linux-kernel - [PATCH] cgroup: rstat: Mark benign data race to silence KCSAN

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Date:   Wed,  3 Nov 2021 17:58:45 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     cgroups@...r.kernel.org
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Li Zefan <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>,
        Hao Sun <sunhao.th@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] cgroup: rstat: Mark benign data race to silence KCSAN

There is a race between updaters and flushers (flush can possibly miss
the latest update(s)). This is expected as explained in
cgroup_rstat_updated() comment, add also machine readable annotation so
that KCSAN results aren't noisy.

Reported-by: Hao Sun <sunhao.th@...il.com>
Link: https://lore.kernel.org/r/CACkBjsbPVdkub=e-E-p1WBOLxS515ith-53SFdmFHWV_QMo40w@mail.gmail.com
Suggested-by: Hao Sun <sunhao.th@...il.com>

Signed-off-by: Michal Koutný <mkoutny@...e.com>
---
 kernel/cgroup/rstat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Hao was silent in the reporting mail thread, so I'm sending the
suggested annotating patch.

diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index 1486768f2318..1abe74114527 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -35,7 +35,7 @@ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
 	 * instead of NULL, we can tell whether @cgrp is on the list by
 	 * testing the next pointer for NULL.
 	 */
-	if (cgroup_rstat_cpu(cgrp, cpu)->updated_next)
+	if (data_race(cgroup_rstat_cpu(cgrp, cpu)->updated_next))
 		return;
 
 	raw_spin_lock_irqsave(cpu_lock, flags);
-- 
2.33.1