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

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Message-ID: <20081029132654.GE31673@kernel.dk>
Date:	Wed, 29 Oct 2008 14:26:55 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Mike Anderson <andmike@...ux.vnet.ibm.com>,
	James Bottomley <James.Bottomley@...senPartnership.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

On Tue, Oct 28 2008, Tejun Heo wrote:
> Mike Anderson wrote:
> > 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?
> 
> Not at all.  That's the only write command I issued.

It's all extremely puzzling. Any chance I could talk you into stuffing
some debug printks in there to see what the hell is going on?

-- 
Jens Axboe

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