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db4d12fc97
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 |
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