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

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Commit 478de3380c ("block, bfq: deschedule empty bfq_queues not
referred by any process") fixed commit 3726112ec7 ("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: 3726112ec7 ("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>
This commit is contained in:
Paolo Valente 2020-02-03 11:40:54 +01:00 committed by Jens Axboe
parent 49d08d596e
commit f718b09327
1 changed files with 12 additions and 0 deletions
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12
block/bfq-iosched.c
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@ -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;