From: Paolo Valente <paolo.valente@linaro.org>
Date: Thu, 16 Aug 2018 18:51:15 +0200
Subject: [PATCH] block, bfq: readd missing reset of parent-entity service
Git-commit: 8a511ba5feec5947bee0635cff8bd796d5f77e3e
Patch-mainline: v4.19-rc1
References: bsc#1104967,FATE#325924

The received-service counter needs to be equal to 0 when an entity is
set in service. Unfortunately, commit "block, bfq: fix service being
wrongly set to zero in case of preemption" mistakenly removed the
resetting of this counter for the parent entities of the bfq_queue
being set in service. This commit fixes this issue by resetting
service for parent entities, directly on the expiration of the
in-service bfq_queue.

Fixes: 9fae8dd59ff3 ("block, bfq: fix service being wrongly set to zero in case of preemption")
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 block/bfq-iosched.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 41d9036b1822..62efc1b97afb 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -3298,6 +3298,27 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
 		 */
 	} else
 		entity->service = 0;
+
+	/*
+	 * Reset the received-service counter for every parent entity.
+	 * Differently from what happens with bfqq->entity.service,
+	 * the resetting of this counter never needs to be postponed
+	 * for parent entities. In fact, in case bfqq may have a
+	 * chance to go on being served using the last, partially
+	 * consumed budget, bfqq->entity.service needs to be kept,
+	 * because if bfqq then actually goes on being served using
+	 * the same budget, the last value of bfqq->entity.service is
+	 * needed to properly decrement bfqq->entity.budget by the
+	 * portion already consumed. In contrast, it is not necessary
+	 * to keep entity->service for parent entities too, because
+	 * the bubble up of the new value of bfqq->entity.budget will
+	 * make sure that the budgets of parent entities are correct,
+	 * even in case bfqq and thus parent entities go on receiving
+	 * service with the same budget.
+	 */
+	entity = entity->parent;
+	for_each_entity(entity)
+		entity->service = 0;
 }
 
 /*
-- 
2.16.4