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

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Message-ID: <5166FBFB.2030703@sr71.net>
Date:	Thu, 11 Apr 2013 11:07:55 -0700
From:	Dave Hansen <dave@...1.net>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Borislav Petkov <bp@...en8.de>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>, dhillf@...il.com,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] kthread: Prevent unpark race which puts threads on the
 wrong cpu

On 04/11/2013 03:19 AM, Thomas Gleixner wrote:
> --- linux-2.6.orig/kernel/smpboot.c
> +++ linux-2.6/kernel/smpboot.c
> @@ -185,8 +185,18 @@ __smpboot_create_thread(struct smp_hotpl
>  	}
>  	get_task_struct(tsk);
>  	*per_cpu_ptr(ht->store, cpu) = tsk;
> -	if (ht->create)
> -		ht->create(cpu);
> +	if (ht->create) {
> +		/*
> +		 * Make sure that the task has actually scheduled out
> +		 * into park position, before calling the create
> +		 * callback. At least the migration thread callback
> +		 * requires that the task is off the runqueue.
> +		 */
> +		if (!wait_task_inactive(tsk, TASK_PARKED))
> +			WARN_ON(1);
> +		else
> +			ht->create(cpu);
> +	}
>  	return 0;
>  }

This one appears to be doing the trick.  I'll run the cpus in an
online/offline loop for a bit and make sure it's stable.  It's passed
several round so far, which is way more than it's done up to this point,
though.
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