From 092d00ead733563f6d278295e0b5c5f97558b726 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 19 Mar 2025 11:56:38 +0100 Subject: [PATCH] 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 Reviewed-by: Jonathan Cameron Reviewed-by: James Bottomley Link: https://lore.kernel.org/all/20250319105506.083538907@linutronix.de --- include/linux/cleanup.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h index 7e57047e1564..7093e1d08af0 100644 --- a/include/linux/cleanup.h +++ b/include/linux/cleanup.h @@ -216,6 +216,25 @@ const volatile void * __must_check_fn(const volatile void *val) #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...): -- 2.25.1