From: Fam Zheng <zhengfeiran@bytedance.com>
Date: Wed, 28 Aug 2019 11:54:51 +0800
Subject: [PATCH] bfq: Fix the missing barrier in
 __bfq_entity_update_weight_prio
Git-commit: e9d3c866bf4cdbb6637e6cb268c26dfdf06d8cd3
Patch-Mainline: v5.4-rc1
References: bsc#1156419,jsc#SLE-8281

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@bytedance.com>
Reviewed-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.de>
---
 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) {
-- 
2.16.4