linux-kernel - Re: [PATCH 1/7] Freezer: Read PF_BORROWED

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Date:	Sat, 12 May 2007 03:20:24 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 1/7] Freezer: Read PF_BORROWED_MM in a nonracy way

On 05/11, Linus Torvalds wrote:
>
> On Fri, 11 May 2007, Rafael J. Wysocki wrote:
> > 
> > Therefore, by taking the task_lock() here we make sure that the condition
> > is alyways false when we check it for kernel threads.
> 
> Why *test* it then and return anything?
> 
> Why not just doa "task_lock(p); task_unlock(p);" with no return value? 

because we should not freeze a kernel thread at FREEZER_USER_SPACE stage?

without task_lock() we can see "p->mm != NULL" but not PF_BORROWED_MM.

Oleg.

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