From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754622AbcGZKV4 (ORCPT ); Tue, 26 Jul 2016 06:21:56 -0400 Received: from mail-pf0-f195.google.com ([209.85.192.195]:36046 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751646AbcGZKVx (ORCPT ); Tue, 26 Jul 2016 06:21:53 -0400 Date: Tue, 26 Jul 2016 02:21:48 -0800 From: Kent Overstreet To: Stefan Bader Cc: linux-bcache@vger.kernel.org, dm-devel@redhat.com, Linux Kernel Mailing List , liuzhengyuang521@gmail.com, bcache@linux.ewheeler.net, apw@canonical.com Subject: Re: bcache super block corruption with non 4k pages Message-ID: <20160726102148.GA20130@kmo-pixel> References: <1469091513-11233-1-git-send-email-stefan.bader@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 26, 2016 at 11:51:25AM +0200, Stefan Bader wrote: > On 21.07.2016 10:58, Stefan Bader wrote: > > I was pointed at the thread which seems to address the same after > > I wrote most of below text. Did not want to re-write this so please > > bear with the odd layout. > > > > https://www.redhat.com/archives/dm-devel/2016-June/msg00015.html > > > > Zhengyuan tries to fix the problem by relocating the superblock on > > disk. But I am not sure whether there is really any guarantee about > > how __bread fills data into the buffer_head. What if there is the next > > odd arch with 128K pages? > > > > So below is an attempt to be more generic. Still I don't feel completely > > happy with the way that a page moves (or is shared) between buffer_head > > and biovec. What I tried to outline below is to let the register functions > > allocate bio+biovec memory and use the in-memory sb_cache data to initialize > > the biovec buffer. > > Any opinions here? Also adding LKML as I don't seem to get through moderation on > dm-devel. The correct solution is to rip out the __bread() and just read the superblock by issuing a bio, the same way all the other IO in bcache is done. This is the way it's done in the bcache-dev branch - unfortunately, the patch that does that in bcache-dev is big and invasive and probably not worth the hassle to backport: https://evilpiepirate.org/git/linux-bcache.git/commit/?h=bcache-dev&id=303eb67bffad57b4d9e71523e7df04bf258e66d1 Probably best to just do something small and localized.