[PATCH 0/4] tracing: add ref_trace_final_put tracing

[PATCH 0/4] tracing: add ref_trace_final_put tracing

[Eugene Mavick via B4 Relay]

When debugging use-after-free(UAF) bugs, knowing when the object reaches
0 references and enters final release can significantly aide the
debugging process.

There is currently no universal way to trace this information.

This patches traces the final puts in the most widely used refcounting
implementations, refcount_t(and thus kref which uses it), and
percpu-ref.

The tracepoint records three fields:
- caller: function that called the refcounting
  function(refcount_sub_and_test, percpu_ref_put_many)
- fn: refcounting function(eg refcount_sub_and_test)
- obj: refcount object(struct percpu_ref, refcount_t) 

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
Eugene Mavick (4):
      tracing: add ref_trace_final_put tracepoint
      refcount: add ref_trace_final_put tracepoint
      percpu-refcount: add ref_trace_final_put trace
      kunit: add test for ref_trace_final_put

 MAINTAINERS                      |   3 +
 include/linux/percpu-refcount.h  |   5 +-
 include/linux/ref_trace.h        |  26 ++++++++
 include/linux/refcount.h         |   2 +
 include/trace/events/ref_trace.h |  46 +++++++++++++
 lib/Kconfig                      |  10 +++
 lib/Makefile                     |   2 +
 lib/ref_trace.c                  |  12 ++++
 lib/tests/Makefile               |   1 +
 lib/tests/ref_trace_kunit.c      | 138 +++++++++++++++++++++++++++++++++++++++
 10 files changed, 244 insertions(+), 1 deletion(-)
---
base-commit: df685633c3dbc67441cc86f1c3fee58de4652ba2
change-id: 20260624-refcount-final-put-trace-49bd7c39bd5a

Best regards,
-- 
Eugene Mavick <m@mavick.dev>

[PATCH 1/4] tracing: add ref_trace_final_put tracepoint

[Eugene Mavick via B4 Relay]

From: Eugene Mavick <m@mavick.dev>

Add ref_trace_final_put tracepoint and related core infrastructure

ref_trace_final_put fires when a reference
count reaches zero and the object enters its final release path.

The tracepoint records three fields:
- caller: function that called the refcounting
  function(refcount_sub_and_test, percpu_ref_put_many)
- fn: refcounting function(eg refcount_sub_and_test)
- obj: refcount object(struct percpu_ref, refcount_t)

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
 MAINTAINERS                      |  2 ++
 include/linux/ref_trace.h        | 26 +++++++++++++++++++++++
 include/trace/events/ref_trace.h | 46 ++++++++++++++++++++++++++++++++++++++++
 lib/Makefile                     |  2 ++
 lib/ref_trace.c                  | 12 +++++++++++
 5 files changed, 88 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 10e8253181d3..8dab37726b9d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4210,7 +4210,9 @@ S:	Maintained
 F:	Documentation/atomic_*.txt
 F:	arch/*/include/asm/atomic*.h
 F:	include/*/atomic*.h
+F:	include/linux/ref_trace.h
 F:	include/linux/refcount.h
+F:	lib/ref_trace.h
 F:	scripts/atomic/
 F:	rust/kernel/sync/atomic.rs
 F:	rust/kernel/sync/atomic/
diff --git a/include/linux/ref_trace.h b/include/linux/ref_trace.h
new file mode 100644
index 000000000000..54e9fba9e3e9
--- /dev/null
+++ b/include/linux/ref_trace.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_REF_TRACE_H
+#define _LINUX_REF_TRACE_H
+
+#include <linux/tracepoint-defs.h>
+#include <linux/instruction_pointer.h>
+
+/* Declare the tracepoint so tracepoint_enabled() can be used */
+DECLARE_TRACEPOINT(ref_trace_final_put);
+
+#ifdef CONFIG_TRACEPOINTS
+/* Wrapper function implemented in lib/ref_trace.c */
+extern void do_ref_trace_final_put(unsigned long caller, const char *fn, const void *obj);
+
+#define trace_ref_final_put(obj)						\
+	do {									\
+		if (tracepoint_enabled(ref_trace_final_put))			\
+			do_ref_trace_final_put(_RET_IP_, __func__, obj);	\
+	} while (0)
+
+#else /* !CONFIG_TRACEPOINTS */
+static inline void do_ref_trace_final_put(unsigned long caller, const char *fn, const void *obj) { }
+#define trace_ref_final_put(obj) do { } while (0)
+#endif
+
+#endif /* _LINUX_REF_TRACE_H */
diff --git a/include/trace/events/ref_trace.h b/include/trace/events/ref_trace.h
new file mode 100644
index 000000000000..e6037a325be2
--- /dev/null
+++ b/include/trace/events/ref_trace.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM ref_trace
+
+#if !defined(_TRACE_REF_TRACE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_REF_TRACE_H
+
+#include <linux/tracepoint.h>
+
+/**
+ * ref_trace_final_put - trace when a reference count reaches zero
+ * @caller: function that called the refcounting
+ * function(refcount_sub_and_test, percpu_ref_put_many)
+ * @fn: refcounting function(eg refcount_sub_and_test)
+ * @obj: refcount object(struct percpu_ref, refcount_t)
+ *
+ * Tracepoint instrumentation can be added using the ref_trace_final_put
+ * macro defined in include/linux/ref_trace.h
+ * which uses _RET_IP_ and __func__ for caller and fn arguments respectively,
+ * thus only requiring obj arg to be supplied
+ */
+TRACE_EVENT(ref_trace_final_put,
+
+	TP_PROTO(unsigned long caller, const char *fn, const void *obj),
+
+	TP_ARGS(caller, fn, obj),
+
+	TP_STRUCT__entry(
+	__field(unsigned long, caller)
+	__string(fn, fn)
+	__field(const void *, obj)
+	),
+
+	TP_fast_assign(
+	__entry->caller = caller;
+	__assign_str(fn);
+	__entry->obj = obj;
+	),
+
+	TP_printk("caller=%pS fn=%s obj=%p", (void *)__entry->caller, __get_str(fn), __entry->obj)
+);
+
+#endif /* _TRACE_REF_TRACE_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/lib/Makefile b/lib/Makefile
index f33a24bf1c19..41737090a95d 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -335,3 +335,5 @@ CONTEXT_ANALYSIS_test_context-analysis.o := y
 obj-$(CONFIG_CONTEXT_ANALYSIS_TEST) += test_context-analysis.o
 
