Fix a deadlock during ALTER SUBSCRIPTION ... DROP PUBLICATION.

A deadlock can occur when the DDL command and the apply worker acquire
catalog locks in different orders while dropping replication origins.

The issue is rare in PG16 and higher branches because, in most cases, the
tablesync worker performs the origin drop in those branches, and its
locking sequence does not conflict with DDL operations.

This patch ensures consistent lock acquisition to prevent such deadlocks.

As per buildfarm.

Reported-by: Alexander Lakhin <[email protected]>
Author: Ajin Cherian <[email protected]>
Reviewed-by: Hayato Kuroda <[email protected]>
Reviewed-by: vignesh C <[email protected]>
Reviewed-by: Amit Kapila <[email protected]>
Backpatch-through: 14, where it was introduced
Discussion: https://postgr.es/m/bab95e12-6cc5-4ebb-80a8-3e41956aa297@gmail.com

diff --git a/src/backend/catalog/pg_subscription.c b/src/backend/catalog/pg_subscription.c
index 63c2992d19f75eec6d7589fa65bdf1299972a420..244acf52f360220437476ccb1da7a381f00c9e3e 100644 (file)
--- a/src/backend/catalog/pg_subscription.c
+++ b/src/backend/catalog/pg_subscription.c
@@ -320,7 +320,7 @@ AddSubscriptionRelState(Oid subid, Oid relid, char state,
  */
 void
 UpdateSubscriptionRelState(Oid subid, Oid relid, char state,
-                          XLogRecPtr sublsn)
+                          XLogRecPtr sublsn, bool already_locked)
 {
    Relation    rel;
    HeapTuple   tup;
@@ -328,9 +328,24 @@ UpdateSubscriptionRelState(Oid subid, Oid relid, char state,
    Datum       values[Natts_pg_subscription_rel];
    bool        replaces[Natts_pg_subscription_rel];
 
-   LockSharedObject(SubscriptionRelationId, subid, 0, AccessShareLock);
+   if (already_locked)
+   {
+#ifdef USE_ASSERT_CHECKING
+       LOCKTAG     tag;
 
-   rel = table_open(SubscriptionRelRelationId, RowExclusiveLock);
+       Assert(CheckRelationOidLockedByMe(SubscriptionRelRelationId,
+                                         RowExclusiveLock, true));
+       SET_LOCKTAG_OBJECT(tag, InvalidOid, SubscriptionRelationId, subid, 0);
+       Assert(LockHeldByMe(&tag, AccessShareLock, true));
+#endif
+
+       rel = table_open(SubscriptionRelRelationId, NoLock);
+   }
+   else
+   {
+       LockSharedObject(SubscriptionRelationId, subid, 0, AccessShareLock);
+       rel = table_open(SubscriptionRelRelationId, RowExclusiveLock);
+   }
 
    /* Try finding existing mapping. */
    tup = SearchSysCacheCopy2(SUBSCRIPTIONRELMAP,

diff --git a/src/backend/replication/logical/tablesync.c b/src/backend/replication/logical/tablesync.c
index 3fea0a0206ed30d11f3416a974f799bc9def9045..d3356bc84ee0cddc14cab9ecf60989308e078c46 100644 (file)
--- a/src/backend/replication/logical/tablesync.c
+++ b/src/backend/replication/logical/tablesync.c
@@ -316,7 +316,8 @@ process_syncing_tables_for_sync(XLogRecPtr current_lsn)
        UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
                                   MyLogicalRepWorker->relid,
                                   MyLogicalRepWorker->relstate,
-                                  MyLogicalRepWorker->relstate_lsn);
+                                  MyLogicalRepWorker->relstate_lsn,
+                                  false);
 
        /*
         * End streaming so that LogRepWorkerWalRcvConn can be used to drop
@@ -425,6 +426,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
    ListCell   *lc;
    bool        started_tx = false;
    bool        should_exit = false;
+   Relation    rel = NULL;
 
    Assert(!IsTransactionState());
 
@@ -492,7 +494,17 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
                 * worker to remove the origin tracking as if there is any
                 * error while dropping we won't restart it to drop the
                 * origin. So passing missing_ok = true.
+                *
+                * Lock the subscription and origin in the same order as we
+                * are doing during DDL commands to avoid deadlocks. See
+                * AlterSubscription_refresh.
                 */
+               LockSharedObject(SubscriptionRelationId, MyLogicalRepWorker->subid,
+                                0, AccessShareLock);
+
+               if (!rel)
+                   rel = table_open(SubscriptionRelRelationId, RowExclusiveLock);
+
                ReplicationOriginNameForLogicalRep(MyLogicalRepWorker->subid,
                                                   rstate->relid,
                                                   originname,
@@ -504,7 +516,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
                 */
                UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
                                           rstate->relid, rstate->state,
-                                          rstate->lsn);
+                                          rstate->lsn, true);
            }
        }
        else
@@ -555,7 +567,14 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
                         * This is required to avoid any undetected deadlocks
                         * due to any existing lock as deadlock detector won't
                         * be able to detect the waits on the latch.
+                        *
+                        * Also close any tables prior to the commit.
                         */
+                       if (rel)
+                       {
+                           table_close(rel, NoLock);
+                           rel = NULL;
+                       }
                        CommitTransactionCommand();
                        pgstat_report_stat(false);
                    }
@@ -623,6 +642,11 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
        }
    }
 
+   /* Close table if opened */
+   if (rel)
+       table_close(rel, NoLock);
+
+
    if (started_tx)
    {
        /*
@@ -1414,7 +1438,8 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
    UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
                               MyLogicalRepWorker->relid,
                               MyLogicalRepWorker->relstate,
-                              MyLogicalRepWorker->relstate_lsn);
+                              MyLogicalRepWorker->relstate_lsn,
+                              false);
    CommitTransactionCommand();
    pgstat_report_stat(true);
 
@@ -1547,7 +1572,8 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
    UpdateSubscriptionRelState(MyLogicalRepWorker->subid,
                               MyLogicalRepWorker->relid,
                               SUBREL_STATE_FINISHEDCOPY,
-                              MyLogicalRepWorker->relstate_lsn);
+                              MyLogicalRepWorker->relstate_lsn,
+                              false);
 
    CommitTransactionCommand();
 

diff --git a/src/include/catalog/pg_subscription_rel.h b/src/include/catalog/pg_subscription_rel.h
index c91797c869c24611dc76eaca79f724698fc8a527..f458447a0e5fba3cb2927075ac7fcfabe43ae34b 100644 (file)
--- a/src/include/catalog/pg_subscription_rel.h
+++ b/src/include/catalog/pg_subscription_rel.h
@@ -85,7 +85,7 @@ typedef struct SubscriptionRelState
 extern void AddSubscriptionRelState(Oid subid, Oid relid, char state,
                                    XLogRecPtr sublsn, bool retain_lock);
 extern void UpdateSubscriptionRelState(Oid subid, Oid relid, char state,
-                                      XLogRecPtr sublsn);
+                                      XLogRecPtr sublsn, bool already_locked);
 extern char GetSubscriptionRelState(Oid subid, Oid relid, XLogRecPtr *sublsn);
 extern void RemoveSubscriptionRel(Oid subid, Oid relid);