[SCSI] Fix device removal NULL pointer dereference

Use blk_queue_dead() to test whether the queue is dead instead
of !sdev. Since scsi_prep_fn() may be invoked concurrently with
__scsi_remove_device(), keep the queuedata (sdev) pointer in
__scsi_remove_device(). This patch fixes a kernel oops that
can be triggered by USB device removal. See also
http://www.spinics.net/lists/linux-scsi/msg56254.html.

Other changes included in this patch:
- Swap the blk_cleanup_queue() and kfree() calls in
  scsi_host_dev_release() to make that code easier to grasp.
- Remove the queue dead check from scsi_run_queue() since the
  queue state can change anyway at any point in that function
  where the queue lock is not held.
- Remove the queue dead check from the start of scsi_request_fn()
  since it is redundant with the scsi_device_online() check.
Reported-by: NJun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: NBart Van Assche <bvanassche@acm.org>
Reviewed-by: NMike Christie <michaelc@cs.wisc.edu>
Reviewed-by: NTejun Heo <tj@kernel.org>
Cc: <stable@kernel.org>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>

drivers/scsi/hosts.c

@@ -290,6 +290,7 @@ static void scsi_host_dev_release(struct device *dev)
 	struct Scsi_Host *shost = dev_to_shost(dev);
 	struct device *parent = dev->parent;
 	struct request_queue *q;
+	void *queuedata;
 
 	scsi_proc_hostdir_rm(shost->hostt);
 
@@ -299,9 +300,9 @@ static void scsi_host_dev_release(struct device *dev)
 		destroy_workqueue(shost->work_q);
 	q = shost->uspace_req_q;
 	if (q) {
-		kfree(q->queuedata);
-		q->queuedata = NULL;
-		scsi_free_queue(q);
+		queuedata = q->queuedata;
+		blk_cleanup_queue(q);
+		kfree(queuedata);
 	}
 
 	scsi_destroy_command_freelist(shost);

drivers/scsi/scsi_lib.c

@@ -406,10 +406,6 @@ static void scsi_run_queue(struct request_queue *q)
 	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);
@@ -1371,16 +1367,16 @@ static inline int scsi_host_queue_ready(struct request_queue *q,
  * may be changed after request stacking drivers call the function,
  * regardless of taking lock or not.
  *
- * When scsi can't dispatch I/Os anymore and needs to kill I/Os
- * (e.g. !sdev), scsi needs to return 'not busy'.
- * Otherwise, request stacking drivers may hold requests forever.
+ * When scsi can't dispatch I/Os anymore and needs to kill I/Os scsi
+ * needs to return 'not busy'. Otherwise, request stacking drivers
+ * may hold requests forever.
  */
 static int scsi_lld_busy(struct request_queue *q)
 {
 	struct scsi_device *sdev = q->queuedata;
 	struct Scsi_Host *shost;
 
-	if (!sdev)
+	if (blk_queue_dead(q))
 		return 0;
 
 	shost = sdev->host;
@@ -1491,12 +1487,6 @@ static void scsi_request_fn(struct request_queue *q)
 	struct scsi_cmnd *cmd;
 	struct request *req;
 
-	if (!sdev) {
-		while ((req = blk_peek_request(q)) != NULL)
-			scsi_kill_request(req, q);
-		return;
-	}
-
 	if(!get_device(&sdev->sdev_gendev))
 		/* We must be tearing the block queue down already */
 		return;
@@ -1698,20 +1688,6 @@ struct request_queue *scsi_alloc_queue(struct scsi_device *sdev)
 	return q;
 }
 
-void scsi_free_queue(struct request_queue *q)
-{
-	unsigned long flags;
-
-	WARN_ON(q->queuedata);
-
-	/* cause scsi_request_fn() to kill all non-finished requests */
-	spin_lock_irqsave(q->queue_lock, flags);
-	q->request_fn(q);
-	spin_unlock_irqrestore(q->queue_lock, flags);
-
-	blk_cleanup_queue(q);
-}
-
 /*
  * Function:    scsi_block_requests()
  *

drivers/scsi/scsi_priv.h

@@ -85,7 +85,6 @@ extern void scsi_next_command(struct scsi_cmnd *cmd);
 extern void scsi_io_completion(struct scsi_cmnd *, unsigned int);
 extern void scsi_run_host_queues(struct Scsi_Host *shost);
 extern struct request_queue *scsi_alloc_queue(struct scsi_device *sdev);
-extern void scsi_free_queue(struct request_queue *q);
 extern int scsi_init_queue(void);
 extern void scsi_exit_queue(void);
 struct request_queue;

drivers/scsi/scsi_sysfs.c

@@ -972,11 +972,8 @@ void __scsi_remove_device(struct scsi_device *sdev)
 		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);
+	blk_cleanup_queue(sdev->request_queue);
 	put_device(dev);
 }