linux-kernel - Re: [RFC][PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks

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Message-Id: <200706190815.18292.nigel@nigel.suspend2.net>
Date:	Tue, 19 Jun 2007 08:15:13 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	Uli Luckas <u.luckas@...d.de>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [RFC][PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks

Hi.

On Tuesday 19 June 2007 07:29:58 Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> At present, if a user mode helper is running while 
usermodehelper_pm_callback()
> is executed, the helper may be frozen and the completion in
> call_usermodehelper_exec() won't be completed until user space processes are
> thawed.  As a result, the freezing of kernel threads may fail, which is not
> desirable.
> 
> Prevent this from happening by introducing a counter of running user mode
> helpers and allowing usermodehelper_pm_callback() to succeed for
> action = PM_HIBERNATION_PREPARE or action = PM_SUSPEND_PREPARE only if there
> are no helpers running.  [Namely, usermodehelper_pm_callback() waits for at 
most
> RUNNING_HELPERS_TIMEOUT for the number of running helpers to become zero and
> fails if that doesn't happen.]
> 
> Special thanks to Uli Luckas <u.luckas@...d.de> for reviewing the previous
> versions of this patch and for very useful comments.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>

Acked-by: Nigel Cunningham <nigel@...el.suspend2.net>

Regards,

Nigel

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