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.

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: Andi Kleen <ak@linux.intel.com>

diff --git a/block/blk.h b/block/blk.h
index 5ee3d7e72feb0eda7a3abb127f06e82d96142b51..141483695145a097b07f1429810ac6ea5a950d6f 100644 (file)
--- 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;
        }
 }