linux-kernel - [PATCH] sched/cpuacct: fix charge percpu cpuusage

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Message-Id: <20220213120118.93471-1-zhouchengming@bytedance.com>
Date:   Sun, 13 Feb 2022 20:01:18 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     tj@...nel.org, arbn@...dex-team.com, mingo@...hat.com,
        peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>,
        Minye Zhu <zhuminye@...edance.com>
Subject: [PATCH] sched/cpuacct: fix charge percpu cpuusage

The cpuacct_account_field() is always called by the current task
itself, so it's ok to use __this_cpu_add() to charge the tick time.

But cpuacct_charge() maybe called by update_curr() in load_balance()
on a random CPU, different from the CPU on which the task is running.
So __this_cpu_add() will charge that cputime to a random incorrect CPU.

Reported-by: Minye Zhu <zhuminye@...edance.com>
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 kernel/sched/cpuacct.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 3d06c5e4220d..75fbc212cb71 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -335,11 +335,12 @@ static struct cftype files[] = {
 void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
 	struct cpuacct *ca;
+	unsigned int cpu = task_cpu(tsk);
 
 	rcu_read_lock();
 
 	for (ca = task_ca(tsk); ca; ca = parent_ca(ca))
-		__this_cpu_add(*ca->cpuusage, cputime);
+		*per_cpu_ptr(ca->cpuusage, cpu) += cputime;
 
 	rcu_read_unlock();
 }
-- 
2.20.1