linux-kernel - Re: [PATCH] led: simplify led_trigger_register

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Message-Id: <1227192359.22263.23.camel@ted>
Date:	Thu, 20 Nov 2008 14:45:59 +0000
From:	Richard Purdie <rpurdie@...ux.intel.com>
To:	felipe.balbi@...ia.com
Cc:	me@...ipebalbi.com, linux-kernel@...r.kernel.org,
	Anton Vorontsov <cbou@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>,
	Greg KH <greg@...ah.com>, Pierre Ossman <drzeus@...eus.cx>
Subject: Re: [PATCH] led: simplify led_trigger_register_simple

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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