postgres.git / summary / log / commit / refs

commit    734be249d2c8aab31b25bcb073a1e98692bc73f6
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sun Jul 11 16:54:24 2021 +0000
First released in: 15.0, 9.6.23, 10.18, 11.13, 12.8, 13.4, 14.0

    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.  This
    allowed the ALTER to proceed in parallel with a DROP EXTENSION,
    which is problematic for a couple of reasons.  If both commands
    succeeded we'd be left with a dangling link in pg_depend, which
    would cause problems later.  Also, if the ALTER failed for some
    reason, it might try to print the extension's name, and that could
    result in a crash or (in older branches) a silly error message
    complaining about extension "(null)".
    
    Per bug #17098 from Alexander Lakhin.  Back-patch to all
    supported branches.
    
    Discussion: https://postgr.es/m/17098-b960f3616c861f83@postgresql.org


 src/backend/commands/extension.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/backend/commands/extension.c b/src/backend/commands/extension.c
index 66723275360..0cc814cf8b6 100644
--- a/src/backend/commands/extension.c
+++ b/src/backend/commands/extension.c
@@ -3003,9 +3003,17 @@ ExecAlterExtensionContentsStmt(AlterExtensionContentsStmt *stmt,
 	Relation	relation;
 	Oid			oldExtension;
 
-	extension.classId = ExtensionRelationId;
-	extension.objectId = get_extension_oid(stmt->extname, false);
-	extension.objectSubId = 0;
+	/*
+	 * Find the extension and acquire a lock on it, to ensure it doesn't get
+	 * dropped concurrently.  A sharable lock seems sufficient: there's no
+	 * reason not to allow other sorts of manipulations, such as add/drop of
+	 * other objects, to occur concurrently.  Concurrently adding/dropping the
+	 * *same* object would be bad, but we prevent that by using a non-sharable
+	 * lock on the individual object, below.
+	 */
+	extension = get_object_address(OBJECT_EXTENSION,
+								   list_make1(makeString(stmt->extname)), NIL,
+								   &relation, AccessShareLock, false);
 
 	/* Permission check: must own extension */
 	if (!pg_extension_ownercheck(extension.objectId, GetUserId()))


[parent: f8abf6944b12]