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From:   Chengming Zhou <zhouchengming@bytedance.com>
To:     tj@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org,
        peterz@infradead.org
Cc:     cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        songmuchun@bytedance.com,
        Chengming Zhou <zhouchengming@bytedance.com>,
        Linux Kernel Functional Testing <lkft@linaro.org>,
        syzbot+16e3f2c77e7c5a0113f9@syzkaller.appspotmail.com,
        Zhouyi Zhou <zhouzhouyi@gmail.com>
Subject: [PATCH linux-next] cgroup: fix suspicious rcu_dereference_check() usage warning
Date:   Sat,  5 Mar 2022 11:41:03 +0800
Message-Id: <20220305034103.57123-1-zhouchengming@bytedance.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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))
-- 
2.20.1