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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. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download/ See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.