Re: [PATCH] Check return value of fc_block_scsi_eh()

[Hannes Reinecke <hare@suse.de>]

Mike Christie wrote:
> On 10/14/2010 01:45 AM, Hannes Reinecke wrote:
>> Mike Christie wrote:
>>> On 10/13/2010 06:42 AM, Hannes Reinecke wrote:
>>>>
>>>> fc_block_scsi_eh() might return with status FAST_IO_FAIL
>>>> indicating I/O has been terminated due to fast_io_fail timeout.
>>>> In this case the rport is still blocked, so any error recovery
>>>> will be failing on this port.
>>>> Hence each driver needs to check if the return value from
>>>> fc_block_scsi_eh() is something other than SUCCESS, in which
>>>> case it should just return with that status.
>>>> And we need to update the error handler to deal with a
>>>> status of FAST_IO_FAIL, too.
>>>> And fc_block_scsi_eh() should return SUCCESS on success,
>>>> not 0. Otherwise the calling routine will become confused
>>>> when reusing that value.
>>>>
>>>
>>> Is this patch supposed to fix the problem I described or is there more
>>> patches to follow or do you think I am being too paranoid? It seems the
>>> patch alone is going to make the problem worse in the drivers you are
>>> speeding up failure in. In the drivers now checking fc_block_scsi_eh and
>>> returning when fast io fail is returned then the scsi eh
>>> scsi_eh_flush_done_q's scsi_finish_command/scsi_queue_insert processing
>>> is going to get done faster and more likely to conflict with the
>>> termiante_rport_io callback processing, right?
>>
>> No, this patch does _not_ fix the race you've described, it just
>> fixes the problem of fc_block_scsi_eh() returning FAST_IO_FAIL,
>> which screws the error handler in drivers not checking the return value.
>> So it's partially covered by your patchset.
>>
>> However, in your patchset you're missing two issues:
>> - The current implementation of fc_block_scsi_eh() return '0' on
>>    success. This screws over drivers which re-uses this value;
>>    check eg. lpfc_abort_handler(). So we should be returning
>>    'SUCCESS' here.
> 
> Yeah, my patchset is actually backwards. I converted the other drivers
> to check for 0 (forgot to fix lpfc though). I think your patch patch
> where we return SUCCESS is better than what I was doing.
> 
> 
>> - scsi_error needs to be fixed up to handle FAST_IO_FAIL.
>>    Any of the functions called from scsi_abort_eh_cmnd() can return
>>    FAST_IO_FAIL, in which case escalating to the next function
>>    becomes pointless.
> 
> There is a problem with fnic (it is also a bug in my patches). If fnic's
> terminate_rport_io fails to abort the cmds, it is relying on the scsi eh
> callouts to clean things up. So if fc_scsi_block_eh returns non-success
> then we cannot return immediately from the callout. The drivers scsi eh
> callout may still need to clean up the command internally.
> 
Maybe it's better to change fnic to modify the FAST_IO_FAIL return
value from fc_block_scsi_eh() and return FAILED here.

> iSCSI/qla4xxx also needs to be changed to return SUCCESS instead of
> zero. Luckily there is only one driver using it so far.
> 
Yes, that would be preferable.

>>
>> I guess it would make sense to merge these two patchsets, either
>> having two patchsets (one for the FAST_IO_FAIL changes and one for
>> the rport race) or indeed merge them both into one.
>> I'm okay with either of it.
>>
> 
> My patches for the race do not work though. When you replied to my
> thread I thought you mean you were going to fix that too :)
> 
> I have been thinking of how to fix the race. I will make my patches over
> yours since your return SUCCESS fix is better.
Ok, I'll be sending an updated patch.

Cheers,

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