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>
(cherry picked from commit 1551ebb63238073d2fd30201e6b656a8988e958c)

diff --git a/src/mon/Monitor.cc b/src/mon/Monitor.cc
index 371341c998b99a0a4eb48656cd6947e14762ef8c..f6f08e08f360c287ac32de685e31692447ab2ed2 100644 (file)
--- a/src/mon/Monitor.cc
+++ b/src/mon/Monitor.cc
@@ -642,7 +642,7 @@ 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 1b21689863bc6bb0f9ea8d52b91d40438ea6dd3b..7ba8e9ca359fc82684ffb3f6441b5344b6fafbb4 100644 (file)
--- a/src/mon/PaxosService.cc
+++ b/src/mon/PaxosService.cc
@@ -127,6 +127,16 @@ 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 5321bebcacefcc210a570ebe11276732049c5310..4138b20afd208c9d98be45ba710c54138be86be4 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