From 12cccff72b487bcedc1b9a057f479c16055bd4be Mon Sep 17 00:00:00 2001
From: Martin Sumner <martin.sumner@adaptip.co.uk>
Date: Wed, 27 Oct 2021 13:04:03 +0100
Subject: [PATCH] Correct unavailable spaces

don't create a [0, -1] case
---
 src/riak_core_coverage_plan.erl | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/riak_core_coverage_plan.erl b/src/riak_core_coverage_plan.erl
index 72ac083fb..aeebddd32 100644
--- a/src/riak_core_coverage_plan.erl
+++ b/src/riak_core_coverage_plan.erl
@@ -840,7 +840,13 @@ multi_failure_tester(PartitionCount, CoverageFun) when PartitionCount >= 32 ->
     % Fail two vnodes together - now can only get partial coverage from a r=2
     % plan
     RVN = rand:uniform(PartitionCount),
-    UnavailableKeySpaces1 = [RVN - 1, (RVN - 2) rem PartitionCount],
+    UnavailableKeySpaces1 = 
+        case RVN of
+            1 ->
+                [0, PartitionCount - 1];
+            _ ->
+                [RVN - 1, RVN - 2]
+        end,
     {insufficient_vnodes_available, _, VnodeCovers1} =
         CoverageFun(ReqId, NVal, PartitionCount,
                     UnavailableKeySpaces1, PVC),