NFS: check for req==NULL in nfs_try_to_update_request cleanup

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 2c68818..9b8d4d4 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -682,7 +682,8 @@
 		req->wb_bytes = rqend - req->wb_offset;
 out_unlock:
 	spin_unlock(&inode->i_lock);
-	nfs_clear_request_commit(req);
+	if (req)
+		nfs_clear_request_commit(req);
 	return req;
 out_flushme:
 	spin_unlock(&inode->i_lock);