linux-kernel - Re: scsi: aic7xxx hang since v2.6.28-rc1 ...

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Date:	Wed, 18 Feb 2009 20:20:07 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Anderson <andmike@...ux.vnet.ibm.com>
Cc:	Alan Stern <stern@...land.harvard.edu>, linux-scsi@...r.kernel.org,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org
Subject: Re: scsi: aic7xxx hang since v2.6.28-rc1 ...


* Mike Anderson <andmike@...ux.vnet.ibm.com> wrote:

> Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > * Alan Stern <stern@...land.harvard.edu> wrote:
> > 
> > > I have no idea if this will make any difference for the 
> > > problem you're seeing, but it has been submitted and it's 
> > > worth trying out.  If the problem still occurs, I'll write a 
> > > diagnostic patch to add log messages giving the destiny of 
> > > each request in scsi_io_completion().
> > 
> > OK, i've undone the reverts and have applied your fix - it will 
> > take a few hours to see whether the hang still occurs.
> 
> I know already started your testing, but..

and that particular box already survived 20 test iterations in 
the past few hours - while it would hang after 5-10 iterations 
before. So i think Alan's fix is making a difference. I'll be 
able to tell for sure tomorrow morning.

> I find it informative to set my scsi logging to the value 
> below to display non-zero IO status on commands. The overhead 
> impact is low for good completions.
> 
> sysctl -w dev.scsi.logging_level=4100
> 
> Note: This does not provide the exact policy that 
> scsi_io_completion will take on the IO, but it provides the 
> input to scsi_io_completion which should help.

will do that next time around i have a bug like this. (or if 
this bug triggers again)

OTOH, the hang took quite a bit of IO to occur. Sometimes the 
box would be able to build a new kernel and reboot into it, 
without the hang.

	Ingo
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