Tweak a few comments on adaptive spinning.

2 files changed, 15 insertions, 6 deletions

diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
index 49f9c59..17c72eb 100644
--- a/sys/kern/kern_mutex.c
+++ b/sys/kern/kern_mutex.c
@@ -399,8 +399,11 @@ _mtx_lock_sleep(struct mtx *m, uintptr_t tid, int opts, const char *file,
 
 #ifdef ADAPTIVE_MUTEXES
 		/*
-		 * If the current owner of the lock is executing on another
-		 * CPU quit the hard path and try to spin.
+		 * The current lock owner might have started executing
+		 * on another CPU (or the lock could have changed
+		 * owners) while we were waiting on the turnstile
+		 * chain lock.  If so, drop the turnstile lock and try
+		 * again.
 		 */
 		owner = (struct thread *)(v & ~MTX_FLAGMASK);
 		if (TD_IS_RUNNING(owner)) {
diff --git a/sys/kern/kern_rwlock.c b/sys/kern/kern_rwlock.c
index 993acfa..cc5f4f132 100644
--- a/sys/kern/kern_rwlock.c
+++ b/sys/kern/kern_rwlock.c
@@ -412,8 +412,11 @@ _rw_rlock(struct rwlock *rw, const char *file, int line)
 
 #ifdef ADAPTIVE_RWLOCKS
 		/*
-		 * If the current owner of the lock is executing on another
-		 * CPU quit the hard path and try to spin.
+		 * The current lock owner might have started executing
+		 * on another CPU (or the lock could have changed
+		 * owners) while we were waiting on the turnstile
+		 * chain lock.  If so, drop the turnstile lock and try
+		 * again.
 		 */
 		if ((v & RW_LOCK_READ) == 0) {
 			owner = (struct thread *)RW_OWNER(v);
@@ -714,8 +717,11 @@ _rw_wlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line)
 
 #ifdef ADAPTIVE_RWLOCKS
 		/*
-		 * If the current owner of the lock is executing on another
-		 * CPU quit the hard path and try to spin.
+		 * The current lock owner might have started executing
+		 * on another CPU (or the lock could have changed
+		 * owners) while we were waiting on the turnstile
+		 * chain lock.  If so, drop the turnstile lock and try
+		 * again.
 		 */
 		if (!(v & RW_LOCK_READ)) {
 			owner = (struct thread *)RW_OWNER(v);