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

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

[Michal Koutný]

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

Signed-off-by: Michal Koutný <mkoutny@suse.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

Re: [PATCH] cgroup: rstat: Mark benign data race to silence KCSAN

[Shakeel Butt]

On Wed, Nov 3, 2021 at 9:59 AM Michal Koutný <mkoutny@suse.com> wrote:
>
> 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@gmail.com>
> Link: https://lore.kernel.org/r/CACkBjsbPVdkub=e-E-p1WBOLxS515ith-53SFdmFHWV_QMo40w@mail.gmail.com
> Suggested-by: Hao Sun <sunhao.th@gmail.com>
>
> Signed-off-by: Michal Koutný <mkoutny@suse.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>

Re: [PATCH] cgroup: rstat: Mark benign data race to silence KCSAN

[Tejun Heo]

On Wed, Nov 03, 2021 at 05:58:45PM +0100, Michal Koutný wrote:
> 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@gmail.com>
> Link: https://lore.kernel.org/r/CACkBjsbPVdkub=e-E-p1WBOLxS515ith-53SFdmFHWV_QMo40w@mail.gmail.com
> Suggested-by: Hao Sun <sunhao.th@gmail.com>
> 
> Signed-off-by: Michal Koutný <mkoutny@suse.com>

Applied to cgroup/for-5.17.

Thanks.

-- 
tejun