Remove XLogFileNameP() from the tree

XLogFileNameP() is a wrapper routine able to build a palloc'd string for
a WAL segment name, which is used for error string generation.  There
were several code paths where it gets called in a critical section,
where memory allocation is not allowed.  This results in triggering
an assertion failure instead of generating the wanted error message.

Another, more annoying, problem is that if the allocation to generate
the WAL segment name fails on OOM, then the failure would be escalated
to a PANIC.

This removes the routine and all its callers are replaced with a logic
using a fixed-size buffer.  This way, all the existing mistakes are
fixed and future ones are prevented.

Author: Masahiko Sawada
Reviewed-by: Michael Paquier, Álvaro Herrera
Discussion: https://postgr.es/m/CA+fd4k5gC9H4uoWMLg9K_QfNrnkkdEw+-AFveob9YX7z8JnKTA@mail.gmail.com

src/backend/access/transam/xlog.c

@@ -2499,14 +2499,21 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
 				pgstat_report_wait_end();
 				if (written <= 0)
 				{
+					char		xlogfname[MAXFNAMELEN];
+					int			save_errno;
+
 					if (errno == EINTR)
 						continue;
+
+					save_errno = errno;
+					XLogFileName(xlogfname, ThisTimeLineID, openLogSegNo,
+								 wal_segment_size);
+					errno = save_errno;
 					ereport(PANIC,
 							(errcode_for_file_access(),
 							 errmsg("could not write to log file %s "
 									"at offset %u, length %zu: %m",
-									XLogFileNameP(ThisTimeLineID, openLogSegNo),
-									startoffset, nleft)));
+									xlogfname, startoffset, nleft)));
 				}
 				nleft -= written;
 				from += written;
@@ -3792,10 +3799,17 @@ XLogFileClose(void)
 #endif
 
 	if (close(openLogFile) != 0)
+	{
+		char		xlogfname[MAXFNAMELEN];
+		int			save_errno = errno;
+
+		XLogFileName(xlogfname, ThisTimeLineID, openLogSegNo, wal_segment_size);
+		errno = save_errno;
 		ereport(PANIC,
 				(errcode_for_file_access(),
-				 errmsg("could not close file \"%s\": %m",
-						XLogFileNameP(ThisTimeLineID, openLogSegNo))));
+				 errmsg("could not close file \"%s\": %m", xlogfname)));
+	}
+
 	openLogFile = -1;
 }
 
@@ -5510,10 +5524,17 @@ exitArchiveRecovery(TimeLineID endTLI, XLogRecPtr endOfLog)
 		fd = XLogFileInit(startLogSegNo, &use_existent, true);
 
 		if (close(fd) != 0)
+		{
+			char		xlogfname[MAXFNAMELEN];
+			int			save_errno = errno;
+
+			XLogFileName(xlogfname, ThisTimeLineID, openLogSegNo,
+						 wal_segment_size);
+			errno = save_errno;
 			ereport(ERROR,
 					(errcode_for_file_access(),
-					 errmsg("could not close file \"%s\": %m",
-							XLogFileNameP(ThisTimeLineID, startLogSegNo))));
+					 errmsg("could not close file \"%s\": %m", xlogfname)));
+		}
 	}
 
