linux-kernel - Re: [PATCH v3] xen/smp: Use die_complete completion when taking CPU down

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Date:	Wed, 29 Oct 2014 15:37:53 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	hpa@...or.com, mingo@...hat.com, tglx@...utronix.de
CC:	david.vrabel@...rix.com, konrad.wilk@...cle.com,
	tianyu.lan@...el.com, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v3] xen/smp: Use die_complete completion when taking CPU
 down

On 10/22/2014 01:09 PM, Boris Ostrovsky wrote:
> Commit 2ed53c0d6cc9 ("x86/smpboot: Speed up suspend/resume by avoiding
> 100ms sleep for CPU offline during S3") introduced completions to CPU
> offlining process. These completions are not initialized on Xen kernels
> causing a panic in play_dead_common().
>
> Move handling of die_complete into common routines to make them
> available to Xen guests.
>
> (While at it, move die_complete definition under #ifdef CONFIG_HOTPLUG_CPU)
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Reviewed-by: David Vrabel <david.vrabel@...rix.com>
> ---
>
> v3: Don't #ifdef function prototypes in smp.h
> v2: Keep die_complete private to smpboot.c
>
>
>   arch/x86/include/asm/smp.h |  1 +
>   arch/x86/kernel/smpboot.c  | 13 +++++++++++--
>   arch/x86/xen/smp.c         |  3 +++
>   3 files changed, 15 insertions(+), 2 deletions(-)


Does anything else need to be done in this patch? We have CPU hotplug 
broken currently in Xen and it would be nice to have it fixed in rc3.

-boris


>
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 8cd27e0..8cd1cc3 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -150,6 +150,7 @@ static inline void arch_send_call_function_ipi_mask(const struct cpumask *mask)
>   }
>   
>   void cpu_disable_common(void);
> +void cpu_die_common(unsigned int cpu);
>   void native_smp_prepare_boot_cpu(void);
>   void native_smp_prepare_cpus(unsigned int max_cpus);
>   void native_smp_cpus_done(unsigned int max_cpus);
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 2d5200e..6fe0fc1 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -102,7 +102,9 @@ DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
>   DEFINE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);
>   EXPORT_PER_CPU_SYMBOL(cpu_info);
>   
> +#ifdef CONFIG_HOTPLUG_CPU
>   static DEFINE_PER_CPU(struct completion, die_complete);
> +#endif
>   
>   atomic_t init_deasserted;
>   
> @@ -1309,6 +1311,8 @@ void cpu_disable_common(void)
>   {
>   	int cpu = smp_processor_id();
>   
> +	init_completion(&per_cpu(die_complete, smp_processor_id()));
> +
>   	remove_siblinginfo(cpu);
>   
>   	/* It's now safe to remove this processor from the online map */
> @@ -1327,16 +1331,21 @@ int native_cpu_disable(void)
>   		return ret;
>   
>   	clear_local_APIC();
> -	init_completion(&per_cpu(die_complete, smp_processor_id()));
>   	cpu_disable_common();
>   
>   	return 0;
>   }
>   
> +void cpu_die_common(unsigned int cpu)
> +{
> +	wait_for_completion_timeout(&per_cpu(die_complete, cpu), HZ);
> +}
> +
>   void native_cpu_die(unsigned int cpu)
>   {
>   	/* We don't do anything here: idle task is faking death itself. */
> -	wait_for_completion_timeout(&per_cpu(die_complete, cpu), HZ);
> +
> +	cpu_die_common(cpu);
>   
>   	/* They ack this in play_dead() by setting CPU_DEAD */
>   	if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 8650cdb..4c071ae 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -510,6 +510,9 @@ static void xen_cpu_die(unsigned int cpu)
>   		current->state = TASK_UNINTERRUPTIBLE;
>   		schedule_timeout(HZ/10);
>   	}
> +
> +	cpu_die_common(cpu);
> +
>   	xen_smp_intr_free(cpu);
>   	xen_uninit_lock_cpu(cpu);
>   	xen_teardown_timer(cpu);

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