linux-kernel - [ 089/173] [SCSI] qla2xxx: Test and clear FCPORT_UPDATE

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Message-Id: <20121228190348.832174310@decadent.org.uk>
Date:	Fri, 28 Dec 2012 20:04:59 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	David Jeffery <djeffery@...hat.com>,
	Chad Dupuis <chad.dupuis@...gic.com>,
	Saurav Kashyap <saurav.kashyap@...gic.com>,
	James Bottomley <JBottomley@...allels.com>
Subject: [ 089/173] [SCSI] qla2xxx: Test and clear FCPORT_UPDATE_NEEDED atomically.

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Jeffery <djeffery@...hat.com>

commit a394aac88506159e047630fc90dc2242568382d8 upstream.

When the qla2xxx driver loses access to multiple, remote ports, there is a race
condition which can occur which will keep the request stuck on a scsi request
queue indefinitely.

This bad state occurred do to a race condition with how the FCPORT_UPDATE_NEEDED
bit is set in qla2x00_schedule_rport_del(), and how it is cleared in
qla2x00_do_dpc().  The problem port has its drport pointer set, but it has never
been processed by the driver to inform the fc transport that the port has been
lost.  qla2x00_schedule_rport_del() sets drport, and then sets the
FCPORT_UPDATE_NEEDED bit.  In qla2x00_do_dpc(), the port lists are walked and
any drport pointer is handled and the fc transport informed of the port loss,
then the FCPORT_UPDATE_NEEDED bit is cleared.  This leaves a race where the
dpc thread is processing one port removal, another port removal is marked
with a call to qla2x00_schedule_rport_del(), and the dpc thread clears the
bit for both removals, even though only the first removal was actually
handled.  Until another event occurs to set FCPORT_UPDATE_NEEDED, the later
port removal is never finished and qla2xxx stays in a bad state which causes
requests to become stuck on request queues.

This patch updates the driver to test and clear FCPORT_UPDATE_NEEDED
atomically.  This ensures the port state changes are processed and not lost.

Signed-off-by: David Jeffery <djeffery@...hat.com>
Signed-off-by: Chad Dupuis <chad.dupuis@...gic.com>
Signed-off-by: Saurav Kashyap <saurav.kashyap@...gic.com>
Signed-off-by: James Bottomley <JBottomley@...allels.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/scsi/qla2xxx/qla_os.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/scsi/qla2xxx/qla_os.c
+++ b/drivers/scsi/qla2xxx/qla_os.c
@@ -3541,9 +3541,9 @@ qla2x00_do_dpc(void *data)
 			    "ISP abort end.\n");
 		}

-		if (test_bit(FCPORT_UPDATE_NEEDED, &base_vha->dpc_flags)) {
+		if (test_and_clear_bit(FCPORT_UPDATE_NEEDED,
+		    &base_vha->dpc_flags)) {
 			qla2x00_update_fcports(base_vha);
-			clear_bit(FCPORT_UPDATE_NEEDED, &base_vha->dpc_flags);
 		}

 		if (test_bit(ISP_QUIESCE_NEEDED, &base_vha->dpc_flags)) {

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