linux-kernel - [tip: sched/core] sched/cpuacct: Fix charge percpu cpuusage

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Date:   Tue, 01 Mar 2022 15:24:42 -0000
From:   "tip-bot2 for Chengming Zhou" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Minye Zhu <zhuminye@...edance.com>,
        Chengming Zhou <zhouchengming@...edance.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/cpuacct: Fix charge percpu cpuusage

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

Commit-ID:     248cc9993d1cc12b8e9ed716cc3fc09f6c3517dd
Gitweb:        https://git.kernel.org/tip/248cc9993d1cc12b8e9ed716cc3fc09f6c3517dd
Author:        Chengming Zhou <zhouchengming@...edance.com>
AuthorDate:    Sun, 20 Feb 2022 13:14:24 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 01 Mar 2022 16:18:37 +01:00

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.

Fixes: 73e6aafd9ea8 ("sched/cpuacct: Simplify the cpuacct code")
Reported-by: Minye Zhu <zhuminye@...edance.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>
Link: https://lore.kernel.org/r/20220220051426.5274-1-zhouchengming@bytedance.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 3d06c5e..3078005 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -334,12 +334,13 @@ static struct cftype files[] = {
  */
 void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
+	unsigned int cpu = task_cpu(tsk);
 	struct cpuacct *ca;
 
 	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();
 }