linux-kernel - Re: scsi_error: do not allow IO errors with certain ILLEGAL

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Date:	Mon, 13 Feb 2012 13:13:59 -0500
From:	Mike Snitzer <snitzer@...hat.com>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	linux-scsi@...r.kernel.org,
	James Bottomley <jbottomley@...allels.com>,
	Hannes Reinecke <hare@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: scsi_error: do not allow IO errors with certain ILLEGAL_REQUEST
 sense to be retryable

On Mon, Feb 13 2012 at 12:53pm -0500,
Martin K. Petersen <martin.petersen@...cle.com> wrote:

> >>>>> "Mike" == Mike Snitzer <snitzer@...hat.com> writes:
> 
> Mike> So that makes 3 different _prominent_ storage vendors, that I am
> Mike> aware of, that are bitten by their broken storage (relative to
> Mike> discard and properly advertising which variant they actually
> Mike> support).  I'd much rather deal with the storage vendors (or their
> Mike> customers) reporting that discards aren't working than mutual
> Mike> customers reporting that they cannot even install to the storage.
> 
> More graceful handling of the sense data aside, we do have a couple of
> options:
> 
>  1. Now that the provisioning portion seems to be stable in SBC-3 we can
>     nuke the interim spec heuristics and only support devices that
>     report the right thing. This may disable provisioning for some
>     existing users whose arrays run non-compliant firmware.
> 
>  2. We can add another layer of heuristics based on the RSOC wrapper I
>     introduced for write same. Maybe you could send me sg_opcodes output
>     for the arrays in question?

Yeah, I think that would be welcomed evolution (but as you say,
independent of improving additional ILLEGAL REQUEST processing).

> Mike> The ultimate fix is clear: storage vendors need to fix their
> Mike> storage (2 of the 3 have, 1 is working on it).  But a Linux-only
> Mike> workaround for this series of unfortunate events (particularly as
> Mike> it happens with multipath in the mix) is to have SCSI classify
> Mike> certain ILLEGAL_REQUEST as the TARGET_ERROR that they are.
> 
> I don't have a fundamental problem with your patch. But since we
> explicitly handle ILLEGAL REQUEST with 0x20 and 0x24 in sd.c I wonder
> what's broken? We should disable discard support if the WRITE SAME w/
> UNMAP fails.

Yeah, I thought the disabling would be sufficient too.  But
unfortunately multipath doesn't inspect the request it is retrying
(after it fails the path the request just failed on).  So even though
discards get disabled: the first discard (which caused discards to
become disabled) is still in-flight and keeps getting retried
indefinitely by the multipath layer (if the paths recover quickly).

Mike
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