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

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Date:   Thu, 20 Jul 2017 15:33:00 -0700
From:   Paul McKenney <paulmckrcu@...il.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        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

On Wed, Jul 19, 2017 at 4:38 PM, Paul McKenney <paulmckrcu@...il.com> wrote:
> On Thu, Jul 13, 2017 at 11:49 PM, Wanpeng Li <kernellwp@...il.com> wrote:
>>
>> 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.
>
>
> I am hitting this with rcutorture, so have kicked off an overnight
> run with this patch.

Which passed, so:

Tested-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

                                                     Thanx, Paul


>> > 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
>> >
>
>