public inbox for linux-kernel@vger.kernel.org
 help / color / mirror / Atom feed
* failure to boot after dc6e0818bc9a "sched/cpuacct: Optimize away RCU read lock"
@ 2022-03-16 17:43 J. Bruce Fields
  2022-03-16 17:49 ` J. Bruce Fields
  2022-03-16 20:48 ` Peter Zijlstra
  0 siblings, 2 replies; 4+ messages in thread
From: J. Bruce Fields @ 2022-03-16 17:43 UTC (permalink / raw)
  To: Chengming Zhou; +Cc: Peter Zijlstra, Ingo Molnar, linux-kernel

One of my test VMs has been failing to boot linux-next recently.  I
finally got around to a bisect this morning, and it landed on the below.

What other information would be useful to debug this?

--b.

commit dc6e0818bc9a
Author: Chengming Zhou <zhouchengming@bytedance.com>
Date:   Sun Feb 20 13:14:25 2022 +0800

    sched/cpuacct: Optimize away RCU read lock
    
    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@infradead.org>
    Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lore.kernel.org/r/20220220051426.5274-2-zhouchengming@bytedance.com

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 75c151413fda..9a109c6ac0e0 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -791,11 +791,9 @@ 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 307800586ac8..f79f88456d72 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -337,12 +337,10 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 	unsigned int cpu = task_cpu(tsk);
 	struct cpuacct *ca;
 
-	rcu_read_lock();
+	lockdep_assert_rq_held(cpu_rq(cpu));
 
 	for (ca = task_ca(tsk); ca; ca = parent_ca(ca))
 		*per_cpu_ptr(ca->cpuusage, cpu) += cputime;
-
-	rcu_read_unlock();
 }
 
 /*

^ permalink raw reply related	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-03-16 23:27 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2022-03-16 17:43 failure to boot after dc6e0818bc9a "sched/cpuacct: Optimize away RCU read lock" J. Bruce Fields
2022-03-16 17:49 ` J. Bruce Fields
2022-03-16 20:48 ` Peter Zijlstra
2022-03-16 23:27   ` J. Bruce Fields

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox