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| author | Darrick J. Wong <djwong@us.ibm.com> | 2011-10-18 10:53:51 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2011-10-18 10:53:51 -0400 |
| commit | f6f96fdb8c2779f9bd8ed7b0b08405b4439c982b (patch) | |
| tree | 310c22fa079a169a824910bd3c3b13464a22c12c /fs/ext4/mmp.c | |
| parent | bdfc230f33a9dab316dcb6be4696ae59e1562e3c (diff) | |
| download | lwn-f6f96fdb8c2779f9bd8ed7b0b08405b4439c982b.tar.gz lwn-f6f96fdb8c2779f9bd8ed7b0b08405b4439c982b.zip | |
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>
Diffstat (limited to 'fs/ext4/mmp.c')
| -rw-r--r-- | 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 6b327423e622..7ea4ba4eff2a 100644 --- a/fs/ext4/mmp.c +++ b/fs/ext4/mmp.c @@ -296,7 +296,8 @@ 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) |