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DROP TABLESPACE checked pg_shdepend for dependent objects without first locking the tablespace. A concurrent command that recorded a shared dependency on the tablespace right after that check could still commit, leaving an object whose pg_shdepend entry (or, for a relation, pg_class.reltablespace) pointed to a tablespace that no longer existed. Close the race by having DropTableSpace() take an AccessExclusiveLock on the tablespace before calling checkSharedDependencies(). That conflicts with the AccessShareLock shdepLockAndCheckObject() takes when recording a new dependency, so the loser of the race blocks and rechecks once the winner commits. That AccessExclusiveLock creates a new deadlock: ALTER TABLESPACE RENAME/SET and the internal ACL/owner updates in DROP OWNED and REASSIGN OWNED touched the catalog tuple without locking the tablespace, risking a lock-order cycle with DROP. Fix by taking an AccessShareLock first in all four paths, rechecking pg_shdepend after any wait in the DROP OWNED and REASSIGN OWNED cases. GRANT, REVOKE, and ALTER TABLESPACE ... OWNER TO already lock the object. Add isolation tests covering both orderings of the original race (dependency-first and drop-first) and all four previously-unlocked update paths. Author: Ayush Tiwari <ayushtiwari.slg01@gmail.com> Reviewed-by: Andrew Dunstan <andrew@dunslane.net> Discussion: https://postgr.es/m/CAJTYsWXjAQFnGKzXsht3XK8KHhyhontwFJw4JAHsUSfs_ptR4g@mail.gmail.com Backpatch-through: 14
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.