[028/146] block: add proper state guards to __elv_next_request

[Greg KH]

2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------

From: James Bottomley <James.Bottomley@xxxxxxx>

commit 0a58e077eb600d1efd7e54ad9926a75a39d7f8ae upstream.

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@xxxxxxx>
Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 block/blk.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/block/blk.h
+++ b/block/blk.h
@@ -68,7 +68,8 @@ static inline struct request *__elv_next
 				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;
 	}
 }


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