Fix resource leak when a FDW's ForeignAsyncRequest function fails

If an error is thrown after calling CreateWaitEventSet(), the memory
of a WaitEventSet is free'd as it's allocated in the short-lived
memory context, but the file descriptor (on epoll- or kqueue-based
systems) or handles (on Windows) that it contains are leaked.

Use PG_TRY-FINALLY to ensure it gets freed. (On master, I will apply a
better fix, using ResourceOwners to track the WaitEventSet, but that's
not backpatchable.)

The added test doesn't check for leaking resources, so it passed even
before this commit. But at least it covers the code path.

In the passing, fix misleading comment on what the 'nevents' argument
to WaitEventSetWait means.

Report by Alexander Lakhin, analysis and suggestion for the fix by Tom
Lane. Fixes bug #17828. Backpatch to v14 where async execution was
introduced, but master gets a different fix.

Discussion: https://www.postgresql.org/message-id/17828-122da8cba23236be@postgresql.org
Discussion: https://www.postgresql.org/message-id/472235.1678387869@sss.pgh.pa.us

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index fa8c56c6122e19f8764336811fe6a81a46ccabba..5811b732505dfe169393bc2f7ef2005b8726e04f 100644 (file)
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -10403,6 +10403,13 @@ SELECT * FROM result_tbl ORDER BY a;
 (2 rows)
 
 DELETE FROM result_tbl;
+-- Test error handling, if accessing one of the foreign partitions errors out
+CREATE FOREIGN TABLE async_p_broken PARTITION OF async_pt FOR VALUES FROM (10000) TO (10001)
+  SERVER loopback OPTIONS (table_name 'non_existent_table');
+SELECT * FROM async_pt;
+ERROR:  relation "public.non_existent_table" does not exist
+CONTEXT:  remote SQL command: SELECT a, b, c FROM public.non_existent_table
+DROP FOREIGN TABLE async_p_broken;
 -- Check case where multiple partitions use the same connection
 CREATE TABLE base_tbl3 (a int, b int, c text);
 CREATE FOREIGN TABLE async_p3 PARTITION OF async_pt FOR VALUES FROM (3000) TO (4000)

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 063ae181452a955b3a8a983e095dc9e2b824c9bb..d19e4c3c7de82bbdeef25a2dfdf0e15c7514c68a 100644 (file)
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -3341,6 +3341,12 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test error handling, if accessing one of the foreign partitions errors out
+CREATE FOREIGN TABLE async_p_broken PARTITION OF async_pt FOR VALUES FROM (10000) TO (10001)
+  SERVER loopback OPTIONS (table_name 'non_existent_table');
+SELECT * FROM async_pt;
+DROP FOREIGN TABLE async_p_broken;
+
 -- Check case where multiple partitions use the same connection
 CREATE TABLE base_tbl3 (a int, b int, c text);
 CREATE FOREIGN TABLE async_p3 PARTITION OF async_pt FOR VALUES FROM (3000) TO (4000)

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index 6a2daa6e767d7f845a431605d691de5ae5fddc4c..baba3ceea23b1dd7227a56a70d4b45eba53b21d9 100644 (file)
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -1029,43 +1029,51 @@ ExecAppendAsyncEventWait(AppendState *node)
    /* We should never be called when there are no valid async subplans. */
    Assert(node->as_nasyncremain > 0);
 
+   Assert(node->as_eventset == NULL);
    node->as_eventset = CreateWaitEventSet(CurrentMemoryContext, nevents);
-   AddWaitEventToSet(node->as_eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
-                     NULL, NULL);
-
-   /* Give each waiting subplan a chance to add an event. */
-   i = -1;
-   while ((i = bms_next_member(node->as_asyncplans, i)) >= 0)
+   PG_TRY();
    {
-       AsyncRequest *areq = node->as_asyncrequests[i];
+       AddWaitEventToSet(node->as_eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
+                         NULL, NULL);
 
-       if (areq->callback_pending)
-           ExecAsyncConfigureWait(areq);
-   }
+       /* Give each waiting subplan a chance to add an event. */
+       i = -1;
+       while ((i = bms_next_member(node->as_asyncplans, i)) >= 0)
+       {
+           AsyncRequest *areq = node->as_asyncrequests[i];
 
-   /*
-    * No need for further processing if there are no configured events other
-    * than the postmaster death event.
-    */
-   if (GetNumRegisteredWaitEvents(node->as_eventset) == 1)
+           if (areq->callback_pending)
+               ExecAsyncConfigureWait(areq);
+       }
+
+       /*
+        * No need for further processing if there are no configured events
+        * other than the postmaster death event.
+        */
+       if (GetNumRegisteredWaitEvents(node->as_eventset) == 1)
+       {
+           FreeWaitEventSet(node->as_eventset);
+           node->as_eventset = NULL;
+           return;
+       }
+
+       /* Return at most EVENT_BUFFER_SIZE events in one call. */
+       if (nevents > EVENT_BUFFER_SIZE)
+           nevents = EVENT_BUFFER_SIZE;
+
+       /*
+        * If the timeout is -1, wait until at least one event occurs.  If the
+        * timeout is 0, poll for events, but do not wait at all.
+        */
+       noccurred = WaitEventSetWait(node->as_eventset, timeout, occurred_event,
+                                    nevents, WAIT_EVENT_APPEND_READY);
+   }
+   PG_FINALLY();
    {
        FreeWaitEventSet(node->as_eventset);
        node->as_eventset = NULL;
-       return;
    }
-
-   /* We wait on at most EVENT_BUFFER_SIZE events. */
-   if (nevents > EVENT_BUFFER_SIZE)
-       nevents = EVENT_BUFFER_SIZE;
-
-   /*
-    * If the timeout is -1, wait until at least one event occurs.  If the
-    * timeout is 0, poll for events, but do not wait at all.
-    */
-   noccurred = WaitEventSetWait(node->as_eventset, timeout, occurred_event,
-                                nevents, WAIT_EVENT_APPEND_READY);
-   FreeWaitEventSet(node->as_eventset);
-   node->as_eventset = NULL;
+   PG_END_TRY();
    if (noccurred == 0)
        return;