Fix locking bugs that could corrupt pg_control.

macdice · macdice · commit fd11b842eba9 · 2020-06-08T14:01:07.000+12:00
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
@@ -9647,6 +9647,8 @@ XLogReportParameters(void)
 			XLogFlush(recptr);
 		}
 
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+
 		ControlFile->MaxConnections = MaxConnections;
 		ControlFile->max_worker_processes = max_worker_processes;
 		ControlFile->max_prepared_xacts = max_prepared_xacts;
@@ -9655,6 +9657,8 @@ XLogReportParameters(void)
 		ControlFile->wal_log_hints = wal_log_hints;
 		ControlFile->track_commit_timestamp = track_commit_timestamp;
 		UpdateControlFile();
+
+		LWLockRelease(ControlFileLock);
 	}
 }
 
@@ -9879,8 +9883,10 @@ xlog_redo(XLogReaderState *record)
 		}
 
 		/* ControlFile->checkPointCopy always tracks the latest ckpt XID */
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
 		ControlFile->checkPointCopy.nextXidEpoch = checkPoint.nextXidEpoch;
 		ControlFile->checkPointCopy.nextXid = checkPoint.nextXid;
+		LWLockRelease(ControlFileLock);
 
 		/* Update shared-memory copy of checkpoint XID/epoch */
 		SpinLockAcquire(&XLogCtl->info_lck);
@@ -9938,8 +9944,10 @@ xlog_redo(XLogReaderState *record)
 			SetTransactionIdLimit(checkPoint.oldestXid,
 								  checkPoint.oldestXidDB);
 		/* ControlFile->checkPointCopy always tracks the latest ckpt XID */
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
 		ControlFile->checkPointCopy.nextXidEpoch = checkPoint.nextXidEpoch;
 		ControlFile->checkPointCopy.nextXid = checkPoint.nextXid;
+		LWLockRelease(ControlFileLock);
 
 		/* Update shared-memory copy of checkpoint XID/epoch */
 		SpinLockAcquire(&XLogCtl->info_lck);
