Ocfs2 devel - Dec 2017 - [PATCH v2] ocfs2: check the metadate alloc before marking extent written

On 2017/12/13 15:25, alex chen wrote:
> Hi Changwei,
> 
> On 2017/12/12 9:05, Changwei Ge wrote:
>> Hi Alex,
>>
>> On 2017/12/5 11:31, alex chen wrote:
>>> We need to check the free number of the records in each loop to
mark
>>> extent written, because the last extent block may be changed
through
>>> many times marking extent written and the
'num_free_extents' also be
>>> changed. In the worst case, the 'num_free_extents' may
become less
>>> than the beginning of the loop. So we should not estimate the free
>>> number of the records at the beginning of the loop to mark extent
>>> written.
>>>
>>> Reported-by: John Lightsey <john at nixnuts.net>
>>> Signed-off-by: Alex Chen <alex.chen at huawei.com>
>>> Reviewed-by: Jun Piao <piaojun at huawei.com>
>>> ---
>>>    fs/ocfs2/aops.c | 77
+++++++++++++++++++++++++++++++++++++++++++++++----------
>>>    1 file changed, 64 insertions(+), 13 deletions(-)
>>>
>>
>> If there isn't enough extent records here, you break this loop and
also
>> commit transaction.
>> After re-executing from _restart_all_, a new transaction is started.
>> So you separate 'before _restart_all_' and 'after
_restart_all_' into
>> different transactions.
>>
>>
>>>
>>> -	if (end > i_size_read(inode)) {
>>> +	if (!restart && end > i_size_read(inode)) {
>>
>> Here you don't change inode size, however, obviously you already
mark
>> extents as *written*.
> 
> Here we should not change inode size, otherwise, the user may read some of
the data
> he wrote and the other part of data is zero, which breaks the consistency
of WRITE.
> Here it just mark extents to written and do not allocated data spaces.
Very true.
> 
>>
>>>    		ret = ocfs2_set_inode_size(handle, inode, di_bh, end);
>>>    		if (ret < 0)
>>>    			mlog_errno(ret);
>>>    	}
>>> +
>>>    commit:
>>>    	ocfs2_commit_trans(osb, handle);
>>
>> You commit transaction here and host just crashes at this point.
>> Then you will have a file with a smaller size than its real size.
>> Moreover, those space could not be declaimed.
> 
> The problem you described above is exist. But it is a new problem and is
not introduced by this patch.
> It is introduced in commit c15471f79506(ocfs2: fix sparse file & data
ordering issue in direct io).
> Those space was allocated in
ocfs2_dio_wr_get_block()->ocfs2_write_begin_nolock()->
> ocfs2_write_cluster_by_desc() and it could not be declaimed when any errors
happen in
> ocfs2_dio_end_io_write().
Hi Alex,
Actually, 1)the space can be declaimed via ocfs2 journal recovery by other nodes
or itself during its
next mount, since it also resided in orphan directory. 2)If deleting
corresponding inode is done, I suppose,
unwritten cluster might be declaimed by _fsck_ with a *consistent* inode
size.(not very sure on this point).

The original version of ocfs2_dio_end_io_write() before your patch being
applied, it ties _mark_extent_written_
to _set_inode_size_ in an unique jbd2 transaction. So it can guarantee the
consistency between changing them.

As for your patch, you split them into different transactions which breaks the
consistency, since your patch
starts and commit a transaction once _restart_all_ is needed(2 times at least),
but only the last jbd2 committed
transaction includes changing inode size.

I think your way to fix this issue is acceptable.

If you have no idea how to improve patch, I will try to compose a patch to do
some help based on your patch.

Perhaps Andrew can fold them into a single one, it's up to Andrew.

Thanks,
Changwei
> This patch corrects the calculation method of the free number of the
records.
> 
> At present, I have no idea to solve the new problem you described above, I
think you can send the patch
> to solve this problem if you have a good idea.
> 
> Thanks,
> Alex
> 
>>
>> Should we do more work on JBD2?
>>
>> Thanks,
>> Changwei
>>
>>
>>> +free_ac:
>>> +	if (meta_ac) {
>>> +		ocfs2_free_alloc_context(meta_ac);
>>> +		meta_ac = NULL;
>>> +	}
>>> +	if (restart) {
>>> +		restart = 0;
>>> +		goto restart_all;
>>> +	}
>>>    unlock:
>>>    	up_write(&oi->ip_alloc_sem);
> 
>

