linux-kernel - [tip: irq/msi] cleanup: Provide retain

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Message-ID: <174403631219.31282.15932130919927326104.tip-bot2@tip-bot2>
Date: Mon, 07 Apr 2025 14:31:52 -0000
From: "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 James Bottomley <James.Bottomley@...senPartnership.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: irq/msi] cleanup: Provide retain_ptr()

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

Commit-ID:     47d482d3dd6e9469f650b34667c4f0faf9f268d0
Gitweb:        https://git.kernel.org/tip/47d482d3dd6e9469f650b34667c4f0faf9f268d0
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Wed, 19 Mar 2025 11:56:38 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 07 Apr 2025 16:24:55 +02:00

cleanup: Provide retain_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_ptr(), which NULLs the cleanup
pointer. That makes it easy to analyze and reason about.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Reviewed-by: James Bottomley <James.Bottomley@...senPartnership.com>
Link: https://lore.kernel.org/all/20250319105506.083538907@linutronix.de

---
 include/linux/cleanup.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
index 7e57047..be4a53a 100644
--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -216,6 +216,22 @@ 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_ptr(f);
+ *	return ret;
+ */
+#define retain_ptr(p)		((void)__get_and_null(p, NULL))
 
 /*
  * DEFINE_CLASS(name, type, exit, init, init_args...):