On Thu, Apr 26, 2018 at 03:23:49PM -0400, jeffm@xxxxxxxx wrote:
> From: Jeff Mahoney <jeffm@xxxxxxxx>
>
> Commit d2c609b834d6 (Btrfs: fix qgroup rescan worker initialization)
> fixed the issue with BTRFS_IOC_QUOTA_RESCAN_WAIT being racy, but
> ended up reintroducing the hang-on-unmount bug that the commit it
> intended to fix addressed.
>
> The race this time is between qgroup_rescan_init setting
> ->qgroup_rescan_running = true and the worker starting. There are
> many scenarios where we initialize the worker and never start it. The
> completion btrfs_ioctl_quota_rescan_wait waits for will never come.
> This can happen even without involving error handling, since mounting
> the file system read-only returns between initializing the worker and
> queueing it.
>
> The right place to do it is when we're queuing the worker. The flag
> really just means that btrfs_ioctl_quota_rescan_wait should wait for
> a completion.
>
> This patch introduces a new helper, queue_rescan_worker, that handles
> the ->qgroup_rescan_running flag, including any races with umount.
>
> While we're at it, ->qgroup_rescan_running is protected only by the
> ->qgroup_rescan_mutex. btrfs_ioctl_quota_rescan_wait doesn't need
> to take the spinlock too.
>
> Fixes: d2c609b834d6 (Btrfs: fix qgroup rescan worker initialization)
> Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
I've added this to misc-next as I'd like to push it to the next rc. The
Fixes is fixed.
> + /* qgroup rescan worker is running or queued to run */
> bool qgroup_rescan_running; /* protected by qgroup_rescan_lock */
Comments merged.
> /* filesystem state */
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index aa259d6986e1..be491b6c020a 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -2072,6 +2072,30 @@ int btrfs_qgroup_account_extents(struct btrfs_trans_handle *trans,
> return ret;
> }
>
> +static void queue_rescan_worker(struct btrfs_fs_info *fs_info)
> +{
And this had to be moved upwards as there was earlier use of
btrfs_queue_work that matched following the hunk.
> +}
> +
> /*
> * called from commit_transaction. Writes all changed qgroups to disk.
> */
> @@ -2123,8 +2147,7 @@ int btrfs_run_qgroups(struct btrfs_trans_handle *trans,
> ret = qgroup_rescan_init(fs_info, 0, 1);
> if (!ret) {
> qgroup_rescan_zero_tracking(fs_info);
> - btrfs_queue_work(fs_info->qgroup_rescan_workers,
> - &fs_info->qgroup_rescan_work);
> + queue_rescan_worker(fs_info);
> }
> ret = 0;
> }
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