[Ocfs2-devel] [PATCH] ocfs2: should wait dio before inode lock in ocfs2_setattr()

[Changwei Ge]

Hi Alex,
On 2017/10/28 10:35, alex chen wrote:
> Hi Changwei,
> 
> Thanks for you reply.
> 
> On 2017/10/27 18:21, Changwei Ge wrote:
>> Hi Alex,
>>
>> Thanks for reporting.
>> I probably get your point. You mean that for a lock resource(say A), it
>> is used to protect metadata changing  among nodes in cluster.
>>
>> Unfortunately, it was marks as BLOCKED since it was granted with a EX
>> lock, and the lock can't be unblocked since it has more or equal to one
>> ::ex_holder(s), furthermore, since process 1 is waiting for all inflight
>> dio accomplishment, it won't give up its ownership of lock source A.
>>
>> Thus, hang, right?
> 
> Yes, I'm glad you can understand this.
> 
>>
>>   From code reviewing, I admit that the hang situation does exit.
>>
>> But as for your patch, how can you guarantee no more bio will be issued
>> from other nodes in cluster?
>>
> 
> First of all, we use the inode_lock() in do_truncate() to prevent another bio to
> be issued from this node.
> Furthermore, we use the ocfs2_rw_lock() and ocfs2_inode_lock() in ocfs2_setattr()
> to guarantee no more bio will be issued from the other nodes in this cluster.
Thanks for your particular elaboration.
I think this patch makes sense.
Acked.

Thanks,
Changwei

> 
> Thanks,
> Alex
> 
>> Also, I cc this patch to ocfs2 maintainers.
>>
>> Thanks,
>> Changwei
>>
>> On 2017/10/27 16:01, alex chen wrote:
>>> we should wait dio requests to finish before inode lock in
>>> ocfs2_setattr(), otherwise the following deadlock will be happened:
>>> process 1                  process 2                    process 3
>>> truncate file 'A'          end_io of writing file 'A'   receiving the bast messages
>>> ocfs2_setattr
>>>    ocfs2_inode_lock_tracker
>>>     ocfs2_inode_lock_full
>>>    inode_dio_wait
>>>     __inode_dio_wait
>>>     -->waiting for all dio
>>>     requests finish
>>>                                                           dlm_proxy_ast_handler
>>>                                                            dlm_do_local_bast
>>>                                                             ocfs2_blocking_ast
>>>                                                              ocfs2_generic_handle_bast
>>>                                                               set OCFS2_LOCK_BLOCKED flag
>>>                           dio_end_io
>>>                            dio_bio_end_aio
>>>                             dio_complete
>>>                              ocfs2_dio_end_io
>>>                               ocfs2_dio_end_io_write
>>>                                ocfs2_inode_lock
>>>                                 __ocfs2_cluster_lock
>>>                                  ocfs2_wait_for_mask
>>>                                  -->waiting for OCFS2_LOCK_BLOCKED
>>>                                  flag to be cleared, that is waiting
>>>                                  for 'process 1' unlocking the inode lock
>>>                              inode_dio_end
>>>                              -->here dec the i_dio_count, but will never
>>>                              be called, so a deadlock happened.
>>>
>>> Signed-off-by: Alex Chen <alex.chen at huawei.com>
>>> Reviewed-by: Jun Piao <piaojun at huawei.com>
Acked-by: Changwei Ge <ge.changwei at h3c.com>

>>>
>>> ---
>>>    fs/ocfs2/file.c | 9 +++++++--
>>>    1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>>> index 6e41fc8..50e09a6 100644
>>> --- a/fs/ocfs2/file.c
>>> +++ b/fs/ocfs2/file.c
>>> @@ -1161,6 +1161,13 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>>>    	}
>>>    	size_change = S_ISREG(inode->i_mode) && attr->ia_valid & ATTR_SIZE;
>>>    	if (size_change) {
>>> +
>>> +		/* here we should wait dio to finish before inode lock
>>> +		 * to avoid a deadlock between ocfs2_setattr() and
>>> +		 * ocfs2_dio_end_io_write()
>>> +		 */
>>> +		inode_dio_wait(inode);
>>> +
>>>    		status = ocfs2_rw_lock(inode, 1);
>>>    		if (status < 0) {
>>>    			mlog_errno(status);
>>> @@ -1200,8 +1207,6 @@ int ocfs2_setattr(struct dentry *dentry, struct iattr *attr)
>>>    		if (status)
>>>    			goto bail_unlock;
>>>
>>> -		inode_dio_wait(inode);
>>> -
>>>    		if (i_size_read(inode) >= attr->ia_size) {
>>>    			if (ocfs2_should_order_data(inode)) {
>>>    				status = ocfs2_begin_ordered_truncate(inode,
>>>
>>
>>
>> .
>>
> 
>