 subdir-$(CONFIG_FORTIFY_SOURCE) += test_fortify
+
+obj-$(CONFIG_TRACEPOINTS) += ref_trace.o
diff --git a/lib/ref_trace.c b/lib/ref_trace.c
new file mode 100644
index 000000000000..25f7c17c7c47
--- /dev/null
+++ b/lib/ref_trace.c
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+#define CREATE_TRACE_POINTS
+#include <trace/events/ref_trace.h>
+
+//Wrapper function for functions defined entirely in header files
+void do_ref_trace_final_put(unsigned long caller, const char *fn, const void *obj)
+{
+	trace_ref_trace_final_put(caller, fn, obj);
+}
+EXPORT_SYMBOL_GPL(do_ref_trace_final_put);
+
+EXPORT_TRACEPOINT_SYMBOL_GPL(ref_trace_final_put);

-- 
2.51.2

[PATCH 2/4] refcount: add ref_trace_final_put tracepoint

[Eugene Mavick via B4 Relay]

From: Eugene Mavick <m@mavick.dev>

Add the ref_trace_final_put tracepoint to __refcount_sub_and_test().
This fires when a refcount_t reaches zero, capturing the caller
address, the function name, and the refcount_t address.

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
 include/linux/refcount.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index ba7657ced281..7b1fbf326a21 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -107,6 +107,7 @@
 #include <linux/limits.h>
 #include <linux/refcount_types.h>
 #include <linux/spinlock_types.h>
+#include <linux/ref_trace.h>
 
 struct mutex;
 
@@ -393,6 +394,7 @@ bool __refcount_sub_and_test(int i, refcount_t *r, int *oldp)
 
 	if (old > 0 && old == i) {
 		smp_acquire__after_ctrl_dep();
+		trace_ref_final_put(r);
 		return true;
 	}
 

-- 
2.51.2

Re: [PATCH 2/4] refcount: add ref_trace_final_put tracepoint

[Usama Arif]

On Sun, 05 Jul 2026 09:20:52 +0800 Eugene Mavick via B4 Relay <devnull+m.mavick.dev@kernel.org> wrote:

> From: Eugene Mavick <m@mavick.dev>
> 
> Add the ref_trace_final_put tracepoint to __refcount_sub_and_test().
> This fires when a refcount_t reaches zero, capturing the caller
> address, the function name, and the refcount_t address.
> 
> Signed-off-by: Eugene Mavick <m@mavick.dev>
> ---
>  include/linux/refcount.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/refcount.h b/include/linux/refcount.h
> index ba7657ced281..7b1fbf326a21 100644
> --- a/include/linux/refcount.h
> +++ b/include/linux/refcount.h
> @@ -107,6 +107,7 @@
>  #include <linux/limits.h>
>  #include <linux/refcount_types.h>
>  #include <linux/spinlock_types.h>
> +#include <linux/ref_trace.h>
>  
>  struct mutex;
>  
> @@ -393,6 +394,7 @@ bool __refcount_sub_and_test(int i, refcount_t *r, int *oldp)
>  
>  	if (old > 0 && old == i) {
>  		smp_acquire__after_ctrl_dep();
> +		trace_ref_final_put(r);

Should refcount_dec_if_one() also fire the tracepoint?

