Commit 3f758e84 authored by Paolo Valente's avatar Paolo Valente Committed by Jens Axboe
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block, bfq: move update of waker and woken list to queue freeing 



Since commit 13a857a4 ("block, bfq: detect wakers and
unconditionally inject their I/O"), every bfq_queue has a pointer to a
waker bfq_queue and a list of the bfq_queues it may wake. In this
respect, when a bfq_queue, say Q, remains with no I/O source attached
to it, Q cannot be woken by any other bfq_queue, and cannot wake any
other bfq_queue. Then Q must be removed from the woken list of its
possible waker bfq_queue, and all bfq_queues in the woken list of Q
must stop having a waker bfq_queue.

Q remains with no I/O source in two cases: when the last process
associated with Q exits or when such a process gets associated with a
different bfq_queue. Unfortunately, commit 13a857a4 ("block, bfq:
detect wakers and unconditionally inject their I/O") performed the
above updates only in the first case.

This commit fixes this bug by moving these updates to when Q gets
freed. This is a simple and safe way to handle all cases, as both the
above events, process exit and re-association, lead to Q being freed
soon, and because dangling references would come out only after Q gets
freed (if no update were performed).

Fixes: 13a857a4 ("block, bfq: detect wakers and unconditionally inject their I/O")
Reported-by: default avatarDouglas Anderson <dianders@chromium.org>
Tested-by: default avatarDouglas Anderson <dianders@chromium.org>
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 08d383a7

block/bfq-iosched.c

+29 −15
Original line number Diff line number Diff line
@@ -4765,6 +4765,8 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx) 
 */

void bfq_put_queue(struct bfq_queue *bfqq)

{

	struct bfq_queue *item;

	struct hlist_node *n;

#ifdef CONFIG_BFQ_GROUP_IOSCHED

	struct bfq_group *bfqg = bfqq_group(bfqq);

#endif
@@ -4809,6 +4811,33 @@ void bfq_put_queue(struct bfq_queue *bfqq) 
			bfqq->bfqd->burst_size--;

	}



	/*

	 * bfqq does not exist any longer, so it cannot be woken by

	 * any other queue, and cannot wake any other queue. Then bfqq

	 * must be removed from the woken list of its possible waker

	 * queue, and all queues in the woken list of bfqq must stop

	 * having a waker queue. Strictly speaking, these updates

	 * should be performed when bfqq remains with no I/O source

	 * attached to it, which happens before bfqq gets freed. In

	 * particular, this happens when the last process associated

	 * with bfqq exits or gets associated with a different

	 * queue. However, both events lead to bfqq being freed soon,

	 * and dangling references would come out only after bfqq gets

	 * freed. So these updates are done here, as a simple and safe

	 * way to handle all cases.

	 */

	/* remove bfqq from woken list */

	if (!hlist_unhashed(&bfqq->woken_list_node))

		hlist_del_init(&bfqq->woken_list_node);



	/* reset waker for all queues in woken list */

	hlist_for_each_entry_safe(item, n, &bfqq->woken_list,

				  woken_list_node) {

		item->waker_bfqq = NULL;

		bfq_clear_bfqq_has_waker(item);

		hlist_del_init(&item->woken_list_node);

	}



	if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq)

		bfqq->bfqd->last_completed_rq_bfqq = NULL;
@@ -4839,9 +4868,6 @@ static void bfq_put_cooperator(struct bfq_queue *bfqq) 


static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)

{

	struct bfq_queue *item;

	struct hlist_node *n;



	if (bfqq == bfqd->in_service_queue) {

		__bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);

		bfq_schedule_dispatch(bfqd);
@@ -4851,18 +4877,6 @@ static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq) 


	bfq_put_cooperator(bfqq);



	/* remove bfqq from woken list */

	if (!hlist_unhashed(&bfqq->woken_list_node))

		hlist_del_init(&bfqq->woken_list_node);



	/* reset waker for all queues in woken list */

	hlist_for_each_entry_safe(item, n, &bfqq->woken_list,

				  woken_list_node) {

		item->waker_bfqq = NULL;

		bfq_clear_bfqq_has_waker(item);

		hlist_del_init(&item->woken_list_node);

	}



	bfq_put_queue(bfqq); /* release process reference */

}

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