[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>
diff --git a/drivers/block/elevator.c b/drivers/block/elevator.c
index 36f1057..d4a49a3 100644
--- a/drivers/block/elevator.c
+++ b/drivers/block/elevator.c
@@ -369,9 +369,14 @@
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: