diff options
| author | Sidong Yang <realwakka@gmail.com> | 2022-02-28 01:43:40 +0000 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2022-03-02 16:53:04 +0100 |
| commit | d4aef1e122d8bbdc15ce3bd0bc813d6b44a7d63a (patch) | |
| tree | 00a4d6475f7cd417896d1cde7bcc5444dff95425 /fs | |
| parent | 5fd76bf31ccfecc06e2e6b29f8c809e934085b99 (diff) | |
btrfs: qgroup: fix deadlock between rescan worker and remove qgroup
The commit e804861bd4e6 ("btrfs: fix deadlock between quota disable and
qgroup rescan worker") by Kawasaki resolves deadlock between quota
disable and qgroup rescan worker. But also there is a deadlock case like
it. It's about enabling or disabling quota and creating or removing
qgroup. It can be reproduced in simple script below.
for i in {1..100}
do
btrfs quota enable /mnt &
btrfs qgroup create 1/0 /mnt &
btrfs qgroup destroy 1/0 /mnt &
btrfs quota disable /mnt &
done
Here's why the deadlock happens:
1) The quota rescan task is running.
2) Task A calls btrfs_quota_disable(), locks the qgroup_ioctl_lock
mutex, and then calls btrfs_qgroup_wait_for_completion(), to wait for
the quota rescan task to complete.
3) Task B calls btrfs_remove_qgroup() and it blocks when trying to lock
the qgroup_ioctl_lock mutex, because it's being held by task A. At that
point task B is holding a transaction handle for the current transaction.
4) The quota rescan task calls btrfs_commit_transaction(). This results
in it waiting for all other tasks to release their handles on the
transaction, but task B is blocked on the qgroup_ioctl_lock mutex
while holding a handle on the transaction, and that mutex is being held
by task A, which is waiting for the quota rescan task to complete,
resulting in a deadlock between these 3 tasks.
To resolve this issue, the thread disabling quota should unlock
qgroup_ioctl_lock before waiting rescan completion. Move
btrfs_qgroup_wait_for_completion() after unlock of qgroup_ioctl_lock.
Fixes: e804861bd4e6 ("btrfs: fix deadlock between quota disable and qgroup rescan worker")
CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Sidong Yang <realwakka@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/qgroup.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c index f12dc687350c..30d42ea655ce 100644 --- a/fs/btrfs/qgroup.c +++ b/fs/btrfs/qgroup.c @@ -1197,13 +1197,20 @@ int btrfs_quota_disable(struct btrfs_fs_info *fs_info) goto out; /* + * Unlock the qgroup_ioctl_lock mutex before waiting for the rescan worker to + * complete. Otherwise we can deadlock because btrfs_remove_qgroup() needs + * to lock that mutex while holding a transaction handle and the rescan + * worker needs to commit a transaction. + */ + mutex_unlock(&fs_info->qgroup_ioctl_lock); + + /* * Request qgroup rescan worker to complete and wait for it. This wait * must be done before transaction start for quota disable since it may * deadlock with transaction by the qgroup rescan worker. */ clear_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags); btrfs_qgroup_wait_for_completion(fs_info, false); - mutex_unlock(&fs_info->qgroup_ioctl_lock); /* * 1 For the root item |