linux-kernel - Re: [PATCH v3 2/2] gpio: sim: initialize a managed pointer when declaring it

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Message-ID: <ZQf22FxCiPe2GUcd@smile.fi.intel.com>
Date:   Mon, 18 Sep 2023 10:06:00 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        akpm@...ux-foundation.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 2/2] gpio: sim: initialize a managed pointer when
 declaring it

On Sun, Sep 17, 2023 at 11:12:25AM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> Variables managed with __free() should typically be initialized where
> they are declared so that the __free() callback is paired with its
> counterpart resource allocator. Fix the second instance of using
> __free() in gpio-sim to follow this pattern.

...

>  {
> -	struct gpio_sim_device *dev __free(kfree) = NULL;
>  	int id;
>  
> -	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +	struct gpio_sim_device *dev __free(kfree) = kzalloc(sizeof(*dev),
> +							    GFP_KERNEL);
>  	if (!dev)
>  		return ERR_PTR(-ENOMEM);

Aside: Oh, this might be a downside of the __free() sugar, as we can
theoretically end up with a code in the future like

	struct bar *foo;
	...
	struct baz *foo __free() = ...
	...

and I am not sure how it goes to work. Or relaxed variant with

	struct bar *foo;
	...
	{
		struct baz *foo __free() = ...
		...
	}

where we would have two variables with the same name, but different scope
(this, perhaps, would work, but I assume compiler should warn about shadowed
 name for the variable).

(Also what if in both cases bar == baz, i.e. same type?)

-- 
With Best Regards,
Andy Shevchenko