reef: mon/OSDMonitor: fix get_min_last_epoch_clean()

src/mon/OSDMonitor.cc

@@ -395,7 +395,7 @@ void LastEpochClean::report(unsigned pg_num, const pg_t& pg,
   return lec.report(pg_num, pg.ps(), last_epoch_clean);
 }
 
-epoch_t LastEpochClean::get_lower_bound(const OSDMap& latest) const
+epoch_t LastEpochClean::get_lower_bound_by_pool(const OSDMap& latest) const
 {
   auto floor = latest.get_epoch();
   for (auto& pool : latest.get_pools()) {
@@ -901,12 +901,7 @@ void OSDMonitor::update_from_paxos(bool *need_bootstrap)
       if (state & CEPH_OSD_UP) {
 	// could be marked up *or* down, but we're too lazy to check which
 	last_osd_report.erase(osd);
-      }
-    }
-    for (auto [osd, weight] : inc.new_weight) {
-      if (weight == CEPH_OSD_OUT) {
-        // manually marked out, so drop it
-        osd_epochs.erase(osd);
+	osd_epochs.erase(osd);
       }
     }
   }
@@ -2329,13 +2324,21 @@ version_t OSDMonitor::get_trim_to() const
   return 0;
 }
 
+/* There are two constraints on trimming:
+ * 1. we must not trim past the last_epoch_clean for any pg
+ * 2. we must not trim past the last reported epoch for any up
+ *    osds.
+ *
+ * LastEpochClean::get_lower_bound_by_pool gives a value <= constraint 1.
+ * For constraint 2, we take the min over osd_epochs, which is populated with
+ * MOSDBeacon::version, see OSDMonitor::prepare_beacon
+ */
 epoch_t OSDMonitor::get_min_last_epoch_clean() const
 {
-  auto floor = last_epoch_clean.get_lower_bound(osdmap);
-  // also scan osd epochs
-  // don't trim past the oldest reported osd epoch
+  auto floor = last_epoch_clean.get_lower_bound_by_pool(osdmap);
   for (auto [osd, epoch] : osd_epochs) {
     if (epoch < floor) {
+      ceph_assert(osdmap.is_up(osd));
       floor = epoch;
     }
   }
@@ -4443,8 +4446,8 @@ bool OSDMonitor::prepare_beacon(MonOpRequestRef op)
 
   last_osd_report[from].first = ceph_clock_now();
   last_osd_report[from].second = beacon->osd_beacon_report_interval;
+  ceph_assert(osdmap.is_up(from));
   osd_epochs[from] = beacon->version;
-
   for (const auto& pg : beacon->pgs) {
     if (auto* pool = osdmap.get_pg_pool(pg.pool()); pool != nullptr) {
       unsigned pg_num = pool->get_pg_num();

src/mon/OSDMonitor.h

@@ -114,7 +114,13 @@ class LastEpochClean {
 public:
   void report(unsigned pg_num, const pg_t& pg, epoch_t last_epoch_clean);
   void remove_pool(uint64_t pool);
-  epoch_t get_lower_bound(const OSDMap& latest) const;
+  /**
+   * get_lower_bound_by_pool
+   *
+   * Returns epoch e such that e <= pg.last_epoch_clean for all pgs in cluster.
+   * May return 0 if any pool does not have comprehensive values for all pgs.
+  */
+  epoch_t get_lower_bound_by_pool(const OSDMap& latest) const;
 
   void dump(Formatter *f) const;
 };
@@ -643,8 +649,18 @@ class OSDMonitor : public PaxosService,
 
   // when we last received PG stats from each osd and the osd's osd_beacon_report_interval
   std::map<int, std::pair<utime_t, int>> last_osd_report;
-  // TODO: use last_osd_report to store the osd report epochs, once we don't
-  //       need to upgrade from pre-luminous releases.
+  /**
+    * osd_epochs
+    *
+    * Records the MOSDBeacon::version (the osd epoch at which the OSD sent the
+    * beacon) of the most recent beacon recevied from each currently up OSD.
+    * Used in OSDMonitor::get_min_last_epoch_clean().
+    * Down osds are trimmed upon commit of each map
+    *  (OSDMonitor::update_from_paxos).
+    *
+    * TODO: use last_osd_report to store the osd report epochs, once we don't
+    * need to upgrade from pre-luminous releases.
+    */
   std::map<int,epoch_t> osd_epochs;
   LastEpochClean last_epoch_clean;
   bool preprocess_beacon(MonOpRequestRef op);