linux-kernel - Re: [tip:sched/urgent] sched/cputime: Don't use smp_processor

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Date:   Mon, 17 Jul 2017 04:31:14 +0200
From:   Frederic Weisbecker <fweisbec@...il.com>
To:     riel@...hat.com, peterz@...radead.org, wanpeng.li@...mail.com,
        torvalds@...ux-foundation.org, xiaolong.ye@...el.com,
        mingo@...nel.org, tglx@...utronix.de, hpa@...or.com,
        lcapitulino@...hat.com, linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/urgent] sched/cputime: Don't use smp_processor_id()
 in preemptible context

On Fri, Jul 14, 2017 at 02:10:14AM -0700, tip-bot for Wanpeng Li wrote:
> Commit-ID:  0e4097c3354e2f5a5ad8affd9dc7f7f7d00bb6b9
> Gitweb:     http://git.kernel.org/tip/0e4097c3354e2f5a5ad8affd9dc7f7f7d00bb6b9
> Author:     Wanpeng Li <wanpeng.li@...mail.com>
> AuthorDate: Sun, 9 Jul 2017 00:40:28 -0700
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Fri, 14 Jul 2017 10:27:15 +0200
> 
> sched/cputime: Don't use smp_processor_id() in preemptible context
> 
> Recent kernels trigger this warning:
> 
>  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()
>   debug_smp_processor_id()
>   vtime_delta()
>   task_cputime()
>   thread_group_cputime()
>   thread_group_cputime_adjusted()
>   wait_consider_task()
>   do_wait()
>   SYSC_wait4()
>   do_syscall_64()
>   entry_SYSCALL64_slow_path()
> 
> 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() with sched_clock() to
> avoid calling smp_processor_id() in a preemptible context.
> 
> Reported-by: Xiaolong Ye <xiaolong.ye@...el.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Luiz Capitulino <lcapitulino@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Link: http://lkml.kernel.org/r/1499586028-7402-1-git-send-email-wanpeng.li@hotmail.com
> [ Prettified the changelog. ]
> Signed-off-by: Ingo Molnar <mingo@...nel.org>

Thanks! The patch looks good!