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Re: Still seeing hangs in xlog_grant_log_space

To: Juerg Haefliger <juergh@xxxxxxxxx>
Subject: Re: Still seeing hangs in xlog_grant_log_space
From: Peter Watkins <treestem@xxxxxxxxx>
Date: Fri, 25 May 2012 13:03:04 -0400
Cc: bpm@xxxxxxx, xfs@xxxxxxxxxxx
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On Fri, May 25, 2012 at 2:28 AM, Juerg Haefliger <juergh@xxxxxxxxx> wrote:
>> Does your kernel have the effect of
>>
>> 0bf6a5bd4b55b466964ead6fa566d8f346a828ee xfs: convert the xfsaild
>> thread to a workqueue
>
> No.
>
>
>> c7eead1e118fb7e34ee8f5063c3c090c054c3820 xfs: revert to using a
>> kthread for AIL pushing
>
> No.
>
>
>> In particular, is this code in xfs_trans_ail_push:
>>
>>       smp_wmb();
>>       xfs_trans_ail_copy_lsn(ailp, &ailp->xa_target, &threshold_lsn);
>>       smp_wmb();
>
> No. xfs_trans_ail_push looks like this:
>
> void
> xfs_trans_ail_push(
>        struct xfs_ail  *ailp,
>        xfs_lsn_t       threshold_lsn)
> {
>        xfs_log_item_t  *lip;
>
>        lip = xfs_ail_min(ailp);
>        if (lip && !XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
>                if (XFS_LSN_CMP(threshold_lsn, ailp->xa_target) > 0)
>                        xfsaild_wakeup(ailp, threshold_lsn);
>        }
> }
>
>
> FWIW, the XFS driver in my kernel is identical to the vanilla 2.6.38
> driver. I'm still trying to get a XFS trace from a production hang. I
> do have a crash dump from a production machine with /tmp hanging.
> Would it be helpful to share that dump?
>
> ...Juerg

It looks like the combined effect of those patches, perhaps the write
barriers, fix one log space hang. That problem exists in 2.6.38.

Reading bug #922 I see your test case reproduces in recent kernels, so
there must be a newer problem also.

I find the reproducer the most useful, so no need to upload the dump.

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