答复: [PATCH][RFC] sched/cpuacct: Fix cpuacct charge

["Li,Rongqing" <lirongqing@baidu.com>]

> -----邮件原件-----
> 发件人: Peter Zijlstra <peterz@infradead.org>
> 发送时间: 2021年7月29日 18:20
> 收件人: Li,Rongqing <lirongqing@baidu.com>
> 抄送: mingo@redhat.com; juri.lelli@redhat.com; vincent.guittot@linaro.org;
> dietmar.eggemann@arm.com; rostedt@goodmis.org; bsegall@google.com;
> mgorman@suse.de; bristot@redhat.co; linux-kernel@vger.kernel.org;
> songmuchun@bytedance.com
> 主题: Re: [PATCH][RFC] sched/cpuacct: Fix cpuacct charge
> 
> On Tue, Jul 20, 2021 at 02:04:41PM +0800, Li RongQing wrote:
> > get_irq_regs only work for current running cpu, but the task, whose
> > cpuacct will be charged, maybe run different cpu, like Cpu 2 wake up a
> > kernel thread to CPU 3, cause CPU 3 task are charged with the
> > following stack
> >
> >   cpuacct_charge+0xd8/0x100
> >   update_curr+0xe1/0x1e0
> >   enqueue_entity+0x144/0x6e0
> >   enqueue_task_fair+0x93/0x900
> >   ttwu_do_activate+0x4b/0x90
> >   try_to_wake_up+0x20b/0x530
> >   ? update_dl_rq_load_avg+0x10f/0x210
> >   swake_up_locked.part.1+0x13/0x40
> >   swake_up_one+0x27/0x40
> >   rcu_process_callbacks+0x484/0x4f0
> >   ? run_rebalance_domains_bt+0x5a/0x180
> >   __do_softirq+0xe3/0x308
> >   irq_exit+0xf0/0x100
> >   smp_apic_timer_interrupt+0x74/0x160
> >   apic_timer_interrupt+0xf/0x20
> >   </IRQ>
> >  RIP: 0033:0x456947
> >
> > so define a get_irq_regs_cpu which returns the required cpu irq
> > registers
> >
> > BUT it should be not safe, and do not know what it should be like in MIPS?
> >
> > Fixes: dbe9337109c2 "(sched/cpuacct: Fix charge cpuacct.usage_sys)"
> > Co-developed-by: Zhao Jie <zhaojie17@baidu.com>
> > Signed-off-by: Zhao Jie <zhaojie17@baidu.com>
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > ---
> >  include/asm-generic/irq_regs.h | 5 +++++
> >  kernel/sched/cpuacct.c         | 3 ++-
> >  2 files changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/asm-generic/irq_regs.h
> > b/include/asm-generic/irq_regs.h index 2e7c6e8..93e2579 100644
> > --- a/include/asm-generic/irq_regs.h
> > +++ b/include/asm-generic/irq_regs.h
> > @@ -21,6 +21,11 @@ static inline struct pt_regs *get_irq_regs(void)
> >  	return __this_cpu_read(__irq_regs);
> >  }
> >
> > +static inline struct pt_regs *get_irq_regs_cpu(int cpu) {
> > +	return per_cpu(__irq_regs, cpu);
> > +}
> 
> This primitive just cannot be right... it'll get you some random data.

True

Seem no easy to fix. How about a partial fix


diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 893eece..48b117e 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -340,7 +340,12 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime)
 {
        struct cpuacct *ca;
        int index = CPUACCT_STAT_SYSTEM;
-       struct pt_regs *regs = get_irq_regs() ? : task_pt_regs(tsk);
+       struct pt_regs *regs;
+
+       if (task_cpu(tsk) == raw_smp_processor_id())
+               regs = get_irq_regs() ? : task_pt_regs(tsk);
+       else
+               regs = task_pt_regs(tsk);

        if (regs && user_mode(regs))
                index = CPUACCT_STAT_USER;