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@xxxxxxxxxx>
---
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)
--
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