>  		return true;
>  	}
>  
> 
> -- 
> 2.51.2
> 
> 
> 

[PATCH 3/4] percpu-refcount: add ref_trace_final_put trace

[Eugene Mavick via B4 Relay]

From: Eugene Mavick <m@mavick.dev>

Add the ref_trace_final_put tracepoint to percpu_ref_put_many().
The tracepoint fires when the atomic counter reaches zero in the
atomic fallback path (after percpu_ref_kill() has been called).

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
 include/linux/percpu-refcount.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index d73a1c08c3e3..55543ecdf60c 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -55,6 +55,7 @@
 #include <linux/rcupdate.h>
 #include <linux/types.h>
 #include <linux/gfp.h>
+#include <linux/ref_trace.h>
 
 struct percpu_ref;
 typedef void (percpu_ref_func_t)(struct percpu_ref *);
@@ -331,8 +332,10 @@ static inline void percpu_ref_put_many(struct percpu_ref *ref, unsigned long nr)
 
 	if (__ref_is_percpu(ref, &percpu_count))
 		this_cpu_sub(*percpu_count, nr);
-	else if (unlikely(atomic_long_sub_and_test(nr, &ref->data->count)))
+	else if (unlikely(atomic_long_sub_and_test(nr, &ref->data->count))) {
+		trace_ref_final_put(ref);
 		ref->data->release(ref);
+	}
 
 	rcu_read_unlock();
 }

-- 
2.51.2

[PATCH 4/4] kunit: add test for ref_trace_final_put

[Eugene Mavick via B4 Relay]

From: Eugene Mavick <m@mavick.dev>

Add a KUnit test suite for the ref_trace_final_put tracepoint.

The test registers a probe function and triggers both refcount_t and
percpu_ref final put paths, verifying that the tracepoint fires
correctly and that the recorded fields match expected values.

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
 MAINTAINERS                 |   1 +
 lib/Kconfig                 |  10 ++++
 lib/tests/Makefile          |   1 +
 lib/tests/ref_trace_kunit.c | 138 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 150 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 8dab37726b9d..7c387ed746ee 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4213,6 +4213,7 @@ F:	include/*/atomic*.h
 F:	include/linux/ref_trace.h
 F:	include/linux/refcount.h
 F:	lib/ref_trace.h
+F:	lib/tests/ref_trace_kunit.c
 F:	scripts/atomic/
 F:	rust/kernel/sync/atomic.rs
 F:	rust/kernel/sync/atomic/
diff --git a/lib/Kconfig b/lib/Kconfig
index 00a9509636c1..c29b2ccb3c31 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -52,6 +52,16 @@ config PACKING_KUNIT_TEST
 
 	  When in doubt, say N.
 
+config REF_TRACE_KUNIT_TEST
+	bool "ref_trace kunit test" if !KUNIT_ALL_TESTS
+	depends on KUNIT && FTRACE
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables the KUnit test suite for the ref_trace_final_put
+	  tracepoint.
+
+	  If unsure, say N
+
 config BITREVERSE
 	tristate
 
diff --git a/lib/tests/Makefile b/lib/tests/Makefile
index 7e9c2fa52e35..828a030ad8c7 100644
--- a/lib/tests/Makefile
+++ b/lib/tests/Makefile
@@ -57,5 +57,6 @@ obj-$(CONFIG_USERCOPY_KUNIT_TEST) += usercopy_kunit.o
 obj-$(CONFIG_UTIL_MACROS_KUNIT) += util_macros_kunit.o
 obj-$(CONFIG_RATELIMIT_KUNIT_TEST) += test_ratelimit.o
 obj-$(CONFIG_UUID_KUNIT_TEST) += uuid_kunit.o
+obj-$(CONFIG_REF_TRACE_KUNIT_TEST) += ref_trace_kunit.o
 
