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[PATCH] blk: fix dangling pointer access in __elv_add_request

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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>
This commit is contained in:
Tejun Heo 2005-11-01 17:23:49 +09:00 committed by Linus Torvalds
parent 6c2af71f7f
commit ca23509fba
1 changed files with 6 additions and 1 deletions
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7
drivers/block/elevator.c
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@ -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: