From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7AF93C43334 for ; Mon, 13 Jun 2022 23:34:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241052AbiFMXeU (ORCPT ); Mon, 13 Jun 2022 19:34:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39168 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241478AbiFMXeS (ORCPT ); Mon, 13 Jun 2022 19:34:18 -0400 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [IPv6:2a03:a000:7:0:5054:ff:fe1c:15ff]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3237C326E5; Mon, 13 Jun 2022 16:34:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=zObLgYLKaX93eqNdhzg3WCjAdYsBSVDmp1swEyP75Z8=; b=KowdyPlmA1k3oZhYWZ+axPGuPF w01vx8DloeDtGGYdCjeAMqAI5RU2QAQCmyI+qVgyNUd3SYQ20o3MpcHh1+JEnrG5WchLgzZ8LhrEY FLjzAii9mRwNr8Juav+Z8yA+I2mU0wxt5fNnv1CB+FFNmhO3EtTFOXWa6FK6+pQZYqLNyIhmytLcZ Uye67DsxU0yLicruRin9LPCeA3ZGDPyJfiYtJhQA50Qn8vMWfz7G01K8nHA1n+rD+lNiyi5uoXX6d yjIg/+qy/WVCfwi8vR7hMqnIvdyhBm9tWseTjq6WK6JsJYyz/qxF9tYvpG6Mll4SLwsbFZEiSr7w8 utn9yywg==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.95 #2 (Red Hat Linux)) id 1o0tZW-0005lI-5G; Mon, 13 Jun 2022 23:34:14 +0000 Date: Tue, 14 Jun 2022 00:34:14 +0100 From: Al Viro To: Linus Torvalds Cc: Dan Williams , Linux Kernel Mailing List , linux-fsdevel , nvdimm@lists.linux.dev, David Howells Subject: Re: [RFC][PATCH] fix short copy handling in copy_mc_pipe_to_iter() Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Jun 14, 2022 at 12:25:03AM +0100, Al Viro wrote: > The more I'm looking at that thing, the more it smells like a bug; > it had the same 3 callers since the time it had been introduced. > > 1) pipe_get_pages(). We are about to try and allocate up to that > many pipe buffers. Allocation (done in push_pipe()) is done only > if we have !pipe_full(pipe->head, pipe->tail, pipe->max_usage). > > It simply won't give you more than max_usage - occupancy. > Your function returns min(ring_size - occupancy, max_usage), which > is always greater than or equal to that (ring_size >= max_usage). > > 2) pipe_get_pages_alloc(). Same story, same push_pipe() being > called, same "we'll never get that much - it'll hit the limit > first". > > 3) iov_iter_npages() in case of ITER_PIPE. Again, the value > is bogus - it should not be greater than the amount of pages > we would be able to write there. > > AFAICS, 6718b6f855a0 "pipe: Allow pipes to have kernel-reserved slots" > broke it for cases when ring_size != max_usage... Unless I'm missing something, the following would do the right thing. Dave? diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h index 4ea496924106..c22173d6e500 100644 --- a/include/linux/pipe_fs_i.h +++ b/include/linux/pipe_fs_i.h @@ -165,15 +165,10 @@ static inline bool pipe_full(unsigned int head, unsigned int tail, static inline unsigned int pipe_space_for_user(unsigned int head, unsigned int tail, struct pipe_inode_info *pipe) { - unsigned int p_occupancy, p_space; - - p_occupancy = pipe_occupancy(head, tail); + unsigned int p_occupancy = pipe_occupancy(head, tail); if (p_occupancy >= pipe->max_usage) return 0; - p_space = pipe->ring_size - p_occupancy; - if (p_space > pipe->max_usage) - p_space = pipe->max_usage; - return p_space; + return pipe->max_usage - p_occupancy; } /**