linux-kernel - [PATCH v3 1/3] bfq: Fix the missing barrier in __bfq_entity_update_weight

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Message-Id: <20190828035453.18129-2-zhengfeiran@bytedance.com>
Date:   Wed, 28 Aug 2019 11:54:51 +0800
From:   Fam Zheng <zhengfeiran@...edance.com>
To:     linux-kernel@...r.kernel.org
Cc:     axboe@...nel.dk, paolo.valente@...aro.org, fam@...hon.net,
        duanxiongchun@...edance.com, cgroups@...r.kernel.org,
        zhangjiachen.jc@...edance.com, tj@...nel.org,
        linux-block@...r.kernel.org
Subject: [PATCH v3 1/3] bfq: Fix the missing barrier in __bfq_entity_update_weight_prio

The comment of bfq_group_set_weight says the reading of prio_changed
should happen before the reading of weight, but a memory barrier is
missing here. Add it now, to match the smp_wmb() there.

Signed-off-by: Fam Zheng <zhengfeiran@...edance.com>
Reviewed-by: Paolo Valente <paolo.valente@...aro.org>
---
 block/bfq-wf2q.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
index c9ba225081ce..05f0bf4a1144 100644
--- a/block/bfq-wf2q.c
+++ b/block/bfq-wf2q.c
@@ -744,6 +744,8 @@ __bfq_entity_update_weight_prio(struct bfq_service_tree *old_st,
 		}
 #endif
 
+		/* Matches the smp_wmb() in bfq_group_set_weight. */
+		smp_rmb();
 		old_st->wsum -= entity->weight;
 
 		if (entity->new_weight != entity->orig_weight) {
-- 
2.22.1