Subject: Re: [PATCH] led: simplify led_trigger_register_simple
From: Richard Purdie <rpurdie@linux.intel.com>
To: felipe.balbi@nokia.com
Cc: me@felipebalbi.com, linux-kernel@vger.kernel.org,
       Anton Vorontsov <cbou@mail.ru>, David Woodhouse <dwmw2@infradead.org>,
       Greg KH <greg@kroah.com>, Pierre Ossman <drzeus@drzeus.cx>
In-Reply-To: <20081120141438.GK7476@gandalf.research.nokia.com>
References: <1226545753-6640-1-git-send-email-me@felipebalbi.com>
	 <1226579912.5402.21.camel@dax.rpnet.com> <20081113181407.GC17166@frodo>
	 <20081113191046.GA25855@frodo> <1227188008.22263.9.camel@ted>
	 <20081120141438.GK7476@gandalf.research.nokia.com>
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Date: Thu, 20 Nov 2008 14:45:59 +0000
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On Thu, 2008-11-20 at 16:14 +0200, Felipe Balbi wrote:
> > In answer to your question about kfree, I agree it needs to be called
> > upon error. The callers should just be calling
> > led_trigger_unregister_simple() in their failure paths though which
> > should take care of all problems? I know we used to register the simple
> > triggers late in paths so no error handling was needed to keep the code
> > simple and minimise the LED triggers impact on those systems.
> 
> Well, led_trigger_register_simple() doesn't return anything. Imagine
> led_trigger_register_simple() fails, but the driver author decides
> it's not a failure if, let's say, a led doesn't turn on when we insert
> a mmc card to the slot since it doesn't change functionality.
> 
> Now, imagine the user notes the led is not turning on and decides to
> unload and reload the module to try again. Once again the led doesn't go
> on. If the user keeps trying, it's quite a dangerous memory leak, right
> ?

So we have the module loading and one of two things happens:

led_trigger_register_simple() succeeds
led_trigger_register_simple() fails (probably from kmalloc failure)

The module doesn't know or care which happened. When the module unloads
it calls led_trigger_unregister_simple() which will free the memory in
the success case and do nothing in the case where it had failed.

So there is no memory leak?

Cheers,

Richard

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