btrfs: resume qgroup rescan on rw remount
authorAleksa Sarai <asarai@suse.de>
Tue, 4 Jul 2017 11:49:06 +0000 (21:49 +1000)
committerDavid Sterba <dsterba@suse.com>
Wed, 16 Aug 2017 14:12:01 +0000 (16:12 +0200)
commit6c6b5a39c4bf3dbd8cf629c9f5450e983c19dbb9
tree7c2a42b4c3ec9ccb33004b10bd85efd11e45a4e2
parent01747e92a996cc2f2965c28fde485da932836ef8
btrfs: resume qgroup rescan on rw remount

Several distributions mount the "proper root" as ro during initrd and
then remount it as rw before pivot_root(2). Thus, if a rescan had been
aborted by a previous shutdown, the rescan would never be resumed.

This issue would manifest itself as several btrfs ioctl(2)s causing the
entire machine to hang when btrfs_qgroup_wait_for_completion was hit
(due to the fs_info->qgroup_rescan_running flag being set but the rescan
itself not being resumed). Notably, Docker's btrfs storage driver makes
regular use of BTRFS_QUOTA_CTL_DISABLE and BTRFS_IOC_QUOTA_RESCAN_WAIT
(causing this problem to be manifested on boot for some machines).

Cc: <stable@vger.kernel.org> # v3.11+
Cc: Jeff Mahoney <jeffm@suse.com>
Fixes: b382a324b60f ("Btrfs: fix qgroup rescan resume on mount")
Signed-off-by: Aleksa Sarai <asarai@suse.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Tested-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
fs/btrfs/super.c