Re: [PATCH] kthread: Prevent unpark race which puts threads on the wrong cpu

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 04/11/2013 05:13 PM, Srivatsa S. Bhat wrote:
[...] 
> So Dave, could you kindly test the below patch on mainline?
> 

BTW, you don't need to try out any of the previous patches that I sent,
just this one is good enough. Thanks!

Regards,
Srivatsa S. Bhat

> 
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 691dc2e..9558355 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -308,6 +308,15 @@ struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
>  	to_kthread(p)->cpu = cpu;
>  	/* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
>  	kthread_park(p);
> +
> +	/*
> +	 * Wait for p->on_rq to be reset to 0, to ensure that the per-cpu
> +	 * migration thread (which belongs to the stop_task sched class)
> +	 * doesn't run until the cpu is actually onlined and the thread is
> +	 * unparked.
> +	 */
> +	if (!wait_task_inactive(p, TASK_INTERRUPTIBLE))
> +		WARN_ON(1);
>  	return p;
>  }
>