[34-longterm 007/179] block: add proper state guards to __elv_next_request

From: Paul Gortmaker
Date: Mon May 14 2012 - 22:56:59 EST

From: James Bottomley <James.Bottomley@xxxxxxx>

This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.

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: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
block/blk.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/blk.h b/block/blk.h
index 5ee3d7e..1414836 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;

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