From 614b7f18b3bda738f352a8732cf749eb5fa56dae Mon Sep 17 00:00:00 2001 From: Fujii Masao Date: Thu, 18 Feb 2021 23:22:23 +0900 Subject: [PATCH] Fix "invalid spinlock number: 0" error in pg_stat_wal_receiver. 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 --- src/backend/replication/walreceiver.c | 11 +++++++++-- src/backend/replication/walreceiverfuncs.c | 1 + src/test/regress/expected/sysviews.out | 7 +++++++ src/test/regress/sql/sysviews.sql | 3 +++ 4 files changed, 20 insertions(+), 2 deletions(-) diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c index 723f513d8bc..9ec71238c48 100644 --- a/src/backend/replication/walreceiver.c +++ b/src/backend/replication/walreceiver.c @@ -249,7 +249,7 @@ WalReceiverMain(void) SpinLockRelease(&walrcv->mutex); - pg_atomic_init_u64(&WalRcv->writtenUpto, 0); + pg_atomic_write_u64(&WalRcv->writtenUpto, 0); /* Arrange to clean up at walreceiver exit */ on_shmem_exit(WalRcvDie, 0); @@ -1325,7 +1325,6 @@ pg_stat_get_wal_receiver(PG_FUNCTION_ARGS) state = WalRcv->walRcvState; receive_start_lsn = WalRcv->receiveStart; receive_start_tli = WalRcv->receiveStartTLI; - written_lsn = pg_atomic_read_u64(&WalRcv->writtenUpto); flushed_lsn = WalRcv->flushedUpto; received_tli = WalRcv->receivedTLI; last_send_time = WalRcv->lastMsgSendTime; @@ -1345,6 +1344,14 @@ pg_stat_get_wal_receiver(PG_FUNCTION_ARGS) if (pid == 0 || !ready_to_display) PG_RETURN_NULL(); + /* + * Read "writtenUpto" without holding a spinlock. Note that it may not be + * consistent with the other shared variables of the WAL receiver + * protected by a spinlock, but this should not be used for data integrity + * checks. + */ + written_lsn = pg_atomic_read_u64(&WalRcv->writtenUpto); + /* determine result type */ if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE) elog(ERROR, "return type must be a row type"); diff --git a/src/backend/replication/walreceiverfuncs.c b/src/backend/replication/walreceiverfuncs.c index 69b91a7dab8..63e60478ea6 100644 --- a/src/backend/replication/walreceiverfuncs.c +++ b/src/backend/replication/walreceiverfuncs.c @@ -63,6 +63,7 @@ WalRcvShmemInit(void) MemSet(WalRcv, 0, WalRcvShmemSize()); WalRcv->walRcvState = WALRCV_STOPPED; SpinLockInit(&WalRcv->mutex); + pg_atomic_init_u64(&WalRcv->writtenUpto, 0); WalRcv->latch = NULL; } } diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out index 81bdacf59da..6d048e309cb 100644 --- a/src/test/regress/expected/sysviews.out +++ b/src/test/regress/expected/sysviews.out @@ -83,6 +83,13 @@ select count(*) = 1 as ok from pg_stat_wal; t (1 row) +-- We expect no walreceiver running in this test +select count(*) = 0 as ok from pg_stat_wal_receiver; + ok +---- + t +(1 row) + -- This is to record the prevailing planner enable_foo settings during -- a regression test run. select name, setting from pg_settings where name like 'enable%'; diff --git a/src/test/regress/sql/sysviews.sql b/src/test/regress/sql/sysviews.sql index b9b875bc6ab..dc8c9a3ac23 100644 --- a/src/test/regress/sql/sysviews.sql +++ b/src/test/regress/sql/sysviews.sql @@ -40,6 +40,9 @@ select count(*) >= 0 as ok from pg_prepared_xacts; -- There must be only one record select count(*) = 1 as ok from pg_stat_wal; +-- We expect no walreceiver running in this test +select count(*) = 0 as ok from pg_stat_wal_receiver; + -- This is to record the prevailing planner enable_foo settings during -- a regression test run. select name, setting from pg_settings where name like 'enable%';