Commit f718b093 authored Feb 03, 2020 by Paolo Valente Committed by Jens Axboe Feb 03, 2020

block, bfq: do not plug I/O for bfq_queues with no proc refs

Commit 478de338 ("block, bfq: deschedule empty bfq_queues not
referred by any process") fixed commit 3726112e ("block, bfq:
re-schedule empty queues if they deserve I/O plugging") by
descheduling an empty bfq_queue when it remains with not process
reference. Yet, this still left a case uncovered: an empty bfq_queue
with not process reference that remains in service. This happens for
an in-service sync bfq_queue that is deemed to deserve I/O-dispatch
plugging when it remains empty. Yet no new requests will arrive for
such a bfq_queue if no process sends requests to it any longer. Even
worse, the bfq_queue may happen to be prematurely freed while still in
service (because there may remain no reference to it any longer).

This commit solves this problem by preventing I/O dispatch from being
plugged for the in-service bfq_queue, if the latter has no process
reference (the bfq_queue is then prevented from remaining in service).

Fixes: 3726112e ("block, bfq: re-schedule empty queues if they deserve I/O plugging")
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Reported-by: Patrick Dung <patdung100@gmail.com>
Tested-by: Patrick Dung <patdung100@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 49d08d59

block/bfq-iosched.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -3443,6 +3443,10 @@ static void bfq_dispatch_remove(struct request_queue q, struct request rq)
		static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
		struct bfq_queue *bfqq)
		{
		/* No point in idling for bfqq if it won't get requests any longer */
		if (unlikely(!bfqq_process_refs(bfqq)))
		return false;

		return (bfqq->wr_coeff > 1 &&
		(bfqd->wr_busy_queues <
		bfq_tot_busy_queues(bfqd) \|\|
		@@ -4076,6 +4080,10 @@ static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
		bfqq_sequential_and_IO_bound,
		idling_boosts_thr;

		/* No point in idling for bfqq if it won't get requests any longer */
		if (unlikely(!bfqq_process_refs(bfqq)))
		return false;

		bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
		bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);

		@@ -4169,6 +4177,10 @@ static bool bfq_better_to_idle(struct bfq_queue *bfqq)
		struct bfq_data *bfqd = bfqq->bfqd;
		bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar;

		/* No point in idling for bfqq if it won't get requests any longer */
		if (unlikely(!bfqq_process_refs(bfqq)))
		return false;

		if (unlikely(bfqd->strict_guarantees))
		return true;

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