8000 Avoid "you don't own a lock of type ExclusiveLock" in GRANT TABLESPACE. · postgres/postgres@4ba84de · GitHub
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nmischnmisch
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Avoid "you don't own a lock of type ExclusiveLock" in GRANT TABLESPACE.
This WARNING appeared because SearchSysCacheLocked1() read cc_relisshared before catcache initialization, when the field is false unconditionally. On the basis of reading false there, it constructed a locktag as though pg_tablespace weren't relisshared. Only shared catalogs could be affected, and only GRANT TABLESPACE was affected in practice. SearchSysCacheLocked1() callers use one other shared-relation syscache, DATABASEOID. DATABASEOID is initialized by the end of CheckMyDatabase(), making the problem unreachable for pg_database. Back-patch to v13 (all supported versions). This has no known impact before v16, where ExecGrant_common() first appeared. Earlier branches avoid trouble by having a separate ExecGrant_Tablespace() that doesn't use LOCKTAG_TUPLE. However, leaving this unfixed in v15 could ensnare a future back-patch of a SearchSysCacheLocked1() call. Reported by Aya Iwata. Discussion: https://postgr.es/m/OS7PR01MB11964507B5548245A7EE54E70EA212@OS7PR01MB11964.jpnprd01.prod.outlook.com
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‎src/backend/utils/cache/syscache.c

Lines changed: 10 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -287,11 +287,9 @@ HeapTuple
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SearchSysCacheLocked1(int cacheId,
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Datum key1)
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{
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CatCache *cache = SysCache[cacheId];
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ItemPointerData tid;
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LOCKTAG tag;
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Oid dboid =
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SysCache[cacheId]->cc_relisshared ? InvalidOid : MyDatabaseId;
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Oid reloid = cacheinfo[cacheId].reloid;
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/*----------
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* Since inplace updates may happen just before our LockTuple(), we must
@@ -343,8 +341,15 @@ SearchSysCacheLocked1(int cacheId,
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tid = tuple->t_self;
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ReleaseSysCache(tuple);
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/* like: LockTuple(rel, &tid, lockmode) */
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SET_LOCKTAG_TUPLE(tag, dboid, reloid,
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/*
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* Do like LockTuple(rel, &tid, lockmode). While cc_relisshared won't
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* change from one iteration to another, it may have been a temporary
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* "false" until our first SearchSysCache1().
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*/
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SET_LOCKTAG_TUPLE(tag,
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cache->cc_relisshared ? InvalidOid : MyDatabaseId,
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cache->cc_reloid,
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ItemPointerGetBlockNumber(&tid),
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ItemPointerGetOffsetNumber(&tid));
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(void) LockAcquire(&tag, lockmode, false, false);

‎src/test/regress/expected/tablespace.out

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -927,6 +927,11 @@ ALTER INDEX testschema.part_a_idx SET TABLESPACE pg_default;
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-- Fail, not empty
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DROP TABLESPACE regress_tblspace;
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ERROR: tablespace "regress_tblspace" is not empty
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-- Adequate cache initialization before GRANT
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\c -
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BEGIN;
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GRANT ALL ON TABLESPACE regress_tblspace TO PUBLIC;
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ROLLBACK;
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CREATE ROLE regress_tablespace_user1 login;
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CREATE ROLE regress_tablespace_user2 login;
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GRANT USAGE ON SCHEMA testschema TO regress_tablespace_user2;

‎src/test/regress/sql/tablespace.sql

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -396,6 +396,12 @@ ALTER INDEX testschema.part_a_idx SET TABLESPACE pg_default;
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-- Fail, not empty
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DROP TABLESPACE regress_tblspace;
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-- Adequate cache initialization before GRANT
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\c -
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BEGIN;
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GRANT ALL ON TABLESPACE regress_tblspace TO PUBLIC;
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ROLLBACK;
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CREATE ROLE regress_tablespace_user1 login;
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CREATE ROLE regress_tablespace_user2 login;
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GRANT USAGE ON SCHEMA testschema TO regress_tablespace_user2;

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