linux-kernel - Re: [PATCH] kernel/kthread.c: need spin_lock_irq() for 'worker' before main looping, since it can "WARN

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Message-ID: <alpine.DEB.2.02.1306191041570.4013@ionos.tec.linutronix.de>
Date:	Wed, 19 Jun 2013 10:43:28 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Chen Gang <gang.chen@...anux.com>
cc:	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	laijs@...fujitsu.com, Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel/kthread.c: need spin_lock_irq() for 'worker'
 before main looping, since it can "WARN_ON(worker->task)".

On Wed, 19 Jun 2013, Chen Gang wrote:

> 
> Since "WARN_ON(worker->task)", we can not assume that 'worker->task'
> will be NULL before set 'current' to it.

It better is NULL and all that WARN_ON does is to verify that.
 
> So need let 'worker' lock protected too, just like it already lock
> protected all time in main looping.

No. That's pointless. This happens when the new worker starts up and
there is nothing which can modify worker->task at this point.
 
Thanks,

	tglx
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