Fix SIGSEGV caused by incorrect setting of error_context_stack within external_endscan

Within external_beginscan(), scan->errcontext.previous may link to local error contexts such as spierrcontext, if errors occur, abort routines call external_endscan() to set global value error_context_stack to those local error contexts whose stack are not exist anymore, so everytime elog() or ereport() are called, a SIGSEGV occurs. To avoid this, setting up and restoring error_context_stack within a single function.

src/backend/access/external/fileam.c

@@ -279,11 +279,6 @@ external_beginscan(Relation relation, Index scanrelid, uint32 scancounter,
 		scan->fs_formatter->fmt_perrow_ctx = scan->fs_pstate->rowcontext;
 	}
 
-	/* Set up callback to identify error line number */
-	scan->errcontext.callback = external_scan_error_callback;
-	scan->errcontext.arg = (void *) scan->fs_pstate;
-	scan->errcontext.previous = error_context_stack;
-
 	/* pgstat_initstats(relation); */
 
 	return scan;
@@ -405,11 +400,6 @@ external_endscan(FileScanDesc scan)
 		scan->fs_pstate = NULL;
 	}
 
-	/*
-	 * clean up error context
-	 */
-	error_context_stack = scan->errcontext.previous;
-
 	PG_TRY();
 	{
 		/*
@@ -1200,10 +1190,16 @@ externalgettup(FileScanDesc scan,
 {
 	CopyState	pstate = scan->fs_pstate;
 	bool		custom = pstate->custom;
+	HeapTuple	tup = NULL;
+	ErrorContextCallback externalscan_error_context;
 
 	Assert(ScanDirectionIsForward(dir));
 
-	error_context_stack = &scan->errcontext;
+	externalscan_error_context.callback = external_scan_error_callback;
+	externalscan_error_context.arg = (void *) scan->fs_pstate;
+	externalscan_error_context.previous = error_context_stack;
+
+	error_context_stack = &externalscan_error_context;
 
 	if (!scan->fs_inited)
 	{
@@ -1217,10 +1213,14 @@ externalgettup(FileScanDesc scan,
 	}
 
 	if (!custom)
-		return externalgettup_defined(scan);	/* text/csv */
+		tup = externalgettup_defined(scan); /* text/csv */
 	else
-		return externalgettup_custom(scan);		/* custom	*/
+		tup = externalgettup_custom(scan);  /* custom */
+
+	/* Restore the previous error callback */
+	error_context_stack = externalscan_error_context.previous;
 
+	return tup;
 }
 
 /*

src/include/access/relscan.h

@@ -118,7 +118,6 @@ typedef struct FileScanDescData
 	FmgrInfo   *in_functions;
 	Oid		   *typioparams;
 	Oid			in_func_oid;
-	ErrorContextCallback errcontext;
 	
 	/* current file scan state */
 	bool		fs_inited;		/* false = scan not init'd yet */

src/test/regress/input/external_table.source

@@ -1421,3 +1421,32 @@ FORMAT 'csv';
 
 -- drop temp external table
 DROP EXTERNAL TABLE IF EXISTS serial;
+
+-- External table query within plpgSQL function get error
+CREATE EXTERNAL TABLE exttab_error_context_callback(c1 int, c2 int)
+LOCATION ('file://@hostname@@abs_srcdir@/data/exttab.data') FORMAT 'TEXT';
+
+CREATE or REPLACE FUNCTION exttab_error_context_callback_func()
+RETURNS SETOF INTEGER
+AS
+$$
+DECLARE
+    ret INTEGER;
+BEGIN
+    FOR ret IN
+        SELECT c2 from exttab_error_context_callback
+    LOOP
+        RETURN NEXT ret;
+    END LOOP;
+END
+$$
+LANGUAGE plpgSQL READS SQL DATA;
+
+SET gp_log_gang TO DEBUG;
+
+SELECT * FROM exttab_error_context_callback_func();
+
+SET gp_log_gang TO DEFAULT;
+
+DROP FUNCTION exttab_error_context_callback_func();
+DROP EXTERNAL TABLE exttab_error_context_callback;

src/test/regress/output/external_table.source

@@ -2886,3 +2886,29 @@ FORMAT 'csv';
 NOTICE:  CREATE EXTERNAL TABLE will create implicit sequence "serial_a_seq" for serial column "serial.a"
 -- drop temp external table
 DROP EXTERNAL TABLE IF EXISTS serial;
+-- External table query within plpgSQL function get error
+CREATE EXTERNAL TABLE exttab_error_context_callback(c1 int, c2 int)
+LOCATION ('file://@hostname@@abs_srcdir@/data/exttab.data') FORMAT 'TEXT';
+CREATE or REPLACE FUNCTION exttab_error_context_callback_func()
+RETURNS SETOF INTEGER
+AS
+$$
+DECLARE
+    ret INTEGER;
+BEGIN
+    FOR ret IN
+        SELECT c2 from exttab_error_context_callback
+    LOOP
+        RETURN NEXT ret;
+    END LOOP;
+END
+$$
+LANGUAGE plpgSQL READS SQL DATA;
+SET gp_log_gang TO DEBUG;
+SELECT * FROM exttab_error_context_callback_func();
+ERROR:  missing data for column "c2"  (seg1 slice2 @hostname@:25532 pid=20960)
+DETAIL:  External table exttab_error_context_callback, line 1 of file://@hostname@@abs_srcdir@/data/exttab.data: "1|1_number"
+CONTEXT:  PL/pgSQL function "exttab_error_context_callback_func" line 4 at FOR over SELECT rows
+SET gp_log_gang TO DEFAULT;
+DROP FUNCTION exttab_error_context_callback_func();
+DROP EXTERNAL TABLE exttab_error_context_callback;