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In rebuild_relation(), don't access an already-closed relcache entry.

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This reliably fails with -DRELCACHE_FORCE_RELEASE, as reported by
Andrew Dunstan, and could sometimes fail in normal operation, resulting
in a wrong persistence value being used for the transient table.
It's not immediately clear to me what effects that might have beyond
the risk of a crash while accessing OldHeap->rd_rel->relpersistence,
but it's probably not good.

Bug introduced by commit f41872d0c, and made substantially worse by
commit 85b506bbf, which added a second such access significantly
later than the heap_close.  I doubt the first reference could fail
in a production scenario, but the second one definitely could.

Discussion: https://postgr.es/m/7b52f900-0579-cda9-ae2e-de5da17090e6@2ndQuadrant.com
This commit is contained in:
Tom Lane 2017-03-04 16:09:33 -05:00
parent d77ff69341
commit dbca84f04e
1 changed files with 5 additions and 3 deletions
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8
src/backend/commands/cluster.c
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@ -557,6 +557,7 @@ rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
Oid tableOid = RelationGetRelid(OldHeap);
Oid tableSpace = OldHeap->rd_rel->reltablespace;
Oid OIDNewHeap;
char relpersistence;
bool is_system_catalog;
bool swap_toast_by_content;
TransactionId frozenXid;
@ -566,7 +567,8 @@ rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
if (OidIsValid(indexOid))
mark_index_clustered(OldHeap, indexOid, true);
/* Remember if it's a system catalog */
/* Remember info about rel before closing OldHeap */
relpersistence = OldHeap->rd_rel->relpersistence;
is_system_catalog = IsSystemRelation(OldHeap);
/* Close relcache entry, but keep lock until transaction commit */
@ -574,7 +576,7 @@ rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
/* Create the transient table that will receive the re-ordered data */
OIDNewHeap = make_new_heap(tableOid, tableSpace,
OldHeap->rd_rel->relpersistence,
relpersistence,
AccessExclusiveLock);
/* Copy the heap data into the new table in the desired order */
@ -588,7 +590,7 @@ rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
finish_heap_swap(tableOid, OIDNewHeap, is_system_catalog,
swap_toast_by_content, false, true,
frozenXid, cutoffMulti,
OldHeap->rd_rel->relpersistence);
relpersistence);
}