bcachefs: Fix error reporting from bch2_journal_flush_seq

- bch2_journal_halt() was unconditionally overwriting j->err_seq, the
  sequence number that we failed to write
- journal_write_done was updating seq_ondisk and flushed_seq_ondisk even
  for writes that errored, which broke the way bch2_journal_flush_seq_async()
  locklessly checked for completions.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/journal.c

@@ -106,7 +106,12 @@ void bch2_journal_halt(struct journal *j)
 	} while ((v = atomic64_cmpxchg(&j->reservations.counter,
 				       old.v, new.v)) != old.v);
 
-	j->err_seq = journal_cur_seq(j);
+	/*
+	 * XXX: we're not using j->lock here because this can be called from
+	 * interrupt context, this can race with journal_write_done()
+	 */
+	if (!j->err_seq)
+		j->err_seq = journal_cur_seq(j);
 	journal_wake(j);
 	closure_wake_up(&journal_cur_buf(j)->wait);
 }

fs/bcachefs/journal_io.c

@@ -1258,14 +1258,15 @@ static void journal_write_done(struct closure *cl)
 	if (seq >= j->pin.front)
 		journal_seq_pin(j, seq)->devs = w->devs_written;
 
-	j->seq_ondisk		= seq;
-	if (err && (!j->err_seq || seq < j->err_seq))
-		j->err_seq	= seq;
+	if (!err) {
+		j->seq_ondisk		= seq;
 
-	if (!JSET_NO_FLUSH(w->data)) {
-		j->flushed_seq_ondisk = seq;
-		j->last_seq_ondisk = w->last_seq;
-	}
+		if (!JSET_NO_FLUSH(w->data)) {
+			j->flushed_seq_ondisk = seq;
+			j->last_seq_ondisk = w->last_seq;
+		}
+	} else if (!j->err_seq || seq < j->err_seq)
+		j->err_seq	= seq;
 
 	/*
 	 * Updating last_seq_ondisk may let bch2_journal_reclaim_work() discard

fs/bcachefs/recovery.c

@@ -1480,7 +1480,7 @@ int bch2_fs_initialize(struct bch_fs *c)
 	}
 
 	err = "error writing first journal entry";
-	ret = bch2_journal_meta(&c->journal);
+	ret = bch2_journal_flush(&c->journal);
 	if (ret)
 		goto err;