Messages in this thread | | | Date | Wed, 22 Dec 2021 10:34:42 +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 10:24:33AM +0100, Johan Hovold wrote: > On Wed, Dec 22, 2021 at 10:03:17AM +0100, Johan Hovold wrote: > > On Wed, Dec 22, 2021 at 09:56:29AM +0100, Greg Kroah-Hartman wrote: > > > On Wed, Dec 22, 2021 at 09:38:27AM +0100, 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. > > > > > > A short search found almost everyone getting this wrong. Arguably > > > platform_device_register() can clean up properly on its own if we want > > > it to do so. Will take a lot of auditing of the current codebase first > > > to see if it's safe... > > > > Right, but I found at least a couple of callers getting it it right, so > > changing the behaviour now risks introducing a double free (which is > > worse than a memleak on registration failure). But yeah, a careful > > review might suffice. > > Actually, I'm not sure we can (should) change > platform_device_register(). The platform device has been allocated by > the caller and it would be quite counterintuitive to have the > registration function deallocate that memory if registration fails. > > Heh, we even have statically allocated structures being registered with > this function and we certainly don't want the helper to try to free > those.
Yeah, it's a mess. I'll try to look at it this break if things calm down...
greg k-h
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