linux-kernel - Re: [PATCH arm] Use common outgoing-CPU-notification code

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Message-ID: <20190617130657.GL26519@linux.ibm.com>
Date:   Mon, 17 Jun 2019 06:06:57 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux@....linux.org.uk, dietmar.eggemann@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH arm] Use common outgoing-CPU-notification code

On Mon, Jun 17, 2019 at 12:58:19PM +0100, Mark Rutland wrote:
> On Tue, Jun 11, 2019 at 12:24:10PM -0700, Paul E. McKenney wrote:
> > This commit removes the open-coded CPU-offline notification with new
> > common code.  In particular, this change avoids calling scheduler code
> > using RCU from an offline CPU that RCU is ignoring.  This is a minimal
> > change.  A more intrusive change might invoke the cpu_check_up_prepare()
> > and cpu_set_state_online() functions at CPU-online time, which would
> > allow onlining throw an error if the CPU did not go offline properly.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Cc: linux-arm-kernel@...ts.infradead.org
> > Cc: Russell King <linux@....linux.org.uk>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>
> 
> FWIW:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>
> 
> On the assumption that Russell is ok with this, I think this should be
> dropped into the ARM patch system [1].
> 
> Paul, are you familiar with that, or would you prefer that someone else
> submits the patch there? I can do so if you'd like.

I never have used this system, so please do drop it in there!  Let me
know when you have done so, and I will then drop it from -rcu.

							Thanx, Paul

> Thanks,
> Mark.
> 
> [1] https://www.armlinux.org.uk/developer/patches/info.php
> 
> > 
> > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> > index ebc53804d57b..8687d619260f 100644
> > --- a/arch/arm/kernel/smp.c
> > +++ b/arch/arm/kernel/smp.c
> > @@ -267,15 +267,13 @@ int __cpu_disable(void)
> >  	return 0;
> >  }
> >  
> > -static DECLARE_COMPLETION(cpu_died);
> > -
> >  /*
> >   * called on the thread which is asking for a CPU to be shutdown -
> >   * waits until shutdown has completed, or it is timed out.
> >   */
> >  void __cpu_die(unsigned int cpu)
> >  {
> > -	if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) {
> > +	if (!cpu_wait_death(cpu, 5)) {
> >  		pr_err("CPU%u: cpu didn't die\n", cpu);
> >  		return;
> >  	}
> > @@ -322,7 +320,7 @@ void arch_cpu_idle_dead(void)
> >  	 * this returns, power and/or clocks can be removed at any point
> >  	 * from this CPU and its cache by platform_cpu_kill().
> >  	 */
> > -	complete(&cpu_died);
> > +	(void)cpu_report_death();
> >  
> >  	/*
> >  	 * Ensure that the cache lines associated with that completion are
> > 
>