linux-kernel - Re: [PATCH v2] arm64: Reduce verbosity on SMP CPU stop

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Message-ID: <20160418121930.GH28645@arm.com>
Date:	Mon, 18 Apr 2016 13:19:31 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jan Glauber <jan.glauber@...iumnetworks.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] arm64: Reduce verbosity on SMP CPU stop

On Mon, Apr 18, 2016 at 09:43:33AM +0200, Jan Glauber wrote:
> On Fri, Apr 15, 2016 at 12:37:06PM +0100, Will Deacon wrote:
> > You can remove stop_lock altogether now, right? I also wonder whether
> > it would be worth printing out which CPUs are still online in the case where
> > we fail to stop all the secondaries?
> 
> Sorry, I've been a bit offline. Yes, the stop_lock can also be removed. 
> 
> How about below patch that prints the CPU ids for all CPUs that failed
> to stop?

Yeah, this looks better, thanks. We might want to clear the "stopper"
CPU from the mask, but it's hard to really care that much.

Will

> 
> Jan
> 
> --------------------------------
> 
> When CPUs are stopped during an abnormal operation like panic
> for each CPU a line is printed and the stack trace is dumped.
> 
> This information is only interesting for the aborting CPU
> and on systems with many CPUs it only makes it harder to
> debug if after the aborting CPU the log is flooded with data
> about all other CPUs too.
> 
> Therefore remove the stack dump and printk of other CPUs
> and only print a single line that the other CPUs are going to be
> stopped and, in case any CPUs remain online list them.
> 
> Signed-off-by: Jan Glauber <jglauber@...ium.com>
> ---
>  arch/arm64/kernel/smp.c | 16 +++++-----------
>  1 file changed, 5 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index b2d5f4e..29f4e37 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -763,21 +763,11 @@ void arch_irq_work_raise(void)
>  }
>  #endif
>  
> -static DEFINE_RAW_SPINLOCK(stop_lock);
> -
>  /*
>   * ipi_cpu_stop - handle IPI from smp_send_stop()
>   */
>  static void ipi_cpu_stop(unsigned int cpu)
>  {
> -	if (system_state == SYSTEM_BOOTING ||
> -	    system_state == SYSTEM_RUNNING) {
> -		raw_spin_lock(&stop_lock);
> -		pr_crit("CPU%u: stopping\n", cpu);
> -		dump_stack();
> -		raw_spin_unlock(&stop_lock);
> -	}
> -
>  	set_cpu_online(cpu, false);
>  
>  	local_irq_disable();
> @@ -872,6 +862,9 @@ void smp_send_stop(void)
>  		cpumask_copy(&mask, cpu_online_mask);
>  		cpumask_clear_cpu(smp_processor_id(), &mask);
>  
> +		if (system_state == SYSTEM_BOOTING ||
> +		    system_state == SYSTEM_RUNNING)
> +			pr_crit("SMP: stopping secondary CPUs\n");
>  		smp_cross_call(&mask, IPI_CPU_STOP);
>  	}
>  
> @@ -881,7 +874,8 @@ void smp_send_stop(void)
>  		udelay(1);
>  
>  	if (num_online_cpus() > 1)
> -		pr_warning("SMP: failed to stop secondary CPUs\n");
> +		pr_warning("SMP: failed to stop secondary CPUs %*pbl\n",
> +			   cpumask_pr_args(cpu_online_mask));
>  }
>  
>  /*
> -- 
> 1.9.1
>