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Fix LOAD_CRIT_INDEX() macro to take out AccessShareLock on the system index

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it is trying to build a relcache entry for.  This is an oversight in my 8.2
patch that tried to ensure we always took a lock on a relation before trying
to build its relcache entry.  The implication is that if someone committed a
reindex of a critical system index at about the same time that some other
backend were starting up without a valid pg_internal.init file, the second one
might PANIC due to not seeing any valid version of the index's pg_class row.
Improbable case, but definitely not impossible.
This commit is contained in:
Tom Lane 2008-04-16 18:23:19 +00:00
parent 79522dfb35
commit 5132e34005
1 changed files with 18 additions and 6 deletions
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24
src/backend/utils/cache/relcache.c vendored
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.250.2.1 2008/02/27 17:44:33 tgl Exp $
* $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.250.2.2 2008/04/16 18:23:19 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -212,8 +212,11 @@ static OpClassCacheEnt *LookupOpclassInfo(Oid operatorClassOid,
/*
* ScanPgRelation
*
* this is used by RelationBuildDesc to find a pg_class
* tuple matching targetRelId.
* This is used by RelationBuildDesc to find a pg_class
* tuple matching targetRelId. The caller must hold at least
* AccessShareLock on the target relid to prevent concurrent-update
* scenarios --- else our SnapshotNow scan might fail to find any
* version that it thinks is live.
*
* NB: the returned tuple has been copied into palloc'd storage
* and must eventually be freed with heap_freetuple.
@ -773,18 +776,18 @@ equalRuleLocks(RuleLock *rlock1, RuleLock *rlock2)
}
/* ----------------------------------
/*
* RelationBuildDesc
*
* Build a relation descriptor --- either a new one, or by
* recycling the given old relation object. The latter case
* supports rebuilding a relcache entry without invalidating
* pointers to it.
* pointers to it. The caller must hold at least
* AccessShareLock on the target relid.
*
* Returns NULL if no pg_class row could be found for the given relid
* (suggesting we are trying to access a just-deleted relation).
* Any other error is reported via elog.
* --------------------------------
*/
static Relation
RelationBuildDesc(Oid targetRelId, Relation oldrelation)
@ -1528,6 +1531,10 @@ RelationClose(Relation relation)
* RelationClearRelation just marks the entry as invalid by setting
* rd_isvalid to false. This routine is called to fix the entry when it
* is next needed.
*
* We assume that at the time we are called, we have at least AccessShareLock
* on the target index. (Note: in the calls from RelationClearRelation,
* this is legitimate because we know the rel has positive refcount.)
*/
static void
RelationReloadClassinfo(Relation relation)
@ -1581,6 +1588,9 @@ RelationReloadClassinfo(Relation relation)
* usually used when we are notified of a change to an open relation
* (one with refcount > 0). However, this routine just does whichever
* it's told to do; callers must determine which they want.
*
* NB: when rebuilding, we'd better hold some lock on the relation.
* In current usages this is presumed true because it has refcnt > 0.
*/
static void
RelationClearRelation(Relation relation, bool rebuild)
@ -2385,12 +2395,14 @@ RelationCacheInitializePhase2(void)
#define LOAD_CRIT_INDEX(indexoid) \
do { \
LockRelationOid(indexoid, AccessShareLock); \
ird = RelationBuildDesc(indexoid, NULL); \
if (ird == NULL) \
elog(PANIC, "could not open critical system index %u", \
indexoid); \
ird->rd_isnailed = true; \
ird->rd_refcnt = 1; \
UnlockRelationOid(indexoid, AccessShareLock); \
} while (0)
LOAD_CRIT_INDEX(ClassOidIndexId);