Re: [PATCH linux-next] cgroup: fix suspicious rcu_dereference_check() usage warning

[Tejun Heo <tj@kernel.org>]

On Sat, Mar 05, 2022 at 11:41:03AM +0800, Chengming Zhou wrote:
> task_css_set_check() will use rcu_dereference_check() to check for
> rcu_read_lock_held() on the read-side, which is not true after commit
> dc6e0818bc9a ("sched/cpuacct: Optimize away RCU read lock"). This
> commit drop explicit rcu_read_lock(), change to RCU-sched read-side
> critical section. So fix the RCU warning by adding check for
> rcu_read_lock_sched_held().
> 
> Fixes: dc6e0818bc9a ("sched/cpuacct: Optimize away RCU read lock")
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Reported-by: syzbot+16e3f2c77e7c5a0113f9@syzkaller.appspotmail.com
> Tested-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> ---
>  include/linux/cgroup.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> 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))

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun