linux-kernel - Re: [PATCH] checkpatch: add uninitialized pointer with _

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Message-ID: <CAMB6jUG+ES6XY7NL5TF-hFVDmz6O5rd9T-HNk7Q+pJA2_9g4Mw@mail.gmail.com>
Date: Thu, 23 Oct 2025 16:38:43 +0530
From: ally heev <allyheev@...il.com>
To: dan.j.williams@...el.com, Dwaipayan Ray <dwaipayanray1@...il.com>, 
	Lukas Bulwahn <lukas.bulwahn@...il.com>, Joe Perches <joe@...ches.com>, 
	Jonathan Corbet <corbet@....net>, Andy Whitcroft <apw@...onical.com>
Cc: workflows@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Dan Carpenter <dan.carpenter@...aro.org>, 
	David Hunter <david.hunter.linux@...il.com>, Shuah Khan <skhan@...uxfoundation.org>, 
	Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>, 
	linux-pm <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] checkpatch: add uninitialized pointer with __free
 attribute check

On Thu, Oct 23, 2025 at 4:01 PM ally heev <allyheev@...il.com> wrote:
> > I would go futher and suggest that the pattern of:
> >
> >       type foo __free(free_foo) = NULL;
> >
> > ...be made into a warning because that easily leads to situations where
> > declaration order is out of sync with allocation order. I.e. can be made
> > technically correct, but at a level of cleverness that undermines the
> > benefit.
>
> But, does this pattern cause any real issue? I found allocating memory
> later useful in cases like below
>
> arch/powerpc/perf/vpa-dtl.c
> ```
>
>         struct vpa_pmu_buf *buf __free(kfree) = NULL;
>         struct page **pglist __free(kfree) = NULL;
>
>         /* We need at least one page for this to work. */
>         if (!nr_pages)
>                 return NULL;
>
>         if (cpu == -1)
>                 cpu = raw_smp_processor_id();
>
>         buf = kzalloc_node(sizeof(*buf), GFP_KERNEL,
> cpu_to_node(cpu));
> ```
>

I will take this back. Found this in `include/linux/cleanup.h`
```
* Given that the "__free(...) = NULL" pattern for variables defined at
* the top of the function poses this potential interdependency problem
* the recommendation is to always define and assign variables in one
* statement and not group variable definitions at the top of the
* function when __free() is used.
```