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Date:   Tue, 13 Jun 2023 12:55:22 +0200
From:   Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [PATCH v3 03/57] locking: Introduce __cleanup() based
 infrastructure
Message-ID: <20230613105522.GU4253@hirez.programming.kicks-ass.net>
References: <20230612090713.652690195@infradead.org>
 <20230612093537.614161713@infradead.org>
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On Mon, Jun 12, 2023 at 11:07:16AM +0200, Peter Zijlstra wrote:

> --- /dev/null
> +++ b/include/linux/cleanup.h
> @@ -0,0 +1,167 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __LINUX_GUARDS_H
> +#define __LINUX_GUARDS_H
> +
> +#include <linux/compiler.h>
> +
> +/*
> + * DEFINE_FREE(name, type, free):
> + *	simple helper macro that defines the required wrapper for a __free()
> + *	based cleanup function. @free is an expression using '_T' to access
> + *	the variable.
> + *
> + * __free(name):
> + *	variable attribute to add a scoped based cleanup to the variable.
> + *

	no_free_ptr(var):
	  like a non-atomic xchg(var, NULL), such that the cleanup
	  function will be inhibited -- provided it sanely deals with a
	  NULL value.

> + * return_ptr(p):
> + *	returns p while inhibiting the __free().
> + *
> + * Ex.
> + *
> + * DEFINE_FREE(kfree, void *, if (_T) kfree(_T))
> + *
> + *	struct obj *p = kmalloc(...);

That should obviously have been:

	struct obj *p __free(kfree) = kmalloc(...);

> + *	if (!p)
> + *		return NULL;
> + *
> + *	if (!init_obj(p))
> + *		return NULL;
> + *
> + *	return_ptr(p);
> + */
> +
> +#define DEFINE_FREE(name, type, free) \
> +	static inline void __free_##name(void *p) { type _T = *(type *)p; free; }
> +
> +#define __free(name)	__cleanup(__free_##name)
> +
> +#define no_free_ptr(p) \
> +	({ __auto_type __ptr = (p); (p) = NULL; __ptr; })
> +
> +#define return_ptr(p)	return no_free_ptr(p)