Commit ca23509f authored Nov 01, 2005 by Tejun Heo Committed by Linus Torvalds Nov 01, 2005

[PATCH] blk: fix dangling pointer access in __elv_add_request



cfq's add_req_fn callback may invoke q->request_fn directly and
depending on low-level driver used and timing, a queued request may be
finished & deallocated before add_req_fn callback returns.  So,
__elv_add_request must not access rq after it's passed to add_req_fn
callback.

This patch moves rq_mergeable test above add_req_fn().  This may
result in q->last_merge pointing to REQ_NOMERGE request if add_req_fn
callback sets it but as RQ_NOMERGE is checked again when blk layer
actually tries to merge requests, this does not cause any problem.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 6c2af71f

drivers/block/elevator.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -369,9 +369,14 @@ void __elv_add_request(request_queue_t q, struct request rq, int where,
		case ELEVATOR_INSERT_SORT:
		BUG_ON(!blk_fs_request(rq));
		rq->flags \|= REQ_SORTED;
		q->elevator->ops->elevator_add_req_fn(q, rq);
		if (q->last_merge == NULL && rq_mergeable(rq))
		q->last_merge = rq;
		/*
		* Some ioscheds (cfq) run q->request_fn directly, so
		* rq cannot be accessed after calling
		* elevator_add_req_fn.
		*/
		q->elevator->ops->elevator_add_req_fn(q, rq);
		break;

		default: