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

[Eric Ren]

Hello,

On 08/30/2016 03:23 AM, Ashish Samant wrote:
> 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! I have a try myself, but I'm not sure what is our expected output and if the test 
result meet
it:

1. After applying this patch:
ocfs2dev1:/mnt/ocfs2 # rm 10MBfile reflnktest
ocfs2dev1:/mnt/ocfs2 # xfs_io -c 'pwrite -b 4k 0 10M' -f 10MBfile
wrote 10485760/10485760 bytes at offset 0
10 MiB, 2560 ops; 0.0000 sec (1.089 GiB/sec and 285427.5839 ops/sec)
ocfs2dev1:/mnt/ocfs2 # reflink -f 10MBfile reflnktest
ocfs2dev1:/mnt/ocfs2 # fallocate -p -o 0 -l 1048615 reflnktest
ocfs2dev1:/mnt/ocfs2 # dd if=10MBfile iflag=direct bs=1048576 count=1 | hexdump -C
00000000  cd cd cd cd cd cd cd cd  cd cd cd cd cd cd cd cd |................|
*
1+0 records in
1+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0952464 s, 11.0 MB/s
00100000

2. Before this patch:
....
ocfs2dev1:/mnt/ocfs2 # dd if=10MBfile iflag=direct bs=1048576 count=1 | hexdump -C
00000000  cd cd cd cd cd cd cd cd  cd cd cd cd cd cd cd cd |................|
*
1+0 records in
1+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.0954648 s, 11.0 MB/s
00100000

3. debugfs.ocfs2 -R stats /dev/sdb
...
Block Size Bits: 12   Cluster Size Bits: 20
...

Eric
>
> 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) {
>>>           /*
>>
>>
>