[PATCH 4.4 34/34] rcu: Force boolean subscript for expedited stall warnings

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

commit ec3833ed02ae6ef2a933ece9de7cbab0c64c699e upstream.

The cpu_online() function can return values other than 0 and 1, which
can result in subscript overflow when applied to a two-element array.
This commit allows for this behavior by using "!!" on the return value
from cpu_online() when used as a subscript.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: "Rantala, Tommi" <tommi.t.rantala@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/rcu/tree.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3817,7 +3817,7 @@ static void synchronize_sched_expedited_
 					continue;
 				rdp = per_cpu_ptr(rsp->rda, cpu);
 				pr_cont(" %d-%c%c%c", cpu,
-					"O."[cpu_online(cpu)],
+					"O."[!!cpu_online(cpu)],
 					"o."[!!(rdp->grpmask & rnp->expmaskinit)],
 					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
 			}