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

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Message-ID: <YcLkA0e48+xuGsHk@hovoldconsulting.com>
Date:   Wed, 22 Dec 2021 09:38:27 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Rafał Miłecki <zajec5@...il.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH] nvmem: fix unregistering device in nvmem_register()
 error path

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@...ecki.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.

Johan