From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner+w=401wt.eu-S1755605AbZCEAOR@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755605AbZCEAOR (ORCPT <rfc822;w@1wt.eu>);
	Wed, 4 Mar 2009 19:14:17 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751809AbZCEAN6
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Wed, 4 Mar 2009 19:13:58 -0500
Received: from accolon.hansenpartnership.com ([76.243.235.52]:59057 "EHLO
	accolon.hansenpartnership.com" rhost-flags-OK-OK-OK-OK)
	by vger.kernel.org with ESMTP id S1751445AbZCEAN5 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 4 Mar 2009 19:13:57 -0500
Subject: Re: [BUG] 2.6.29-rc6-2450cf in scsi_lib.c (was: Large amount of
	scsi-sgpool)objects
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Jan Engelhardt <jengelh@medozas.de>, Boaz Harrosh <bharrosh@panasas.com>,
       linux-scsi@vger.kernel.org,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-ide <linux-ide@vger.kernel.org>
In-Reply-To: <1236207389.21486.19.camel@localhost.localdomain>
References: <alpine.LSU.2.00.0903030220050.2438@fbirervta.pbzchgretzou.qr>
	 <49ACF8FE.2020904@panasas.com>
	 <1236093718.3263.3.camel@localhost.localdomain>
	 <alpine.LSU.2.00.0903031703270.855@fbirervta.pbzchgretzou.qr>
	 <1236097526.3263.17.camel@localhost.localdomain>
	 <alpine.LFD.2.00.0903031818230.29264@localhost.localdomain>
	 <alpine.LFD.2.00.0903032247170.29264@localhost.localdomain>
	 <1236119195.24019.24.camel@localhost.localdomain>
	 <alpine.LFD.2.00.0903040249460.29264@localhost.localdomain>
	 <alpine.LFD.2.00.0903042232270.29264@localhost.localdomain>
	 <1236207389.21486.19.camel@localhost.localdomain>
Content-Type: text/plain
Date: Wed, 04 Mar 2009 18:13:49 -0600
Message-Id: <1236212029.32072.4.camel@localhost.localdomain>
Mime-Version: 1.0
X-Mailer: Evolution 2.22.3.1 (2.22.3.1-1.fc9) 
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 2009-03-04 at 22:56 +0000, James Bottomley wrote:
> On Wed, 2009-03-04 at 22:45 +0100, Thomas Gleixner wrote:
> > On Wed, 4 Mar 2009, Thomas Gleixner wrote:
> > 
> > Instrumented the code and the result of the failing request is
> > below. Looks like the function which sets up the request gets
> > nr_phys_segments wrong by one. 
> > 
> > If you need further trace data feel free to ask.
> 
> OK, the mapping all checks out correctly ... there must be something
> wrong with the way we count before mapping.
> 
> If you're tracing everything, could you add these static prints to the
> trace ... they'll trigger a lot, but capturing how they applied to the
> failing request might tell us why the count is wrong.

Debugging this on IRC, this is the point we reached:

ftrace debugging patch:

http://tglx.de/~tglx/dbg.patch

We're tracing both blk_recalc_rq_segments() and
blk_phys_contig_segment()

The results are here:

http://tglx.de/~tglx/t.txt.bz2

Although what they show is that we're missing the point where the
counting goes wrong (blk_recalc_rq_segments only goes up to 5 max).

James