[PATCH 6/6] mm, memcg: Prevent mem_cgroup_protected store tearing

From: Chris Down <chris@chrisdown.name>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
	Roman Gushchin <guro@fb.com>,
	linux-mm@kvack.org, cgroups@vger.kernel.org,
	linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: [PATCH 6/6] mm, memcg: Prevent mem_cgroup_protected store tearing
Date: Thu, 12 Mar 2020 17:33:16 +0000	[thread overview]
Message-ID: <d1e9fbc0379fe8db475d82c8b6fbe048876e12ae.1584034301.git.chris@chrisdown.name> (raw)
In-Reply-To: <cover.1584034301.git.chris@chrisdown.name>

The read side of this is all protected, but we can still tear if
multiple iterations of mem_cgroup_protected are going at the same time.

There's some intentional racing in mem_cgroup_protected which is ok, but
load/store tearing should be avoided.

Signed-off-by: Chris Down <chris@chrisdown.name>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: linux-mm@kvack.org
Cc: cgroups@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@fb.com
---
 mm/memcontrol.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 57048a38c75d..e9af606238ab 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6301,8 +6301,8 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
 	}
 
 exit:
-	memcg->memory.emin = emin;
-	memcg->memory.elow = elow;
+	WRITE_ONCE(memcg->memory.emin, emin);
+	WRITE_ONCE(memcg->memory.elow, elow);
 
 	if (usage <= emin)
 		return MEMCG_PROT_MIN;
-- 
2.25.1

