[PATCH v5 2/5] refcount: add refcount_final_put tracepoint

[Eugene Mavick <m@mavick.dev>]

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

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

refcount_final_put records three fields:
- caller: function that called the refcounting
  function(refcount_sub_and_test, percpu_ref_put_many)
- ip: return address of trace wrapper macro call
- obj: refcount object(struct percpu_ref, refcount_t)

Signed-off-by: Eugene Mavick <m@mavick.dev>
---
 include/linux/refcount.h | 2 ++
 lib/refcount.c           | 6 +++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index ba7657ced281..23291a31d1be 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/refcount_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_refcount_final_put(r);
 		return true;
 	}
 
diff --git a/lib/refcount.c b/lib/refcount.c
index a207a8f22b3c..8b148b576503 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/refcount_trace.h>
 
 #define REFCOUNT_WARN(str)	WARN_ONCE(1, "refcount_t: " str ".\n")
 
@@ -56,7 +57,10 @@ 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);
+
+	do_trace_refcount_final_put_cond(ret, r);
+	return ret;
 }
 EXPORT_SYMBOL(refcount_dec_if_one);
 

-- 
2.51.2