Re: virtio-scsi issues duplicate tags when async_abort is enabled

[Hannes Reinecke <hare@suse.de>]

On 06/13/2014 07:58 PM, Venkatesh Srinivas wrote:
> Hi,
>
> In Linux 3.14+, SCSI timeouts are handled first without invoking EH;
> this behavior is on by default but can be disabled with the
> per-shost-template no_async_abort flag.
>
> When a SCSI target is attached to a virtio-scsi HBA and is under I/O
> stress (lots of concurrent I/O + some I/O running slowly), we see
> Linux issue commands with duplicate tags, sometimes with tags matching
> commands which are in the process of being aborted; we see this
> readily in the Google Compute Engine hypervisor.
>
> This behaviour is not seen on Linux <= 3.13 and is not seen if 3.14's
> virtio_scsi driver has no_async_abort set to 1.
>
> An ordering we have seen, from the device perspective:
> t0: I/O with tag 18446612135224154432 issued
> t1: TMF Abort for tag 18446612135224154432
> t2: Another I/O with the same tag, 18446612135224154432, issued; same
> offset/size as at t0
> [neither the t0 I/O nor the TMF ABORT have yet returned!]
>
> Another ordering we have seen, from the device perspective:
> t0: I/O with tag 18446612135454768576 issued
> t1: TMF ABORT for tag 18446612135454768576
> t2: I/O 18446612135454768576 completes with appropriate cancelled status
> t3: TMF ABORT completes with OK status
> t4: New I/O with tag 18446612135454768576, matching size/offset as t0
> t5...: [Some other I/Os issued to the same SCSI target]
> t6...: [TMF ABORT for one of the new I/Os; proper return sequence]
> t7...: New I/O with tag 18446612135454768576.
>    [Tag 18446612135454768576 has neither completed nor has it been
> aborted by Linux.]
>
> CC-ing stable as 3.14 and 3.15 are affected; a conservative fix is to
> enable no_async_abort until the problem is better-understood.
>
Paolo, you had some fixes for virtio_scsi which should solve this, right?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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