linux-kernel - Re: [PATCH 5/7] x86/mcheck: reorganize the hotplug callbacks

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Date:   Fri, 11 Nov 2016 19:44:53 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, rt@...utronix.de,
        Tony Luck <tony.luck@...el.com>, linux-edac@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH 5/7] x86/mcheck: reorganize the hotplug callbacks

On Thu, Nov 10, 2016 at 06:44:45PM +0100, Sebastian Andrzej Siewior wrote:
> Initially I wanted to remove mcheck_cpu_init() from identify_cpu() and let it
> become an independent early hotplug callback. The main problem here was that
> the init on the boot CPU may happen too late
> (device_initcall_sync(mcheck_init_device)) and nobody wanted to risk receiving
> and MCE event at boot time leading to a shutdown (if the MCE feature is not yet
> enabled).
> 
> Here is attempt two: the timming stays as-is but the ordering of the functions

			   timing

> is changed:
> - mcheck_cpu_init() (which is run from identify_cpu()) will setup the timer
>   struct but won't fire the timer. This is moved to CPU_ONLINE since its
>   cleanup part is in CPU_DOWN_PREPARE. So if it is okay to stop the timer early
>   in the shutdown phase, it should be okay to start it late in the bring up phase.
> 
> - CPU_DOWN_PREPARE disables the MCE feature flags for !INTEL CPUs in

		     disables the MCE error reporting...

>   mce_disable_cpu(). If a failure occures it would be re-enabled on all vendor

				    occurs

>   CPUs (including Intel where it was not disabled during shutdown). To keep this
>   working I am moving it to CPU_ONLINE. smp_call_function_single() is dropped
>   beause the notifier runs nowdays on the target CPU.

"... because the notifier runs on the target CPU now."

Please run your commit messages text through a spellchecker.

> - CPU_ONLINE is invoking mce_device_create() + mce_threshold_create_device()
>   but its cleanup part is in CPU_DEAD (mce_threshold_remove_device() and
>   mce_device_remove()). In order to keep this symmetrical I am moving the clean
>   up from CPU_DEAD to CPU_DOWN_PREPARE.

   cleanup

> 
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: linux-edac@...r.kernel.org
> Cc: x86@...nel.org
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  arch/x86/kernel/cpu/mcheck/mce.c | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index 052b5e05c3c4..3da6fd94fa2e 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -1771,6 +1771,9 @@ void (*machine_check_vector)(struct pt_regs *, long error_code) =
>   */
>  void mcheck_cpu_init(struct cpuinfo_x86 *c)
>  {
> +	struct timer_list *t = this_cpu_ptr(&mce_timer);
> +	unsigned int cpu = smp_processor_id();
> +
>  	if (mca_cfg.disabled)
>  		return;
>  
> @@ -1796,7 +1799,7 @@ void mcheck_cpu_init(struct cpuinfo_x86 *c)
>  	__mcheck_cpu_init_generic();
>  	__mcheck_cpu_init_vendor(c);
>  	__mcheck_cpu_init_clear_banks();
> -	__mcheck_cpu_init_timer();
> +	setup_pinned_timer(t, mce_timer_fn, cpu);

Why not leave all that setup stuff in __mcheck_cpu_init_timer() ?

...

> @@ -2517,11 +2518,10 @@ mce_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
>  			mce_device_remove(cpu);
>  			return NOTIFY_BAD;
>  		}
> -
> +		mce_reenable_cpu();
> +		mce_start_timer(cpu, t);
>  		break;
>  	case CPU_DEAD:
> -		mce_threshold_remove_device(cpu);
> -		mce_device_remove(cpu);
>  		mce_intel_hcpu_update(cpu);
>  
>  		/* intentionally ignoring frozen here */

There's another place for cpuhp_tasks_frozen replacement here:

                /* intentionally ignoring frozen here */
                if (!(action & CPU_TASKS_FROZEN))
                        cmci_rediscover();

into

		if (!cpuhp_tasks_frozen)
			cmci_rediscover();

> @@ -2529,12 +2529,11 @@ mce_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
>  			cmci_rediscover();
>  		break;
>  	case CPU_DOWN_PREPARE:
> -		smp_call_function_single(cpu, mce_disable_cpu, &action, 1);
> +		mce_disable_cpu();
>  		del_timer_sync(t);
> -		break;
> -	case CPU_DOWN_FAILED:
> -		smp_call_function_single(cpu, mce_reenable_cpu, &action, 1);
> -		mce_start_timer(cpu, t);
> +
> +		mce_threshold_remove_device(cpu);
> +		mce_device_remove(cpu);
>  		break;
>  	}
>  
> -- 
> 2.10.2
> 
> 

-- 
Regards/Gruss,
    Boris.

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