On 05/24/2012 12:06 PM, Brian Foster wrote:
> xfsaild idle mode logic currently leads to a couple hangs:
>
> 1.) If xfsaild is rescheduled in during an incremental scan
> (i.e., tout != 0) and the target has been updated since
> the previous run, we can hit the new target and go into
> idle mode with a still populated ail.
> 2.) A wake up is only issued when the target is pushed forward.
> The wake up can race with xfsaild if it is currently in the
> process of entering idle mode, causing future wake up
> events to be lost.
>
> Both hangs are reproducible by running xfstests 273 in a loop.
> Modify xfsaild to enter idle mode only when the ail is empty
> and the push target has not been moved forward since the last
> push.
>
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> ---
>
> This is a lightly tested version against the xfs tree. I'll be more
> heavily testing a version based on my upstream reproducer tree over the
> next few days followed by similar testing on this patch if all goes
> well. Sending in advance for review.
>
FYI, I've done a decent amount of testing at this point and can no
longer reproduce the original lockups due to idle mode. I can still
reproduce the sync worker lockup in the xfs tree, but I verify that
xfsaild is actually still running in that case (thus it's a different
issue). Unless there are other objections, this patch seems good to me.
Thanks.
Brian
> fs/xfs/xfs_trans_ail.c | 29 ++++++++++++++++++++++++++---
> fs/xfs/xfs_trans_priv.h | 1 +
> 2 files changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
> index 9c51448..0819cd3 100644
> --- a/fs/xfs/xfs_trans_ail.c
> +++ b/fs/xfs/xfs_trans_ail.c
> @@ -383,6 +383,12 @@ xfsaild_push(
> }
>
> spin_lock(&ailp->xa_lock);
> +
> + /* barrier matches the xa_target update in xfs_ail_push() */
> + smp_rmb();
> + target = ailp->xa_target;
> + ailp->xa_target_prev = target;
> +
> lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->xa_last_pushed_lsn);
> if (!lip) {
> /*
> @@ -397,7 +403,6 @@ xfsaild_push(
> XFS_STATS_INC(xs_push_ail);
>
> lsn = lip->li_lsn;
> - target = ailp->xa_target;
> while ((XFS_LSN_CMP(lip->li_lsn, target) <= 0)) {
> int lock_result;
>
> @@ -527,8 +532,26 @@ xfsaild(
> __set_current_state(TASK_KILLABLE);
> else
> __set_current_state(TASK_INTERRUPTIBLE);
> - schedule_timeout(tout ?
> - msecs_to_jiffies(tout) : MAX_SCHEDULE_TIMEOUT);
> +
> + spin_lock(&ailp->xa_lock);
> +
> + /* barrier matches the xa_target update in xfs_ail_push() */
> + smp_rmb();
> + if (!xfs_ail_min(ailp) && (ailp->xa_target == ailp->xa_target_prev)) {
> + /* the ail is empty and no change to the push target - idle */
> + spin_unlock(&ailp->xa_lock);
> + schedule();
> + tout = 0;
> + continue;
> + }
> + spin_unlock(&ailp->xa_lock);
> +
> + if (tout) {
> + /* more work to do soon */
> + schedule_timeout(msecs_to_jiffies(tout));
> + }
> +
> + __set_current_state(TASK_RUNNING);
>
> try_to_freeze();
>
> diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h
> index fb62377..53b7c9b 100644
> --- a/fs/xfs/xfs_trans_priv.h
> +++ b/fs/xfs/xfs_trans_priv.h
> @@ -67,6 +67,7 @@ struct xfs_ail {
> struct task_struct *xa_task;
> struct list_head xa_ail;
> xfs_lsn_t xa_target;
> + xfs_lsn_t xa_target_prev;
> struct list_head xa_cursors;
> spinlock_t xa_lock;
> xfs_lsn_t xa_last_pushed_lsn;
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