Commit 08d383a7 authored Aug 07, 2019 by Paolo Valente Committed by Jens Axboe Aug 08, 2019

block, bfq: reset last_completed_rq_bfqq if the pointed queue is freed



Since commit 13a857a4 ("block, bfq: detect wakers and
unconditionally inject their I/O"), BFQ stores, in a per-device
pointer last_completed_rq_bfqq, the last bfq_queue that had an I/O
request completed. If some bfq_queue receives new I/O right after the
last request of last_completed_rq_bfqq has been completed, then
last_completed_rq_bfqq may be a waker bfq_queue.

But if the bfq_queue last_completed_rq_bfqq points to is freed, then
last_completed_rq_bfqq becomes a dangling reference. This commit
resets last_completed_rq_bfqq if the pointed bfq_queue is freed.

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

parent 430380b4

block/bfq-iosched.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -1924,7 +1924,8 @@ static void bfq_add_request(struct request *rq)
		* confirmed no later than during the next
		* I/O-plugging interval for bfqq.
		*/
		if (!bfq_bfqq_has_short_ttime(bfqq) &&
		if (bfqd->last_completed_rq_bfqq &&
		!bfq_bfqq_has_short_ttime(bfqq) &&
		ktime_get_ns() - bfqd->last_completion <
		200 * NSEC_PER_USEC) {
		if (bfqd->last_completed_rq_bfqq != bfqq &&
		@@ -4808,6 +4809,9 @@ void bfq_put_queue(struct bfq_queue *bfqq)
		bfqq->bfqd->burst_size--;
		}

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

		kmem_cache_free(bfq_pool, bfqq);
		#ifdef CONFIG_BFQ_GROUP_IOSCHED
		bfqg_and_blkg_put(bfqg);

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