 	/*
@@ -10079,10 +10100,19 @@ assign_xlog_sync_method(int new_sync_method, void *extra)
 		{
 			pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC_METHOD_ASSIGN);
 			if (pg_fsync(openLogFile) != 0)
+			{
+				char		xlogfname[MAXFNAMELEN];
+				int			save_errno;
+
+				save_errno = errno;
+				XLogFileName(xlogfname, ThisTimeLineID, openLogSegNo,
+							 wal_segment_size);
+				errno = save_errno;
 				ereport(PANIC,
 						(errcode_for_file_access(),
-						 errmsg("could not fsync file \"%s\": %m",
-								XLogFileNameP(ThisTimeLineID, openLogSegNo))));
+						 errmsg("could not fsync file \"%s\": %m", xlogfname)));
+			}
+
 			pgstat_report_wait_end();
 			if (get_sync_bit(sync_method) != get_sync_bit(new_sync_method))
 				XLogFileClose();
@@ -10100,32 +10130,25 @@ assign_xlog_sync_method(int new_sync_method, void *extra)
 void
 issue_xlog_fsync(int fd, XLogSegNo segno)
 {
+	char	   *msg = NULL;
+
 	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
 	switch (sync_method)
 	{
 		case SYNC_METHOD_FSYNC:
 			if (pg_fsync_no_writethrough(fd) != 0)
-				ereport(PANIC,
-						(errcode_for_file_access(),
-						 errmsg("could not fsync file \"%s\": %m",
-								XLogFileNameP(ThisTimeLineID, segno))));
+				msg = _("could not fsync file \"%s\": %m");
 			break;
 #ifdef HAVE_FSYNC_WRITETHROUGH
 		case SYNC_METHOD_FSYNC_WRITETHROUGH:
 			if (pg_fsync_writethrough(fd) != 0)
-				ereport(PANIC,
-						(errcode_for_file_access(),
-						 errmsg("could not fsync write-through file \"%s\": %m",
-								XLogFileNameP(ThisTimeLineID, segno))));
+				msg = _("could not fsync write-through file \"%s\": %m");
 			break;
 #endif
 #ifdef HAVE_FDATASYNC
 		case SYNC_METHOD_FDATASYNC:
 			if (pg_fdatasync(fd) != 0)
-				ereport(PANIC,
-						(errcode_for_file_access(),
-						 errmsg("could not fdatasync file \"%s\": %m",
-								XLogFileNameP(ThisTimeLineID, segno))));
+				msg = _("could not fdatasync file \"%s\": %m");
 			break;
 #endif
 		case SYNC_METHOD_OPEN:
@@ -10136,19 +10159,22 @@ issue_xlog_fsync(int fd, XLogSegNo segno)
 			elog(PANIC, "unrecognized wal_sync_method: %d", sync_method);
 			break;
 	}
-	pgstat_report_wait_end();
-}
 
-/*
- * Return the filename of given log segment, as a palloc'd string.
- */
-char *
-XLogFileNameP(TimeLineID tli, XLogSegNo segno)
-{
-	char	   *result = palloc(MAXFNAMELEN);
+	/* PANIC if failed to fsync */
+	if (msg)
+	{
+		char		xlogfname[MAXFNAMELEN];
+		int			save_errno = errno;
 
-	XLogFileName(result, tli, segno, wal_segment_size);
-	return result;
+		XLogFileName(xlogfname, ThisTimeLineID, openLogSegNo,
+					 wal_segment_size);
+		errno = save_errno;
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg(msg, xlogfname)));
+	}
+
+	pgstat_report_wait_end();
 }
 
 /*

src/backend/access/transam/xlogutils.c

@@ -776,7 +776,7 @@ XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wa
 
 /* openSegment callback for WALRead */
 static int
-wal_segment_open(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
+wal_segment_open(XLogSegNo nextSegNo, WALSegmentContext * segcxt,
 				 TimeLineID *tli_p)
 {
 	TimeLineID	tli = *tli_p;
@@ -944,7 +944,9 @@ void
 WALReadRaiseError(WALReadError *errinfo)
 {
 	WALOpenSegment *seg = &errinfo->wre_seg;
-	char	   *fname = XLogFileNameP(seg->ws_tli, seg->ws_segno);
+	char		fname[MAXFNAMELEN];
+
+	XLogFileName(fname, seg->ws_tli, seg->ws_segno, wal_segment_size);
 
 	if (errinfo->wre_read < 0)
 	{

src/backend/replication/walreceiver.c

@@ -576,17 +576,17 @@ WalReceiverMain(void)
 			char		xlogfname[MAXFNAMELEN];
 
 			XLogWalRcvFlush(false);
+			XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
 			if (close(recvFile) != 0)
 				ereport(PANIC,
 						(errcode_for_file_access(),
 						 errmsg("could not close log segment %s: %m",
-								XLogFileNameP(recvFileTLI, recvSegNo))));
+								xlogfname)));
 
