[PATCH] shared signals require shared VM

Elimination of this nonsense allows for the assumption
that a task group shares VM. This lets procps run faster.

kernel/fork.c

@@ -774,6 +774,14 @@ struct task_struct *copy_process(unsigned long clone_flags,
 	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
 		return ERR_PTR(-EINVAL);
 
+	/*
+	 * Shared signal handlers imply shared VM. By way of the above,
+	 * thread groups also imply shared VM. Blocking this case allows
+	 * for various simplifications in other code.
+	 */
+	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
+		return ERR_PTR(-EINVAL);
+
 	/*
 	 * CLONE_DETACHED must match CLONE_THREAD: it's a historical
 	 * thing.