[PATCH 2/5] scsi: Fix device removal NULL pointer dereference

[Bart Van Assche <bvanassche@acm.org>]

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: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: James Bottomley <JBottomley@parallels.com>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: <stable@kernel.org>
---
 drivers/scsi/hosts.c      |    7 ++++---
 drivers/scsi/scsi_lib.c   |   32 ++++----------------------------
 drivers/scsi/scsi_priv.h  |    1 -
 drivers/scsi/scsi_sysfs.c |    5 +----
 4 files changed, 9 insertions(+), 36 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index a3a056a..b48c24f 100644
--- a/drivers/scsi/hosts.c
+++ b/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);
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 6dfb978..7ebe167 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/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);
@@ -1370,16 +1366,16 @@ 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;
@@ -1490,12 +1486,6 @@ 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;
@@ -1697,20 +1687,6 @@ 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()
  *
diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index 07ce3f5..2b8d8b5 100644
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -84,7 +84,6 @@ 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;
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 04c2a27..42c35ff 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -971,11 +971,8 @@ 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);
 }
 
-- 
1.7.7