bcachefs: Fix a null ptr deref in bch2_fs_alloc() error path

This fixes a null ptr deref in bch2_free_pending_node_rewrites() when
the list head wasn't initialized.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_update_interior.c

@@ -2452,7 +2452,7 @@ void bch2_fs_btree_interior_update_exit(struct bch_fs *c)
 	mempool_exit(&c->btree_interior_update_pool);
 }
 
-int bch2_fs_btree_interior_update_init(struct bch_fs *c)
+void bch2_fs_btree_interior_update_init_early(struct bch_fs *c)
 {
 	mutex_init(&c->btree_reserve_cache_lock);
 	INIT_LIST_HEAD(&c->btree_interior_update_list);
@@ -2462,7 +2462,10 @@ int bch2_fs_btree_interior_update_init(struct bch_fs *c)
 
 	INIT_LIST_HEAD(&c->pending_node_rewrites);
 	mutex_init(&c->pending_node_rewrites_lock);
+}
 
+int bch2_fs_btree_interior_update_init(struct bch_fs *c)
+{
 	c->btree_interior_update_worker =
 		alloc_workqueue("btree_update", WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
 	if (!c->btree_interior_update_worker)

fs/bcachefs/btree_update_interior.h

@@ -322,6 +322,7 @@ void bch2_do_pending_node_rewrites(struct bch_fs *);
 void bch2_free_pending_node_rewrites(struct bch_fs *);
 
 void bch2_fs_btree_interior_update_exit(struct bch_fs *);
+void bch2_fs_btree_interior_update_init_early(struct bch_fs *);
 int bch2_fs_btree_interior_update_init(struct bch_fs *);
 
 #endif /* _BCACHEFS_BTREE_UPDATE_INTERIOR_H */

fs/bcachefs/super.c

@@ -686,6 +686,7 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
 
 	bch2_fs_copygc_init(c);
 	bch2_fs_btree_key_cache_init_early(&c->btree_key_cache);
+	bch2_fs_btree_interior_update_init_early(c);
 	bch2_fs_allocator_background_init(c);
 	bch2_fs_allocator_foreground_init(c);
 	bch2_fs_rebalance_init(c);