BUG #19530: Crash (SIGSEGV/SIGBUS) in parallel B-tree index vacuum during plain VACUUM

The following bug has been logged on the website:

Bug reference: 19530
Logged by: Maciej
Email address: webmaster@algedi.pl
PostgreSQL version: 17.7
Operating system: FreeBSD 14.4-RELEASE, x86-64
Description:

PostgreSQL 17.7 intermittently crashes a parallel maintenance worker during
routine VACUUM, taking the server through automatic crash recovery each
time.

Summary:
Recurring backend / parallel-worker terminations with signal 11 (SIGSEGV)
and signal 10 (SIGBUS). Each crash is followed by "terminating any other
active server processes" and crash recovery (~5 s). It is intermittent:
about 16 process terminations over 5 days, with fully clean days in between;
the same nightly maintenance succeeds on most days. Hardware was checked
and is clean (no MCE/ECC/I/O errors).

Environment:
PostgreSQL 17.7, FreeBSD 14.4-RELEASE, x86-64, physical server, 256 GB
RAM. dynamic_shared_memory_type=posix, huge_pages=try.
max_parallel_workers=8, max_parallel_maintenance_workers=4,
max_parallel_workers_per_gather=4. Extensions: pg_stat_statements, pg_trgm,
unaccent,
plpgsql only — no custom C extensions, no PL/Perl/Python.

What the crashing process was doing:
The crashing process is a parallel maintenance worker. A preserved core
dump shows the process title "parallel worker for PID <leader>", with memory
contexts "BTree Vacuum State" and "AutoVacuum Data" present and no
executor/query state — i.e. parallel index vacuum, not parallel query. The
trigger is a scheduled VACUUM (SKIP_DATABASE_STATS, VERBOSE, ANALYZE) run
via vacuumdb over several large tables, each carrying many (~10–30) btree
indexes, so parallel index vacuuming is engaged. The SIGBUS variant is
consistent with a DSM (POSIX shared memory) problem in the parallel path.

Expected vs actual:
Expected: VACUUM completes normally. Actual: a parallel index-vacuum
worker crashes (SIGSEGV/SIGBUS) and the server goes through crash recovery.

Possibly related:
This appears to reach the same btbulkdelete / btvacuumscan code as the
report "Segmentation fault in PostgreSQL 17.7 during REINDEX TABLE
CONCURRENTLY"
(/messages/by-id/VI0PR07MB10718A4DC292E068C51404AB2974EA@VI0PR07MB10718.eurprd07.prod.outlook.com),
but reached
via the plain-VACUUM index-vacuum path rather than validate_index /
ReindexRelationConcurrently. That suggests the fault is in the (parallel)
B-tree
index-vacuum code, reachable from both paths.

Workaround:
Setting max_parallel_maintenance_workers = 0 (sequential index vacuuming)
appears to stop the crashes (observation ongoing).