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Fix lock upgrade hazard in ATExecAttachPartition.

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Amit Langote

Discussion: http://postgr.es/m/CAFjFpReT_kq_uwU_B8aWDxR7jNGE=P0iELycdq5oupi=xSQTOw@mail.gmail.com
This commit is contained in:
Robert Haas 2017-08-03 14:21:00 -04:00
parent 583df3b5c5
commit 972b6ec20b
1 changed files with 13 additions and 10 deletions
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23
src/backend/commands/tablecmds.c
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@ -13489,9 +13489,20 @@ ATExecAttachPartition(List **wqueue, Relation rel, PartitionCmd *cmd)
/*
* Prevent circularity by seeing if rel is a partition of attachrel. (In
* particular, this disallows making a rel a partition of itself.)
*
* We do that by checking if rel is a member of the list of attachRel's
* partitions provided the latter is partitioned at all. We want to avoid
* having to construct this list again, so we request the strongest lock
* on all partitions. We need the strongest lock, because we may decide
* to scan them if we find out that the table being attached (or its leaf
* partitions) may contain rows that violate the partition constraint.
* If the table has a constraint that would prevent such rows, which by
* definition is present in all the partitions, we need not scan the
* table, nor its partitions. But we cannot risk a deadlock by taking a
* weaker lock now and the stronger one only when needed.
*/
attachrel_children = find_all_inheritors(RelationGetRelid(attachrel),
AccessShareLock, NULL);
AccessExclusiveLock, NULL);
if (list_member_oid(attachrel_children, RelationGetRelid(rel)))
ereport(ERROR,
(errcode(ERRCODE_DUPLICATE_TABLE),
@ -13694,17 +13705,9 @@ ATExecAttachPartition(List **wqueue, Relation rel, PartitionCmd *cmd)
else
{
/* Constraints proved insufficient, so we need to scan the table. */
List *all_parts;
ListCell *lc;
/* Take an exclusive lock on the partitions to be checked */
if (attachrel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
all_parts = find_all_inheritors(RelationGetRelid(attachrel),
AccessExclusiveLock, NULL);
else
all_parts = list_make1_oid(RelationGetRelid(attachrel));
foreach(lc, all_parts)
foreach(lc, attachrel_children)
{
AlteredTableInfo *tab;
Oid part_relid = lfirst_oid(lc);