block, bfq: fix weight-raising resume with !low_latency

When the io_latency heuristic is off, bfq_queues must not start to be
weight-raised. Unfortunately, by mistake, this may happen when the
state of a previously weight-raised bfq_queue is resumed after a queue
split. This commit fixes this error.

Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-5-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -1012,7 +1012,7 @@ static void
 bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
 		      struct bfq_io_cq *bic, bool bfq_already_existing)
 {
-	unsigned int old_wr_coeff = bfqq->wr_coeff;
+	unsigned int old_wr_coeff = 1;
 	bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
 
 	if (bic->saved_has_short_ttime)
@@ -1033,7 +1033,13 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
 	bfqq->ttime = bic->saved_ttime;
 	bfqq->io_start_time = bic->saved_io_start_time;
 	bfqq->tot_idle_time = bic->saved_tot_idle_time;
-	bfqq->wr_coeff = bic->saved_wr_coeff;
+	/*
+	 * Restore weight coefficient only if low_latency is on
+	 */
+	if (bfqd->low_latency) {
+		old_wr_coeff = bfqq->wr_coeff;
+		bfqq->wr_coeff = bic->saved_wr_coeff;
+	}
 	bfqq->service_from_wr = bic->saved_service_from_wr;
 	bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
 	bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;