ceph_test_rados: do not let rollback race with snap deletewip-6254-model

Note that the OSD behaves in a weird way when you rollback to a non-
existent snap, so the test probably isn't the only party at fault here.

Fixes (test half of): #6254
Backport: dumpling, cuttlefish
Signed-off-by: Sage Weil <sage@inktank.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/test/osd/TestRados.cc b/src/test/osd/TestRados.cc
index be919161579..7158f50a74a 100644
--- a/src/test/osd/TestRados.cc
+++ b/src/test/osd/TestRados.cc
@@ -120,13 +120,16 @@ private:
       }
 
     case TEST_OP_ROLLBACK:
-      if (context.snaps.empty()) {
+      if (context.snaps.size() <= context.snaps_in_use.size()) {
 	return NULL;
-      } else {
+      }
+      while (true) {
 	int snap = rand_choose(context.snaps)->first;
+	if (context.snaps_in_use.count(snap))
+	  continue;  // in use; try again!
 	string oid = *(rand_choose(context.oid_not_in_use));
 	cout << "rollback oid " << oid << " to " << snap << std::endl;
-        return new RollbackOp(m_op, &context, oid, snap);
+	return new RollbackOp(m_op, &context, oid, snap);
       }
 
     case TEST_OP_SETATTR: