linux-kernel - [tip: sched/core] cgroup: Fix suspicious rcu_dereference

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Date:   Sat, 12 Mar 2022 12:37:01 -0000
From:   "tip-bot2 for Chengming Zhou" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Linux Kernel Functional Testing <lkft@...aro.org>,
        syzbot+16e3f2c77e7c5a0113f9@...kaller.appspotmail.com,
        Chengming Zhou <zhouchengming@...edance.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>, Zhouyi Zhou <zhouzhouyi@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] cgroup: Fix suspicious rcu_dereference_check()
 usage warning

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     f2aa197e4794bf4c2c0c9570684f86e6fa103e8b
Gitweb:        https://git.kernel.org/tip/f2aa197e4794bf4c2c0c9570684f86e6fa103e8b
Author:        Chengming Zhou <zhouchengming@...edance.com>
AuthorDate:    Sat, 05 Mar 2022 11:41:03 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sat, 12 Mar 2022 13:22:11 +01:00

cgroup: Fix suspicious rcu_dereference_check() usage warning

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@...aro.org>
Reported-by: syzbot+16e3f2c77e7c5a0113f9@...kaller.appspotmail.com
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Tejun Heo <tj@...nel.org>
Tested-by: Zhouyi Zhou <zhouzhouyi@...il.com>
Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
Link: https://lore.kernel.org/r/20220305034103.57123-1-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 1e356c2..0d1ada8 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))