From 48e0ee172a80a3ecd12fe086726c6b9e94e772cc Mon Sep 17 00:00:00 2001
From: mjg <mjg@FreeBSD.org>
Date: Mon, 20 Feb 2017 19:08:36 +0000
Subject: [PATCH] mtx: fix spin mutexes interaction with failed fcmpset

While doing so move recursion support down to the fallback routine.
---
 sys/kern/kern_mutex.c | 8 ++++++++
 sys/sys/mutex.h       | 9 +++------
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
index 7ad6507bb325..f2aed4907b3e 100644
--- a/sys/kern/kern_mutex.c
+++ b/sys/kern/kern_mutex.c
@@ -696,6 +696,14 @@ _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t v, uintptr_t tid,
 	lock_delay_arg_init(&lda, &mtx_spin_delay);
 	m = mtxlock2mtx(c);
 
+	if (__predict_false(v == MTX_UNOWNED))
+		v = MTX_READ_VALUE(m);
+
+	if (__predict_false(v == tid)) {
+		m->mtx_recurse++;
+		return;
+	}
+
 	if (LOCK_LOG_TEST(&m->lock_object, opts))
 		CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
 	KTR_STATE1(KTR_SCHED, "thread", sched_tdname((struct thread *)tid),
diff --git a/sys/sys/mutex.h b/sys/sys/mutex.h
index 9d8ca4e467b0..cc56c907f4b4 100644
--- a/sys/sys/mutex.h
+++ b/sys/sys/mutex.h
@@ -223,12 +223,9 @@ void	thread_lock_flags_(struct thread *, int, const char *, int);
 	uintptr_t _v = MTX_UNOWNED;					\
 									\
 	spinlock_enter();						\
-	if (!_mtx_obtain_lock_fetch((mp), &_v, _tid)) {			\
-		if (_v == _tid)						\
-			(mp)->mtx_recurse++;				\
-		else							\
-			_mtx_lock_spin((mp), _v, _tid, (opts), (file), (line));\
-	} else 								\
+	if (!_mtx_obtain_lock_fetch((mp), &_v, _tid)) 			\
+		_mtx_lock_spin((mp), _v, _tid, (opts), (file), (line)); \
+	else 								\
 		LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(spin__acquire,	\
 		    mp, 0, 0, file, line);				\
 } while (0)