[SCSI] fix oops in scsi_run_queue()

The recent commit closing the race window in device teardown:

commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b
Author: James Bottomley <James.Bottomley@suse.de>
Date:   Fri Apr 22 10:39:59 2011 -0500

    [SCSI] put stricter guards on queue dead checks

is causing a potential NULL deref in scsi_run_queue() because the
q->queuedata may already be NULL by the time this function is called.
Since we shouldn't be running a queue that is being torn down, simply
add a NULL check in scsi_run_queue() to forestall this.

Tested-by: Jim Schutt <jaschut@sandia.gov>
Cc: stable@kernel.org
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9901b8f8443..0bac91e72370 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -400,10 +400,15 @@ static inline int scsi_host_is_busy(struct Scsi_Host *shost)
 static void scsi_run_queue(struct request_queue *q)
 {
         struct scsi_device *sdev = q->queuedata;
-        struct Scsi_Host *shost = sdev->host;
+        struct Scsi_Host *shost;
         LIST_HEAD(starved_list);
         unsigned long flags;
 
+        /* if the device is dead, sdev will be NULL, so no queue to run */
+        if (!sdev)
+                return;
+
+        shost = sdev->host;
         if (scsi_target(sdev)->single_lun)
                 scsi_single_lun_run(sdev);