[PATCH 77/91] block: add proper state guards to __elv_next_request

[Willy Tarreau]

2.6.27-longterm review patch.  If anyone has any objections, please let us know.

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

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@xxxxxxx>
Signed-off-by: Jens Axboe <jaxboe@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
---
 block/clk.h |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

Index: longterm-2.6.27/block/elevator.c
===================================================================
--- longterm-2.6.27.orig/block/elevator.c	2012-02-05 22:34:32.624915301 +0100
+++ longterm-2.6.27/block/elevator.c	2012-02-05 22:34:45.849915230 +0100
@@ -729,7 +729,8 @@
 				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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