pack-bitmap-write: deep-clear the bb_commit slab

The `bb_commit` commit slab is used by the pack-bitmap-write machinery
to track various pieces of bookkeeping used to generate reachability
bitmaps.

Even though we clear the slab when freeing the bitmap_builder struct
(with `bitmap_builder_clear()`), there are still pointers which point to
locations in memory that have not yet been freed, resulting in a leak.

Plug the leak by introducing a suitable `free_fn` for the `struct
bb_commit` type, and make sure it is called on each member of the slab
via the `deep_clear_bb_data()` function.

Note that it is possible for both of the arguments to `bitmap_free()` to
be NULL, but `bitmap_free()` is a noop for NULL arguments, so it is OK
to pass them unconditionally.

Signed-off-by: Taylor Blau <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ttaylorr

pack-bitmap-write.c

@@ -198,6 +198,13 @@ struct bb_commit {
 	unsigned idx; /* within selected array */
 };
 
+static void clear_bb_commit(struct bb_commit *commit)
+{
+	free_commit_list(commit->reverse_edges);
+	bitmap_free(commit->commit_mask);
+	bitmap_free(commit->bitmap);
+}
+
 define_commit_slab(bb_data, struct bb_commit);
 
 struct bitmap_builder {
@@ -339,7 +346,7 @@ static void bitmap_builder_init(struct bitmap_builder *bb,
 
 static void bitmap_builder_clear(struct bitmap_builder *bb)
 {
-	clear_bb_data(&bb->data);
+	deep_clear_bb_data(&bb->data, clear_bb_commit);
 	free(bb->commits);
 	bb->commits_nr = bb->commits_alloc = 0;
 }