block: add proper state guards to __elv_next_request

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.

[WT: in 2.6.27, __elv_next_request() is in elevator.c]

Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/block/elevator.c b/block/elevator.c
index ed6f8f32d27ee8d09f5c3673852d416bad228862..3e37ca822d8f82f1ce29420d78d51bbaccf76426 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -729,7 +729,8 @@ 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;
        }
 }