Acquire all_tasks_mutex in forkProcess

Summary: (for the same reason that we acquire all the other mutexes)

Test Plan: validate

Reviewers: simonmar, austin, duncan

Reviewed By: simonmar, austin, duncan

Subscribers: simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D60

rts/Schedule.c

@@ -1802,6 +1802,10 @@ forkProcess(HsStablePtr *entry
         ACQUIRE_LOCK(&capabilities[i]->lock);
     }
 
+#ifdef THREADED_RTS
+    ACQUIRE_LOCK(&all_tasks_mutex);
+#endif
+
     stopTimer(); // See #4074
 
 #if defined(TRACING)
@@ -1823,13 +1827,18 @@ forkProcess(HsStablePtr *entry
             releaseCapability_(capabilities[i],rtsFalse);
             RELEASE_LOCK(&capabilities[i]->lock);
         }
+
+#ifdef THREADED_RTS
+        RELEASE_LOCK(&all_tasks_mutex);
+#endif
+
         boundTaskExiting(task);
 
 	// just return the pid
         return pid;
 	
     } else { // child
-	
+
 #if defined(THREADED_RTS)
         initMutex(&sched_mutex);
         initMutex(&sm_mutex);
@@ -1839,6 +1848,8 @@ forkProcess(HsStablePtr *entry
         for (i=0; i < n_capabilities; i++) {
             initMutex(&capabilities[i]->lock);
         }
+
+        initMutex(&all_tasks_mutex);
 #endif
 
 #ifdef TRACING

rts/Task.c

@@ -39,7 +39,7 @@ static Task * allocTask (void);
 static Task * newTask   (rtsBool);
 
 #if defined(THREADED_RTS)
-static Mutex all_tasks_mutex;
+Mutex all_tasks_mutex;
 #endif
 
 /* -----------------------------------------------------------------------------

rts/Task.h

@@ -171,6 +171,11 @@ isBoundTask (Task *task)
 //
 extern Task *all_tasks;
 
+// The all_tasks list is protected by the all_tasks_mutex
+#if defined(THREADED_RTS)
+extern Mutex all_tasks_mutex;
+#endif
+
 // Start and stop the task manager.
 // Requires: sched_mutex.
 //