Re: [PATCH 4.4 13/16] ocfs2: should wait dio before inode lock in ocfs2_setattr()

[alex chen]

On 2017/12/8 10:26, Ben Hutchings wrote:
> On Fri, 2017-12-08 at 08:39 +0800, alex chen wrote:
>>
>> On 2017/12/8 2:25, Ben Hutchings wrote:
>>> On Wed, 2017-12-06 at 09:02 +0800, alex chen wrote:
>>>> Hi Ben,
>>>>
>>>> Thanks for your reply.
>>>>
>>>> On 2017/12/5 23:49, Ben Hutchings wrote:
>>>>> On Wed, 2017-11-22 at 11:12 +0100, Greg Kroah-Hartman wrote:
>>>>>> 4.4-stable review patch.  If anyone has any objections,
>>>>>> please let me know.
>>>>>>
>>>>>> ------------------
>>>>>>
>>>>>> From: alex chen <alex.chen@xxxxxxxxxx>
>>>>>>
>>>>>> commit 28f5a8a7c033cbf3e32277f4cc9c6afd74f05300 upstream.
>>>>>>
>>>>>> we should wait dio requests to finish before inode lock in
>>>>>> ocfs2_setattr(), otherwise the following deadlock will
>>>>>> happen:
>>>>>
>>>>> [...]
>>>>>
>>>>> I looked at the kernel-doc for inode_dio_wait():
>>>>>
>>>>> /**
>>>>>  * inode_dio_wait - wait for outstanding DIO requests to finish
>>>>>  * @inode: inode to wait for
>>>>>  *
>>>>>  * Waits for all pending direct I/O requests to finish so that we can
>>>>>  * proceed with a truncate or equivalent operation.
>>>>>  *
>>>>>  * Must be called under a lock that serializes taking new references
>>>>>  * to i_dio_count, usually by inode->i_mutex.
>>>>>  */
>>>>>
>>>>> Now that ocfs2_setattr() calls this outside of the inode locked region,
>>>>> what prevents another task adding a new dio request immediately
>>>>> afterward?
>>>>>
>>>>
>>>> In the kernel 4.6, firstly, we use the inode_lock() in do_truncate() to
>>>> prevent another bio to be issued from this node.
>>>
>>> [...]
>>>
>>> Yes but there seems to be a race condition - after the call to
>>> inode_dio_wait() and before the call to inode_lock(), another dio
>>> request can be added.
> 
> Sorry, I've been mixing up inode_lock() and ocfs2_inode_lock(). 
> However:
> 
>> In the truncating file situation, the lock order is as follow:
>> do_truncate()
>>  inode_lock()
>>  notify_change()
>>   ocfs2_setattr()
>>    inode_dio_wait()
>>     --here it is under the protect of inode_lock(), so another dio requests
>>       from another process will not be added.
> 
> only DIO reads seem to take the inode lock.
> 

I do not clearly understand what you mean.
The inode_lock() will be called in ocfs2_file_write_iter().
You mean only DIO writes seem to take the inode_lock()?

BTW, in this patch, I just adjusted the inode_dio_wait() to the front of the ocfs2_rw_lock()
and didn't adjust the order of inode_lock() and inode_dio_wait().

Thanks,
Alex

> Ben.
> 
>>    ocfs2_rw_lock()
>>    ocfs2_inode_lock_tracker()
>>     this function is used to prevent the inode from being modified by another
>>     nodes in the cluster
>>  inode_unlock()
>>
>>>
>>> Ben.
>>>
>>
>>