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Commit1c612bc

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Lock the extension during ALTER EXTENSION ADD/DROP.
Although we were careful to lock the object being added or dropped,we failed to get any sort of lock on the extension itself. Thisallowed the ALTER to proceed in parallel with a DROP EXTENSION,which is problematic for a couple of reasons. If both commandssucceeded we'd be left with a dangling link in pg_depend, whichwould cause problems later. Also, if the ALTER failed for somereason, it might try to print the extension's name, and that couldresult in a crash or (in older branches) a silly error messagecomplaining about extension "(null)".Per bug #17098 from Alexander Lakhin. Back-patch to allsupported branches.Discussion:https://postgr.es/m/17098-b960f3616c861f83@postgresql.org
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‎src/backend/commands/extension.c

Lines changed: 11 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -3282,9 +3282,17 @@ ExecAlterExtensionContentsStmt(AlterExtensionContentsStmt *stmt,
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Relationrelation;
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OidoldExtension;
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3285-
extension.classId=ExtensionRelationId;
3286-
extension.objectId=get_extension_oid(stmt->extname, false);
3287-
extension.objectSubId=0;
3285+
/*
3286+
* Find the extension and acquire a lock on it, to ensure it doesn't get
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* dropped concurrently. A sharable lock seems sufficient: there's no
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* reason not to allow other sorts of manipulations, such as add/drop of
3289+
* other objects, to occur concurrently. Concurrently adding/dropping the
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* *same* object would be bad, but we prevent that by using a non-sharable
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* lock on the individual object, below.
3292+
*/
3293+
extension=get_object_address(OBJECT_EXTENSION,
3294+
(Node*)makeString(stmt->extname),
3295+
&relation,AccessShareLock, false);
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/* Permission check: must own extension */
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if (!pg_extension_ownercheck(extension.objectId,GetUserId()))

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