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

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Date:	Mon, 16 Sep 2013 10:22:53 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Wang YanQing <udknight@...il.com>, Jiang Liu <liuj97@...il.com>,
	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 <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v2 01/25] Revert smp: Fix SMP function call empty cpu
 mask race

On 09/14/2013 12:43 PM, Wang YanQing wrote:
> On Sat, Sep 14, 2013 at 12:41:36PM +0800, Wang YanQing wrote:
>> 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.
> 
> Add Cc:gang.chen@...anux.com

Thank you, and, I should continue trying to familiar with kernel step by
step.

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-- 
Chen Gang

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