 obj-$(CONFIG_TEST_RUNTIME_MODULE)		+= module/
diff --git a/lib/tests/ref_trace_kunit.c b/lib/tests/ref_trace_kunit.c
new file mode 100644
index 000000000000..2ece6c840fe0
--- /dev/null
+++ b/lib/tests/ref_trace_kunit.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <kunit/test.h>
+#include <linux/wait_bit.h>
+#include <linux/instruction_pointer.h>
+#include <linux/kallsyms.h>
+#include <linux/percpu-refcount.h>
+#include <linux/refcount.h>
+#include <trace/events/ref_trace.h>
+
+struct data {
+	unsigned long caller;
+	const char *fn;
+	const void *obj;
+	int *flag;
+	struct kunit *test;
+};
+
+struct data refc_chk;
+struct data pcpu_chk;
+
+//called when tracepoint fires
+static void probe(
+	  void *ignore,
+	  unsigned long caller,
+	  const char *fn,
+	  const void *obj)
+{
+	struct data *chk_val;
+
+	char func_name[KSYM_SYMBOL_LEN];
+
+	sprint_symbol_no_offset(func_name, caller);
+
+	if (!strcmp(func_name, "test_refcount")) {
+		chk_val = &refc_chk;
+		KUNIT_EXPECT_FALSE(chk_val->test, memcmp(obj, chk_val->obj, sizeof(refcount_t)));
+	} else if (!strcmp(func_name, "test_percpu")) {
+		chk_val = &pcpu_chk;
+		KUNIT_EXPECT_FALSE(chk_val->test, memcmp(
+			obj, chk_val->obj, sizeof(struct percpu_ref)));
+	} else {
+		//non test function origin trace events
+		return;
+	}
+
+	struct kunit *test = chk_val->test;
+	int *flag = chk_val->flag;
+
+	//ensure past flag writes are done before reading
+	KUNIT_EXPECT_EQ(test, 1, smp_load_acquire(flag));
+	KUNIT_EXPECT_EQ(test, caller, chk_val->caller);
+
+	smp_store_release(flag, 0); //signal probe completion
+}
+
+
+
+static void test_refcount(struct kunit *test)
+{
+	refcount_t refc;
+	int flag_addr = 0;
+
+	refc_chk.caller = (unsigned long)&test_refcount;
+	refc_chk.fn = "__refcount_sub_and_test";
+	refc_chk.obj = &refc;
+	refc_chk.flag = &flag_addr;
+	refc_chk.test = test;
+
+	int *flag = refc_chk.flag;
+
+	KUNIT_EXPECT_FALSE(test, register_trace_ref_trace_final_put(probe, NULL));
+
+	refcount_set(&refc, 2);
+
+	KUNIT_EXPECT_FALSE(test, refcount_dec_and_test(&refc));
+
+	smp_store_release(flag, 1); //signal final put can happen
+
+	KUNIT_EXPECT_TRUE(test, refcount_dec_and_test(&refc));
+
+	wait_var_event(flag, smp_load_acquire(flag)); //wait for probe completion
+	unregister_trace_ref_trace_final_put(probe, NULL);
+}
+
+static void dummy_release(struct percpu_ref *ref) {}
+
+static void test_percpu(struct kunit *test)
+{
+	struct percpu_ref pcpu_ref;
+
+	int flag_addr = 1;
+
+	pcpu_chk.caller = (unsigned long)&test_percpu;
+	pcpu_chk.fn = "percpu_ref_put_many";
+	pcpu_chk.obj = &pcpu_ref;
+	pcpu_chk.flag = &flag_addr;
+	pcpu_chk.test = test;
+
+	int *flag = pcpu_chk.flag;
+
+	KUNIT_EXPECT_FALSE(test, register_trace_ref_trace_final_put(probe, NULL));
+
+	KUNIT_EXPECT_FALSE(test, percpu_ref_init(&pcpu_ref, dummy_release, 0, GFP_KERNEL));
+
+	percpu_ref_get(&pcpu_ref);
+	percpu_ref_get(&pcpu_ref);
+
+	percpu_ref_put(&pcpu_ref);
+	percpu_ref_put(&pcpu_ref);
+
+	percpu_ref_switch_to_atomic_sync(&pcpu_ref);
+
+	smp_store_release(flag, 1); //signal final put can happen
+
+	percpu_ref_put(&pcpu_ref);
+
+	wait_var_event(flag, smp_load_acquire(flag)); //wait for probe completion
+	unregister_trace_ref_trace_final_put(probe, NULL);
+	percpu_ref_exit(&pcpu_ref);
+}
+
+static struct kunit_case __refdata ref_trace_test_cases[] = {
+	KUNIT_CASE(test_refcount),
+	KUNIT_CASE(test_percpu),
+	{}
+};
+
+static struct kunit_suite ref_trace_test_suite = {
+	.name = "ref-trace",
+	.test_cases = ref_trace_test_cases,
+};
+
+kunit_test_suites(&ref_trace_test_suite);
+
+MODULE_AUTHOR("Eugene Mavick <m@mavick.dev>");
+MODULE_DESCRIPTION("KUnit test for ref_trace");
+MODULE_LICENSE("GPL");

-- 
2.51.2

[PATCH 0/4] tracing: add ref_trace_final_put tracing

[Eugene Mavick]

When debugging use-after-free(UAF) bugs, knowing when the object reaches
0 references and enters final release can significantly aide the
debugging process.

