Messages in this thread | | | Date | Wed, 22 Dec 2021 10:29:25 +0100 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH] nvmem: fix unregistering device in nvmem_register() error path |
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On Wed, Dec 22, 2021 at 10:00:03AM +0100, Rafał Miłecki wrote: > On 22.12.2021 09:38, Johan Hovold wrote: > > On Wed, Dec 22, 2021 at 08:44:44AM +0100, Greg Kroah-Hartman wrote: > > > On Tue, Dec 21, 2021 at 06:46:01PM +0100, Rafał Miłecki wrote: > > > > On 21.12.2021 17:06, Greg Kroah-Hartman wrote: > > > > > On Tue, Dec 21, 2021 at 04:45:50PM +0100, Rafał Miłecki wrote: > > > > > > From: Rafał Miłecki <rafal@milecki.pl> > > > > > > > > > > > > 1. Drop incorrect put_device() calls > > > > > > > > > > > > If device_register() fails then underlaying device_add() takes care of > > > > > > calling put_device() if needed. There is no need to do that in a driver. > > > > > > > > > > Did you read the documentation for device_register() that says: > > > > > > > > > > * NOTE: _Never_ directly free @dev after calling this function, even > > > > > * if it returned an error! Always use put_device() to give up the > > > > > * reference initialized in this function instead. > > > > > > > > I clearly tried to be too smart and ignored documentation. > > > > > > > > I'd say device_add() behaviour is rather uncommon and a bit unintuitive. > > > > Most kernel functions are safe to assume to do nothing that requires > > > > cleanup if they fail. > > > > > > > > E.g. if I call platform_device_register() and it fails I don't need to > > > > call anything like platform_device_put(). I just free previously > > > > allocated memory. > > > > > > And that is wrong. > > > > It seems Rafał is mistaken here too; you certainly need to call > > platform_device_put() if platform_device_register() fail, even if many > > current users do appear to get this wrong. > > Yes I was! Gosh I made up that "platform_device_put()" name and only > now I realized it actually exists! > > I stand by saying this design is really misleading. Even though > platform_device_put() was obviously a bad example. > > Please remember I'm just a minor kernel developer however in my humble > opinion behaviour of device_register() and platform_device_register() > should be changed. > > If any function fails I expect: > 1. That function to clean up its mess if any > 2. Me to be responsible to clean up my mess if any > > This is how "most" code (whatever it means) works. > 1. If POSIX snprintf() fails I'm not expected to call *printf_put() sth > 2. If POSIX bind() fails I'm not expected to call bind_put() sth > 3. (...) > > I'm not sure if those are the best examples but you should get my point.
I do understand, and for platform_device_register() I agree with you.
But for device_register() we can not do this as the driver core is not the "owner" of the structure being passed into it. If you call device_register() you are bus and you have to know how to handle an error here as there is usually much more that needs to be done that a device_put() can not do by the core.
Yes, it's well down on the "Rusty's API usability scale", but it is documented well and in a number of places for device_register().
platform_device_register() is not documented, and that's not good, so we should fix it up. Although there's the larger issue of everyone using static 'struct device' for this which is yet-another-reason I hate the platform device code.
thanks,
greg k-h
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