[PATCH] Btrfs: fix qgroup rescan worker initialization

[PATCH] Btrfs: fix qgroup rescan worker initialization

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

We were setting the qgroup_rescan_running flag to true only after the
rescan worker started (which is a task run by a queue). So if a user
space task starts a rescan and immediately after asks to wait for the
rescan worker to finish, this second call might happen before the rescan
worker task starts running, in which case the rescan wait ioctl returns
immediatley, not waiting for the rescan worker to finish.

This was making the fstest btrfs/022 fail very often.

Fixes: d2c609b834d6 (btrfs: properly track when rescan worker is running)
Cc: stable@vger.kernel.org # 4.4+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/qgroup.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 11f4fff..dfd9986 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2335,10 +2335,6 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
 	int err = -ENOMEM;
 	int ret = 0;
 
-	mutex_lock(&fs_info->qgroup_rescan_lock);
-	fs_info->qgroup_rescan_running = true;
-	mutex_unlock(&fs_info->qgroup_rescan_lock);
-
 	path = btrfs_alloc_path();
 	if (!path)
 		goto out;
@@ -2449,6 +2445,7 @@ qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
 		sizeof(fs_info->qgroup_rescan_progress));
 	fs_info->qgroup_rescan_progress.objectid = progress_objectid;
 	init_completion(&fs_info->qgroup_rescan_completion);
+	fs_info->qgroup_rescan_running = true;
 
 	spin_unlock(&fs_info->qgroup_lock);
 	mutex_unlock(&fs_info->qgroup_rescan_lock);
-- 
2.7.0.rc3

Re: [PATCH] Btrfs: fix qgroup rescan worker initialization

[David Sterba]

On Thu, Nov 24, 2016 at 02:18:29AM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> We were setting the qgroup_rescan_running flag to true only after the
> rescan worker started (which is a task run by a queue). So if a user
> space task starts a rescan and immediately after asks to wait for the
> rescan worker to finish, this second call might happen before the rescan
> worker task starts running, in which case the rescan wait ioctl returns
> immediatley, not waiting for the rescan worker to finish.
> 
> This was making the fstest btrfs/022 fail very often.
> 
> Fixes: d2c609b834d6 (btrfs: properly track when rescan worker is running)
> Cc: stable@vger.kernel.org # 4.4+
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Reviewed-by: David Sterba <dsterba@suse.com>