There is currently no universal way to trace this information.

This patches traces the final puts in the most widely used refcounting
implementations, refcount_t(and thus kref which uses it), and
percpu-ref.

The tracepoint records three fields:
- caller: function that called the refcounting
  function(refcount_sub_and_test, percpu_ref_put_many)
- fn: refcounting function(eg refcount_sub_and_test)
- obj: refcount object(struct percpu_ref, refcount_t) 

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
Eugene Mavick (4):
      tracing: add ref_trace_final_put tracepoint
      refcount: add ref_trace_final_put tracepoint
      percpu-refcount: add ref_trace_final_put trace
      kunit: add test for ref_trace_final_put

 MAINTAINERS                      |   3 +
 include/linux/percpu-refcount.h  |   5 +-
 include/linux/ref_trace.h        |  26 ++++++++
 include/linux/refcount.h         |   2 +
 include/trace/events/ref_trace.h |  46 +++++++++++++
 lib/Kconfig                      |  10 +++
 lib/Makefile                     |   2 +
 lib/ref_trace.c                  |  12 ++++
 lib/tests/Makefile               |   1 +
 lib/tests/ref_trace_kunit.c      | 138 +++++++++++++++++++++++++++++++++++++++
 10 files changed, 244 insertions(+), 1 deletion(-)
---
base-commit: df685633c3dbc67441cc86f1c3fee58de4652ba2
change-id: 20260624-refcount-final-put-trace-49bd7c39bd5a

Best regards,
-- 
Eugene Mavick <m@mavick.dev>

[PATCH 4/4] kunit: add test for ref_trace_final_put

[Eugene Mavick]

Add a KUnit test suite for the ref_trace_final_put tracepoint.

The test registers a probe function and triggers both refcount_t and
percpu_ref final put paths, verifying that the tracepoint fires
correctly and that the recorded fields match expected values.

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
 MAINTAINERS                 |   1 +
 lib/Kconfig                 |  10 ++++
 lib/tests/Makefile          |   1 +
 lib/tests/ref_trace_kunit.c | 138 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 150 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 8dab37726b9d..7c387ed746ee 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4213,6 +4213,7 @@ F:	include/*/atomic*.h
 F:	include/linux/ref_trace.h
 F:	include/linux/refcount.h
 F:	lib/ref_trace.h
+F:	lib/tests/ref_trace_kunit.c
 F:	scripts/atomic/
 F:	rust/kernel/sync/atomic.rs
 F:	rust/kernel/sync/atomic/
diff --git a/lib/Kconfig b/lib/Kconfig
index 00a9509636c1..c29b2ccb3c31 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -52,6 +52,16 @@ config PACKING_KUNIT_TEST
 
 	  When in doubt, say N.
 
+config REF_TRACE_KUNIT_TEST
+	bool "ref_trace kunit test" if !KUNIT_ALL_TESTS
+	depends on KUNIT && FTRACE
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables the KUnit test suite for the ref_trace_final_put
+	  tracepoint.
+
+	  If unsure, say N
+
 config BITREVERSE
 	tristate
 
diff --git a/lib/tests/Makefile b/lib/tests/Makefile
index 7e9c2fa52e35..828a030ad8c7 100644
--- a/lib/tests/Makefile
+++ b/lib/tests/Makefile
@@ -57,5 +57,6 @@ obj-$(CONFIG_USERCOPY_KUNIT_TEST) += usercopy_kunit.o
 obj-$(CONFIG_UTIL_MACROS_KUNIT) += util_macros_kunit.o
 obj-$(CONFIG_RATELIMIT_KUNIT_TEST) += test_ratelimit.o
 obj-$(CONFIG_UUID_KUNIT_TEST) += uuid_kunit.o
+obj-$(CONFIG_REF_TRACE_KUNIT_TEST) += ref_trace_kunit.o
 
