From: Hannes Reinecke <hare@suse.de>
Subject: Kernel bug triggered in multipath
References: bnc#486001
Patch-mainline: not yet

Starting multipath on a cciss device will cause a kernel
warning to be triggered. Problem is that we're using the
->queuedata field of the request_queue to derefence the
scsi device; however, for other (non-SCSI) devices this
points to a totally different structure.
So we should rather be using accessors here which make
sure we're only returning valid SCSI device structures.

Signed-off-by: Hannes Reinecke <hare@suse.de>

---
 drivers/scsi/device_handler/scsi_dh.c |   10 +++++-----
 drivers/scsi/scsi_lib.c               |   11 +++++++++++
 include/scsi/scsi_device.h            |    1 +
 3 files changed, 17 insertions(+), 5 deletions(-)

--- a/drivers/scsi/device_handler/scsi_dh.c
+++ b/drivers/scsi/device_handler/scsi_dh.c
@@ -439,7 +439,7 @@ int scsi_dh_activate(struct request_queu
 	struct scsi_device_handler *scsi_dh = NULL;
 
 	spin_lock_irqsave(q->queue_lock, flags);
-	sdev = q->queuedata;
+	sdev = scsi_device_from_queue(q);
 	if (sdev && sdev->scsi_dh_data)
 		scsi_dh = sdev->scsi_dh_data->scsi_dh;
 	if (!scsi_dh || !get_device(&sdev->sdev_gendev) ||
@@ -501,7 +501,7 @@ int scsi_dh_handler_exist(const char *na
 EXPORT_SYMBOL_GPL(scsi_dh_handler_exist);
 
 /*
- * scsi_dh_handler_attach - Attach device handler
+ * scsi_dh_attach - Attach device handler
  * @sdev - sdev the handler should be attached to
  * @name - name of the handler to attach
  */
@@ -517,7 +517,7 @@ int scsi_dh_attach(struct request_queue
 		return -EINVAL;
 
 	spin_lock_irqsave(q->queue_lock, flags);
-	sdev = q->queuedata;
+	sdev = scsi_device_from_queue(q);
 	if (!sdev || !get_device(&sdev->sdev_gendev))
 		err = -ENODEV;
 	spin_unlock_irqrestore(q->queue_lock, flags);
@@ -531,7 +531,7 @@ int scsi_dh_attach(struct request_queue
 EXPORT_SYMBOL_GPL(scsi_dh_attach);
 
 /*
- * scsi_dh_handler_detach - Detach device handler
+ * scsi_dh_detach - Detach device handler
  * @sdev - sdev the handler should be detached from
  *
  * This function will detach the device handler only
@@ -545,7 +545,7 @@ void scsi_dh_detach(struct request_queue
 	struct scsi_device_handler *scsi_dh = NULL;
 
 	spin_lock_irqsave(q->queue_lock, flags);
-	sdev = q->queuedata;
+	sdev = scsi_device_from_queue(q);
 	if (!sdev || !get_device(&sdev->sdev_gendev))
 		sdev = NULL;
 	spin_unlock_irqrestore(q->queue_lock, flags);
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1587,6 +1587,17 @@ static void scsi_request_fn(struct reque
 	spin_lock_irq(q->queue_lock);
 }
 
+struct scsi_device *scsi_device_from_queue(struct request_queue *q)
+{
+	struct scsi_device *sdev = NULL;
+
+	if (q->request_fn == scsi_request_fn)
+		sdev = q->queuedata;
+
+	return sdev;
+}
+EXPORT_SYMBOL_GPL(scsi_device_from_queue);
+
 u64 scsi_calculate_bounce_limit(struct Scsi_Host *shost)
 {
 	struct device *host_dev;
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -297,6 +297,7 @@ extern void starget_for_each_device(stru
 extern void __starget_for_each_device(struct scsi_target *, void *,
 				      void (*fn)(struct scsi_device *,
 						 void *));
+extern struct scsi_device *scsi_device_from_queue(struct request_queue *);
 
 /* only exposed to implement shost_for_each_device */
 extern struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *,