Patch "sched/cpuacct: Optimize away RCU read lock" 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

    sched/cpuacct: Optimize away RCU read lock

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:
     sched-cpuacct-optimize-away-rcu-read-lock.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 88617226583184a6e4d79326741cec43648b2f7e
Author: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Date:   Fri Sep 29 16:14:17 2023 +0300

    sched/cpuacct: Optimize away RCU read lock
    
    commit dc6e0818bc9a0336d9accf3ea35d146d72aa7a18 upstream.
    
    Since cpuacct_charge() is called from the scheduler update_curr(),
    we must already have rq lock held, then the RCU read lock can
    be optimized away.
    
    And do the same thing in it's wrapper cgroup_account_cputime(),
    but we can't use lockdep_assert_rq_held() there, which defined
    in kernel/sched/sched.h.
    
    Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220220051426.5274-2-zhouchengming@xxxxxxxxxxxxx
    [OP: adjusted lockdep_assert_rq_held() -> lockdep_assert_held()]
    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 959b370733f09..7653f54189502 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -779,11 +779,9 @@ static inline void cgroup_account_cputime(struct task_struct *task,
 
 	cpuacct_charge(task, delta_exec);
 
-	rcu_read_lock();
 	cgrp = task_dfl_cgroup(task);
 	if (cgroup_parent(cgrp))
 		__cgroup_account_cputime(cgrp, delta_exec);
-	rcu_read_unlock();
 }
 
 static inline void cgroup_account_cputime_field(struct task_struct *task,
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 3c59c541dd314..8ee298321d78b 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -331,12 +331,10 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 	unsigned int cpu = task_cpu(tsk);
 	struct cpuacct *ca;
 
-	rcu_read_lock();
+	lockdep_assert_held(&cpu_rq(cpu)->lock);
 
 	for (ca = task_ca(tsk); ca; ca = parent_ca(ca))
 		*per_cpu_ptr(ca->cpuusage, cpu) += cputime;
-
-	rcu_read_unlock();
 }
 
 /*



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