Fix locking bugs that could corrupt pg_control.

The redo routines for XLOG_CHECKPOINT_{ONLINE,SHUTDOWN} must acquire
ControlFileLock before modifying ControlFile->checkPointCopy, or the
checkpointer could write out a control file with a bad checksum.

Likewise, XLogReportParameters() must acquire ControlFileLock before
modifying ControlFile and calling UpdateControlFile().

Back-patch to all supported releases.

Author: Nathan Bossart <bossartn@amazon.com>
Author: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/70BF24D6-DC51-443F-B55A-95735803842A%40amazon.com

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index ca09d81b08cfeb885390650fe7da632a5b79504a..55cac186dc71fcc2f4628f9974b30850bb51eb5d 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9743,6 +9743,8 @@ XLogReportParameters(void)
            XLogFlush(recptr);
        }
 
+       LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+
        ControlFile->MaxConnections = MaxConnections;
        ControlFile->max_worker_processes = max_worker_processes;
        ControlFile->max_wal_senders = max_wal_senders;
@@ -9752,6 +9754,8 @@ XLogReportParameters(void)
        ControlFile->wal_log_hints = wal_log_hints;
        ControlFile->track_commit_timestamp = track_commit_timestamp;
        UpdateControlFile();
+
+       LWLockRelease(ControlFileLock);
    }
 }
 
@@ -9976,7 +9980,9 @@ xlog_redo(XLogReaderState *record)
        }
 
        /* ControlFile->checkPointCopy always tracks the latest ckpt XID */
+       LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
        ControlFile->checkPointCopy.nextFullXid = checkPoint.nextFullXid;
+       LWLockRelease(ControlFileLock);
 
        /* Update shared-memory copy of checkpoint XID/epoch */
        SpinLockAcquire(&XLogCtl->info_lck);
@@ -10033,7 +10039,9 @@ xlog_redo(XLogReaderState *record)
            SetTransactionIdLimit(checkPoint.oldestXid,
                                  checkPoint.oldestXidDB);
        /* ControlFile->checkPointCopy always tracks the latest ckpt XID */
+       LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
        ControlFile->checkPointCopy.nextFullXid = checkPoint.nextFullXid;
+       LWLockRelease(ControlFileLock);
 
        /* Update shared-memory copy of checkpoint XID/epoch */
        SpinLockAcquire(&XLogCtl->info_lck);