 obj-$(CONFIG_TEST_RUNTIME_MODULE)		+= module/
diff --git a/lib/tests/ref_trace_kunit.c b/lib/tests/ref_trace_kunit.c
new file mode 100644
index 000000000000..2ece6c840fe0
--- /dev/null
+++ b/lib/tests/ref_trace_kunit.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <kunit/test.h>
+#include <linux/wait_bit.h>
+#include <linux/instruction_pointer.h>
+#include <linux/kallsyms.h>
+#include <linux/percpu-refcount.h>
+#include <linux/refcount.h>
+#include <trace/events/ref_trace.h>
+
+struct data {
+	unsigned long caller;
+	const char *fn;
+	const void *obj;
+	int *flag;
+	struct kunit *test;
+};
+
+struct data refc_chk;
+struct data pcpu_chk;
+
+//called when tracepoint fires
+static void probe(
+	  void *ignore,
+	  unsigned long caller,
+	  const char *fn,
+	  const void *obj)
+{
+	struct data *chk_val;
+
+	char func_name[KSYM_SYMBOL_LEN];
+
+	sprint_symbol_no_offset(func_name, caller);
+
+	if (!strcmp(func_name, "test_refcount")) {
+		chk_val = &refc_chk;
+		KUNIT_EXPECT_FALSE(chk_val->test, memcmp(obj, chk_val->obj, sizeof(refcount_t)));
+	} else if (!strcmp(func_name, "test_percpu")) {
+		chk_val = &pcpu_chk;
+		KUNIT_EXPECT_FALSE(chk_val->test, memcmp(
+			obj, chk_val->obj, sizeof(struct percpu_ref)));
+	} else {
+		//non test function origin trace events
+		return;
+	}
+
+	struct kunit *test = chk_val->test;
+	int *flag = chk_val->flag;
+
+	//ensure past flag writes are done before reading
+	KUNIT_EXPECT_EQ(test, 1, smp_load_acquire(flag));
+	KUNIT_EXPECT_EQ(test, caller, chk_val->caller);
+
+	smp_store_release(flag, 0); //signal probe completion
+}
+
+
+
+static void test_refcount(struct kunit *test)
+{
+	refcount_t refc;
+	int flag_addr = 0;
+
+	refc_chk.caller = (unsigned long)&test_refcount;
+	refc_chk.fn = "__refcount_sub_and_test";
+	refc_chk.obj = &refc;
+	refc_chk.flag = &flag_addr;
+	refc_chk.test = test;
+
+	int *flag = refc_chk.flag;
+
+	KUNIT_EXPECT_FALSE(test, register_trace_ref_trace_final_put(probe, NULL));
+
+	refcount_set(&refc, 2);
+
+	KUNIT_EXPECT_FALSE(test, refcount_dec_and_test(&refc));
+
+	smp_store_release(flag, 1); //signal final put can happen
+
+	KUNIT_EXPECT_TRUE(test, refcount_dec_and_test(&refc));
+
+	wait_var_event(flag, smp_load_acquire(flag)); //wait for probe completion
+	unregister_trace_ref_trace_final_put(probe, NULL);
+}
+
+static void dummy_release(struct percpu_ref *ref) {}
+
+static void test_percpu(struct kunit *test)
+{
+	struct percpu_ref pcpu_ref;
+
+	int flag_addr = 1;
+
+	pcpu_chk.caller = (unsigned long)&test_percpu;
+	pcpu_chk.fn = "percpu_ref_put_many";
+	pcpu_chk.obj = &pcpu_ref;
+	pcpu_chk.flag = &flag_addr;
+	pcpu_chk.test = test;
+
+	int *flag = pcpu_chk.flag;
+
+	KUNIT_EXPECT_FALSE(test, register_trace_ref_trace_final_put(probe, NULL));
+
+	KUNIT_EXPECT_FALSE(test, percpu_ref_init(&pcpu_ref, dummy_release, 0, GFP_KERNEL));
+
+	percpu_ref_get(&pcpu_ref);
+	percpu_ref_get(&pcpu_ref);
+
+	percpu_ref_put(&pcpu_ref);
+	percpu_ref_put(&pcpu_ref);
+
+	percpu_ref_switch_to_atomic_sync(&pcpu_ref);
+
+	smp_store_release(flag, 1); //signal final put can happen
+
+	percpu_ref_put(&pcpu_ref);
+
+	wait_var_event(flag, smp_load_acquire(flag)); //wait for probe completion
+	unregister_trace_ref_trace_final_put(probe, NULL);
+	percpu_ref_exit(&pcpu_ref);
+}
+
+static struct kunit_case __refdata ref_trace_test_cases[] = {
+	KUNIT_CASE(test_refcount),
+	KUNIT_CASE(test_percpu),
+	{}
+};
+
+static struct kunit_suite ref_trace_test_suite = {
+	.name = "ref-trace",
+	.test_cases = ref_trace_test_cases,
+};
+
+kunit_test_suites(&ref_trace_test_suite);
+
+MODULE_AUTHOR("Eugene Mavick <m@mavick.dev>");
+MODULE_DESCRIPTION("KUnit test for ref_trace");
+MODULE_LICENSE("GPL");

-- 
2.51.2

[PATCH 0/4] tracing: add ref_trace_final_put tracing

[Eugene Mavick]

When debugging use-after-free(UAF) bugs, knowing when the object reaches
0 references and enters final release can significantly aide the
debugging process.

