linux-kernel - Re: [PATCH v3] sched/cputime: Fix using smp_processor

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Date:   Fri, 14 Jul 2017 14:49:53 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Luiz Capitulino <lcapitulino@...hat.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v3] sched/cputime: Fix using smp_processor_id() in preemptible

Ping for the merge window. :)
2017-07-09 15:40 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
> From: Wanpeng Li <wanpeng.li@...mail.com>
>
>  BUG: using smp_processor_id() in preemptible [00000000] code: 99-trinity/181
>  caller is debug_smp_processor_id+0x17/0x19
>  CPU: 0 PID: 181 Comm: 99-trinity Not tainted 4.12.0-01059-g2a42eb9 #1
>  Call Trace:
>   dump_stack+0x82/0xb8
>   check_preemption_disabled+0xd1/0xe3
>   debug_smp_processor_id+0x17/0x19
>   vtime_delta+0xd/0x2c
>   task_cputime+0x89/0xdb
>   thread_group_cputime+0x11b/0x1ed
>   thread_group_cputime_adjusted+0x1f/0x47
>   wait_consider_task+0x2a9/0xaf9
>   ? lock_acquire+0x97/0xa4
>   do_wait+0xdf/0x1f4
>   SYSC_wait4+0x8e/0xb5
>   ? list_add+0x34/0x34
>   SyS_wait4+0x9/0xb
>   do_syscall_64+0x70/0x82
>   entry_SYSCALL64_slow_path+0x25/0x25
>
> As Frederic pointed out:
>
> | Although those sched_clock_cpu() things seem to only matter when the
> | sched_clock() is unstable. And that stability is a condition for nohz_full
> | to work anyway. So probably sched_clock() alone would be enough.
>
> This patch fixes it by replacing sched_clock_cpu() by sched_clock() to
> avoid to call smp_processor_id() in preemptible context.
>
> Reported-by: Xiaolong Ye <xiaolong.ye@...el.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Luiz Capitulino <lcapitulino@...hat.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
>  kernel/sched/cputime.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> index 6e3ea4a..14d2dbf 100644
> --- a/kernel/sched/cputime.c
> +++ b/kernel/sched/cputime.c
> @@ -683,7 +683,7 @@ static u64 vtime_delta(struct vtime *vtime)
>  {
>         unsigned long long clock;
>
> -       clock = sched_clock_cpu(smp_processor_id());
> +       clock = sched_clock();
>         if (clock < vtime->starttime)
>                 return 0;
>
> @@ -814,7 +814,7 @@ void arch_vtime_task_switch(struct task_struct *prev)
>
>         write_seqcount_begin(&vtime->seqcount);
>         vtime->state = VTIME_SYS;
> -       vtime->starttime = sched_clock_cpu(smp_processor_id());
> +       vtime->starttime = sched_clock();
>         write_seqcount_end(&vtime->seqcount);
>  }
>
> @@ -826,7 +826,7 @@ void vtime_init_idle(struct task_struct *t, int cpu)
>         local_irq_save(flags);
>         write_seqcount_begin(&vtime->seqcount);
>         vtime->state = VTIME_SYS;
> -       vtime->starttime = sched_clock_cpu(cpu);
> +       vtime->starttime = sched_clock();
>         write_seqcount_end(&vtime->seqcount);
>         local_irq_restore(flags);
>  }
> --
> 2.7.4
>