linux-kernel - [patch V3 01/10] cleanup: Provide retain

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Message-ID: <20250317092945.764490535@linutronix.de>
Date: Mon, 17 Mar 2025 14:29:22 +0100 (CET)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Marc Zyngier <maz@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Nishanth Menon <nm@...com>,
 Dhruva Gole <d-gole@...com>,
 Tero Kristo <kristo@...nel.org>,
 Santosh Shilimkar <ssantosh@...nel.org>,
 Logan Gunthorpe <logang@...tatee.com>,
 Dave Jiang <dave.jiang@...el.com>,
 Jon Mason <jdmason@...zu.us>,
 Allen Hubbe <allenbh@...il.com>,
 ntb@...ts.linux.dev,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 linux-pci@...r.kernel.org,
 Michael Kelley <mhklinux@...look.com>,
 Wei Liu <wei.liu@...nel.org>,
 Haiyang Zhang <haiyangz@...rosoft.com>,
 linux-hyperv@...r.kernel.org,
 Wei Huang <wei.huang2@....com>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 linux-scsi@...r.kernel.org,
 Jonathan Cameron <Jonathan.Cameron@...ei.com>
Subject: [patch V3 01/10] 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>
Cc: Peter Zijlstra <peterz@...radead.org>

---
 include/linux/cleanup.h |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -216,6 +216,23 @@ const volatile void * __must_check_fn(co

 #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)				\
+	__get_and_null(p, NULL)

 /*
  * DEFINE_CLASS(name, type, exit, init, init_args...):