[PATCH 07/34] bcachefs: Fix btree node scan when unknown btree IDs are present

[Kent Overstreet <kent.overstreet@linux.dev>]

btree_root entries for unknown btree IDs are created during recovery,
before reading those btree roots.

But btree_node_scan may find btree nodes with unknown btree IDs when we
haven't seen roots for those btrees.

Reported-by: syzbot+1f202d4da221ec6ebf8e@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
 fs/bcachefs/btree_cache.c | 11 ++++++++---
 fs/bcachefs/btree_cache.h |  9 +++++++--
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/fs/bcachefs/btree_cache.c b/fs/bcachefs/btree_cache.c
index 36dfa6a48aa6..1f06e24e53fc 100644
--- a/fs/bcachefs/btree_cache.c
+++ b/fs/bcachefs/btree_cache.c
@@ -1406,9 +1406,14 @@ void bch2_btree_id_level_to_text(struct printbuf *out, enum btree_id btree, unsi
 void bch2_btree_pos_to_text(struct printbuf *out, struct bch_fs *c, const struct btree *b)
 {
 	bch2_btree_id_to_text(out, b->c.btree_id);
-	prt_printf(out, " level %u/%u\n  ",
-		   b->c.level,
-		   bch2_btree_id_root(c, b->c.btree_id)->level);
+	prt_printf(out, " level %u/", b->c.level);
+	struct btree_root *r = bch2_btree_id_root(c, b->c.btree_id);
+	if (r)
+		prt_printf(out, "%u", r->level);
+	else
+		prt_printf(out, "(unknown)");
+	prt_printf(out, "\n  ");
+
 	bch2_bkey_val_to_text(out, c, bkey_i_to_s_c(&b->key));
 }
 
diff --git a/fs/bcachefs/btree_cache.h b/fs/bcachefs/btree_cache.h
index 6cfacacb6769..dcc34fe4996d 100644
--- a/fs/bcachefs/btree_cache.h
+++ b/fs/bcachefs/btree_cache.h
@@ -128,14 +128,19 @@ static inline struct btree_root *bch2_btree_id_root(struct bch_fs *c, unsigned i
 	} else {
 		unsigned idx = id - BTREE_ID_NR;
 
-		EBUG_ON(idx >= c->btree_roots_extra.nr);
+		/* This can happen when we're called from btree_node_scan */
+		if (idx >= c->btree_roots_extra.nr)
+			return NULL;
+
 		return &c->btree_roots_extra.data[idx];
 	}
 }
 
 static inline struct btree *btree_node_root(struct bch_fs *c, struct btree *b)
 {
-	return bch2_btree_id_root(c, b->c.btree_id)->b;
+	struct btree_root *r = bch2_btree_id_root(c, b->c.btree_id);
+
+	return r ? r->b : NULL;
 }
 
 const char *bch2_btree_id_str(enum btree_id);	/* avoid */
-- 
2.45.2