linux-kernel - Re: [PATCH cpuset] Use rebuild_sched_domains() in cpuset_hotplug

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Date:	Wed, 3 Apr 2013 17:32:39 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
CC:	<linux-kernel@...r.kernel.org>, <tj@...nel.org>
Subject: Re: [PATCH cpuset] Use rebuild_sched_domains() in cpuset_hotplug_workfn()

On 2013/4/2 15:16, Li Zhong wrote:
> In cpuset_hotplug_workfn(), partition_sched_domains() is called without
> hotplug lock held, which is actually needed (stated in the function
> header of partition_sched_domains()). 
> 
> This patch tries to use rebuild_sched_domains() to solve the above
> issue, and makes the code looks a little simpler.
> 

I guess you found this just by code inspection, right?

The change looks fine and safe at a first glance, but we don't have
time to review the patch for now.

However I don't know why partition_sched_domains() has to be called
with hotplug lock held.

After a quick scan, seems the only place in partition_sched_domains()
that might need hotplug lock is arch_update_cpu_topology().

It would be better if you had CCed the scheduler guys...They may
know the answer.

> Signed-off-by: Li Zhong <zhong@...ux.vnet.ibm.com>
> ---
>  kernel/cpuset.c |   13 ++-----------
>  1 files changed, 2 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 4f9dfe4..515a713 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -2222,17 +2222,8 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
>  	flush_workqueue(cpuset_propagate_hotplug_wq);
>  
>  	/* rebuild sched domains if cpus_allowed has changed */
> -	if (cpus_updated) {
> -		struct sched_domain_attr *attr;
> -		cpumask_var_t *doms;
> -		int ndoms;
> -
> -		mutex_lock(&cpuset_mutex);
> -		ndoms = generate_sched_domains(&doms, &attr);
> -		mutex_unlock(&cpuset_mutex);
> -
> -		partition_sched_domains(ndoms, doms, attr);
> -	}
> +	if (cpus_updated)
> +		rebuild_sched_domains();
>  }
>  


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