614b7f18b3
Commit 2c8dd05d6c added the atomic variable writtenUpto into walreceiver's shared memory information. It's initialized only when walreceiver started up but could be read via pg_stat_wal_receiver view anytime, i.e., even before it's initialized. In the server built with --disable-atomics and --disable-spinlocks, this uninitialized atomic variable read could cause "invalid spinlock number: 0" error. This commit changed writtenUpto so that it's initialized at the postmaster startup, to avoid the uninitialized variable read via pg_stat_wal_receiver and fix the error. Also this commit moved the read of writtenUpto after the release of spinlock protecting walreceiver's shared variables. This is necessary to prevent new spinlock from being taken by atomic variable read while holding another spinlock, and to shorten the spinlock duration. This change leads writtenUpto not to be consistent with the other walreceiver's shared variables protected by a spinlock. But this is OK because writtenUpto should not be used for data integrity checks. Back-patch to v13 where commit 2c8dd05d6c introduced the bug. Author: Fujii Masao Reviewed-by: Michael Paquier, Thomas Munro, Andres Freund Discussion: https://postgr.es/m/7ef8708c-5b6b-edd3-2cf2-7783f1c7c175@oss.nttdata.com
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