linux-kernel - [PATCH cgroup/for-6.1] cgroup: Remove data-race around cgrp_dfl

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Date:   Sun, 4 Sep 2022 09:23:32 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Gabriel Ryan <gabe@...columbia.edu>,
        Abhishek Shah <abhishek.shah@...umbia.edu>,
        linux-kernel@...r.kernel.org, andrii@...nel.org, ast@...nel.org,
        bpf@...r.kernel.org, cgroups@...r.kernel.org, daniel@...earbox.net,
        hannes@...xchg.org, john.fastabend@...il.com, kafai@...com,
        kpsingh@...nel.org, lizefan.x@...edance.com,
        netdev@...r.kernel.org, songliubraving@...com, yhs@...com
Subject: [PATCH cgroup/for-6.1] cgroup: Remove data-race around
 cgrp_dfl_visible

>From dc79ec1b232ad2c165d381d3dd2626df4ef9b5a4 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.org>
Date: Sun, 4 Sep 2022 09:16:19 -1000

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/
---
Applied to cgroup/for-6.1.

Thanks.

 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 0005de2e2ed9..e0b72eb5d283 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2173,7 +2173,7 @@ 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;
 
@@ -6098,7 +6098,7 @@ 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);
-- 
2.37.3