linux-kernel - Re: [PATCH] nvmem: fix unregistering device in nvmem

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Date:   Wed, 22 Dec 2021 10:30:06 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Rafał Miłecki <rafal@...ecki.pl>
Cc:     Johan Hovold <johan@...nel.org>,
        Rafał Miłecki <zajec5@...il.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvmem: fix unregistering device in nvmem_register()
 error path

On Wed, Dec 22, 2021 at 10:16:20AM +0100, Rafał Miłecki wrote:
> On 22.12.2021 10:08, Johan Hovold wrote:
> > On Wed, Dec 22, 2021 at 10:00:03AM +0100, Rafał Miłecki wrote:
> > > On 22.12.2021 09:38, Johan Hovold wrote:
> > 
> > > > 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.
> > 
> > Yes, and we all agree that it's not the best interface. But it exists,
> > and changing it now risks introducing worse problem than a minor, mostly
> > theoretical, memleak.
> 
> Thanks for confirming that, I was wondering if it's just my mind that
> doesn't find this design clear enough.
> 
> Now, assuming this design isn't perfect and some purists would like it
> cleaned up:
> 
> Would that make sense to introduce something like
> 1. device_register2() / device_add2()
> and
> 2. platform_device_register2() / platform_device_add2()
> 
> that would *not* require calling *_put() on failure? Then start
> converting existing drivers to those new (clearner?) helpers?

See my other response, but no, this is not a good idea.
device_register() is correct as-is, but platform_device_register()
isn't.

thanks,

greg k-h