Fix inadequately-tested code path in tuplesort_skiptuples().

Per report from Jeff Davis.

diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c
index 6221f6db7ed7bdfd1740185043983941317627c4..52f05e6d9ad8b4de676525bb5e67b0e4f9a41a81 100644 (file)
--- a/src/backend/utils/sort/tuplesort.c
+++ b/src/backend/utils/sort/tuplesort.c
@@ -1725,6 +1725,8 @@ tuplesort_getdatum(Tuplesortstate *state, bool forward,
 bool
 tuplesort_skiptuples(Tuplesortstate *state, int64 ntuples, bool forward)
 {
+   MemoryContext oldcontext;
+
    /*
     * We don't actually support backwards skip yet, because no callers need
     * it.  The API is designed to allow for that later, though.
@@ -1760,6 +1762,7 @@ tuplesort_skiptuples(Tuplesortstate *state, int64 ntuples, bool forward)
             * We could probably optimize these cases better, but for now it's
             * not worth the trouble.
             */
+           oldcontext = MemoryContextSwitchTo(state->sortcontext);
            while (ntuples-- > 0)
            {
                SortTuple   stup;
@@ -1767,11 +1770,15 @@ tuplesort_skiptuples(Tuplesortstate *state, int64 ntuples, bool forward)
 
                if (!tuplesort_gettuple_common(state, forward,
                                               &stup, &should_free))
+               {
+                   MemoryContextSwitchTo(oldcontext);
                    return false;
-               if (should_free)
+               }
+               if (should_free && stup.tuple)
                    pfree(stup.tuple);
                CHECK_FOR_INTERRUPTS();
            }
+           MemoryContextSwitchTo(oldcontext);
            return true;
 
        default: