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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        "Rantala, Tommi" <tommi.t.rantala@nokia.com>
Subject: [PATCH 4.4 34/34] rcu: Force boolean subscript for expedited stall warnings
Date:   Thu,  7 Feb 2019 12:42:16 +0100
Message-Id: <20190207113026.866667243@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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@linux.vnet.ibm.com>
Cc: "Rantala, Tommi" <tommi.t.rantala@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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)]);
 			}