attempt to fix #1391, hold locks across fork() and initialize them in the child

diff --git a/rts/Schedule.c b/rts/Schedule.c
index 5ebb685..22e6120 100644 (file)
--- a/rts/Schedule.c
+++ b/rts/Schedule.c
@@ -2137,16 +2137,31 @@ forkProcess(HsStablePtr *entry
     // ToDo: for SMP, we should probably acquire *all* the capabilities
     cap = rts_lock();
     
+    // no funny business: hold locks while we fork, otherwise if some
+    // other thread is holding a lock when the fork happens, the data
+    // structure protected by the lock will forever be in an
+    // inconsistent state in the child.  See also #1391.
+    ACQUIRE_LOCK(&sched_mutex);
+    ACQUIRE_LOCK(&cap->lock);
+
     pid = fork();
     
     if (pid) { // parent
        
+        RELEASE_LOCK(&sched_mutex);
+        RELEASE_LOCK(&cap->lock);
+
        // just return the pid
        rts_unlock(cap);
        return pid;
        
     } else { // child
        
+#if defined(THREADED_RTS)
+        initMutex(&sched_mutex);
+        initMutex(&cap->lock);
+#endif
+
        // Now, all OS threads except the thread that forked are
        // stopped.  We need to stop all Haskell threads, including
        // those involved in foreign calls.  Also we need to delete