From 1a5cb534d9e72b92f93496bd4caf2c2c3468deb0 Mon Sep 17 00:00:00 2001
From: Michal Jarzabek <stiopa@gmail.com>
Date: Sun, 15 Jan 2017 15:32:04 +0000
Subject: [PATCH] mds/Server.cc: Don't evict a slow client if...

... it's the only client

Fixes: http://tracker.ceph.com/issues/17855
Signed-off-by: Michal Jarzabek <stiopa@gmail.com>
---
 qa/tasks/cephfs/test_misc.py | 39 ++++++++++++++++++++++++++++++++++++
 src/mds/Server.cc            |  7 +++++++
 2 files changed, 46 insertions(+)

diff --git a/qa/tasks/cephfs/test_misc.py b/qa/tasks/cephfs/test_misc.py
index 3f98c3719b8..a48e0a2a63b 100644
--- a/qa/tasks/cephfs/test_misc.py
+++ b/qa/tasks/cephfs/test_misc.py
@@ -4,9 +4,14 @@ from tasks.cephfs.fuse_mount import FuseMount
 from tasks.cephfs.cephfs_test_case import CephFSTestCase
 from teuthology.orchestra.run import CommandFailedError
 import errno
+import time
 
 class TestMisc(CephFSTestCase):
     CLIENTS_REQUIRED = 2
+
+    LOAD_SETTINGS = ["mds_session_autoclose"]
+    mds_session_autoclose = None
+
     def test_getattr_caps(self):
         """
         Check if MDS recognizes the 'mask' parameter of open request.
@@ -89,3 +94,37 @@ class TestMisc(CephFSTestCase):
         self.fs.mon_manager.raw_cluster_cmd('fs', 'new', self.fs.name,
                                             self.fs.metadata_pool_name,
                                             data_pool_name)
+
+    def test_evict_client(self):
+        """
+        Check that a slow client session won't get evicted if it's the
+        only session
+        """
+
+        self.mount_b.umount_wait();
+        ls_data = self.fs.mds_asok(['session', 'ls'])
+        self.assert_session_count(1, ls_data)
+
+        self.mount_a.kill();
+        self.mount_a.kill_cleanup();
+
+        time.sleep(self.mds_session_autoclose * 1.5)
+        ls_data = self.fs.mds_asok(['session', 'ls'])
+        self.assert_session_count(1, ls_data)
+
+        self.mount_a.mount()
+        self.mount_a.wait_until_mounted()
+        self.mount_b.mount()
+        self.mount_b.wait_until_mounted()
+
+        ls_data = self._session_list()
+        self.assert_session_count(2, ls_data)
+
+        self.mount_a.kill()
+        self.mount_a.kill()
+        self.mount_b.kill_cleanup()
+        self.mount_b.kill_cleanup()
+
+        time.sleep(self.mds_session_autoclose * 1.5)
+        ls_data = self.fs.mds_asok(['session', 'ls'])
+        self.assert_session_count(1, ls_data)
diff --git a/src/mds/Server.cc b/src/mds/Server.cc
index d62720b4609..48e1e5aa030 100644
--- a/src/mds/Server.cc
+++ b/src/mds/Server.cc
@@ -651,6 +651,13 @@ void Server::find_idle_sessions()
     return;
   }
 
+  if (mds->sessionmap.get_sessions().size() == 1 &&
+      mds->mdsmap->get_num_in_mds() == 1) {
+    dout(20) << "not evicting a slow client, because there is only one"
+             << dendl;
+    return;
+  }
+
   while (1) {
     Session *session = mds->sessionmap.get_oldest_session(Session::STATE_STALE);
     if (!session)