 			/*
 			 * Create .done file forcibly to prevent the streamed segment from
 			 * being archived later.
 			 */
-			XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
 			if (XLogArchiveMode != ARCHIVE_MODE_ALWAYS)
 				XLogArchiveForceDone(xlogfname);
 			else
@@ -900,6 +900,8 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 
 				XLogWalRcvFlush(false);
 
+				XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
+
 				/*
 				 * XLOG segment files will be re-read by recovery in startup
 				 * process soon, so we don't advise the OS to release cache
@@ -909,13 +911,12 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 					ereport(PANIC,
 							(errcode_for_file_access(),
 							 errmsg("could not close log segment %s: %m",
-									XLogFileNameP(recvFileTLI, recvSegNo))));
+									xlogfname)));
 
 				/*
 				 * Create .done file forcibly to prevent the streamed segment
 				 * from being archived later.
 				 */
-				XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
 				if (XLogArchiveMode != ARCHIVE_MODE_ALWAYS)
 					XLogArchiveForceDone(xlogfname);
 				else
@@ -943,11 +944,18 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 		if (recvOff != startoff)
 		{
 			if (lseek(recvFile, (off_t) startoff, SEEK_SET) < 0)
+			{
+				char		xlogfname[MAXFNAMELEN];
+				int			save_errno = errno;
+
+				XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
+				errno = save_errno;
 				ereport(PANIC,
 						(errcode_for_file_access(),
 						 errmsg("could not seek in log segment %s to offset %u: %m",
-								XLogFileNameP(recvFileTLI, recvSegNo),
-								startoff)));
+								xlogfname, startoff)));
+			}
+
 			recvOff = startoff;
 		}
 
@@ -957,15 +965,21 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 		byteswritten = write(recvFile, buf, segbytes);
 		if (byteswritten <= 0)
 		{
+			char		xlogfname[MAXFNAMELEN];
+			int			save_errno;
+
 			/* if write didn't set errno, assume no disk space */
 			if (errno == 0)
 				errno = ENOSPC;
+
+			save_errno = errno;
+			XLogFileName(xlogfname, recvFileTLI, recvSegNo, wal_segment_size);
+			errno = save_errno;
 			ereport(PANIC,
 					(errcode_for_file_access(),
 					 errmsg("could not write to log segment %s "
 							"at offset %u, length %lu: %m",
-							XLogFileNameP(recvFileTLI, recvSegNo),
-							recvOff, (unsigned long) segbytes)));
+							xlogfname, recvOff, (unsigned long) segbytes)));
 		}
 
 		/* Update state for write */

src/backend/replication/walsender.c

@@ -2434,10 +2434,17 @@ WalSndSegmentOpen(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
 	 * too old WAL segment that has already been removed or recycled.
 	 */
 	if (errno == ENOENT)
+	{
+		char		xlogfname[MAXFNAMELEN];
+		int			save_errno = errno;
+
+		XLogFileName(xlogfname, *tli_p, nextSegNo, wal_segment_size);
+		errno = save_errno;
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("requested WAL segment %s has already been removed",
-						XLogFileNameP(*tli_p, nextSegNo))));
+						xlogfname)));
+	}
 	else
 		ereport(ERROR,
 				(errcode_for_file_access(),

src/include/access/xlog.h

@@ -288,7 +288,6 @@ extern bool RecoveryIsPaused(void);
 extern void SetRecoveryPause(bool recoveryPause);
 extern TimestampTz GetLatestXTime(void);
 extern TimestampTz GetCurrentChunkReplayStartTime(void);
-extern char *XLogFileNameP(TimeLineID tli, XLogSegNo segno);
 
 extern void UpdateControlFile(void);
 extern uint64 GetSystemIdentifier(void);

src/include/access/xlog_internal.h

@@ -152,6 +152,10 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
 /* Length of XLog file name */
 #define XLOG_FNAME_LEN	   24
 
+/*
+ * Generate a WAL segment file name.  Do not use this macro in a helper
+ * function allocating the result generated.
+ */
 #define XLogFileName(fname, tli, logSegNo, wal_segsz_bytes)	\
 	snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli,		\
 			 (uint32) ((logSegNo) / XLogSegmentsPerXLogId(wal_segsz_bytes)), \