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cleanup: Provide retain_and_null_ptr() 

In cases where an allocation is consumed by another function, the
allocation needs to be retained on success or freed on failure. The code
pattern is usually:

	struct foo *f = kzalloc(sizeof(*f), GFP_KERNEL);
	struct bar *b;

	,,,
	// Initialize f
	...
	if (ret)
		goto free;
        ...
	bar = bar_create(f);
	if (!bar) {
		ret = -ENOMEM;
	   	goto free;
	}
	...
	return 0;
free:
	kfree(f);
	return ret;

This prevents using __free(kfree) on @f because there is no canonical way
to tell the cleanup code that the allocation should not be freed.

Abusing no_free_ptr() by force ignoring the return value is not really a
sensible option either.

Provide an explicit macro retain_and_null_ptr(), which NULLs the cleanup
pointer. That makes it easy to analyze and reason about.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Link: https://lore.kernel.org/all/20250319105506.083538907@linutronix.de
pull/1250/head
Thomas Gleixner 2025-03-19 11:56:38 +01:00
parent 0af2f6be1b
commit 092d00ead7
1 changed files with 19 additions and 0 deletions
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19
include/linux/cleanup.h
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@ -216,6 +216,25 @@ const volatile void * __must_check_fn(const volatile void *val)
#define return_ptr(p) return no_free_ptr(p) #define return_ptr(p) return no_free_ptr(p)
/*
* Only for situations where an allocation is handed in to another function
* and consumed by that function on success.
*
* struct foo *f __free(kfree) = kzalloc(sizeof(*f), GFP_KERNEL);
*
* setup(f);
* if (some_condition)
* return -EINVAL;
* ....
* ret = bar(f);
* if (!ret)
* retain_and_null_ptr(f);
* return ret;
*
* After retain_and_null_ptr(f) the variable f is NULL and cannot be
* dereferenced anymore.
*/
#define retain_and_null_ptr(p) ((void)__get_and_null(p, NULL))
/* /*
* DEFINE_CLASS(name, type, exit, init, init_args...): * DEFINE_CLASS(name, type, exit, init, init_args...):