[SCSI] put stricter guards on queue dead checks

SCSI uses request_queue->queuedata == NULL as a signal that the queue
is dying.  We set this state in the sdev release function.  However,
this allows a small window where we release the last reference but
haven't quite got to this stage yet and so something will try to take
a reference in scsi_request_fn and oops.  It's very rare, but we had a
report here, so we're pushing this as a bug fix

The actual fix is to set request_queue->queuedata to NULL in
scsi_remove_device() before we drop the reference.  This causes
correct automatic rejects from scsi_request_fn as people who hold
additional references try to submit work and prevents anything from
getting a new reference to the sdev that way.

Cc: stable@kernel.org
Signed-off-by: James Bottomley <James.Bottomley@suse.de>

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index e44ff64..e639125 100644 (file)
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -322,14 +322,8 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
                kfree(evt);
        }
 
-       if (sdev->request_queue) {
-               sdev->request_queue->queuedata = NULL;
-               /* user context needed to free queue */
-               scsi_free_queue(sdev->request_queue);
-               /* temporary expedient, try to catch use of queue lock
-                * after free of sdev */
-               sdev->request_queue = NULL;
-       }
+       /* NULL queue means the device can't be used */
+       sdev->request_queue = NULL;
 
        scsi_target_reap(scsi_target(sdev));
 
@@ -937,6 +931,12 @@ void __scsi_remove_device(struct scsi_device *sdev)
        if (sdev->host->hostt->slave_destroy)
                sdev->host->hostt->slave_destroy(sdev);
        transport_destroy_device(dev);
+
+       /* cause the request function to reject all I/O requests */
+       sdev->request_queue->queuedata = NULL;
+
+       /* Freeing the queue signals to block that we're done */
+       scsi_free_queue(sdev->request_queue);
        put_device(dev);
 }