From 00e407beda9b6e2d9190b8b07d442115dd306568 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Mon, 1 Dec 2025 22:31:44 -0500 Subject: [PATCH v9 01/10] freespace: Don't modify page without any lock Before this commit fsm_vacuum_page() modified the page without any lock on the page. Historically that was kind of ok, as we didn't rely on the freespace to really stay consistent and we did not have checksums. But these days pages are checksummed and there are ways for FSM pages to be included in WAL records, even if the FSM itself is still not WAL logged. If a FSM page ever were modified while a WAL record referenced that page, we'd be in trouble, as the WAL CRC could end up getting corrupted. The reason to address this right now is a series of patches with the goal to only allow modifications of pages with an appropriate lock level. Obviously not having any lock is not appropriate :) Discussion: https://postgr.es/m/4wggb7purufpto6x35fd2kwhasehnzfdy3zdcu47qryubs2hdz@fa5kannykekr Discussion: https://postgr.es/m/e6a8f734-2198-4958-a028-aba863d4a204@iki.fi --- src/backend/storage/freespace/freespace.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/src/backend/storage/freespace/freespace.c b/src/backend/storage/freespace/freespace.c index 19cf4155263..ad337c00871 100644 --- a/src/backend/storage/freespace/freespace.c +++ b/src/backend/storage/freespace/freespace.c @@ -906,10 +906,12 @@ fsm_vacuum_page(Relation rel, FSMAddress addr, /* * Reset the next slot pointer. This encourages the use of low-numbered * pages, increasing the chances that a later vacuum can truncate the - * relation. We don't bother with a lock here, nor with marking the page - * dirty if it wasn't already, since this is just a hint. + * relation. We don't bother with marking the page dirty if it wasn't + * already, since this is just a hint. */ + LockBuffer(buf, BUFFER_LOCK_SHARE); ((FSMPage) PageGetContents(page))->fp_next_slot = 0; + LockBuffer(buf, BUFFER_LOCK_UNLOCK); ReleaseBuffer(buf); -- 2.48.1.76.g4e746b1a31.dirty