From: "Darrick J. Wong" Subject: [PATCH 05/28] ext4: Fix endian problem in MMP initialization Date: Sat, 08 Oct 2011 00:54:16 -0700 Message-ID: <20111008075416.20506.12005.stgit@elm3c44.beaverton.ibm.com> References: <20111008075343.20506.23155.stgit@elm3c44.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: Sunil Mushran , Martin K Petersen , Greg Freemyer , Amir Goldstein , linux-kernel , Andi Kleen , Mingming Cao , Joel Becker , linux-fsdevel , linux-ext4@vger.kernel.org, Coly Li To: Andreas Dilger , Theodore Tso , "Darrick J. Wong" Return-path: Received: from e39.co.us.ibm.com ([32.97.110.160]:41694 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751343Ab1JHH46 (ORCPT ); Sat, 8 Oct 2011 03:56:58 -0400 In-Reply-To: <20111008075343.20506.23155.stgit@elm3c44.beaverton.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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. Signed-off-by: Darrick J. Wong --- fs/ext4/mmp.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c index 9bdef3f..a7a4986 100644 --- a/fs/ext4/mmp.c +++ b/fs/ext4/mmp.c @@ -295,7 +295,8 @@ skip: /* * write a new random sequence number. */ - mmp->mmp_seq = seq = cpu_to_le32(mmp_new_seq()); + seq = mmp_new_seq(); + mmp->mmp_seq = cpu_to_le32(seq); retval = write_mmp_block(bh); if (retval)