[Ocfs2-devel] [PATCH v2] ocfs2: Fix start offset to ocfs2_zero_range_for_truncate()
Ashish Samant
ashish.samant at oracle.com
Tue Aug 30 16:17:27 PDT 2016
Hi Eric,
I am able to reproduce this on 4.8.0-rc3 as well. Can you try again and
issue a sync between fallocate and dd?
On 08/30/2016 12:38 AM, Eric Ren wrote:
> Hi,
>
> I'm on 4.8.0-rc3 kernel. Hope someone else can double-confirm this;-)
>
> On 08/30/2016 12:11 PM, Ashish Samant wrote:
>> 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
>> |................|
>
> I'm not familiar with this code. So why is the output "cd ..."?
> because we didn't write anything
> into "10MBfile". Is it a magic number when reading from a hole?
No, "cd" is what xfs_io wrote into the file. Those are the original
contents of the file which are overwritten by 0 in the first cluster
because of this bug.
Thanks,
Ashish
>
> Eric
>
>> *
>> 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 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) {
>>>>>> /*
>>>>>
>>>>>
>>>>
>>>
>>
>>
>
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