ocfs2: Support nested transactions

OCFS2 can easily support nested transactions. We just have to
take care and not spoil statistics acquire semaphore unnecessarily.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

fs/ocfs2/journal.c

@@ -256,11 +256,9 @@ handle_t *ocfs2_start_trans(struct ocfs2_super *osb, int max_buffs)
 	BUG_ON(osb->journal->j_state == OCFS2_JOURNAL_FREE);
 	BUG_ON(max_buffs <= 0);
 
-	/* JBD might support this, but our journalling code doesn't yet. */
-	if (journal_current_handle()) {
-		mlog(ML_ERROR, "Recursive transaction attempted!\n");
-		BUG();
-	}
+	/* Nested transaction? Just return the handle... */
+	if (journal_current_handle())
+		return jbd2_journal_start(journal, max_buffs);
 
 	down_read(&osb->journal->j_trans_barrier);
 
@@ -285,15 +283,17 @@ handle_t *ocfs2_start_trans(struct ocfs2_super *osb, int max_buffs)
 int ocfs2_commit_trans(struct ocfs2_super *osb,
 		       handle_t *handle)
 {
-	int ret;
+	int ret, nested;
 	struct ocfs2_journal *journal = osb->journal;
 
 	BUG_ON(!handle);
 
+	nested = handle->h_ref > 1;
 	ret = jbd2_journal_stop(handle);
 	if (ret < 0)
 		mlog_errno(ret);
 
+	if (!nested)
 		up_read(&journal->j_trans_barrier);
 
 	return ret;