linux-kernel - Re: Timeout regression introduced by 242f9dcb8ba6f68fcd217a119a7648a4f69290e9

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Message-ID: <20081027213006.GB17946@linux.vnet.ibm.com>
Date:	Mon, 27 Oct 2008 14:30:06 -0700
From:	Mike Anderson <andmike@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Timeout regression introduced by
	242f9dcb8ba6f68fcd217a119a7648a4f69290e9

Tejun Heo <tj@...nel.org> wrote:
> James Bottomley wrote:
> > On Sun, 2008-10-26 at 18:46 +0900, Tejun Heo wrote:
> >> Hello, Jens.
> >>
> >> Commit 242f9dcb8ba6f68fcd217a119a7648a4f69290e9 introduces a strange
> >> regression for libata.  The second timeout gives puts different
> >> pointer from the issued command onto eh_cmd_q breaking libata EH
> >> command matching which triggers WARN_ON() in ata_eh_finish() and hangs
> >> command processing or causes oops later depending on circumstances.
> >>
> >> Here are logs with induced timeouts (patch attached).  In commit
> >> 242f9dcb8, the XXX messages for the second timeout shows different
> >> scsi_cmd pointers for eh_cmd_q and qc->scmd which is initialized by
> >> ata_scsi_qc_new() during command translation.
> > 
> > I can't see a way we could be getting a different command passed in from
> > the actual one, since the only way to lose the command from the request
> > is to go through the command completion routines which free it (and end
> > the request).
> 
> I have no idea either.  It's something in the timeout logic because on
> the issue path the scmd pointer is identical but on tiemout pointer
> for another scmd is queued on eh_cmd_q, which doesn't make much sense.
> 

I was trying to recreate this error using ata_ram wth v2.6.28-rc2.
Currently I am not able to see this error on timeout recovery using this
setup. Does IO load (or other factors) effect the error being seen?

-andmike
--
Michael Anderson
andmike@...ux.vnet.ibm.com
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