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    SubjectRe: [PATCH] led: simplify led_trigger_register_simple
    On Thu, Nov 20, 2008 at 02:45:59PM +0000, ext Richard Purdie wrote:
    > 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?

    Hmmm, you are right. Didin't think about the exit path. But freeing in
    led_triger_register_simple() if led_trigger_register() fails, also
    doesn't seem wrong.


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