Re: [PATCH] scsi_dh_alua: Fix a reference counting bug

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On 11/01/2016 03:19 PM, Bart Van Assche wrote:
The code at the end of alua_rtpg_work() is as follows:

	scsi_device_put(sdev);
	kref_put(&pg->kref, release_port_group);

In other words, alua_rtpg_queue() must hold an sdev reference and
a pg reference before queueing rtpg work. If no rtpg work is queued
no additional references should be held when alua_rtpg_queue()
returns. If no rtpg work is queued, ensure that alua_rtpg_queue()
only gives up the sdev reference if that reference was obtained by
the same alua_rtpg_queue() call.

Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Tang Junhui <tang.junhui@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 drivers/scsi/device_handler/scsi_dh_alua.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index f375167..7bb2068 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -891,6 +891,7 @@ static void alua_rtpg_queue(struct alua_port_group *pg,
 		/* Do not queue if the worker is already running */
 		if (!(pg->flags & ALUA_PG_RUNNING)) {
 			kref_get(&pg->kref);
+			sdev = NULL;
 			start_queue = 1;
 		}
 	}
@@ -902,7 +903,8 @@ static void alua_rtpg_queue(struct alua_port_group *pg,
 	if (start_queue &&
 	    !queue_delayed_work(alua_wq, &pg->rtpg_work,
 				msecs_to_jiffies(ALUA_RTPG_DELAY_MSECS))) {
-		scsi_device_put(sdev);
+		if (sdev)
+			scsi_device_put(sdev);
 		kref_put(&pg->kref, release_port_group);
 	}
 }

Reviewed-by: Hannes Reinecke <hare@xxxxxxxx>

Cheers,

Hannes
--
Dr. Hannes Reinecke		      zSeries & Storage
hare@xxxxxxx			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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