rcutorture: Flag nonexistent RCU GP kthread

Currently, if the RCU grace-period kthread has not yet been created,
in which case the starvation-check code will print zero for the state,
which maps to TASK_RUNNING.  This could clearly be quite confusing, so
this commit prints ~0, which does not map to any legal ->state value.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 81aa1cd..e2315fb 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1201,7 +1201,7 @@
 		       rsp->name, j - gpa,
 		       rsp->gpnum, rsp->completed,
 		       rsp->gp_flags, rsp->gp_state,
-		       rsp->gp_kthread ? rsp->gp_kthread->state : 0);
+		       rsp->gp_kthread ? rsp->gp_kthread->state : ~0);
 }
 
 /*