Fix broken logic for reporting PL/Python function names in errcontext.

tglsfdc · tglsfdc · commit db1c597f3c33 · 2018-02-14T14:47:18.000-05:00
plpython_error_callback() reported the name of the function associated with the topmost PL/Python execution context. This was not merely wrong if there were nested PL/Python contexts, but it risked a core dump if the topmost one is an inline code block rather than a named function. That will have proname = NULL, and so we were passing a NULL pointer to snprintf("%s"). It seems that none of the PL/Python-testing machines in the buildfarm will dump core for that, but some platforms do, as reported by Marina Polyakova. Investigation finds that there actually is an existing regression test that used to prove that the behavior was wrong, though apparently no one had noticed that it was printing the wrong function name. It stopped showing the problem in 9.6 when we adjusted psql to not print CONTEXT by default for NOTICE messages. The problem is masked (if your platform avoids the core dump) in error cases, because PL/Python will throw away the originally generated error info in favor of a new traceback produced at the outer level. Repair by using ErrorContextCallback.arg to pass the correct context to the error callback. Add a regression test illustrating correct behavior. Back-patch to all supported branches, since they're all broken this way. Discussion: https://postgr.es/m/156b989dbc6fe7c4d3223cf51da61195@postgrespro.ru
diff --git a/src/pl/plpython/expected/plpython_error.out b/src/pl/plpython/expected/plpython_error.out
@@ -426,3 +426,26 @@ EXCEPTION WHEN SQLSTATE 'SILLY' THEN
 	-- NOOP
 END
 $$ LANGUAGE plpgsql;
+/* test the context stack trace for nested execution levels
+ */
+CREATE FUNCTION notice_innerfunc() RETURNS int AS $$
+plpy.execute("DO LANGUAGE plpythonu $x$ plpy.notice('inside DO') $x$")
+return 1
+$$ LANGUAGE plpythonu;
+CREATE FUNCTION notice_outerfunc() RETURNS int AS $$
+plpy.execute("SELECT notice_innerfunc()")
+return 1
+$$ LANGUAGE plpythonu;
+\set SHOW_CONTEXT always
+SELECT notice_outerfunc();
+NOTICE:  inside DO
+CONTEXT:  PL/Python anonymous code block
+SQL statement "DO LANGUAGE plpythonu $x$ plpy.notice('inside DO') $x$"
+PL/Python function "notice_innerfunc"
+SQL statement "SELECT notice_innerfunc()"
+PL/Python function "notice_outerfunc"
+ notice_outerfunc 
+------------------
+                1
+(1 row)
+
diff --git a/src/pl/plpython/expected/plpython_error_0.out b/src/pl/plpython/expected/plpython_error_0.out
@@ -426,3 +426,26 @@ EXCEPTION WHEN SQLSTATE 'SILLY' THEN
 	-- NOOP
 END
 $$ LANGUAGE plpgsql;
+/* test the context stack trace for nested execution levels
+ */
+CREATE FUNCTION notice_innerfunc() RETURNS int AS $$
+plpy.execute("DO LANGUAGE plpythonu $x$ plpy.notice('inside DO') $x$")
+return 1
+$$ LANGUAGE plpythonu;
+CREATE FUNCTION notice_outerfunc() RETURNS int AS $$
+plpy.execute("SELECT notice_innerfunc()")
+return 1
+$$ LANGUAGE plpythonu;
+\set SHOW_CONTEXT always
+SELECT notice_outerfunc();
+NOTICE:  inside DO
+CONTEXT:  PL/Python anonymous code block
+SQL statement "DO LANGUAGE plpythonu $x$ plpy.notice('inside DO') $x$"
+PL/Python function "notice_innerfunc"
+SQL statement "SELECT notice_innerfunc()"
+PL/Python function "notice_outerfunc"
+ notice_outerfunc 
+------------------
+                1
+(1 row)
+
diff --git a/src/pl/plpython/expected/plpython_error_5.out b/src/pl/plpython/expected/plpython_error_5.out
@@ -426,3 +426,26 @@ EXCEPTION WHEN SQLSTATE 'SILLY' THEN
 	-- NOOP
 END
 $$ LANGUAGE plpgsql;
+/* test the context stack trace for nested execution levels
+ */
+CREATE FUNCTION notice_innerfunc() RETURNS int AS $$
+plpy.execute("DO LANGUAGE plpythonu $x$ plpy.notice('inside DO') $x$")
+return 1
+$$ LANGUAGE plpythonu;
+CREATE FUNCTION notice_outerfunc() RETURNS int AS $$
+plpy.execute("SELECT notice_innerfunc()")
+return 1
+$$ LANGUAGE plpythonu;
+\set SHOW_CONTEXT always
+SELECT notice_outerfunc();
+NOTICE:  inside DO
+CONTEXT:  PL/Python anonymous code block
+SQL statement "DO LANGUAGE plpythonu $x$ plpy.notice('inside DO') $x$"
+PL/Python function "notice_innerfunc"
+SQL statement "SELECT notice_innerfunc()"
+PL/Python function "notice_outerfunc"
+ notice_outerfunc 
+------------------
+                1
+(1 row)
+
diff --git a/src/pl/plpython/expected/plpython_subtransaction.out b/src/pl/plpython/expected/plpython_subtransaction.out
@@ -182,7 +182,7 @@ SELECT subtransaction_deeply_nested_test();
 NOTICE:  Swallowed SyntaxError('syntax error at or near "error"',)
 CONTEXT:  PL/Python function "subtransaction_nested_test"
 SQL statement "SELECT subtransaction_nested_test('t')"
-PL/Python function "subtransaction_nested_test"
+PL/Python function "subtransaction_deeply_nested_test"
  subtransaction_deeply_nested_test 
 -----------------------------------
  ok
diff --git a/src/pl/plpython/plpy_main.c b/src/pl/plpython/plpy_main.c
@@ -257,23 +257,26 @@ plpython_call_handler(PG_FUNCTION_ARGS)
 	/*
 	 * Push execution context onto stack.  It is important that this get
 	 * popped again, so avoid putting anything that could throw error between
-	 * here and the PG_TRY.  (plpython_error_callback expects the stack entry
-	 * to be there, so we have to make the context first.)
+	 * here and the PG_TRY.
 	 */
 	exec_ctx = PLy_push_execution_context();
 