There is currently no universal way to trace this information.

This patches traces the final puts in the most widely used refcounting
implementations, refcount_t(and thus kref which uses it), and
percpu-ref.

The tracepoint records three fields:
- caller: function that called the refcounting
  function(refcount_sub_and_test, percpu_ref_put_many)
- fn: refcounting function(eg refcount_sub_and_test)
- obj: refcount object(struct percpu_ref, refcount_t) 

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
Eugene Mavick (4):
      tracing: add ref_trace_final_put tracepoint
      refcount: add ref_trace_final_put tracepoint
      percpu-refcount: add ref_trace_final_put trace
      kunit: add test for ref_trace_final_put

 MAINTAINERS                      |   3 +
 include/linux/percpu-refcount.h  |   5 +-
 include/linux/ref_trace.h        |  26 ++++++++
 include/linux/refcount.h         |   2 +
 include/trace/events/ref_trace.h |  46 +++++++++++++
 lib/Kconfig                      |  10 +++
 lib/Makefile                     |   2 +
 lib/ref_trace.c                  |  12 ++++
 lib/tests/Makefile               |   1 +
 lib/tests/ref_trace_kunit.c      | 138 +++++++++++++++++++++++++++++++++++++++
 10 files changed, 244 insertions(+), 1 deletion(-)
---
base-commit: df685633c3dbc67441cc86f1c3fee58de4652ba2
change-id: 20260624-refcount-final-put-trace-49bd7c39bd5a

Best regards,
-- 
Eugene Mavick <m@mavick.dev>

[PATCH 4/4] kunit: add test for ref_trace_final_put

[Eugene Mavick]

Add a KUnit test suite for the ref_trace_final_put tracepoint.

The test registers a probe function and triggers both refcount_t and
percpu_ref final put paths, verifying that the tracepoint fires
correctly and that the recorded fields match expected values.

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
 MAINTAINERS                 |   1 +
 lib/Kconfig                 |  10 ++++
 lib/tests/Makefile          |   1 +
 lib/tests/ref_trace_kunit.c | 138 ++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 150 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 8dab37726b9d..7c387ed746ee 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4213,6 +4213,7 @@ F:	include/*/atomic*.h
 F:	include/linux/ref_trace.h
 F:	include/linux/refcount.h
 F:	lib/ref_trace.h
+F:	lib/tests/ref_trace_kunit.c
 F:	scripts/atomic/
 F:	rust/kernel/sync/atomic.rs
 F:	rust/kernel/sync/atomic/
diff --git a/lib/Kconfig b/lib/Kconfig
index 00a9509636c1..c29b2ccb3c31 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -52,6 +52,16 @@ config PACKING_KUNIT_TEST
 
 	  When in doubt, say N.
 
+config REF_TRACE_KUNIT_TEST
+	bool "ref_trace kunit test" if !KUNIT_ALL_TESTS
+	depends on KUNIT && FTRACE
+	default KUNIT_ALL_TESTS
+	help
+	  This option enables the KUnit test suite for the ref_trace_final_put
+	  tracepoint.
+
+	  If unsure, say N
+
 config BITREVERSE
 	tristate
 
diff --git a/lib/tests/Makefile b/lib/tests/Makefile
index 7e9c2fa52e35..828a030ad8c7 100644
--- a/lib/tests/Makefile
+++ b/lib/tests/Makefile
@@ -57,5 +57,6 @@ obj-$(CONFIG_USERCOPY_KUNIT_TEST) += usercopy_kunit.o
 obj-$(CONFIG_UTIL_MACROS_KUNIT) += util_macros_kunit.o
 obj-$(CONFIG_RATELIMIT_KUNIT_TEST) += test_ratelimit.o
 obj-$(CONFIG_UUID_KUNIT_TEST) += uuid_kunit.o
+obj-$(CONFIG_REF_TRACE_KUNIT_TEST) += ref_trace_kunit.o
 
