Commit dac07ec1 authored by Jens Axboe's avatar Jens Axboe Committed by Linus Torvalds
Browse files

[BLOCK] limit request_fn recursion 



Don't recurse back into the driver even if the unplug threshold is met,
when the driver asks for a requeue. This is both silly from a logical
point of view (requeues typically happen due to driver/hardware
shortage), and also dangerous since we could hit an endless request_fn
-> requeue -> unplug -> request_fn loop and crash on stack overrun.

Also limit blk_run_queue() to one level of recursion, similar to how
blk_start_queue() works.

This patch fixed a real problem with SLES10 and lpfc, and it could hit
any SCSI lld that returns non-zero from it's ->queuecommand() handler.

Signed-off-by: default avatarJens Axboe <axboe@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent f358166a

block/elevator.c

+7 −1
Original line number Diff line number Diff line
@@ -333,6 +333,7 @@ void elv_insert(request_queue_t *q, struct request *rq, int where) 
{

	struct list_head *pos;

	unsigned ordseq;

	int unplug_it = 1;



	blk_add_trace_rq(q, rq, BLK_TA_INSERT);
@@ -399,6 +400,11 @@ void elv_insert(request_queue_t *q, struct request *rq, int where) 
		}



		list_add_tail(&rq->queuelist, pos);

		/*

		 * most requeues happen because of a busy condition, don't

		 * force unplug of the queue for that case.

		 */

		unplug_it = 0;

		break;



	default:
@@ -407,7 +413,7 @@ void elv_insert(request_queue_t *q, struct request *rq, int where) 
		BUG();

	}



	if (blk_queue_plugged(q)) {

	if (unplug_it && blk_queue_plugged(q)) {

		int nrq = q->rq.count[READ] + q->rq.count[WRITE]

			- q->in_flight;

block/ll_rw_blk.c

+15 −2
Original line number Diff line number Diff line
@@ -1732,8 +1732,21 @@ void blk_run_queue(struct request_queue *q) 


	spin_lock_irqsave(q->queue_lock, flags);

	blk_remove_plug(q);

	if (!elv_queue_empty(q))



	/*

	 * Only recurse once to avoid overrunning the stack, let the unplug

	 * handling reinvoke the handler shortly if we already got there.

	 */

	if (!elv_queue_empty(q)) {

		if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {

			q->request_fn(q);

			clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);

		} else {

			blk_plug_device(q);

			kblockd_schedule_work(&q->unplug_work);

		}

	}



	spin_unlock_irqrestore(q->queue_lock, flags);

}

EXPORT_SYMBOL(blk_run_queue);

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