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

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Message-ID: <c5b76d10-c270-21e5-e528-9aa20b1384ef@milecki.pl>
Date:   Wed, 22 Dec 2021 10:16:20 +0100
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     Johan Hovold <johan@...nel.org>,
        Rafał Miłecki <zajec5@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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 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?