] btrfs: assert that relocation is protected with sb_start_write()

Naohiro Aota
2022-03-11T07:38:53Z

btrfs_relocate_chunk() initiates new ordered extents. They can cause a
hang when a process is trying to thaw the filesystem.

We should have called sb_start_write(), so the filesystem is not being
frozen. Add an ASSERT to check it is protected.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
---
fs/btrfs/volumes.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 0d27d8d35c7a..b558fd293ffa 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3239,6 +3239,9 @@ int btrfs_relocate_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
u64 length;
int ret;

+ /* Assert we called sb_start_write(), not to race with FS freezing */
+ ASSERT(sb_write_started(fs_info->sb));
+
if (btrfs_fs_incompat(fs_info, EXTENT_TREE_V2)) {
btrfs_err(fs_info,
"relocate: not supported on extent tree v2 yet");
--
2.35.1