From 5b9031fecca852c090ab9b4540c82e9b538e0e08 Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Sun, 7 May 2023 23:17:51 +0300
Subject: [PATCH] Fix monitor possibly applying incorrect PG history under
 heavy load

Monitor could deceive itself by immediately saving PG configuration changes
which weren't applied to etcd yet in memory, and apply incorrect PG history
changes next time if the first update fails.

This usually only happened under heavy load and was caught in CI. :-)
---
 mon/mon.js | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/mon/mon.js b/mon/mon.js
index 01ef02f8..5a83c43a 100644
--- a/mon/mon.js
+++ b/mon/mon.js
@@ -956,7 +956,7 @@ class Mon
         return alive_set[this.rng() % alive_set.length];
     }
 
-    save_new_pgs_txn(request, pool_id, up_osds, osd_tree, prev_pgs, new_pgs, pg_history)
+    save_new_pgs_txn(save_to, request, pool_id, up_osds, osd_tree, prev_pgs, new_pgs, pg_history)
     {
         const aff_osds = this.get_affinity_osds(this.state.config.pools[pool_id], up_osds, osd_tree);
         const pg_items = {};
@@ -1009,14 +1009,14 @@ class Mon
                 });
             }
         }
-        this.state.config.pgs.items = this.state.config.pgs.items || {};
+        save_to.items = save_to.items || {};
         if (!new_pgs.length)
         {
-            delete this.state.config.pgs.items[pool_id];
+            delete save_to.items[pool_id];
         }
         else
         {
-            this.state.config.pgs.items[pool_id] = pg_items;
+            save_to.items[pool_id] = pg_items;
         }
     }
 
@@ -1160,6 +1160,7 @@ class Mon
         if (this.state.config.pgs.hash != tree_hash)
         {
             // Something has changed
+            const new_config_pgs = JSON.parse(JSON.stringify(this.state.config.pgs));
             const etcd_request = { compare: [], success: [] };
             for (const pool_id in (this.state.config.pgs||{}).items||{})
             {
@@ -1180,7 +1181,7 @@ class Mon
                     etcd_request.success.push({ requestDeleteRange: {
                         key: b64(this.etcd_prefix+'/pool/stats/'+pool_id),
                     } });
-                    this.save_new_pgs_txn(etcd_request, pool_id, up_osds, osd_tree, prev_pgs, [], []);
+                    this.save_new_pgs_txn(new_config_pgs, etcd_request, pool_id, up_osds, osd_tree, prev_pgs, [], []);
                 }
             }
             for (const pool_id in this.state.config.pools)
@@ -1287,14 +1288,15 @@ class Mon
                     key: b64(this.etcd_prefix+'/pool/stats/'+pool_id),
                     value: b64(JSON.stringify(this.state.pool.stats[pool_id])),
                 } });
-                this.save_new_pgs_txn(etcd_request, pool_id, up_osds, osd_tree, real_prev_pgs, optimize_result.int_pgs, pg_history);
+                this.save_new_pgs_txn(new_config_pgs, etcd_request, pool_id, up_osds, osd_tree, real_prev_pgs, optimize_result.int_pgs, pg_history);
             }
-            this.state.config.pgs.hash = tree_hash;
-            await this.save_pg_config(etcd_request);
+            new_config_pgs.hash = tree_hash;
+            await this.save_pg_config(new_config_pgs, etcd_request);
         }
         else
         {
             // Nothing changed, but we still want to recheck the distribution of primaries
+            let new_config_pgs;
             let changed = false;
             for (const pool_id in this.state.config.pools)
             {
@@ -1314,31 +1316,35 @@ class Mon
                         const new_primary = this.pick_primary(pool_id, pg_cfg.osd_set, up_osds, aff_osds);
                         if (pg_cfg.primary != new_primary)
                         {
+                            if (!new_config_pgs)
+                            {
+                                new_config_pgs = JSON.parse(JSON.stringify(this.state.config.pgs));
+                            }
                             console.log(
                                 `Moving pool ${pool_id} (${pool_cfg.name || 'unnamed'}) PG ${pg_num}`+
                                 ` primary OSD from ${pg_cfg.primary} to ${new_primary}`
                             );
                             changed = true;
-                            pg_cfg.primary = new_primary;
+                            new_config_pgs.items[pool_id][pg_num].primary = new_primary;
                         }
                     }
                 }
             }
             if (changed)
             {
-                await this.save_pg_config();
+                await this.save_pg_config(new_config_pgs);
             }
         }
     }
 
-    async save_pg_config(etcd_request = { compare: [], success: [] })
+    async save_pg_config(new_config_pgs, etcd_request = { compare: [], success: [] })
     {
         etcd_request.compare.push(
             { key: b64(this.etcd_prefix+'/mon/master'), target: 'LEASE', lease: ''+this.etcd_lease_id },
             { key: b64(this.etcd_prefix+'/config/pgs'), target: 'MOD', mod_revision: ''+this.etcd_watch_revision, result: 'LESS' },
         );
         etcd_request.success.push(
-            { requestPut: { key: b64(this.etcd_prefix+'/config/pgs'), value: b64(JSON.stringify(this.state.config.pgs)) } },
+            { requestPut: { key: b64(this.etcd_prefix+'/config/pgs'), value: b64(JSON.stringify(new_config_pgs)) } },
         );
         const res = await this.etcd_call('/kv/txn', etcd_request, this.config.etcd_mon_timeout, 0);
         if (!res.succeeded)