When btrfs balance is interrupted with umount, the background balance
resumes on the next mount. There is a potential deadlock with FS freezing
here like as described in commit 26559780b953 ("btrfs: zoned: mark
relocation as writing").
Mark the process as sb_writing. To preserve the order of sb_start_write()
(or mnt_want_write_file()) and btrfs_exclop_start(), call sb_start_write()
at btrfs_resume_balance_async() before taking fs_info->super_lock.
Cc: stable@xxxxxxxxxxxxxxx # 4.9+
Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
fs/btrfs/volumes.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 3fd17e87815a..3471698fd831 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4430,10 +4430,12 @@ static int balance_kthread(void *data)
struct btrfs_fs_info *fs_info = data;
int ret = 0;
+ sb_start_write(fs_info->sb);
mutex_lock(&fs_info->balance_mutex);
if (fs_info->balance_ctl)
ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
mutex_unlock(&fs_info->balance_mutex);
+ sb_end_write(fs_info->sb);
return ret;
}
--
2.35.1
