linux-kernel - Re: [patch 02/13] workqueue: Provide work_on_cpu

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Date:   Thu, 13 Apr 2017 19:11:32 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        "David S. Miller" <davem@...emloft.net>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Len Brown <lenb@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, Tejun Heo <tj@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [patch 02/13] workqueue: Provide work_on_cpu_safe()



At 04/13/2017 04:07 AM, Thomas Gleixner wrote:
> work_on_cpu() is not protected against CPU hotplug. For code which requires
> to be either executed on an online CPU or to fail if the CPU is not
> available the callsite would have to protect against CPU hotplug.
>
> Provide a function which does get/put_online_cpus() around the call to
> work_on_cpu() and fails the call with -ENODEV if the target CPU is not
> online.
>
> Preparatory patch to convert several racy task affinity manipulations.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Lai Jiangshan <jiangshanlai@...il.com>
> ---
>  include/linux/workqueue.h |    5 +++++
>  kernel/workqueue.c        |   23 +++++++++++++++++++++++
>  2 files changed, 28 insertions(+)
>
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -608,8 +608,13 @@ static inline long work_on_cpu(int cpu,
>  {
>  	return fn(arg);
>  }
> +static inline long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
> +{
> +	return fn(arg);
> +}
>  #else
>  long work_on_cpu(int cpu, long (*fn)(void *), void *arg);
> +long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg);
>  #endif /* CONFIG_SMP */
>
>  #ifdef CONFIG_FREEZER
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4735,6 +4735,29 @@ long work_on_cpu(int cpu, long (*fn)(voi
>  	return wfc.ret;
>  }
>  EXPORT_SYMBOL_GPL(work_on_cpu);
> +
> +/**

There is an extra '*' :)

Thanks,
	Liyang

> + * work_on_cpu_safe - run a function in thread context on a particular cpu
> + * @cpu: the cpu to run on
> + * @fn:  the function to run
> + * @arg: the function argument
> + *
> + * Disables CPU hotplug and calls work_on_cpu(). The caller must not hold
> + * any locks which would prevent @fn from completing.
> + *
> + * Return: The value @fn returns.
> + */
> +long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg)
> +{
> +	long ret = -ENODEV;
> +
> +	get_online_cpus();
> +	if (cpu_online(cpu))
> +		ret = work_on_cpu(cpu, fn, arg);
> +	put_online_cpus();
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(work_on_cpu_safe);
>  #endif /* CONFIG_SMP */
>
>  #ifdef CONFIG_FREEZER