fix race condition in dlopen

orig_tail was being saved before the lock was obtained, allowing
dlopen failure to roll-back other dlopens that had succeeded.

src/ldso/dynlink.c

@@ -886,7 +886,7 @@ void *__dynlink(int argc, char **argv)
 
 void *dlopen(const char *file, int mode)
 {
-	struct dso *volatile p, *orig_tail = tail, *next;
+	struct dso *volatile p, *orig_tail, *next;
 	size_t i;
 	int cs;
 
@@ -895,6 +895,8 @@ void *dlopen(const char *file, int mode)
 	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
 	pthread_rwlock_wrlock(&lock);
 
+	orig_tail = tail;
+
 	if (setjmp(rtld_fail)) {
 		/* Clean up anything new that was (partially) loaded */
 		if (p->deps) for (i=0; p->deps[i]; i++)