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LockBufferForCleanup() acquires the exclusive content lock, checks the buffer's shared pin count, and, if other pins remain, registers itself as the BM_PIN_COUNT_WAITER before waiting for an unpin notification. Since commits5310fac6e0andc75ebc657f, however, a shared buffer pin can be released while BM_LOCKED is set, introducing the following race: - LockBufferForCleanup() observes a refcount greater than one. - Before it sets BM_PIN_COUNT_WAITER, another backend releases the last conflicting pin. - Since BM_PIN_COUNT_WAITER is not yet set, no wakeup is sent. - LockBufferForCleanup() then sets BM_PIN_COUNT_WAITER and goes to sleep, even though only its own pin remains. As a result, LockBufferForCleanup() can sleep indefinitely because the wakeup corresponding to the last conflicting unpin has already been missed. Fix this by setting BM_PIN_COUNT_WAITER while holding the buffer header lock, then rechecking the refcount before releasing the content lock. If only our pin remains, clear the waiter state and proceed without sleeping. Otherwise, wait as before. This issue was reported by buildfarm member skink, where it manifested as intermittent timeouts in 048_vacuum_horizon_floor.pl. Backpatch to v19, where commits5310fac6e0andc75ebc657fintroduced the race. Reported-by: Alexander Lakhin <exclusion@gmail.com> Author: Xuneng Zhou <xunengzhou@gmail.com> Reviewed-by: Andres Freund <andres@anarazel.de> Reviewed-by: Fujii Masao <masao.fujii@gmail.com> Discussion: https://postgr.es/m/7685519a-0bf9-4e17-93ca-7e3aa10fa29c@gmail.com Backpatch-through: 19
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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/19/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/19/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.