Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752388AbcCLKhJ (ORCPT ); Sat, 12 Mar 2016 05:37:09 -0500 Received: from mail-yw0-f171.google.com ([209.85.161.171]:35392 "EHLO mail-yw0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751266AbcCLKg5 (ORCPT ); Sat, 12 Mar 2016 05:36:57 -0500 MIME-Version: 1.0 In-Reply-To: <20160312092421.GA20839@kmo-pixel> References: <20160312074329.GA19066@kmo-pixel> <20160312092421.GA20839@kmo-pixel> Date: Sat, 12 Mar 2016 18:36:56 +0800 Message-ID: Subject: Re: e827091cb1 "block: merge: get the 1st and last bvec via helpers" broken From: Ming Lei To: Kent Overstreet Cc: Ming Lin , Jens Axboe , Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1429 Lines: 38 Hi Kent, On Sat, Mar 12, 2016 at 5:24 PM, Kent Overstreet wrote: > On Sat, Mar 12, 2016 at 04:49:41PM +0800, Ming Lei wrote: >> On Sat, Mar 12, 2016 at 3:43 PM, Kent Overstreet >> wrote: >> > I don't know exactly how it's broken, but with that patch segment counting is >> > broken - I'm seeing blk_rq_map_sg() overrun the end of the sgtable. >> > >> > I suggest reverting it for 4.5... >> >> Kent, could you share your test case? I'd like to figure out the root cause. > > xfstest 036 on bcachefs. Given bcachefs isn't merged, could you provide one way to reproduce it with clean upstream kernel? > >> BTW, I don't object to revert it given it is close to v4.5 release, but I am >> curious how it breaks segment couting. > > If you want to debug your version (personally I'd just revert to the simpler > one), I'd start by having your helper use both methods to calculate the last > biovec, and then assert that they're equal. > > Also make sure you're testing with a sub-page sized blocksize, if filesystem > blocksize == page size you're not going to be testing the interesting cases I just run xfstests 036 over bcache and md, with block size 1024/2048, with xfs/ext4/btrfs, looks the segment counting issue can't be reproduced. If the issue can only be reproduced with bcachefs, I suggest we don't revert it until the root cause is figured out. Thanks, Ming Lei