[v4] genirq/msi: Spring cleaning

[patch V4 01/14] cleanup: Provide retain_ptr()

Posted by Thomas Gleixner 9 months ago

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@linutronix.de>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
V4: Cast to void so can't be used as return_ptr() replacement - James
---
 include/linux/cleanup.h |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -216,6 +216,22 @@ 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)		((void)__get_and_null(p, NULL))
 
 /*
  * DEFINE_CLASS(name, type, exit, init, init_args...):

Re: [patch V4 01/14] cleanup: Provide retain_ptr()

Posted by James Bottomley 9 months ago

On Wed, 2025-03-19 at 11:56 +0100, Thomas Gleixner wrote:
> 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@linutronix.de>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> ---
> V4: Cast to void so can't be used as return_ptr() replacement - James

Reviewed-by: James Bottomley <James.Bottomley@HansenPartnership.com>

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

Posted by tip-bot2 for Thomas Gleixner 8 months, 1 week ago

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...):

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

Posted by tip-bot2 for Thomas Gleixner 8 months, 1 week ago

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@linutronix.de>
AuthorDate:    Wed, 19 Mar 2025 11:56:38 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.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@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 | 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...):