On Aug 15, 2015, at 9:37 AM, Theodore Ts'o <tytso@xxxxxxx> wrote:
>
> On Fri, Aug 14, 2015 at 11:03:46AM -0600, Andreas Dilger wrote:
>>> My static check complains because we have:
>>>
>>> if (!*bh)
>>> return -ENOMEM;
>>> if (*bh) {
>>>
>>> The second check is unnecessary.
>>>
>>> I've simplified this code by moving the "if (!*bh)" checks around. Also Andreas Dilger says we should probably print a warning if
>>> sb_getblk() fails.
>>>
>>> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
>>
>> Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
>
> Applied, thanks. I've changed the patch slightly to also print a
> warning if the MMP magic number and/or checksum for the MMP block
> doesn't check out, and to print the error code to disambiguate between
> the various failure cases.
I agree that is an improvement.
> One thing, from looking at the function --- it looks like it might be
> a good idea if we were to move the call to clear_buffer_uptodate() to
> *after* the sb_getblk() call, no?
>
> Otherwise we don't reread the MMP block if it is already in the cache,
> and it is the first time read_mmp_block() is called in a function in
> fs/ext4/mmp.c.....
Good catch. Fortunately, this didn't cause dangerous MMP operation
since the MMP block is invalidated and read a second time after a
delay (to catch cases of concurrent mounts) and compared to the
original.
At worst the first (stale) read would result in the second read
causing a false mismatch and a cause an error during mount. While
not dangerous, this could also be annoying and is good to fix.
Cheers, Andreas
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