linux-kernel - Re: [External] Re: [next] WARNING: suspicious RCU usage : include/linux/cgroup.h:494 suspicious rcu_dereference

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Date:   Mon, 7 Mar 2022 11:24:29 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     Zhouyi Zhou <zhouzhouyi@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, rcu <rcu@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [External] Re: [next] WARNING: suspicious RCU usage :
 include/linux/cgroup.h:494 suspicious rcu_dereference_check() usage

On Sat, 5 Mar 2022 at 06:27, Chengming Zhou <zhouchengming@...edance.com> wrote:
>
> On 2022/3/5 4:28 上午, Zhouyi Zhou wrote:
> > Hi Paul
> >
> > Yes, your suggestion works!
> > Thank you for your guidance, this is the first time I ever did a
> > bisection, I gained greatly during this process!
>
> Hi Zhouyi, thanks for the bisection test.
> Could this patch solve RCU warning? I just tested on my machine and there
> is no RCU warning any more.

This patch solves the reported problem. The test link provided below [1].

Tested-by: Linux Kernel Functional Testing <lkft@...aro.org>

>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 1e356c222756..0d1ada8968d7 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -450,6 +450,7 @@ extern struct mutex cgroup_mutex;
>  extern spinlock_t css_set_lock;
>  #define task_css_set_check(task, __c)                                  \
>         rcu_dereference_check((task)->cgroups,                          \
> +               rcu_read_lock_sched_held() ||                           \
>                 lockdep_is_held(&cgroup_mutex) ||                       \
>                 lockdep_is_held(&css_set_lock) ||                       \
>                 ((task)->flags & PF_EXITING) || (__c))
>


--
Linaro LKFT
https://lkft.linaro.org
[1] https://lkft.validation.linaro.org/scheduler/job/4664565#L339