linux-kernel - Re: [RESEND PATCH v2] clocksource/arm_arch

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Message-ID: <20181210144754.GO5289@hirez.programming.kicks-ass.net>
Date:   Mon, 10 Dec 2018 15:47:54 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Qian Cai <cai@....pw>, akpm@...ux-foundation.org,
        mark.rutland@....com, marc.zyngier@....com,
        daniel.lezcano@...aro.org, tglx@...utronix.de, mingo@...nel.org,
        longman@...hat.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v2] clocksource/arm_arch_timer: fix a lockdep
 warning

On Mon, Dec 10, 2018 at 02:19:53PM +0000, Valentin Schneider wrote:
> Hi,
> 
> On 10/12/2018 14:07, Peter Zijlstra wrote:
> [...]
> > ---
> >  kernel/cpu.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index 91d5c38eb7e5..e1ee8caf28b5 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -313,6 +313,8 @@ void cpus_write_unlock(void)
> >  
> >  void lockdep_assert_cpus_held(void)
> >  {
> > +	if (system_state < SYSTEM_RUNNING)
> > +		return;
> >  	percpu_rwsem_assert_held(&cpu_hotplug_lock);
> >  }
> >  
> 
> Kinda hijacking the thread here - is that something we'd want to replace 
> 
>     40fa3780bac2 ("sched/core: Take the hotplug lock in sched_init_smp()")
> 
> with?
>  

Possibly; and I have vague memories of other people running into this
same thing too.