bcachefs: Fix replay_now_at() assert

Journal replay, in the slowpath where we insert keys in journal order,
was inserting keys in the wrong order; keys from early repair come last.

Reported-by: syzbot+2c4fcb257ce2b6a29d0e@syzkaller.appspotmail.com
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/recovery.c

@@ -241,7 +241,13 @@ static int journal_sort_seq_cmp(const void *_l, const void *_r)
 	const struct journal_key *l = *((const struct journal_key **)_l);
 	const struct journal_key *r = *((const struct journal_key **)_r);
 
-	return cmp_int(l->journal_seq, r->journal_seq);
+	/*
+	 * Map 0 to U64_MAX, so that keys with journal_seq === 0 come last
+	 *
+	 * journal_seq == 0 means that the key comes from early repair, and
+	 * should be inserted last so as to avoid overflowing the journal
+	 */
+	return cmp_int(l->journal_seq - 1, r->journal_seq - 1);
 }
 
 int bch2_journal_replay(struct bch_fs *c)