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

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Message-ID: <490666D6.8090603@kernel.org>
Date:	Tue, 28 Oct 2008 10:11:50 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Mike Anderson <andmike@...ux.vnet.ibm.com>
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

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.

-- 
tejun
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