linux-kernel - Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue resources at blk_release

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Date:	Mon, 12 Dec 2011 13:39:46 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Hannes Reinecke <hare@...e.de>,
	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Steffen Maier <maier@...ux.vnet.ibm.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>,
	"Taraka R. Bodireddy" <tarak.reddy@...ibm.com>,
	"Seshagiri N. Ippili" <seshagiri.ippili@...ibm.com>,
	"Manvanthara B. Puttashankar" <mputtash@...ibm.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Shaohua Li <shaohua.li@...el.com>, gmuelas@...ibm.com,
	dm-devel@...hat.com
Subject: Re: [GIT PULL] Queue free fix (was Re: [PATCH] block: Free queue
 resources at blk_release_queue())

On Tue, Nov 29, 2011 at 03:18:03PM -0500, Mike Snitzer wrote:
> On Tue, Nov 29 2011 at  7:00am -0500,
> Heiko Carstens <heiko.carstens@...ibm.com> wrote:
> > [ 4906.683654] Unable to handle kernel pointer dereference at virtual kernel address 6b6b6b6b6b6b6000
> 
> ...
> 
> > Gonzalo also tried 2.6.38.8 as suggested and ran into this one:
> > 
> > [  292.877936] ------------[ cut here ]------------
> > [  292.877939] Kernel BUG at 6b6b6b6b6b6b6b6d [verbose debug info unavailable]
> 
> Again, more poison.
> 
> Seems this test is causing us to fall on our face no matter what.
> Likely, best to leave this 2.6.38 blk_unplug crash to one side and
> continue focusing on latest upstream.

Sorry again, for taking so long to come back. This time however with good news:

With 3.2.0-rc4.00255.g77a7300 we were unable to reproduce any I/O stall or
user-after-free bugs even after nearly 3000 test iterations.

The only patches on top we have are:

two patches from Hannes:
http://www.spinics.net/lists/linux-scsi/msg55112.html
http://www.spinics.net/lists/linux-scsi/msg55413.html

and the patch below from Steffen:

Btw. James, any chance to get this one upstream soon? It should be in your
queue for quite some time already, IIRC.

Subject: [PATCH] zfcp: return early from slave_destroy if slave_alloc returned early

From: Steffen Maier <maier@...ux.vnet.ibm.com>

zfcp_scsi_slave_destroy erroneously always tried to finish its task
even if the corresponding previous zfcp_scsi_slave_alloc returned
early. This can lead to kernel page faults on accessing uninitialized
fields of struct zfcp_scsi_dev in zfcp_erp_lun_shutdown_wait. Take the
port field of the struct to determine if slave_alloc returned early.

This zfcp bug is exposed by 4e6c82b (in turn fixing f7c9c6b to be
compatible with 21208ae) which can call slave_destroy for a
corresponding previous slave_alloc that did not finish.

This patch is based on James Bottomley's fix suggestion in
http://www.spinics.net/lists/linux-scsi/msg55449.html.

Signed-off-by: Steffen Maier <maier@...ux.vnet.ibm.com>
Cc: <stable@...nel.org> #2.6.38+
---

 drivers/s390/scsi/zfcp_scsi.c |    4 ++++
 1 file changed, 4 insertions(+)

diff -urpN linux-2.6/drivers/s390/scsi/zfcp_scsi.c linux-2.6-patched/drivers/s390/scsi/zfcp_scsi.c
--- linux-2.6/drivers/s390/scsi/zfcp_scsi.c	2011-12-01 13:08:32.000000000 +0100
+++ linux-2.6-patched/drivers/s390/scsi/zfcp_scsi.c	2011-12-01 13:08:52.000000000 +0100
@@ -55,6 +55,10 @@ static void zfcp_scsi_slave_destroy(stru
 {
 	struct zfcp_scsi_dev *zfcp_sdev = sdev_to_zfcp(sdev);
 
+	/* if previous slave_alloc returned early, there is nothing to do */
+	if (!zfcp_sdev->port)
+		return;
+
 	zfcp_erp_lun_shutdown_wait(sdev, "scssd_1");
 	put_device(&zfcp_sdev->port->dev);
 }

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