[tip: irq/msi] cleanup: Provide retain_and_null_ptr()

tip-bot2 for Thomas Gleixner
2025-04-09T18:54:37Z

The following commit has been merged into the irq/msi branch of tip:

Commit-ID: 092d00ead733563f6d278295e0b5c5f97558b726
Gitweb: https://git.kernel.org/tip/092d00ead733563f6d278295e0b5c5f97558b726
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Wed, 19 Mar 2025 11:56:38 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 09 Apr 2025 20:47:29 +02:00

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
---
include/linux/cleanup.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index 7e57047..7093e1d 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...):