Revise the unlock order in _pthread_join(). Also, if the joined

thread is not dead, the join loop is guaranteed to execute at least
once, so there is no need to pick up the thread list lock after
we return from suspenstion only to release it after the loop.

Approved by:	re/blanket libthr

1 files changed, 6 insertions, 12 deletions

diff --git a/lib/libthr/thread/thr_join.c b/lib/libthr/thread/thr_join.c
index 061058a..63f37fa 100644
--- a/lib/libthr/thread/thr_join.c
+++ b/lib/libthr/thread/thr_join.c
@@ -82,13 +82,13 @@ _pthread_join(pthread_t pthread, void **thread_return)
 				_SPINLOCK(&pthread->lock);
 				break;
 			}
-	THREAD_LIST_UNLOCK;
 
 	/* Check if the thread was not found or has been detached: */
 	if (thread == NULL ||
 	    ((pthread->attr.flags & PTHREAD_DETACHED) != 0)) {
 		if (thread != NULL)
 			_SPINUNLOCK(&pthread->lock);
+		THREAD_LIST_UNLOCK;
 		DEAD_LIST_UNLOCK;
 		ret = ESRCH;
 		goto out;
@@ -98,6 +98,7 @@ _pthread_join(pthread_t pthread, void **thread_return)
 		/* Multiple joiners are not supported. */
 		/* XXXTHR - support multiple joiners. */
 		_SPINUNLOCK(&pthread->lock);
+		THREAD_LIST_UNLOCK;
 		DEAD_LIST_UNLOCK;
 		ret = ENOTSUP;
 		goto out;
@@ -112,16 +113,16 @@ _pthread_join(pthread_t pthread, void **thread_return)
 
 		/* Keep track of which thread we're joining to: */
 		curthread->join_status.thread = pthread;
-		_SPINUNLOCK(&pthread->lock);
 
 		while (curthread->join_status.thread == pthread) {
 			PTHREAD_SET_STATE(curthread, PS_JOIN);
 			/* Wait for our signal to wake up. */
 			_thread_critical_exit(curthread);
+			_SPINUNLOCK(&pthread->lock);
+			THREAD_LIST_UNLOCK;
 			DEAD_LIST_UNLOCK;
 			_thread_suspend(curthread, NULL);
-			/* XXX - For correctness reasons. */
-			DEAD_LIST_LOCK;
+
 			_thread_critical_enter(curthread);
 		}
 
@@ -133,14 +134,6 @@ _pthread_join(pthread_t pthread, void **thread_return)
 		if ((ret == 0) && (thread_return != NULL))
 			*thread_return = curthread->join_status.ret;
 		_thread_critical_exit(curthread);
-		/*
-		 * XXX - Must unlock here, instead of doing it earlier,
-		 *	 because it could lead to a deadlock. If the thread
-		 *	 we are joining is waiting on this lock we would
-		 *	 deadlock if we released this lock before unlocking the
-		 *	 joined thread.
-		 */
-		DEAD_LIST_UNLOCK;
 	} else {
 		/*
 		 * The thread exited (is dead) without being detached, and no
@@ -158,6 +151,7 @@ _pthread_join(pthread_t pthread, void **thread_return)
 		_SPINUNLOCK(&pthread->lock);
 		if (pthread_cond_signal(&_gc_cond) != 0)
 			PANIC("Cannot signal gc cond");
+		THREAD_LIST_UNLOCK;
 		DEAD_LIST_UNLOCK;
 	}