[RFC PATCH v2 2/3] xfs: fix xfsaild hang due to premature idle

[Mark Tinguely]

On 05/21/12 13:49, Brian Foster wrote:
> Running xfstests 273 in a loop reproduces an XFS lockup due to
> xfsaild entering idle mode indefinitely. The following
> high-level sequence of events lead to the hang:
>
> - xfsaild is running, hits the stuck item threshold and reschedules,
>    setting xa_last_pushed_lsn appropriately.
> - xa_threshold is updated.
> - xfsaild restarts from the previous xa_last_pushed_lsn, hits the
>    new target and enters idle mode, even though the previously
>    stuck items still populate the ail.
>
> Modify the tout logic to only enter idle mode when the ail is empty.
> IOW, if we hit the target but did not perform the current scan from
> the start of the ail, reschedule at least one more time.
>
> Signed-off-by: Brian Foster<bfoster at redhat.com>
> ---
>   fs/xfs/xfs_trans_ail.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
> index ae620eb..8bc8aa2 100644
> --- a/fs/xfs/xfs_trans_ail.c
> +++ b/fs/xfs/xfs_trans_ail.c
> @@ -503,7 +503,7 @@ xfsaild_push(
>
>   	/* assume we have more work to do in a short while */
>   out_done:
> -	if (!count) {
> +	if (!count&&  !ailp->xa_last_pushed_lsn) {
>   		/* We're past our target or empty, so idle */
>   		ailp->xa_last_pushed_lsn = 0;
>   		ailp->xa_log_flush = 0;

There is another patch in the OSS XFS (43ff2122 in 
git://oss.sgi.com/xfs/xfs) that is not yet in Linus' tree that is in 
this area and that is why it is not applying cleanly.

So the xfs_log_force() will un-stick the stuck items from the previous 
pass which set the ailp->xa_last_pushed_lsn = 0; I am asking to be 
re-assured the count will be non-zero and you won't go idle with still 
stuck items.


The problem that we are chasing in the AIL seems different than lost 
wakeup (next patch), but it would be interesting to have the patch in 
the kernel for testing.

--Mark Tinguely