[PATCH] Fix potential set_child_tid/clear_child_tid bug

From: David Mosberger <davidm@napali.hpl.hp.com>

At the moment, if you don't set CLONE_CHILD_SETTID/CLONE_CHILD_CLEARTID,
the {set,clear}_child_tid values get inherited from the parent task.  I may
be missing something, but I suspect that's not the intended behavior.  The
patch below instead clears the respective members.

kernel/fork.c

@@ -887,13 +887,11 @@ struct task_struct *copy_process(unsigned long clone_flags,
 	if (retval)
 		goto bad_fork_cleanup_namespace;
 
-	if (clone_flags & CLONE_CHILD_SETTID)
-		p->set_child_tid = child_tidptr;
+	p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
 	/*
 	 * Clear TID on mm_release()?
 	 */
-	if (clone_flags & CLONE_CHILD_CLEARTID)
-		p->clear_child_tid = child_tidptr;
+	p->clear_child_tid = (clone_flags & CLONE_CHILD_CLEARTID) ? child_tidptr: NULL;
 
 	/*
 	 * Syscall tracing should be turned off in the child regardless