From 97cc6870f68b3bc545dfb78512cc0e771a93fd70 Mon Sep 17 00:00:00 2001
From: Mark Johnston <markj@FreeBSD.org>
Date: Sun, 19 Jul 2015 22:26:02 +0000
Subject: [PATCH] Don't increment the spin count until after the first attempt
 to acquire a rwlock read lock. Otherwise the lockstat:::rw-spin probe will
 fire spuriously.

MFC after:	1 week
---
 sys/kern/kern_rwlock.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sys/kern/kern_rwlock.c b/sys/kern/kern_rwlock.c
index 2921de4ef71e..370d0d6fca4b 100644
--- a/sys/kern/kern_rwlock.c
+++ b/sys/kern/kern_rwlock.c
@@ -382,9 +382,6 @@ __rw_rlock(volatile uintptr_t *c, const char *file, int line)
 	state = rw->rw_lock;
 #endif
 	for (;;) {
-#ifdef KDTRACE_HOOKS
-		spin_cnt++;
-#endif
 		/*
 		 * Handle the easy case.  If no other thread has a write
 		 * lock, then try to bump up the count of read locks.  Note
@@ -413,6 +410,9 @@ __rw_rlock(volatile uintptr_t *c, const char *file, int line)
 			}
 			continue;
 		}
+#ifdef KDTRACE_HOOKS
+		spin_cnt++;
+#endif
 #ifdef HWPMC_HOOKS
 		PMC_SOFT_CALL( , , lock, failed);
 #endif