[PATCH 1/4] btrfs: mark resumed async balance as writing

Naohiro Aota
2022-03-11T07:38:44Z

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.

Fixes: 5accdf82ba25 ("fs: Improve filesystem freezing handling")
Cc: stable@vger.kernel.org
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
---
fs/btrfs/volumes.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 1be7cb2f955f..0d27d8d35c7a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4443,6 +4443,7 @@ static int balance_kthread(void *data)
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;
}
@@ -4463,6 +4464,7 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
return 0;
}

+ sb_start_write(fs_info->sb);
spin_lock(&fs_info->super_lock);
ASSERT(fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE_PAUSED);
fs_info->exclusive_operation = BTRFS_EXCLOP_BALANCE;
--
2.35.1