linux-kernel - Re: [PATCH 7/7] [RFC] APM emulation driver for class batteries

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Message-ID: <20070420082746.GA22992@elf.ucw.cz>
Date:	Fri, 20 Apr 2007 10:27:46 +0200
From:	Pavel Machek <pavel@....cz>
To:	Anton Vorontsov <cbou@...l.ru>
Cc:	linux-kernel@...r.kernel.org, kernel-discuss@...dhelds.org
Subject: Re: [PATCH 7/7] [RFC] APM emulation driver for class batteries

Hi!

> > > +static void (*old_apm_get_power_status)(struct apm_power_info*);
> > > +
> > > +static int __init apm_battery_init(void)
> > > +{
> > > +	printk(KERN_INFO "APM Battery Driver\n");
> > > +
> > > +	old_apm_get_power_status = apm_get_power_status;
> > > +	apm_get_power_status = apm_battery_apm_get_power_status;
> > > +	return 0;
> > > +}
> > > +
> > > +static void __exit apm_battery_exit(void)
> > > +{
> > > +	apm_get_power_status = old_apm_get_power_status;
> > > +	return;
> > > +}
> > 
> > Utterly unsafe.  What happens if some other module gets loaded which
> > does this, and then this module is unloaded followed by the other
> > module.  Result: Oops.
> 
> Right. And loading two modules which changing apm_get_power_status
> is a race already. Thus, APM interface needs a mutex.
> 
> Or pda_power should be marked "bool" in Kconfig, as it is done
> in arch/arm/common/sharpsl_pm.c. Sharpsl_pm is safe only because it
> can't be a module.

Just mark it bool, when you fix it with mutex, you can go back to
tristate.
								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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