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

1 files changed, 57 insertions, 31 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 5f0ee50092c..ad084684205 100644
--- a/src/backend/access/transam/xlog.c
+++ b/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();
 }
 
 /*