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

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Message-ID: <alpine.LFD.0.98.0705111555090.3986@woody.linux-foundation.org>
Date:	Fri, 11 May 2007 15:56:51 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...sign.ru>, 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 Fri, 11 May 2007, Rafael J. Wysocki wrote:
> 
> For user space processes this condition is always true.
> 
> For kernel threads:
> (1) the change of tsk->mm from NULL to a nonzero value is only made in
> fs/aio.c:use_mm() along with the setting of PF_BORROWED_MM under
> the task_lock(),
> (2) the change of tsk->mm from a nonzero value to NULL is only made in
> fs/aio.c:unuse_mm() along with the resetting of PF_BORROWED_MM
> under the task_lock().
> 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? 

As it is, it sounds like either the code is buggy, or it's pointless.

		Linus
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