bcachefs: Fix journal_buf bitfield accesses

All jounal_buf bitfield updates must happen under the journal lock -
perhaps we should just switch these to atomic bit flags.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_write_buffer.c

@@ -590,7 +590,9 @@ static int bch2_journal_keys_to_write_buffer(struct bch_fs *c, struct journal_bu
 		entry->type = BCH_JSET_ENTRY_btree_keys;
 	}
 
+	spin_lock(&c->journal.lock);
 	buf->need_flush_to_write_buffer = false;
+	spin_unlock(&c->journal.lock);
 out:
 	bch2_journal_keys_to_write_buffer_end(c, &dst);
 	return ret;

fs/bcachefs/journal_io.c

@@ -1831,7 +1831,10 @@ static int bch2_journal_write_prep(struct journal *j, struct journal_buf *w)
 
 	if (wb.wb)
 		bch2_journal_keys_to_write_buffer_end(c, &wb);
+
+	spin_lock(&c->journal.lock);
 	w->need_flush_to_write_buffer = false;
+	spin_unlock(&c->journal.lock);
 
 	start = end = vstruct_last(jset);
 
@@ -1949,12 +1952,20 @@ CLOSURE_CALLBACK(bch2_journal_write)
 	unsigned nr_rw_members = 0;
 	int ret;
 
+	for_each_rw_member(c, ca)
+		nr_rw_members++;
+
 	BUG_ON(BCH_SB_CLEAN(c->disk_sb.sb));
+	BUG_ON(!w->write_started);
 	BUG_ON(w->write_allocated);
+	BUG_ON(w->write_done);
 
 	j->write_start_time = local_clock();
 
 	spin_lock(&j->lock);
+	if (nr_rw_members > 1)
+		w->separate_flush = true;
+
 	ret = bch2_journal_write_pick_flush(j, w);
 	spin_unlock(&j->lock);
 	if (ret)
@@ -2009,12 +2020,6 @@ CLOSURE_CALLBACK(bch2_journal_write)
 	if (c->opts.nochanges)
 		goto no_io;
 
-	for_each_rw_member(c, ca)
-		nr_rw_members++;
-
-	if (nr_rw_members > 1)
-		w->separate_flush = true;
-
 	/*
 	 * Mark journal replicas before we submit the write to guarantee
 	 * recovery will find the journal entries after a crash.