Move return statements out of PG_TRY blocks.

If we exit a PG_TRY block early via "continue", "break", "goto", or
"return", we'll skip unwinding its exception stack.  This change
moves a couple of such "return" statements in PL/Python out of
PG_TRY blocks.  This was introduced in d0aa965c0a and affects all
supported versions.

We might also be able to add compile-time checks to prevent
recurrence, but that is left as a future exercise.

Reported-by: Mikhail Gribkov, Xing Guo
Author: Xing Guo
Reviewed-by: Michael Paquier, Andres Freund, Tom Lane
Discussion: https://postgr.es/m/CAMEv5_v5Y%2B-D%3DCO1%2Bqoe16sAmgC4sbbQjz%2BUtcHmB6zcgS%2B5Ew%40mail.gmail.com
Discussion: https://postgr.es/m/CACpMh%2BCMsGMRKFzFMm3bYTzQmMU5nfEEoEDU2apJcc4hid36AQ%40mail.gmail.com
Backpatch-through: 11 (all supported versions)

diff --git a/src/pl/plpython/plpy_exec.c b/src/pl/plpython/plpy_exec.c
index 923703535a7bb2c13a23e050895821ceaf2a773a..e06fde1dd90f08a703de4e54b2101d8108d8da96 100644 (file)
--- a/src/pl/plpython/plpy_exec.c
+++ b/src/pl/plpython/plpy_exec.c
@@ -411,15 +411,20 @@ static PyObject *
 PLy_function_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc)
 {
        PyObject   *volatile arg = NULL;
-       PyObject   *volatile args = NULL;
+       PyObject   *args;
        int                     i;
 
+       /*
+        * Make any Py*_New() calls before the PG_TRY block so that we can quickly
+        * return NULL on failure.  We can't return within the PG_TRY block, else
+        * we'd miss unwinding the exception stack.
+        */
+       args = PyList_New(proc->nargs);
+       if (!args)
+               return NULL;
+
        PG_TRY();
        {
-               args = PyList_New(proc->nargs);
-               if (!args)
-                       return NULL;
-
                for (i = 0; i < proc->nargs; i++)
                {
                        PLyDatumToOb *arginfo = &proc->args[i];
@@ -683,19 +688,34 @@ PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *r
                           *pltlevel,
                           *pltrelid,
                           *plttablename,
-                          *plttableschema;
-       PyObject   *pltargs,
+                          *plttableschema,
+                          *pltargs = NULL,
                           *pytnew,
-                          *pytold;
-       PyObject   *volatile pltdata = NULL;
+                          *pytold,
+                          *pltdata;
        char       *stroid;
 
-       PG_TRY();
+       /*
+        * Make any Py*_New() calls before the PG_TRY block so that we can quickly
+        * return NULL on failure.  We can't return within the PG_TRY block, else
+        * we'd miss unwinding the exception stack.
+        */
+       pltdata = PyDict_New();
+       if (!pltdata)
+               return NULL;
+
+       if (tdata->tg_trigger->tgnargs)
        {
-               pltdata = PyDict_New();
-               if (!pltdata)
+               pltargs = PyList_New(tdata->tg_trigger->tgnargs);
+               if (!pltargs)
+               {
+                       Py_DECREF(pltdata);
                        return NULL;
+               }
+       }
 
+       PG_TRY();
+       {
                pltname = PLyUnicode_FromString(tdata->tg_trigger->tgname);
                PyDict_SetItemString(pltdata, "name", pltname);
                Py_DECREF(pltname);
@@ -835,12 +855,9 @@ PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *r
                        int                     i;
                        PyObject   *pltarg;
 
-                       pltargs = PyList_New(tdata->tg_trigger->tgnargs);
-                       if (!pltargs)
-                       {
-                               Py_DECREF(pltdata);
-                               return NULL;
-                       }
+                       /* pltargs should have been allocated before the PG_TRY block. */
+                       Assert(pltargs);
+
                        for (i = 0; i < tdata->tg_trigger->tgnargs; i++)
                        {
                                pltarg = PLyUnicode_FromString(tdata->tg_trigger->tgargs[i]);
@@ -861,6 +878,7 @@ PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *r
        }
        PG_CATCH();
        {
+               Py_XDECREF(pltargs);
                Py_XDECREF(pltdata);
                PG_RE_THROW();
        }