[PATCH v2 2/5] refcount: add ref_trace_final_put tracepoint

[Eugene Mavick via B4 Relay <devnull+m.mavick.dev@kernel.org>]

From: Eugene Mavick <m@mavick.dev>

Add the ref_trace_final_put tracepoint to __refcount_sub_and_test() and
refcount_dec_if_one()

This tracepoint 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>
---
v2:
-update commit message
-add tracepoint to refcount_dec_if_one(), suggested by Usuma Arif
-move MAINTAINERS file entries to new MAINTAINERS commit
-v1:https://lore.kernel.org/all/20260705-refcount-final-put-trace-v1-2-cdd0014626a9@mavick.dev/
---
 include/linux/refcount.h | 2 ++
 lib/refcount.c           | 8 +++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index ba7657ced281..70d07a462da1 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();
+		do_trace_ref_final_put(r);
 		return true;
 	}
 
diff --git a/lib/refcount.c b/lib/refcount.c
index a207a8f22b3c..cd7e32df3919 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -7,6 +7,7 @@
 #include <linux/refcount.h>
 #include <linux/spinlock.h>
 #include <linux/bug.h>
+#include <linux/ref_trace.h>
 
 #define REFCOUNT_WARN(str)	WARN_ONCE(1, "refcount_t: " str ".\n")
 
@@ -56,7 +57,12 @@ bool refcount_dec_if_one(refcount_t *r)
 {
 	int val = 1;
 
-	return atomic_try_cmpxchg_release(&r->refs, &val, 0);
+	bool ret = atomic_try_cmpxchg_release(&r->refs, &val, 0);
+
+	if (ret)
+		do_trace_ref_final_put(r);
+
+	return ret;
 }
 EXPORT_SYMBOL(refcount_dec_if_one);
 

-- 
2.51.2