From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:58226 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751633AbeCTJbS (ORCPT ); Tue, 20 Mar 2018 05:31:18 -0400 Subject: Re: [PATCH 4.14 024/110] btrfs: use proper endianness accessors for super_copy To: dsterba@suse.cz, Christoph Biedl , Greg Kroah-Hartman , Liu Bo , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20180307191039.748351103@linuxfoundation.org> <20180307191042.810088712@linuxfoundation.org> <1521139304@msgid.manchmal.in-ulm.de> <20180316123049.GC25079@kroah.com> <1521305582@msgid.manchmal.in-ulm.de> <20180319193221.GP6955@suse.cz> From: Anand Jain Message-ID: Date: Tue, 20 Mar 2018 17:32:56 +0800 MIME-Version: 1.0 In-Reply-To: <20180319193221.GP6955@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 03/20/2018 03:32 AM, David Sterba wrote: > On Sat, Mar 17, 2018 at 06:27:15PM +0100, Christoph Biedl wrote: >> Greg Kroah-Hartman wrote... >> >>> On Thu, Mar 15, 2018 at 07:55:42PM +0100, Christoph Biedl wrote: >> >>>>> commit 3c181c12c431fe33b669410d663beb9cceefcd1b upstream. >> >>>> On big-endian systems, this change intruduces severe corruption, >>>> resulting in complete loss of the data on the used block device. >> >>> That sucks. Can you test Linus's tree to verify the problem is there? >>> I'll gladly revert this if Linus's tree also gets the revert, I don't >>> want you to hit this when you upgrade to a newer kernel. >> >> Confirmed: The problem is, err ... was in Linus' tree as well. The >> rather recent commit 8f5fd927c3a7 reverted the change, after that >> everything is as expected again. > > Thanks for checking. > >> Looking at the original commit, I don't have a clue why things go wrong >> so horribly > > It's a half endianness conversion. The plain in-memory structures are in > LE and has to be accessed via the helpers, super block copy and the > root item. The commit adds only one half of the conversion, that > naturally does not exhibit on LE, because the macros are no-op. > > Originally, the items were stored from the on-disk type to on-disk type, > regardless of the CPU: > > super->chunk_root = root_item->bytenr; > > The patch should have added conversion of both values, like > > btrfs_set_super_chunk_root(super, btrfs_root_bytenr(root_item)); > > and not > > btrfs_set_super_chunk_root(super, root_item->bytenr); > > It's not very obvious from the context though, typically there's one > structure that needs the accessors and is set from a value that's in CPU > byteorder. I think that the exception to this pattern confused all > involved developers. > > The root_item members are annotated as __le64 that should be caught by > sparse/smatch checker in the buggy case, but we don't run the checkers > every the time. Ah! the RC is at the other side of the equation. Makes sense to me. Thanks. >> - otherwise don't be afraid of my data. I took this as a >> chance to verify my data recovery procedure, with success. > > Should that not be the case, the damaged items in superblock can be > byteswapped back. That's 6 x u64 at most, I have a tool for that now. > > Thanks again for the report and sorry for the trouble. It's entirely my mistake. My apologies for the inconvenience. Thanks, Anand > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >