bcachefs: Rewrite btree nodes with errors

This patch adds self healing functionality for btree nodes - if we
notice a problem when reading a btree node, we just rewrite it.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_io.c

@@ -986,6 +986,7 @@ static void btree_node_read_work(struct work_struct *work)
 	struct bch_io_failures failed = { .nr = 0 };
 	char buf[200];
 	struct printbuf out;
+	bool saw_error = false;
 	bool can_retry;
 
 	goto start;
@@ -1022,6 +1023,8 @@ static void btree_node_read_work(struct work_struct *work)
 		    !bch2_btree_node_read_done(c, ca, b, can_retry))
 			break;
 
+		saw_error = true;
+
 		if (!can_retry) {
 			set_btree_node_read_error(b);
 			break;
@@ -1031,6 +1034,10 @@ static void btree_node_read_work(struct work_struct *work)
 	bch2_time_stats_update(&c->times[BCH_TIME_btree_node_read],
 			       rb->start_time);
 	bio_put(&rb->bio);
+
+	if (saw_error && !btree_node_read_error(b))
+		bch2_btree_node_rewrite_async(c, b);
+
 	clear_btree_node_read_in_flight(b);
 	wake_up_bit(&b->flags, BTREE_NODE_read_in_flight);
 }

fs/bcachefs/btree_update.h

@@ -72,6 +72,7 @@ int bch2_btree_delete_range(struct bch_fs *, enum btree_id,
 
 int bch2_btree_node_rewrite(struct bch_fs *c, struct btree_iter *,
 			    __le64, unsigned);
+void bch2_btree_node_rewrite_async(struct bch_fs *, struct btree *);
 int bch2_btree_node_update_key(struct bch_fs *, struct btree_iter *,
 			       struct btree *, struct bkey_i *);
 

fs/bcachefs/btree_update_interior.c

@@ -1797,6 +1797,56 @@ int bch2_btree_node_rewrite(struct bch_fs *c, struct btree_iter *iter,
 	return ret;
 }
 
+struct async_btree_rewrite {
+	struct bch_fs		*c;
+	struct work_struct	work;
+	enum btree_id		btree_id;
+	unsigned		level;
+	struct bpos		pos;
+	__le64			seq;
+};
+
+void async_btree_node_rewrite_work(struct work_struct *work)
+{
+	struct async_btree_rewrite *a =
+		container_of(work, struct async_btree_rewrite, work);
+	struct bch_fs *c = a->c;
+	struct btree_trans trans;
+	struct btree_iter *iter;
+
+	bch2_trans_init(&trans, c, 0, 0);
+	iter = bch2_trans_get_node_iter(&trans, a->btree_id, a->pos,
+					BTREE_MAX_DEPTH, a->level, 0);
+	bch2_btree_node_rewrite(c, iter, a->seq, 0);
+	bch2_trans_iter_put(&trans, iter);
+	bch2_trans_exit(&trans);
+	percpu_ref_put(&c->writes);
+	kfree(a);
+}
+
+void bch2_btree_node_rewrite_async(struct bch_fs *c, struct btree *b)
+{
+	struct async_btree_rewrite *a;
+
+	if (!percpu_ref_tryget(&c->writes))
+		return;
+
+	a = kmalloc(sizeof(*a), GFP_NOFS);
+	if (!a) {
+		percpu_ref_put(&c->writes);
+		return;
+	}
+
+	a->c		= c;
+	a->btree_id	= b->c.btree_id;
+	a->level	= b->c.level;
+	a->pos		= b->key.k.p;
+	a->seq		= b->data->keys.seq;
+
+	INIT_WORK(&a->work, async_btree_node_rewrite_work);
+	queue_work(system_long_wq, &a->work);
+}
+
 static void __bch2_btree_node_update_key(struct bch_fs *c,
 					 struct btree_update *as,
 					 struct btree_iter *iter,