Re: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset

[Oleg Nesterov]

On 08/24, Cliff Wickman wrote:
> 
> @@ -5091,6 +5092,17 @@ restart:
>  	if (dest_cpu == NR_CPUS)
>  		dest_cpu = any_online_cpu(p->cpus_allowed);
>  
> +	/* try to stay on the same cpuset */
> +	if (dest_cpu == NR_CPUS) {
> +		/*
> +		 * The cpuset_cpus_allowed_lock() variant of
> +		 * cpuset_cpus_allowed() will not block
> +		 * It must be called within calls to cpuset_lock/cpuset_unlock.
> +		 */
> +		p->cpus_allowed = cpuset_cpus_allowed_lock(p);
> +		dest_cpu = any_online_cpu(p->cpus_allowed);

Ugh, didn't notice while reading this patch.

We shouldn't change ->cpus_allowed without rq->lock. Please look what
the current code does in "/* No more Mr. Nice Guy. */" case.

Oleg.

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