From: Nitzan Mordechai <nmordech@redhat.com>
Date: Tue, 18 Nov 2025 09:37:48 +0000 (+0000)
Subject: Objecter: respect higher epoch subscription in tick
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F66304%2Fhead;p=ceph.git

Objecter: respect higher epoch subscription in tick

The OSD and Objecter share the same MonClient. During preboot, a potential
race condition exists where the OSD subscribes to osdmap epoch X, while
the Objecter subscribes to epoch X - 1.

The Objecter's subscription overrides the OSD's subscription. Consequently,
the monitor ignores the request (as it believes the OSD already has the
older map), causing the OSD to hang during preboot.

To fix this, check if a higher epoch is already subscribed before calling
_maybe_request_map during Objecter::tick. If a higher epoch is found,
maintain the existing subscription.

Fixes: https://tracker.ceph.com/issues/71931
Signed-off-by: Nitzan Mordechai <nmordech@ibm.com>
---

diff --git a/src/mon/MonClient.h b/src/mon/MonClient.h
index e259a261525a..3b78ea62ae27 100644
--- a/src/mon/MonClient.h
+++ b/src/mon/MonClient.h
@@ -454,6 +454,10 @@ public:
     std::lock_guard l(monc_lock);
     _renew_subs();
   }
+  version_t get_start(const std::string& what) const {
+    std::lock_guard l(monc_lock);
+    return sub.get_start(what);
+  }
   bool sub_want(std::string what, version_t start, unsigned flags) {
     std::lock_guard l(monc_lock);
     return sub.want(what, start, flags);
diff --git a/src/mon/MonSub.h b/src/mon/MonSub.h
index 9938ce39763f..2153c4a66571 100644
--- a/src/mon/MonSub.h
+++ b/src/mon/MonSub.h
@@ -19,6 +19,19 @@ public:
   auto get_subs() const {
     return sub_new;
   }
+  // get the requested start epoch for a subscription
+  // search first in "new" subs - subs that have not yet been sent
+  // but requested and going to be sent, then in "sent" subs.
+  // if not found, return 0
+  version_t get_start(const std::string& what) const {
+    if (auto i = sub_new.find(what); i != sub_new.end()) {
+      return i->second.start;
+    }
+    if (auto i = sub_sent.find(what); i != sub_sent.end()) {
+      return i->second.start;
+    }
+    return 0;
+  }
   bool need_renew() const;
   // change the status of "new" subscriptions to "sent"
   void renewed();
diff --git a/src/osdc/Objecter.cc b/src/osdc/Objecter.cc
index 392ef0f28639..5d001084efcd 100644
--- a/src/osdc/Objecter.cc
+++ b/src/osdc/Objecter.cc
@@ -1321,6 +1321,7 @@ void Objecter::handle_osd_map(MOSDMap *m)
 	ldout(cct, 3) << "handle_osd_map hmm, i want a full map, requesting"
 		      << dendl;
 	monc->sub_want("osdmap", 0, CEPH_SUBSCRIBE_ONETIME);
+    last_osdmap_request_time = ceph::coarse_mono_clock::now();
 	monc->renew_subs();
       }
     }
@@ -2056,7 +2057,6 @@ void Objecter::maybe_request_map()
 
 void Objecter::_maybe_request_map()
 {
-  last_osdmap_request_time = ceph::coarse_mono_clock::now();
   // rwlock is locked
   int flag = 0;
   if (_osdmap_full_flag()
@@ -2069,6 +2069,7 @@ void Objecter::_maybe_request_map()
       << "_maybe_request_map subscribing (onetime) to next osd map" << dendl;
     flag = CEPH_SUBSCRIBE_ONETIME;
   }
+  last_osdmap_request_time = ceph::coarse_mono_clock::now();
   epoch_t epoch = osdmap->get_epoch() ? osdmap->get_epoch()+1 : 0;
   if (monc->sub_want("osdmap", epoch, flag)) {
     monc->renew_subs();
@@ -2247,13 +2248,27 @@ void Objecter::tick()
   if (num_homeless_ops || !toping.empty()) {
     _maybe_request_map();
   } else if (last_osdmap_request_time != ceph::coarse_mono_clock::time_point()) {
+    const epoch_t epoch = osdmap->get_epoch() ? osdmap->get_epoch() + 1 : 0;
     auto now = ceph::coarse_mono_clock::now();
     auto elapsed = now - last_osdmap_request_time;
     auto stale_window = ceph::make_timespan(cct->_conf->objecter_tick_interval) * 2;
-    if (elapsed > stale_window) {
+    auto exist_sub = monc->get_start("osdmap");
+    ldout(cct, 20) << __func__ << ": elapsed since last osdmap request "
+      << std::chrono::duration<double>(elapsed).count() << "s"
+      << ", stale_window "
+      << std::chrono::duration<double>(stale_window).count() << "s"
+      << ", epoch " << epoch
+      << ", monc->get_start(osdmap) " << exist_sub
+      << dendl;
+    // check that:
+    //  1) we passed stale_window since last request AND
+    //  2) we don't have any osdmap subscription in flight OR
+    //     we have subscription - but the epoch we need is newer than the one we subscribed for
+    if (elapsed > stale_window &&
+       ((exist_sub == 0) || (epoch > exist_sub))) {
       double elapsed_s = std::chrono::duration<double>(elapsed).count();
       double thresh_s  = std::chrono::duration<double>(stale_window).count();
-      ldout(cct, 10) << __func__ << ": osdmap stale: " << elapsed_s 
+      ldout(cct, 20) << __func__ << ": osdmap stale: " << elapsed_s
         << "s > " << thresh_s << "s, maybe requesting map" << dendl;
       _maybe_request_map();
     }