From ab14bd6d2021e752c1893ee2c6fb7e46537c94b2 Mon Sep 17 00:00:00 2001 From: Greg Burd Date: Thu, 12 Nov 2026 12:14:43 -0500 Subject: [PATCH v4 16/21] pg_basebackup: Protect the WAL streamer exit flag with a mutex. The WAL streamer thread sets wal_streamer_thread_exited and the main thread polls it, so a volatile bool is a data race under the C11 memory model. sig_atomic_t wouldn't be any better, since it only promises atomicity against a signal handler interrupting the same thread. Frontend code can't use port/atomics.h yet, so take a mutex, as the same file already does for xlogendptr. The main thread checks the flag once per COPY chunk, so the cost doesn't matter. Reported-by: Jakub Wartak Discussion: https://postgr.es/m/CAKZiRmw3gpoXeOc9Pa_PRpfp-bTeQhg6gaY2Jw0Ck6NX4PWPhQ%40mail.gmail.com --- src/bin/pg_basebackup/pg_basebackup.c | 33 +++++++++++++++++++++++---- 1 file changed, 29 insertions(+), 4 deletions(-) diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c index a0f5cab7360..193404c7458 100644 --- a/src/bin/pg_basebackup/pg_basebackup.c +++ b/src/bin/pg_basebackup/pg_basebackup.c @@ -176,7 +176,8 @@ static char *progress_filename = NULL; static pg_thrd_t wal_streamer_thread; /* Flag set by WAL streamer thread if it exits early. */ -static volatile bool wal_streamer_thread_exited = false; +static bool wal_streamer_thread_exited = false; +static pg_mtx_t wal_streamer_thread_exited_lock = PG_MTX_PLAIN_INIT; /* End position for xlog streaming, empty string if unknown yet */ static XLogRecPtr xlogendptr; @@ -465,6 +466,30 @@ typedef struct int wal_compress_level; } logstreamer_param; +/* + * The WAL streamer thread sets this flag when it fails, and the main thread + * polls it while receiving the base backup. + */ +static void +set_wal_streamer_thread_exited(void) +{ + pg_mtx_lock(&wal_streamer_thread_exited_lock); + wal_streamer_thread_exited = true; + pg_mtx_unlock(&wal_streamer_thread_exited_lock); +} + +static bool +get_wal_streamer_thread_exited(void) +{ + bool result; + + pg_mtx_lock(&wal_streamer_thread_exited_lock); + result = wal_streamer_thread_exited; + pg_mtx_unlock(&wal_streamer_thread_exited_lock); + + return result; +} + static int LogStreamerMain(void *argument) { @@ -500,14 +525,14 @@ LogStreamerMain(void *argument) * but we need to tell the parent that we didn't shutdown in a nice * way. */ - wal_streamer_thread_exited = true; + set_wal_streamer_thread_exited(); return 1; } if (!stream.walmethod->ops->finish(stream.walmethod)) { pg_log_error("could not finish writing WAL files: %m"); - wal_streamer_thread_exited = true; + set_wal_streamer_thread_exited(); return 1; } @@ -927,7 +952,7 @@ ReceiveCopyData(PGconn *conn, WriteDataCallback callback, PQerrorMessage(conn)); /* Periodic check for early exit of WAL streamer thread. */ - if (wal_streamer_thread_exited) + if (get_wal_streamer_thread_exited()) pg_fatal("background thread terminated unexpectedly"); (*callback) (r, copybuf, callback_data); -- 2.54.0