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

[Ashish Samant <ashish.samant@oracle.com>]

Hmm, thats weird. I see this on 4.7 kernel without the patch:

# xfs_io -c 'pwrite -b 4k 0 10M' -f 10MBfile
wrote 10485760/10485760 bytes at offset 0
10 MiB, 2560 ops; 0.0000 sec (683.995 MiB/sec and 175102.5992 ops/sec)
# reflink -f 10MBfile reflnktest
# fallocate -p -o 0 -l 1048615 reflnktest
# dd if=10MBfile iflag=direct bs=1048576 count=1 | hexdump -C
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
|................|
*
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.0321517 s, 32.6 MB/s
00100000

and with patch
----
# dd if=10MBfile iflag=direct bs=1M 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
00100000

Thanks,
Ashish


On 08/29/2016 08:33 PM, Eric Ren wrote:
> 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@oracle.com>
>>>> Signed-off-by: Ashish Samant <ashish.samant@oracle.com>
>>>> Reviewed-by: Srinivas Eeda <srinivas.eeda@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) {
>>>>           /*
>>>
>>>
>>
>