From f6f96fdb8c2779f9bd8ed7b0b08405b4439c982b Mon Sep 17 00:00:00 2001
From: "Darrick J. Wong" <djwong@us.ibm.com>
Date: Tue, 18 Oct 2011 10:53:51 -0400
Subject: [PATCH] ext4: Fix comparison endianness problem in MMP initialization
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 <djwong@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
fs/ext4/mmp.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 6b327423e6221..7ea4ba4eff2ac 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -296,7 +296,8 @@ int ext4_multi_mount_protect(struct super_block *sb,
/*
* 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)
--
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