2021-11-03 17:03:25

by Michal Koutný

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

Signed-off-by: Michal Koutný <[email protected]>
---
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

2021-11-03 17:44:12

by Shakeel Butt

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

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

Reviewed-by: Shakeel Butt <[email protected]>

2021-11-16 00:12:17

by Tejun Heo

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

On Wed, Nov 03, 2021 at 05:58:45PM +0100, Michal Koutn? 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 <[email protected]>
> Link: https://lore.kernel.org/r/CACkBjsbPVdkub=e-E-p1WBOLxS515ith-53SFdmFHWV_QMo40w@mail.gmail.com
> Suggested-by: Hao Sun <[email protected]>
>
> Signed-off-by: Michal Koutn? <[email protected]>

Applied to cgroup/for-5.17.

Thanks.

--
tejun