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Michael Paquier
4e8edf53f9
DisownLatch() was executed after the PGPROC entry of the process terminated is pushed back into a freelist. A newly-forked backend that recycles the slot could call OwnLatch() and PANIC with a "latch already owned by PID", taking down the server. There were two scenarios related to lock groups where this issue could be reached: * A follower pushes the leader's PGPROC back to the freelist while the leader has not yet called DisownLatch() in its own ProcKill(). * A leader outliving all its followers pushes its own PGPROC onto the freelist before reaching DisownLatch(), which would be the most common scenario. This issue is fixed by calling SwitchBackToLocalLatch() and DisownLatch() at an earlier phase of ProcKill(), before any freelist manipulation happens, so that the slot of the backend terminated is never exposed as owning a latch. Note that pgstat_reset_wait_event_storage() is kept at a later stage. An upcoming commit will take advantage of that by introducing a test able to check the original PANIC scenario. Author: Vlad Lesin <vladlesin@gmail.com> Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru> Reviewed-by: Michael Paquier <michael@paquier.xyz> Discussion: https://postgr.es/m/d2983796-2603-41b7-a66e-fc8489ddb954@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/.