From: Ted Ts'o Subject: Re: [PATCH] ext4: Fix comparison endianness problem in MMP initialization Date: Sat, 8 Oct 2011 17:27:44 -0400 Message-ID: <20111008212744.GP7948@thunk.org> References: <20110930194900.GY12086@tux1.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel , linux-ext4 To: "Darrick J. Wong" Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:54798 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753790Ab1JHV1p (ORCPT ); Sat, 8 Oct 2011 17:27:45 -0400 Content-Disposition: inline In-Reply-To: <20110930194900.GY12086@tux1.beaverton.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Sep 30, 2011 at 12:49:00PM -0700, Darrick J. Wong wrote: > As part of startup, the MMP initialization code does this: > > mmp->mmp_seq = seq = cpu_to_le32(mmp_new_seq()); > > Next, mmp->mmp_seq is written out to disk, a delay happens, and then the MMP > block is read back in and the sequence value is tested: > > if (seq != le32_to_cpu(mmp->mmp_seq)) { > /* fail the mount */ > > On a LE system such as x86, the *le32* functions do nothing and this works. > Unfortunately, on a BE system such as ppc64, this comparison becomes: > > if (cpu_to_le32(new_seq) != le32_to_cpu(cpu_to_le32(new_seq)) { > /* fail the mount */ > > Except for a few palindromic sequence numbers, this test always causes the > mount to fail, which makes MMP filesystems generally unmountable on ppc64. The > attached patch fixes this situation. > > (This fix came up while testing the metadata checksumming patchset) > > Signed-off-by: Darrick J. Wong Applied, thanks. - Ted