Commit 893d290f authored Nov 22, 2012 by Roland Dreier Committed by Jens Axboe Nov 23, 2012

block: Don't access request after it might be freed



After we've done __elv_add_request() and __blk_run_queue() in
blk_execute_rq_nowait(), the request might finish and be freed
immediately.  Therefore checking if the type is REQ_TYPE_PM_RESUME
isn't safe afterwards, because if it isn't, rq might be gone.
Instead, check beforehand and stash the result in a temporary.

This fixes crashes in blk_execute_rq_nowait() I get occasionally when
running with lots of memory debugging options enabled -- I think this
race is usually harmless because the window for rq to be reallocated
is so small.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 836413e8

block/blk-exec.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -52,11 +52,17 @@ void blk_execute_rq_nowait(struct request_queue q, struct gendisk bd_disk,
		rq_end_io_fn *done)
		{
		int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
		bool is_pm_resume;

		WARN_ON(irqs_disabled());

		rq->rq_disk = bd_disk;
		rq->end_io = done;
		/*
		* need to check this before __blk_run_queue(), because rq can
		* be freed before that returns.
		*/
		is_pm_resume = rq->cmd_type == REQ_TYPE_PM_RESUME;

		spin_lock_irq(q->queue_lock);

		@@ -71,7 +77,7 @@ void blk_execute_rq_nowait(struct request_queue q, struct gendisk bd_disk,
		__elv_add_request(q, rq, where);
		__blk_run_queue(q);
		/* the queue is stopped so it won't be run */
		if (rq->cmd_type == REQ_TYPE_PM_RESUME)
		if (is_pm_resume)
		q->request_fn(q);
		spin_unlock_irq(q->queue_lock);
		}

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