Patch "cgroup: Fix suspicious rcu_dereference_check() usage warning" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    cgroup: Fix suspicious rcu_dereference_check() usage warning

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cgroup-fix-suspicious-rcu_dereference_check-usage-wa.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a7a1ff80a7a0f1b3823b3862fa05c0eb79cf6290
Author: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Date:   Fri Sep 29 16:14:18 2023 +0300

    cgroup: Fix suspicious rcu_dereference_check() usage warning
    
    commit f2aa197e4794bf4c2c0c9570684f86e6fa103e8b upstream.
    
    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@xxxxxxxxxx>
    Reported-by: syzbot+16e3f2c77e7c5a0113f9@xxxxxxxxxxxxxxxxxxxxxxxxx
    Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Acked-by: Tejun Heo <tj@xxxxxxxxxx>
    Tested-by: Zhouyi Zhou <zhouzhouyi@xxxxxxxxx>
    Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220305034103.57123-1-zhouchengming@xxxxxxxxxxxxx
    Signed-off-by: Ovidiu Panait <ovidiu.panait@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 7653f54189502..c9c430712d471 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -451,6 +451,7 @@ 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))



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