-	/*
-	 * Setup error traceback support for ereport()
-	 */
-	plerrcontext.callback = plpython_error_callback;
-	plerrcontext.previous = error_context_stack;
-	error_context_stack = &plerrcontext;
-
 	PG_TRY();
 	{
 		Oid			funcoid = fcinfo->flinfo->fn_oid;
 		PLyProcedure *proc;
 
+		/*
+		 * Setup error traceback support for ereport().  Note that the PG_TRY
+		 * structure pops this for us again at exit, so we needn't do that
+		 * explicitly, nor do we risk the callback getting called after we've
+		 * destroyed the exec_ctx.
+		 */
+		plerrcontext.callback = plpython_error_callback;
+		plerrcontext.arg = exec_ctx;
+		plerrcontext.previous = error_context_stack;
+		error_context_stack = &plerrcontext;
+
 		if (CALLED_AS_TRIGGER(fcinfo))
 		{
 			Relation	tgrel = ((TriggerData *) fcinfo->context)->tg_relation;
@@ -299,9 +302,7 @@ plpython_call_handler(PG_FUNCTION_ARGS)
 	}
 	PG_END_TRY();
 
-	/* Pop the error context stack */
-	error_context_stack = plerrcontext.previous;
-	/* ... and then the execution context */
+	/* Destroy the execution context */
 	PLy_pop_execution_context();
 
 	return retval;
@@ -345,21 +346,22 @@ plpython_inline_handler(PG_FUNCTION_ARGS)
 	/*
 	 * Push execution context onto stack.  It is important that this get
 	 * popped again, so avoid putting anything that could throw error between
-	 * here and the PG_TRY.  (plpython_inline_error_callback doesn't currently
-	 * need the stack entry, but for consistency with plpython_call_handler we
-	 * do it in this order.)
+	 * here and the PG_TRY.
 	 */
 	exec_ctx = PLy_push_execution_context();
 