Hi Changwei,

On 2017/12/14 8:56, Changwei Ge wrote:
> On 2017/12/13 15:25, alex chen wrote:
>> Hi Changwei,
>>
>> On 2017/12/12 9:05, Changwei Ge wrote:
>>> Hi Alex,
>>>
>>> On 2017/12/5 11:31, alex chen wrote:
>>>> We need to check the free number of the records in each loop to
mark
>>>> extent written, because the last extent block may be changed
through
>>>> many times marking extent written and the
'num_free_extents' also be
>>>> changed. In the worst case, the 'num_free_extents' may
become less
>>>> than the beginning of the loop. So we should not estimate the
free
>>>> number of the records at the beginning of the loop to mark
extent
>>>> written.
>>>>
>>>> Reported-by: John Lightsey <john at nixnuts.net>
>>>> Signed-off-by: Alex Chen <alex.chen at huawei.com>
>>>> Reviewed-by: Jun Piao <piaojun at huawei.com>
>>>> ---
>>>>    fs/ocfs2/aops.c | 77
+++++++++++++++++++++++++++++++++++++++++++++++----------
>>>>    1 file changed, 64 insertions(+), 13 deletions(-)
>>>>
> 
>>>
>>> If there isn't enough extent records here, you break this loop
and also
>>> commit transaction.
>>> After re-executing from _restart_all_, a new transaction is
started.
>>> So you separate 'before _restart_all_' and 'after
_restart_all_' into
>>> different transactions.
>>>
>>>
>>>>
>>>> -	if (end > i_size_read(inode)) {
>>>> +	if (!restart && end > i_size_read(inode)) {
>>>
>>> Here you don't change inode size, however, obviously you
already mark
>>> extents as *written*.
>>
>> Here we should not change inode size, otherwise, the user may read some
of the data
>> he wrote and the other part of data is zero, which breaks the
consistency of WRITE.
>> Here it just mark extents to written and do not allocated data spaces.
> 
> Very true.
> 
>>
>>>
>>>>    		ret = ocfs2_set_inode_size(handle, inode, di_bh, end);
>>>>    		if (ret < 0)
>>>>    			mlog_errno(ret);
>>>>    	}
>>>> +
>>>>    commit:
>>>>    	ocfs2_commit_trans(osb, handle);
>>>
>>> You commit transaction here and host just crashes at this point.
>>> Then you will have a file with a smaller size than its real size.
>>> Moreover, those space could not be declaimed.
>>
>> The problem you described above is exist. But it is a new problem and
is not introduced by this patch.
>> It is introduced in commit c15471f79506(ocfs2: fix sparse file &
data ordering issue in direct io).
>> Those space was allocated in
ocfs2_dio_wr_get_block()->ocfs2_write_begin_nolock()->
>> ocfs2_write_cluster_by_desc() and it could not be declaimed when any
errors happen in
>> ocfs2_dio_end_io_write().
> 
> Hi Alex,
> Actually, 1)the space can be declaimed via ocfs2 journal recovery by other
nodes or itself during its
> next mount, since it also resided in orphan directory. 2)If deleting
corresponding inode is done, I suppose,
> unwritten cluster might be declaimed by _fsck_ with a *consistent* inode
size.(not very sure on this point).
> 
I have a different understanding about this.
I think the space can be declaimed until the inode is deleted from orphan
directory, Do you agree?
In ocfs2_dio_end_io_write(), we deleted the inode from orphan directory before
calling ocfs2_lock_allocators()
and ocfs2_mark_extent_written. In other words, the space can't be declaimed
when any errors happened in the
process of marking extent to written unless the file is deleted or we run
fsck.ocfs2.
> The original version of ocfs2_dio_end_io_write() before your patch being
applied, it ties _mark_extent_written_
> to _set_inode_size_ in an unique jbd2 transaction. So it can guarantee the
consistency between changing them.
> 
Yes.
> As for your patch, you split them into different transactions which breaks
the consistency, since your patch
> starts and commit a transaction once _restart_all_ is needed(2 times at
least), but only the last jbd2 committed
> transaction includes changing inode size.
I have understood it. This is indeed a point that can be optimized. Do you have
any good suggestions?

Thanks,
Alex
> 
> I think your way to fix this issue is acceptable.
> 
> If you have no idea how to improve patch, I will try to compose a patch to
do some help based on your patch.
> 
I am honored to be with you to solve this problem.
> Perhaps Andrew can fold them into a single one, it's up to Andrew.
> 
> Thanks,
> Changwei
> 
>> This patch corrects the calculation method of the free number of the
records.
>>
>> At present, I have no idea to solve the new problem you described
above, I think you can send the patch
>> to solve this problem if you have a good idea.
>>
>> Thanks,
>> Alex
>>
>>>
>>> Should we do more work on JBD2?
>>>
>>> Thanks,
>>> Changwei
>>>
>>>
>>>> +free_ac:
>>>> +	if (meta_ac) {
>>>> +		ocfs2_free_alloc_context(meta_ac);
>>>> +		meta_ac = NULL;
>>>> +	}
>>>> +	if (restart) {
>>>> +		restart = 0;
>>>> +		goto restart_all;
>>>> +	}
>>>>    unlock:
>>>>    	up_write(&oi->ip_alloc_sem);
> 
>>
>>
> 
> 
> .
>