Fix bug in the GiST vacuum's 2nd stage.

We mustn't assume that the IndexVacuumInfo pointer passed to bulkdelete()
stage is still valid in the vacuumcleanup() stage.

Per very pink buildfarm.

src/backend/access/gist/gistvacuum.c

@@ -31,8 +31,6 @@ typedef struct
 {
 	IndexBulkDeleteResult stats;	/* must be first */
 
-	IndexVacuumInfo *info;
-
 	/*
 	 * These are used to memorize all internal and empty leaf pages in the 1st
 	 * vacuum stage.  They are used in the 2nd stage, to delete all the empty
@@ -46,6 +44,7 @@ typedef struct
 /* Working state needed by gistbulkdelete */
 typedef struct
 {
+	IndexVacuumInfo *info;
 	GistBulkDeleteResult *stats;
 	IndexBulkDeleteCallback callback;
 	void	   *callback_state;
@@ -56,8 +55,9 @@ static void gistvacuumscan(IndexVacuumInfo *info, GistBulkDeleteResult *stats,
 			   IndexBulkDeleteCallback callback, void *callback_state);
 static void gistvacuumpage(GistVacState *vstate, BlockNumber blkno,
 			   BlockNumber orig_blkno);
-static void gistvacuum_delete_empty_pages(GistBulkDeleteResult *stats);
-static bool gistdeletepage(GistBulkDeleteResult *stats,
+static void gistvacuum_delete_empty_pages(IndexVacuumInfo *info,
+							  GistBulkDeleteResult *stats);
+static bool gistdeletepage(IndexVacuumInfo *info, GistBulkDeleteResult *stats,
 			   Buffer buffer, OffsetNumber downlink,
 			   Buffer leafBuffer);
 
@@ -121,7 +121,7 @@ gistvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
 	 * If we saw any empty pages, try to unlink them from the tree so that
 	 * they can be reused.
 	 */
-	gistvacuum_delete_empty_pages(gist_stats);
+	gistvacuum_delete_empty_pages(info, gist_stats);
 
 	/* we don't need the internal and empty page sets anymore */
 	MemoryContextDelete(gist_stats->page_set_context);
@@ -183,7 +183,7 @@ gistvacuumscan(IndexVacuumInfo *info, GistBulkDeleteResult *stats,
 	stats->empty_leaf_set = intset_create();
 
 	/* Set up info to pass down to gistvacuumpage */
-	stats->info = info;
+	vstate.info = info;
 	vstate.stats = stats;
 	vstate.callback = callback;
 	vstate.callback_state = callback_state;
@@ -269,7 +269,7 @@ static void
 gistvacuumpage(GistVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
 {
 	GistBulkDeleteResult *stats = vstate->stats;
-	IndexVacuumInfo *info = stats->info;
+	IndexVacuumInfo *info = vstate->info;
 	IndexBulkDeleteCallback callback = vstate->callback;
 	void	   *callback_state = vstate->callback_state;
 	Relation	rel = info->index;
@@ -456,9 +456,8 @@ restart:
  * Scan all internal pages, and try to delete their empty child pages.
  */
 static void
-gistvacuum_delete_empty_pages(GistBulkDeleteResult *stats)
+gistvacuum_delete_empty_pages(IndexVacuumInfo *info, GistBulkDeleteResult *stats)
 {
-	IndexVacuumInfo *info = stats->info;
 	Relation	rel = info->index;
 	BlockNumber empty_pages_remaining;
 	uint64		blkno;
@@ -552,7 +551,9 @@ gistvacuum_delete_empty_pages(GistBulkDeleteResult *stats)
 			gistcheckpage(rel, leafbuf);
 
 			LockBuffer(buffer, GIST_EXCLUSIVE);
-			if (gistdeletepage(stats, buffer, todelete[i] - deleted, leafbuf))
+			if (gistdeletepage(info, stats,
+							   buffer, todelete[i] - deleted,
+							   leafbuf))
 				deleted++;
 			LockBuffer(buffer, GIST_UNLOCK);
 
@@ -585,7 +586,7 @@ gistvacuum_delete_empty_pages(GistBulkDeleteResult *stats)
  * prevented it.
  */
 static bool
-gistdeletepage(GistBulkDeleteResult *stats,
+gistdeletepage(IndexVacuumInfo *info, GistBulkDeleteResult *stats,
 			   Buffer parentBuffer, OffsetNumber downlink,
 			   Buffer leafBuffer)
 {
@@ -661,10 +662,10 @@ gistdeletepage(GistBulkDeleteResult *stats,
 	MarkBufferDirty(parentBuffer);
 	PageIndexTupleDelete(parentPage, downlink);
 
-	if (RelationNeedsWAL(stats->info->index))
+	if (RelationNeedsWAL(info->index))
 		recptr = gistXLogPageDelete(leafBuffer, txid, parentBuffer, downlink);
 	else
-		recptr = gistGetFakeLSN(stats->info->index);
+		recptr = gistGetFakeLSN(info->index);
 	PageSetLSN(parentPage, recptr);
 	PageSetLSN(leafPage, recptr);