-	/*
-	 * Setup error traceback support for ereport()
-	 */
-	plerrcontext.callback = plpython_inline_error_callback;
-	plerrcontext.previous = error_context_stack;
-	error_context_stack = &plerrcontext;
-
 	PG_TRY();
 	{
+		/*
+		 * Setup error traceback support for ereport().
+		 * plpython_inline_error_callback doesn't currently need exec_ctx, but
+		 * for consistency with plpython_call_handler we do it the same way.
+		 */
+		plerrcontext.callback = plpython_inline_error_callback;
+		plerrcontext.arg = exec_ctx;
+		plerrcontext.previous = error_context_stack;
+		error_context_stack = &plerrcontext;
+
 		PLy_procedure_compile(&proc, codeblock->source_text);
 		exec_ctx->curr_proc = &proc;
 		PLy_exec_function(&fake_fcinfo, &proc);
@@ -373,9 +375,7 @@ plpython_inline_handler(PG_FUNCTION_ARGS)
 	}
 	PG_END_TRY();
 
-	/* Pop the error context stack */
-	error_context_stack = plerrcontext.previous;
-	/* ... and then the execution context */
+	/* Destroy the execution context */
 	PLy_pop_execution_context();
 
 	/* Now clean up the transient procedure we made */
@@ -403,7 +403,7 @@ PLy_procedure_is_trigger(Form_pg_proc procStruct)
 static void
 plpython_error_callback(void *arg)
 {
-	PLyExecutionContext *exec_ctx = PLy_current_execution_context();
+	PLyExecutionContext *exec_ctx = (PLyExecutionContext *) arg;
 
 	if (exec_ctx->curr_proc)
 		errcontext("PL/Python function \"%s\"",
diff --git a/src/pl/plpython/plpy_procedure.c b/src/pl/plpython/plpy_procedure.c
@@ -47,9 +47,7 @@ init_procedure_caches(void)
 }
 
 /*
- * Get the name of the last procedure called by the backend (the
- * innermost, if a plpython procedure call calls the backend and the
- * backend calls another plpython procedure).
+ * PLy_procedure_name: get the name of the specified procedure.
  *
  * NB: this returns the SQL name, not the internal Python procedure name
  */
diff --git a/src/pl/plpython/sql/plpython_error.sql b/src/pl/plpython/sql/plpython_error.sql
@@ -328,3 +328,19 @@ EXCEPTION WHEN SQLSTATE 'SILLY' THEN
 	-- NOOP
 END
 $$ LANGUAGE plpgsql;
+
+/* test the context stack trace for nested execution levels
+ */
+CREATE FUNCTION notice_innerfunc() RETURNS int AS $$
+plpy.execute("DO LANGUAGE plpythonu $x$ plpy.notice('inside DO') $x$")
+return 1
+$$ LANGUAGE plpythonu;
+
+CREATE FUNCTION notice_outerfunc() RETURNS int AS $$
+plpy.execute("SELECT notice_innerfunc()")
+return 1
+$$ LANGUAGE plpythonu;
+
+\set SHOW_CONTEXT always
+
+SELECT notice_outerfunc();

Original file line number	Diff line number	Diff line change
`@@ -47,9 +47,7 @@ init_procedure_caches(void)`
`47`	`47`	`}`
`48`	`48`
`49`	`49`	`/*`
`50`		`- * Get the name of the last procedure called by the backend (the`
`51`		`- * innermost, if a plpython procedure call calls the backend and the`
`52`		`- * backend calls another plpython procedure).`
	`50`	`+ * PLy_procedure_name: get the name of the specified procedure.`
`53`	`51`	`*`
`54`	`52`	`* NB: this returns the SQL name, not the internal Python procedure name`
`55`	`53`	`*/`