Re: [PATCH 2/5] scsi: improved eh timeout handler

[Hannes Reinecke <hare@suse.de>]

On 11/07/2013 07:33 PM, Douglas Gilbert wrote:
> On 13-11-07 01:45 AM, Hannes Reinecke wrote:
>> On 11/06/2013 06:23 PM, Mike Christie wrote:
>>> On 11/05/2013 10:48 PM, Hannes Reinecke wrote:
>>>> On 11/05/2013 08:19 PM, Mike Christie wrote:
>>>>> On 11/04/2013 11:05 PM, Hannes Reinecke wrote:
>>>>>> +
>>>>>> +    scmd->eh_eflags |= SCSI_EH_ABORT_SCHEDULED;
>>>>>> +    SCSI_LOG_ERROR_RECOVERY(3,
>>>>>> +        scmd_printk(KERN_INFO, scmd,
>>>>>> +                "scmd %p abort scheduled\n", scmd));
>>>>>> +    schedule_delayed_work(&scmd->abort_work, HZ / 100);
>>>>>> +    return SUCCESS;
>>>>>> +}
>>>>>
>>>>> Do we want to use our own workqueue_struct with WQ_MEM_RECLAIM
>>>>> set?
>>>>>
>>>> Errm. Yes, why?
>>>>
>>>> I must admit I'm not _that_ familiar with workqueues ...
>>>> Care to explain?
>>>>
>>>
>>> We all share the above workqueue_structs pool of threads, so if
>>> we get
>>> stuck behind code doing GFP_KERNEL allocs that end up needing to
>>> write
>>> data to the disk we are now trying to aborts on, then we could get
>>> stuck. With WQ_MEM_RECLAIM, we have our own backup thread that gets
>>> created at workqueue_struct create time which can get used in
>>> cases like
>>> that so we can always make forward progress.
>>>
>> Ah. Right. Yes, that makes sense.
>>
>> I guess I'll have to redo the patches _yet again_.
> 
> I wonder if it might be useful to flag a LU (disk)
> with "try really hard to recover me, perhaps at the
> expense of other LUs". Seems like a LU containing the
> rootfs or swap might qualify for setting such a flag.
> And LUs that have this flag cleared could be assumed
> to not get wedged in the fashion that Mike pointed out.
> 
While this would be a good idea in general, I would _very much_ see
to have this patch accepted first. Without that proviso
any discussion is pretty much moot anyway.
So I would like to defer that until the patch has been accepted.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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