block: add proper state guards to __elv_next_request

blk_cleanup_queue() calls elevator_exit() and after this, we can't
touch the elevator without oopsing.  __elv_next_request() must check
for this state because in the refcounted queue model, we can still
call it after blk_cleanup_queue() has been called.

This was reported as causing an oops attributable to scsi.

Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/block/blk.h b/block/blk.h
index 61263463e38e..4df474d37e6d 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -62,7 +62,8 @@ static inline struct request *__elv_next_request(struct request_queue *q)
                         return rq;
                 }
 
-                if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
+                if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags) ||
+                    !q->elevator->ops->elevator_dispatch_fn(q, 0))
                         return NULL;
         }
 }