From: Paolo Valente paolo.valente@linaro.org
[ Upstream commit 9a2ac41b13c573703d6689f51f3e27dd658324be ]
Commit 85686d0dc194 ("block, bfq: keep shared queues out of the waker mechanism") leaves shared bfq_queues out of the waker-detection mechanism. It attains this goal by not updating the pointer last_completed_rq_bfqq, if the last request completed belongs to a shared bfq_queue (so that the pointer will not point to the shared bfq_queue).
Yet this has a side effect: the pointer last_completed_rq_bfqq keeps pointing, deceptively, to a bfq_queue that actually is not the last one to have had a request completed. As a consequence, such a bfq_queue may deceptively be considered as a waker of some bfq_queue, even of some shared bfq_queue.
To address this issue, reset last_completed_rq_bfqq if the last request completed belongs to a shared queue.
Fixes: 85686d0dc194 ("block, bfq: keep shared queues out of the waker mechanism") Signed-off-by: Paolo Valente paolo.valente@linaro.org Link: https://lore.kernel.org/r/20210619140948.98712-8-paolo.valente@linaro.org Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/bfq-iosched.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 7c62bf093199..2a2e6e4ff0b4 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -6143,11 +6143,13 @@ static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd) * of other queues. But a false waker will unjustly steal * bandwidth to its supposedly woken queue. So considering * also shared queues in the waking mechanism may cause more - * control troubles than throughput benefits. Then do not set - * last_completed_rq_bfqq to bfqq if bfqq is a shared queue. + * control troubles than throughput benefits. Then reset + * last_completed_rq_bfqq if bfqq is a shared queue. */ if (!bfq_bfqq_coop(bfqq)) bfqd->last_completed_rq_bfqq = bfqq; + else + bfqd->last_completed_rq_bfqq = NULL;
/* * If we are waiting to discover whether the request pattern