Permit recursive locking in _rthread_dl_lock(), as an so's destructor

may need to call dlclose().

problem observed by Antti Harri (iku at openbsd.fi), ok kurt@

1 files changed, 42 insertions, 2 deletions

diff --git a/lib/librthread/rthread.c b/lib/librthread/rthread.c
index 110c8bab268..72224990978 100644
--- a/lib/librthread/rthread.c
+++ b/lib/librthread/rthread.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rthread.c,v 1.58 2012/03/14 21:23:37 guenther Exp $ */
+/*	$OpenBSD: rthread.c,v 1.59 2012/03/20 00:47:23 guenther Exp $ */
 /*
  * Copyright (c) 2004,2005 Ted Unangst <tedu@openbsd.org>
  * All Rights Reserved.
@@ -580,15 +580,55 @@ _thread_dump_info(void)
 }
 
 #if defined(__ELF__) && defined(PIC)
+/*
+ * _rthread_dl_lock() provides the locking for dlopen(), dlclose(), and
+ * the function called via atexit() to invoke all destructors.  The latter
+ * two call shared-object destructors, which may need to call dlclose(),
+ * so this lock needs to permit recursive locking.
+ * The specific code here was extracted from _rthread_mutex_lock() and
+ * pthread_mutex_unlock() and simplified to use the static variables.
+ */
 void
 _rthread_dl_lock(int what)
 {
 	static _spinlock_lock_t lock = _SPINLOCK_UNLOCKED;
+	static pthread_t owner = NULL;
+	static struct pthread_queue lockers = TAILQ_HEAD_INITIALIZER(lockers);
+	static int count = 0;
 
 	if (what == 0)
+	{
+		pthread_t self = pthread_self();
+
+		/* lock, possibly recursive */
 		_spinlock(&lock);
-	else
+		if (owner == NULL) {
+			owner = self;
+		} else if (owner != self) {
+			TAILQ_INSERT_TAIL(&lockers, self, waiting);
+			while (owner != self) {
+				__thrsleep(self, 0, NULL, &lock, NULL);
+				_spinlock(&lock);
+			}
+		}
+		count++;
 		_spinunlock(&lock);
+	}
+	else
+	{
+		/* unlock, possibly recursive */
+		if (--count == 0) {
+			pthread_t next;
+
+			_spinlock(&lock);
+			owner = next = TAILQ_FIRST(&lockers);
+			if (next != NULL)
+				TAILQ_REMOVE(&lockers, next, waiting);
+			_spinunlock(&lock);
+			if (next != NULL)
+				__thrwakeup(next, 1);
+		}
+	}
 }
 
 void