fd270b728b
The drop database command waits for the logical replication sync worker to accept ProcSignalBarrier and the worker's slot creation waits for the drop database to finish which leads to a deadlock. This happens because the tablesync worker holds interrupts while creating a slot. We prevent cancel/die interrupts while creating a slot in the table sync worker because it is possible that before the server finishes this command, a concurrent drop subscription happens which would complete without removing this slot and that leads to the slot existing until the end of walsender. However, the slot will eventually get dropped at the walsender exit time, so there is no danger of the dangling slot. This patch reallows cancel/die interrupts while creating a slot and modifies the test to wait for slots to become zero to prevent finding an ephemeral slot. The reported hang doesn't happen in PG14 as the drop database starts to wait for ProcSignalBarrier with PG15 (commits 4eb2176318 and e2f65f4255) but it is good to backpatch this till PG14 as it is not a good idea to prevent interrupts during a network call that could block indefinitely. Reported-by: Lakshmi Narayanan Sreethar Diagnosed-by: Andres Freund Author: Hou Zhijie Reviewed-by: Vignesh C, Amit Kapila Backpatch-through: 14, where it was introduced in commit 6b67d72b60 Discussion: https://postgr.es/m/CA+kvmZELXQ4ZD3U=XCXuG3KvFgkuPoN1QrEj8c-rMRodrLOnsg@mail.gmail.com
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