linux-kernel - Re: [linux-pm] [PATCH 3/5] PM: Support for system-wide power transitions in generic power domains

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Message-ID: <Pine.LNX.4.44L0.1105091032190.2002-100000@iolanthe.rowland.org>
Date:	Mon, 9 May 2011 10:36:03 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	<linux-sh@...r.kernel.org>, Greg KH <gregkh@...e.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Guennadi Liakhovetski <g.liakhovetski@....de>
Subject: Re: [linux-pm] [PATCH 3/5] PM: Support for system-wide power
 transitions in generic power domains

On Sun, 8 May 2011, Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> Make generic power domains support system-wide power transitions
> (system suspend and hibernation).  Add suspend, resume, freeze and
> thaw callbacks to be associated with struct generic_power_domain
> objects and make pm_genpd_init() use them as appropriate.

...

> Index: linux-2.6/drivers/base/power/domain.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/domain.c
> +++ linux-2.6/drivers/base/power/domain.c
> @@ -273,6 +273,280 @@ static int pm_genpd_runtime_resume(struc
>  
>  #endif /* CONFIG_PM_RUNTIME */
>  
> +#ifdef CONFIG_PM_SLEEP
> +
> +/**
> + * pm_genpd_powered_down - Check if power has been removed from a power domain.
> + * @genpd: Power domain to check.
> + */
> +static bool pm_genpd_powered_down(struct generic_power_domain *genpd)
> +{
> +	bool ret;
> +
> +	mutex_lock(&genpd->lock);
> +	ret = genpd->power_is_off;
> +	mutex_unlock(&genpd->lock);
> +
> +	return ret;
> +}

What is the purpose of the mutex?  On the face of it, there's nothing 
to prevent another thread from changing the domain's power state in 
between the mutex_unlock() call and the return statement.

Alan Stern

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