On Sat, Aug 26, 2017 at 04:39:02PM +1000, Aleksa Sarai wrote: > On 07/12/2017 03:03 AM, David Sterba wrote: > > On Mon, Jul 10, 2017 at 04:56:36PM +0300, Nikolay Borisov wrote: > >> On 10.07.2017 16:12, Nikolay Borisov wrote: > >>> On 4.07.2017 14:49, Aleksa Sarai wrote: > >>>> 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@xxxxxxxxxxxxxxx> # v3.11+ > >>>> Cc: Jeff Mahoney <jeffm@xxxxxxxx> > >>>> Fixes: b382a324b60f ("Btrfs: fix qgroup rescan resume on mount") > >>>> Signed-off-by: Aleksa Sarai <asarai@xxxxxxx> > >>> > >>> Indeed, looking at the code it seems that b382a324b60f ("Btrfs: fix > >>> qgroup rescan resume on mount") missed adding the qgroup_rescan_resume > >>> in the remount path. One thing which I couldn't verify though is whether > >>> reading fs_info->qgroup_flags without any locking is safe from remount > >>> context. > >>> > >>> During remount I don't see any locks taken that prevent operations which > >>> can modify qgroup_flags. > >> > >> Further inspection reveals that the access rules to qgroup_flags are > >> somewhat broken so this patch doesn't really make things any worse than > >> they are. > > > > The usage follows a pattern for a bitfield, updated by set_bit/clear_bit > > etc. The updates to the state or inconsistency is not safe, so some > > updates could get lost under some circumstances. > > > > Patch added to devel queue, possibly will be submitted to 4.13 so stable > > can pick it. > > Looks like it wasn't merged in the 4.13 window (so stable hasn't picked > it), will this be submitted for 4.14? Thanks. Sorry this didn't make it to 4.13, the patch is in the queue for 4.14.