bcachefs: Convert for_each_btree_node() to lockrestart_do()

for_each_btree_node() now works similarly to for_each_btree_key(), where
the loop body is passed as an argument to be passed to lockrestart_do().

This now calls trans_begin() on every loop iteration - which fixes an
SRCU warning in backpointers fsck.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/backpointers.c

@@ -763,27 +763,22 @@ static int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
 	     btree < BTREE_ID_NR && !ret;
 	     btree++) {
 		unsigned depth = (BIT_ULL(btree) & btree_leaf_mask) ? 0 : 1;
-		struct btree_iter iter;
-		struct btree *b;
 
 		if (!(BIT_ULL(btree) & btree_leaf_mask) &&
 		    !(BIT_ULL(btree) & btree_interior_mask))
 			continue;
 
-		bch2_trans_begin(trans);
-
-		__for_each_btree_node(trans, iter, btree,
+		ret = __for_each_btree_node(trans, iter, btree,
 				      btree == start.btree ? start.pos : POS_MIN,
-				      0, depth, BTREE_ITER_prefetch, b, ret) {
+				      0, depth, BTREE_ITER_prefetch, b, ({
 			mem_may_pin -= btree_buf_bytes(b);
 			if (mem_may_pin <= 0) {
 				c->btree_cache.pinned_nodes_end = *end =
 					BBPOS(btree, b->key.k.p);
-				bch2_trans_iter_exit(trans, &iter);
-				return 0;
+				break;
 			}
-		}
-		bch2_trans_iter_exit(trans, &iter);
+			0;
+		}));
 	}
 
 	return ret;

fs/bcachefs/btree_iter.c

@@ -1900,6 +1900,7 @@ struct btree *bch2_btree_iter_peek_node(struct btree_iter *iter)
 	goto out;
 }
 
+/* Only kept for -tools */
 struct btree *bch2_btree_iter_peek_node_and_restart(struct btree_iter *iter)
 {
 	struct btree *b;

fs/bcachefs/btree_iter.h

@@ -600,23 +600,35 @@ void bch2_trans_srcu_unlock(struct btree_trans *);
 
 u32 bch2_trans_begin(struct btree_trans *);
 
-/*
- * XXX
- * this does not handle transaction restarts from bch2_btree_iter_next_node()
- * correctly
- */
-#define __for_each_btree_node(_trans, _iter, _btree_id, _start,		\
-			      _locks_want, _depth, _flags, _b, _ret)	\
-	for (bch2_trans_node_iter_init((_trans), &(_iter), (_btree_id),	\
-				_start, _locks_want, _depth, _flags);	\
-	     (_b) = bch2_btree_iter_peek_node_and_restart(&(_iter)),	\
-	     !((_ret) = PTR_ERR_OR_ZERO(_b)) && (_b);			\
-	     (_b) = bch2_btree_iter_next_node(&(_iter)))
+#define __for_each_btree_node(_trans, _iter, _btree_id, _start,			\
+			      _locks_want, _depth, _flags, _b, _do)		\
+({										\
+	bch2_trans_begin((_trans));						\
+										\
+	struct btree_iter _iter;						\
+	bch2_trans_node_iter_init((_trans), &_iter, (_btree_id),		\
+				  _start, _locks_want, _depth, _flags);		\
+	int _ret3 = 0;								\
+	do {									\
+		_ret3 = lockrestart_do((_trans), ({				\
+			struct btree *_b = bch2_btree_iter_peek_node(&_iter);	\
+			if (!_b)						\
+				break;						\
+										\
+			PTR_ERR_OR_ZERO(_b) ?: (_do);				\
+		})) ?:								\
+		lockrestart_do((_trans),					\
+			PTR_ERR_OR_ZERO(bch2_btree_iter_next_node(&_iter)));	\
+	} while (!_ret3);							\
+										\
+	bch2_trans_iter_exit((_trans), &(_iter));				\
+	_ret3;									\
+})
 
 #define for_each_btree_node(_trans, _iter, _btree_id, _start,		\
-			    _flags, _b, _ret)				\
-	__for_each_btree_node(_trans, _iter, _btree_id, _start,		\
-			      0, 0, _flags, _b, _ret)
+			    _flags, _b, _do)				\
+	__for_each_btree_node(_trans, _iter, _btree_id, _start,	\
+			      0, 0, _flags, _b, _do)
 
 static inline struct bkey_s_c bch2_btree_iter_peek_prev_type(struct btree_iter *iter,
 							     unsigned flags)

fs/bcachefs/debug.c

@@ -397,47 +397,27 @@ static ssize_t bch2_read_btree_formats(struct file *file, char __user *buf,
 				       size_t size, loff_t *ppos)
 {
 	struct dump_iter *i = file->private_data;
-	struct btree_trans *trans;
-	struct btree_iter iter;
-	struct btree *b;
-	ssize_t ret;
 
 	i->ubuf = buf;
 	i->size	= size;
 	i->ret	= 0;
 
-	ret = flush_buf(i);
+	ssize_t ret = flush_buf(i);
 	if (ret)
 		return ret;
 
 	if (bpos_eq(SPOS_MAX, i->from))
 		return i->ret;
 
-	trans = bch2_trans_get(i->c);
-retry:
-	bch2_trans_begin(trans);
-
-	for_each_btree_node(trans, iter, i->id, i->from, 0, b, ret) {
-		bch2_btree_node_to_text(&i->buf, i->c, b);
-		i->from = !bpos_eq(SPOS_MAX, b->key.k.p)
-			? bpos_successor(b->key.k.p)
-			: b->key.k.p;
-
-		ret = drop_locks_do(trans, flush_buf(i));
-		if (ret)
-			break;
-	}
-	bch2_trans_iter_exit(trans, &iter);
-
-	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
-		goto retry;
-
-	bch2_trans_put(trans);
-
-	if (!ret)
-		ret = flush_buf(i);
+	return bch2_trans_run(i->c,
+		for_each_btree_node(trans, iter, i->id, i->from, 0, b, ({
+			bch2_btree_node_to_text(&i->buf, i->c, b);
+			i->from = !bpos_eq(SPOS_MAX, b->key.k.p)
+				? bpos_successor(b->key.k.p)
+				: b->key.k.p;
 
-	return ret ?: i->ret;
+			drop_locks_do(trans, flush_buf(i));
+		}))) ?: i->ret;
 }
 
 static const struct file_operations btree_format_debug_ops = {