linux-kernel - [PATCH AUTOSEL 5.4 03/13] cgroup: Remove data-race around cgrp_dfl

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Date:   Mon, 17 Oct 2022 20:10:52 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>,
        Abhishek Shah <abhishek.shah@...umbia.edu>,
        Gabriel Ryan <gabe@...columbia.edu>,
        Christian Brauner <brauner@...nel.org>,
        Sasha Levin <sashal@...nel.org>, lizefan.x@...edance.com,
        hannes@...xchg.org, cgroups@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 03/13] cgroup: Remove data-race around cgrp_dfl_visible

From: Tejun Heo <tj@...nel.org>

[ Upstream commit dc79ec1b232ad2c165d381d3dd2626df4ef9b5a4 ]

There's a seemingly harmless data-race around cgrp_dfl_visible detected by
kernel concurrency sanitizer. Let's remove it by throwing WRITE/READ_ONCE at
it.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Abhishek Shah <abhishek.shah@...umbia.edu>
Cc: Gabriel Ryan <gabe@...columbia.edu>
Reviewed-by: Christian Brauner (Microsoft) <brauner@...nel.org>
Link: https://lore.kernel.org/netdev/20220819072256.fn7ctciefy4fc4cu@wittgenstein/
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/cgroup/cgroup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index d14575c0e464..194060a6492a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2178,7 +2178,7 @@ static int cgroup_get_tree(struct fs_context *fc)
 	struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
 	int ret;
 
-	cgrp_dfl_visible = true;
+	WRITE_ONCE(cgrp_dfl_visible, true);
 	cgroup_get_live(&cgrp_dfl_root.cgrp);
 	ctx->root = &cgrp_dfl_root;
 
@@ -6022,7 +6022,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
 		struct cgroup *cgrp;
 		int ssid, count = 0;
 
-		if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
+		if (root == &cgrp_dfl_root && !READ_ONCE(cgrp_dfl_visible))
 			continue;
 
 		seq_printf(m, "%d:", root->hierarchy_id);
-- 
2.35.1