[Ocfs2-devel] [PATCH v2] ocfs2: Fix start offset to ocfs2_zero_range_for_truncate()

[Ashish Samant]

Hi Eric,

The easiest way to reproduce this is :

1. Create a random file of say 10 MB
     xfs_io -c 'pwrite -b 4k 0 10M' -f 10MBfile
2. Reflink  it
     reflink -f 10MBfile reflnktest
3. Punch a hole at starting at cluster boundary  with range greater that 
1MB. You can also use a range that will put the end offset in another 
extent.
     fallocate -p -o 0 -l 1048615 reflnktest
4. sync
5. Check the  first cluster in the source file. (It will be zeroed out).
    dd if=10MBfile iflag=direct bs=<cluster size> count=1 | hexdump -C

Thanks,
Ashish

On 08/28/2016 10:39 PM, Eric Ren wrote:
> Hi,
>
> Thanks for this fix. I'd like to reproduce this issue locally and test 
> this patch,
> could you elaborate the detailed steps of reproduction?
>
> Thanks,
> Eric
>
> On 08/27/2016 07:04 AM, Ashish Samant wrote:
>> If we punch a hole on a reflink such that following conditions are met:
>>
>> 1. start offset is on a cluster boundary
>> 2. end offset is not on a cluster boundary
>> 3. (end offset is somewhere in another extent) or
>>     (hole range > MAX_CONTIG_BYTES(1MB)),
>>
>> we dont COW the first cluster starting at the start offset. But in this
>> case, we were wrongly passing this cluster to
>> ocfs2_zero_range_for_truncate() to zero out. This will modify the 
>> cluster
>> in place and zero it in the source too.
>>
>> Fix this by skipping this cluster in such a scenario.
>>
>> Reported-by: Saar Maoz <saar.maoz at oracle.com>
>> Signed-off-by: Ashish Samant <ashish.samant at oracle.com>
>> Reviewed-by: Srinivas Eeda <srinivas.eeda at oracle.com>
>> ---
>> v1->v2:
>> -Changed the commit msg to include a better and generic description of
>>   the problem, for all cluster sizes.
>> -Added Reported-by and Reviewed-by tags.
>>      fs/ocfs2/file.c | 34 ++++++++++++++++++++++++----------
>>   1 file changed, 24 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>> index 4e7b0dc..0b055bf 100644
>> --- a/fs/ocfs2/file.c
>> +++ b/fs/ocfs2/file.c
>> @@ -1506,7 +1506,8 @@ static int ocfs2_zero_partial_clusters(struct 
>> inode *inode,
>>                          u64 start, u64 len)
>>   {
>>       int ret = 0;
>> -    u64 tmpend, end = start + len;
>> +    u64 tmpend = 0;
>> +    u64 end = start + len;
>>       struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>>       unsigned int csize = osb->s_clustersize;
>>       handle_t *handle;
>> @@ -1538,18 +1539,31 @@ static int ocfs2_zero_partial_clusters(struct 
>> inode *inode,
>>       }
>>         /*
>> -     * We want to get the byte offset of the end of the 1st cluster.
>> +     * If start is on a cluster boundary and end is somewhere in 
>> another
>> +     * cluster, we have not COWed the cluster starting at start, unless
>> +     * end is also within the same cluster. So, in this case, we 
>> skip this
>> +     * first call to ocfs2_zero_range_for_truncate() truncate and 
>> move on
>> +     * to the next one.
>>        */
>> -    tmpend = (u64)osb->s_clustersize + (start & ~(osb->s_clustersize 
>> - 1));
>> -    if (tmpend > end)
>> -        tmpend = end;
>> +    if ((start & (csize - 1)) != 0) {
>> +        /*
>> +         * We want to get the byte offset of the end of the 1st
>> +         * cluster.
>> +         */
>> +        tmpend = (u64)osb->s_clustersize +
>> +            (start & ~(osb->s_clustersize - 1));
>> +        if (tmpend > end)
>> +            tmpend = end;
>>   -    trace_ocfs2_zero_partial_clusters_range1((unsigned long 
>> long)start,
>> -                         (unsigned long long)tmpend);
>> +        trace_ocfs2_zero_partial_clusters_range1(
>> +            (unsigned long long)start,
>> +            (unsigned long long)tmpend);
>>   -    ret = ocfs2_zero_range_for_truncate(inode, handle, start, 
>> tmpend);
>> -    if (ret)
>> -        mlog_errno(ret);
>> +        ret = ocfs2_zero_range_for_truncate(inode, handle, start,
>> +                            tmpend);
>> +        if (ret)
>> +            mlog_errno(ret);
>> +    }
>>         if (tmpend < end) {
>>           /*
>
>