bcachefs: Fix some shutdown path bugs

This fixes some bugs when we hit an error very early in the filesystem
startup path, before most things have been initialized.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/bcachefs.h

@@ -705,6 +705,7 @@ struct bch_fs {
 	struct btree_path_buf  __percpu	*btree_paths_bufs;
 
 	struct srcu_struct	btree_trans_barrier;
+	bool			btree_trans_barrier_initialized;
 
 	struct btree_key_cache	btree_key_cache;
 

fs/bcachefs/btree_iter.c

@@ -2984,22 +2984,27 @@ void bch2_btree_trans_to_text(struct printbuf *out, struct bch_fs *c)
 
 void bch2_fs_btree_iter_exit(struct bch_fs *c)
 {
+	if (c->btree_trans_barrier_initialized)
+		cleanup_srcu_struct(&c->btree_trans_barrier);
 	mempool_exit(&c->btree_trans_mem_pool);
 	mempool_exit(&c->btree_paths_pool);
-	cleanup_srcu_struct(&c->btree_trans_barrier);
 }
 
 int bch2_fs_btree_iter_init(struct bch_fs *c)
 {
 	unsigned nr = BTREE_ITER_MAX;
+	int ret;
 
 	INIT_LIST_HEAD(&c->btree_trans_list);
 	mutex_init(&c->btree_trans_lock);
 
-	return  init_srcu_struct(&c->btree_trans_barrier) ?:
-		mempool_init_kmalloc_pool(&c->btree_paths_pool, 1,
+	ret   = mempool_init_kmalloc_pool(&c->btree_paths_pool, 1,
 			sizeof(struct btree_path) * nr +
 			sizeof(struct btree_insert_entry) * nr) ?:
 		mempool_init_kmalloc_pool(&c->btree_trans_mem_pool, 1,
-					  BTREE_TRANS_MEM_MAX);
+					  BTREE_TRANS_MEM_MAX) ?:
+		init_srcu_struct(&c->btree_trans_barrier);
+	if (!ret)
+		c->btree_trans_barrier_initialized = true;
+	return ret;
 }

fs/bcachefs/btree_key_cache.c

@@ -663,11 +663,12 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc)
 
 	rcu_read_lock();
 	tbl = rht_dereference_rcu(bc->table.tbl, &bc->table);
-	for (i = 0; i < tbl->size; i++)
-		rht_for_each_entry_rcu(ck, pos, tbl, i, hash) {
-			bkey_cached_evict(bc, ck);
-			list_add(&ck->list, &bc->freed);
-		}
+	if (tbl)
+		for (i = 0; i < tbl->size; i++)
+			rht_for_each_entry_rcu(ck, pos, tbl, i, hash) {
+				bkey_cached_evict(bc, ck);
+				list_add(&ck->list, &bc->freed);
+			}
 	rcu_read_unlock();
 
 	list_for_each_entry_safe(ck, n, &bc->freed, list) {