NFS: Fix use after free in write error path

Signed-off-by: Fred Isaman <fred.isaman@gmail.com>
Fixes: 0bcbf039 ("nfs: handle request add failure properly")
Cc: stable@vger.kernel.org # v4.5+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/write.c

@@ -561,9 +561,9 @@ static void nfs_write_error_remove_page(struct nfs_page *req)
 {
 	nfs_unlock_request(req);
 	nfs_end_page_writeback(req);
-	nfs_release_request(req);
 	generic_error_remove_page(page_file_mapping(req->wb_page),
 				  req->wb_page);
+	nfs_release_request(req);
 }
 
 /*