Commit f3218ad8 authored Jan 29, 2019 by Paolo Valente Committed by Jens Axboe Jan 31, 2019

block, bfq: make sure queue budgets are not below service received



With some unlucky sequences of events, the function bfq_updated_next_req
updates the current budget of a bfq_queue to a lower value than the
service received by the queue using such a budget. Unfortunately, if
this happens, then the return value of the function bfq_bfqq_budget_left
becomes inconsistent. This commit solves this problem by lower-bounding
the budget computed in bfq_updated_next_req to the service currently
charged to the queue.

Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 218cb897

block/bfq-iosched.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -907,8 +907,10 @@ static void bfq_updated_next_req(struct bfq_data *bfqd,
		*/
		return;

		new_budget = max_t(unsigned long, bfqq->max_budget,
		bfq_serv_to_charge(next_rq, bfqq));
		new_budget = max_t(unsigned long,
		max_t(unsigned long, bfqq->max_budget,
		bfq_serv_to_charge(next_rq, bfqq)),
		entity->service);
		if (entity->budget != new_budget) {
		entity->budget = new_budget;
		bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",

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