linux-kernel - Re: [PATCH v2 01/25] Revert smp: Fix SMP function call empty cpu mask race

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Date:	Sat, 14 Sep 2013 12:41:36 +0800
From:	Wang YanQing <udknight@...il.com>
To:	Jiang Liu <liuj97@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Shaohua Li <shli@...nel.org>, Jiang Liu <jiang.liu@...wei.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Kosina <trivial@...nel.org>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 01/25] Revert smp: Fix SMP function call empty cpu
 mask race

On Thu, Sep 12, 2013 at 12:07:05AM +0800, Jiang Liu wrote:
> From: Jiang Liu <jiang.liu@...wei.com>
> 
> Commit f44310b98ddb7 "smp: Fix SMP function call empty cpu mask race"
> introduced field call_function_data->cpumask_ipi to resolve a race
> condition in smp_call_function_many().
> 
> Later commit 9a46ad6d6df3 "smp: make smp_call_function_many() use logic
> similar to smp_call_function_single()" fixed the same issue in another
> way when optimizing smp_call_function_many(), which then obsoletes
> changes introduced by commit f44310b98ddb7. So revert it.
> 
> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
> Acked-by: Wang YanQing <udknight@...il.com>
> Cc: Jiang Liu <liuj97@...il.com>
> ---
>  kernel/smp.c | 16 ++--------------
>  1 file changed, 2 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/smp.c b/kernel/smp.c
> index fe9f773..a034712 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -23,7 +23,6 @@ enum {
>  struct call_function_data {
>  	struct call_single_data	__percpu *csd;
>  	cpumask_var_t		cpumask;
> -	cpumask_var_t		cpumask_ipi;
>  };
>  
>  static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
> @@ -47,9 +46,6 @@ hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
>  		if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
>  				cpu_to_node(cpu)))
>  			return notifier_from_errno(-ENOMEM);
> -		if (!zalloc_cpumask_var_node(&cfd->cpumask_ipi, GFP_KERNEL,
> -				cpu_to_node(cpu)))
> -			return notifier_from_errno(-ENOMEM);
>  		cfd->csd = alloc_percpu(struct call_single_data);
>  		if (!cfd->csd) {
>  			free_cpumask_var(cfd->cpumask);
> @@ -64,7 +60,6 @@ hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
>  	case CPU_DEAD:
>  	case CPU_DEAD_FROZEN:
>  		free_cpumask_var(cfd->cpumask);
> -		free_cpumask_var(cfd->cpumask_ipi);
>  		free_percpu(cfd->csd);
>  		break;
>  #endif
> @@ -255,9 +250,9 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
>  				csd = &__get_cpu_var(csd_data);
>  
>  			csd_lock(csd);
> -
>  			csd->func = func;
>  			csd->info = info;
> +
>  			generic_exec_single(cpu, csd, wait);
>  		} else {
>  			err = -ENXIO;	/* CPU not online */
> @@ -410,13 +405,6 @@ void smp_call_function_many(const struct cpumask *mask,
>  	if (unlikely(!cpumask_weight(cfd->cpumask)))
>  		return;
>  
> -	/*
> -	 * After we put an entry into the list, cfd->cpumask may be cleared
> -	 * again when another CPU sends another IPI for a SMP function call, so
> -	 * cfd->cpumask will be zero.
> -	 */
> -	cpumask_copy(cfd->cpumask_ipi, cfd->cpumask);
> -
>  	for_each_cpu(cpu, cfd->cpumask) {
>  		struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
>  		struct call_single_queue *dst =
> @@ -433,7 +421,7 @@ void smp_call_function_many(const struct cpumask *mask,
>  	}
>  
>  	/* Send a message to all CPUs in the map */
> -	arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
> +	arch_send_call_function_ipi_mask(cfd->cpumask);
>  
>  	if (wait) {
>  		for_each_cpu(cpu, cfd->cpumask) {
> -- 
> 1.8.1.2
Hi Liu and all

Commit 60c323699bb308404dcb60e8808531e02651578a 
(kernel/smp.c: free related resources when failure occurs in hotplug_cfd())
is a fix patch for commit you revert, and it had been merged into mainline.

So could you ajust your patch to revert it together? I don't think we need
a separate patch to revert 60c323699bb308404dcb60e8808531e02651578a, because
your patch haven't be merged.

Thanks.
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