mon: PaxosService: call post_refresh() instead of post_paxos_update()

Whenever the monitor finishes committing a proposal, we call
Monitor::refresh_from_paxos() to nudge the services to refresh.  Once
all services have refreshed, we would then call each services
post_paxos_update().

However, due to an unfortunate, non-critical bug, some services (mainly
the LogMonitor) could have messages pending in their
'waiting_for_finished_proposal' callback queue [1], and we need to nudge
those callbacks.

This patch adds a new step during the refresh phase: instead of calling
directly the service's post_paxos_update(), we introduce a
PaxosService::post_refresh() which will call the services
post_paxos_update() function first and then nudge those callbacks when
appropriate.

[1] - Given the monitor will send MLog messages to itself, and given the
service is not readable before its initial state is proposed and
committed, some of the initial MLog's would be stuck waiting for the
proposal to finish.  However, by design, we only nudge those message's
callbacks when an election finishes or, if the leader, when the proposal
finishes.  On peons, however, we would only nudge those callbacks if an
election happened to be triggered, hence the need for an alternate path
to retry any message waiting for the initial proposal to finish.

Fixes: #11470
Signed-off-by: Joao Eduardo Luis <joao@suse.de>

diff --git a/src/mon/Monitor.cc b/src/mon/Monitor.cc
index ab809babc707e4e4cc80fb7914b698d5a9bf3275..5f6147146dc75a4c76ca59199960251f616f07af 100644 (file)
--- a/src/mon/Monitor.cc
+++ b/src/mon/Monitor.cc
@@ -788,7 +788,7 @@ void Monitor::refresh_from_paxos(bool *need_bootstrap)
     paxos_service[i]->refresh(need_bootstrap);
   }
   for (int i = 0; i < PAXOS_NUM; ++i) {
-    paxos_service[i]->post_paxos_update();
+    paxos_service[i]->post_refresh();
   }
 }
 

diff --git a/src/mon/PaxosService.cc b/src/mon/PaxosService.cc
index 8d06b0bed85acbd061e252d084f6419cc47e69df..4bdffc285f4631f4a350c47e33ed028a5127cf8e 100644 (file)
--- a/src/mon/PaxosService.cc
+++ b/src/mon/PaxosService.cc
@@ -128,6 +128,16 @@ void PaxosService::refresh(bool *need_bootstrap)
   update_from_paxos(need_bootstrap);
 }
 
+void PaxosService::post_refresh()
+{
+  dout(10) << __func__ << dendl;
+
+  post_paxos_update();
+
+  if (mon->is_peon() && !waiting_for_finished_proposal.empty()) {
+    finish_contexts(g_ceph_context, waiting_for_finished_proposal, -EAGAIN);
+  }
+}
 
 void PaxosService::remove_legacy_versions()
 {

diff --git a/src/mon/PaxosService.h b/src/mon/PaxosService.h
index dd469288c87efc83fcbc37b730e6e653300513b8..0e7ef7add689f8e39c27136a69a0441c998e5c4f 100644 (file)
--- a/src/mon/PaxosService.h
+++ b/src/mon/PaxosService.h
@@ -322,6 +322,7 @@ public:
   bool dispatch(PaxosServiceMessage *m);
 
   void refresh(bool *need_bootstrap);
+  void post_refresh();
 
   /**
    * @defgroup PaxosService_h_override_funcs Functions that should be