linux-kernel - Re: [PATCH 3/3] PM / hibernate / memory hotplug: Rework mutual exclusion

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Message-ID: <1377908599.10300.901.camel@misato.fc.hp.com>
Date:	Fri, 30 Aug 2013 18:23:19 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	linux-mm@...ck.org
Subject: Re: [PATCH 3/3] PM / hibernate / memory hotplug: Rework mutual
 exclusion

On Thu, 2013-08-29 at 23:18 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Since all of the memory hotplug operations have to be carried out
> under device_hotplug_lock, they won't need to acquire pm_mutex if
> device_hotplug_lock is held around hibernation.
> 
> For this reason, make the hibernation code acquire
> device_hotplug_lock after freezing user space processes and
> release it before thawing them.  At the same tim drop the
> lock_system_sleep() and unlock_system_sleep() calls from
> lock_memory_hotplug() and unlock_memory_hotplug(), respectively.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  kernel/power/hibernate.c |    4 ++++
>  kernel/power/user.c      |    2 ++
>  mm/memory_hotplug.c      |    4 ----
>  3 files changed, 6 insertions(+), 4 deletions(-)
> 
> Index: linux-pm/kernel/power/hibernate.c
> ===================================================================
> --- linux-pm.orig/kernel/power/hibernate.c
> +++ linux-pm/kernel/power/hibernate.c
> @@ -652,6 +652,7 @@ int hibernate(void)
>  	if (error)
>  		goto Exit;
>  
> +	lock_device_hotplug();

Since hibernate() can be called from sysfs, do you think the tool may
see this as a circular dependency with p_active again?  This shouldn't
be a problem in practice, though.

Thanks,
-Toshi

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