mds: fix `tell session evict`

Don't try waiting on empty context gatherbuilder.

Signed-off-by: John Spray <john.spray@redhat.com>

diff --git a/src/mds/MDSRank.cc b/src/mds/MDSRank.cc
index fcb8efdda4bd765b01729f7510bfca972e44fe2a..ba03d133130206ba046bd520754290c1e8502be5 100644 (file)
--- a/src/mds/MDSRank.cc
+++ b/src/mds/MDSRank.cc
@@ -1795,8 +1795,14 @@ std::vector<entity_name_t> MDSRankDispatcher::evict_sessions(
     }
   }
 
+  dout(20) << __func__ << " matched " << victims.size() << " sessions" << dendl;
+
   std::vector<entity_name_t> result;
 
+  if (victims.empty()) {
+    return result;
+  }
+
   C_SaferCond on_safe;
   C_GatherBuilder gather(g_ceph_context, &on_safe);
   for (const auto s : victims) {