bcachefs: more write buffer refactoring

prep work for big rewrite - no functional changes in this patch.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_write_buffer.c

@@ -163,9 +163,6 @@ int bch2_btree_write_buffer_flush_locked(struct btree_trans *trans)
 	keys = wb->keys[s.idx];
 	nr = s.nr;
 
-	if (race_fault())
-		goto slowpath;
-
 	/*
 	 * We first sort so that we can detect and skip redundant updates, and
 	 * then we attempt to flush in sorted btree order, as this is most
@@ -209,6 +206,11 @@ int bch2_btree_write_buffer_flush_locked(struct btree_trans *trans)
 		iter.path->preserve = false;
 
 		do {
+			if (race_fault()) {
+				ret = -BCH_ERR_journal_reclaim_would_deadlock;
+				break;
+			}
+
 			ret = wb_flush_one(trans, &iter, i, &write_locked, &fast);
 			if (!write_locked)
 				bch2_trans_begin(trans);
@@ -227,23 +229,18 @@ int bch2_btree_write_buffer_flush_locked(struct btree_trans *trans)
 		bch2_btree_node_unlock_write(trans, iter.path, iter.path->l[0].b);
 	bch2_trans_iter_exit(trans, &iter);
 
-	trace_write_buffer_flush(trans, nr, skipped, fast, wb->size);
-
-	if (slowpath)
-		goto slowpath;
-
-	bch2_fs_fatal_err_on(ret, c, "%s: insert error %s", __func__, bch2_err_str(ret));
-out:
-	bch2_journal_pin_drop(j, &pin);
-	return ret;
-slowpath:
-	trace_and_count(c, write_buffer_flush_slowpath, trans, slowpath, nr);
+	if (ret)
+		goto err;
 
+	if (slowpath) {
 		/*
-	 * Now sort the rest by journal seq and bump the journal pin as we go.
-	 * The slowpath zapped the seq of keys that were successfully flushed so
+		 * Flush in the order they were present in the journal, so that
+		 * we can release journal pins:
+		 * The fastpath zapped the seq of keys that were successfully flushed so
 		 * we can skip those here.
 		 */
+		trace_and_count(c, write_buffer_flush_slowpath, trans, slowpath, nr);
+
 		sort(keys, nr, sizeof(keys[0]),
 		     btree_write_buffered_journal_cmp,
 		     NULL);
@@ -262,11 +259,15 @@ int bch2_btree_write_buffer_flush_locked(struct btree_trans *trans)
 					BCH_TRANS_COMMIT_no_journal_res|
 					BCH_TRANS_COMMIT_journal_reclaim,
 					btree_write_buffered_insert(trans, i));
-		if (bch2_fs_fatal_err_on(ret, c, "%s: insert error %s", __func__, bch2_err_str(ret)))
-			break;
+			if (ret)
+				goto err;
 		}
-
-	goto out;
+	}
+err:
+	bch2_fs_fatal_err_on(ret, c, "%s: insert error %s", __func__, bch2_err_str(ret));
+	trace_write_buffer_flush(trans, nr, skipped, fast, wb->size);
+	bch2_journal_pin_drop(j, &pin);
+	return ret;
 }
 
 int bch2_btree_write_buffer_flush_sync(struct btree_trans *trans)