 obj-$(CONFIG_TEST_RUNTIME_MODULE)		+= module/
diff --git a/lib/tests/ref_trace_kunit.c b/lib/tests/ref_trace_kunit.c
new file mode 100644
index 000000000000..2ece6c840fe0
--- /dev/null
+++ b/lib/tests/ref_trace_kunit.c
@@ -0,0 +1,138 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <kunit/test.h>
+#include <linux/wait_bit.h>
+#include <linux/instruction_pointer.h>
+#include <linux/kallsyms.h>
+#include <linux/percpu-refcount.h>
+#include <linux/refcount.h>
+#include <trace/events/ref_trace.h>
+
+struct data {
+	unsigned long caller;
+	const char *fn;
+	const void *obj;
+	int *flag;
+	struct kunit *test;
+};
+
+struct data refc_chk;
+struct data pcpu_chk;
+
+//called when tracepoint fires
+static void probe(
+	  void *ignore,
+	  unsigned long caller,
+	  const char *fn,
+	  const void *obj)
+{
+	struct data *chk_val;
+
+	char func_name[KSYM_SYMBOL_LEN];
+
+	sprint_symbol_no_offset(func_name, caller);
+
+	if (!strcmp(func_name, "test_refcount")) {
+		chk_val = &refc_chk;
+		KUNIT_EXPECT_FALSE(chk_val->test, memcmp(obj, chk_val->obj, sizeof(refcount_t)));
+	} else if (!strcmp(func_name, "test_percpu")) {
+		chk_val = &pcpu_chk;
+		KUNIT_EXPECT_FALSE(chk_val->test, memcmp(
+			obj, chk_val->obj, sizeof(struct percpu_ref)));
+	} else {
+		//non test function origin trace events
+		return;
+	}
+
+	struct kunit *test = chk_val->test;
+	int *flag = chk_val->flag;
+
+	//ensure past flag writes are done before reading
+	KUNIT_EXPECT_EQ(test, 1, smp_load_acquire(flag));
+	KUNIT_EXPECT_EQ(test, caller, chk_val->caller);
+
+	smp_store_release(flag, 0); //signal probe completion
+}
+
+
+
+static void test_refcount(struct kunit *test)
+{
+	refcount_t refc;
+	int flag_addr = 0;
+
+	refc_chk.caller = (unsigned long)&test_refcount;
+	refc_chk.fn = "__refcount_sub_and_test";
+	refc_chk.obj = &refc;
+	refc_chk.flag = &flag_addr;
+	refc_chk.test = test;
+
+	int *flag = refc_chk.flag;
+
+	KUNIT_EXPECT_FALSE(test, register_trace_ref_trace_final_put(probe, NULL));
+
+	refcount_set(&refc, 2);
+
+	KUNIT_EXPECT_FALSE(test, refcount_dec_and_test(&refc));
+
+	smp_store_release(flag, 1); //signal final put can happen
+
+	KUNIT_EXPECT_TRUE(test, refcount_dec_and_test(&refc));
+
+	wait_var_event(flag, smp_load_acquire(flag)); //wait for probe completion
+	unregister_trace_ref_trace_final_put(probe, NULL);
+}
+
+static void dummy_release(struct percpu_ref *ref) {}
+
+static void test_percpu(struct kunit *test)
+{
+	struct percpu_ref pcpu_ref;
+
+	int flag_addr = 1;
+
+	pcpu_chk.caller = (unsigned long)&test_percpu;
+	pcpu_chk.fn = "percpu_ref_put_many";
+	pcpu_chk.obj = &pcpu_ref;
+	pcpu_chk.flag = &flag_addr;
+	pcpu_chk.test = test;
+
+	int *flag = pcpu_chk.flag;
+
+	KUNIT_EXPECT_FALSE(test, register_trace_ref_trace_final_put(probe, NULL));
+
+	KUNIT_EXPECT_FALSE(test, percpu_ref_init(&pcpu_ref, dummy_release, 0, GFP_KERNEL));
+
+	percpu_ref_get(&pcpu_ref);
+	percpu_ref_get(&pcpu_ref);
+
+	percpu_ref_put(&pcpu_ref);
+	percpu_ref_put(&pcpu_ref);
+
+	percpu_ref_switch_to_atomic_sync(&pcpu_ref);
+
+	smp_store_release(flag, 1); //signal final put can happen
+
+	percpu_ref_put(&pcpu_ref);
+
+	wait_var_event(flag, smp_load_acquire(flag)); //wait for probe completion
+	unregister_trace_ref_trace_final_put(probe, NULL);
+	percpu_ref_exit(&pcpu_ref);
+}
+
+static struct kunit_case __refdata ref_trace_test_cases[] = {
+	KUNIT_CASE(test_refcount),
+	KUNIT_CASE(test_percpu),
+	{}
+};
+
+static struct kunit_suite ref_trace_test_suite = {
+	.name = "ref-trace",
+	.test_cases = ref_trace_test_cases,
+};
+
+kunit_test_suites(&ref_trace_test_suite);
+
+MODULE_AUTHOR("Eugene Mavick <m@mavick.dev>");
+MODULE_DESCRIPTION("KUnit test for ref_trace");
+MODULE_LICENSE("GPL");

-- 
2.51.2