Re: [Ocfs2-devel] [PATCH V3] ocfs2: fix dead lock caused by ocfs2_defrag_extent

[Joseph Qi <jiangqi903@gmail.com>]

On 18/11/1 20:34, Changwei Ge wrote:
> Hello Joseph,
> 
> On 2018/11/1 20:16, Joseph Qi wrote:
>>
>>
>> On 18/11/1 19:52, Changwei Ge wrote:
>>> Hello Joseph,
>>>
>>> On 2018/11/1 17:01, Joseph Qi wrote:
>>>> Hi Larry,
>>>>
>>>> On 18/11/1 15:14, Larry Chen wrote:
>>>>> ocfs2_defrag_extent may fall into deadlock.
>>>>>
>>>>> ocfs2_ioctl_move_extents
>>>>>       ocfs2_ioctl_move_extents
>>>>>         ocfs2_move_extents
>>>>>           ocfs2_defrag_extent
>>>>>             ocfs2_lock_allocators_move_extents
>>>>>
>>>>>               ocfs2_reserve_clusters
>>>>>                 inode_lock GLOBAL_BITMAP_SYSTEM_INODE
>>>>>
>>>>> 	  __ocfs2_flush_truncate_log
>>>>>                 inode_lock GLOBAL_BITMAP_SYSTEM_INODE
>>>>>
>>>>> As backtrace shows above, ocfs2_reserve_clusters() will call inode_lock
>>>>> against the global bitmap if local allocator has not sufficient cluters.
>>>>> Once global bitmap could meet the demand, ocfs2_reserve_cluster will
>>>>> return success with global bitmap locked.
>>>>>
>>>>> After ocfs2_reserve_cluster(), if truncate log is full,
>>>>> __ocfs2_flush_truncate_log() will definitely fall into deadlock because it
>>>>> needs to inode_lock global bitmap, which has already been locked.
>>>>>
>>>>> To fix this bug, we could remove from ocfs2_lock_allocators_move_extents()
>>>>> the code which intends to lock global allocator, and put the removed code
>>>>> after __ocfs2_flush_truncate_log().
>>>>>
>>>>> ocfs2_lock_allocators_move_extents() is referred by 2 places, one is here,
>>>>> the other does not need the data allocator context, which means this patch
>>>>> does not affect the caller so far.
>>>>>
>>>>> Change log:
>>>>> 1. Correct the function comment.
>>>>> 2. Remove unused argument from ocfs2_lock_meta_allocator_move_extents.
>>>>>
>>>>> Signed-off-by: Larry Chen <lchen@suse.com>
>>>>> ---
>>>>>    fs/ocfs2/move_extents.c | 47 ++++++++++++++++++++++++++---------------------
>>>>>    1 file changed, 26 insertions(+), 21 deletions(-)
>>>>>
>>>
>>>> IMO, here clusters_to_move is only for data_ac, since we change this
>>>> function to only handle meta_ac, I'm afraid clusters_to_move related
>>>> logic has to been changed correspondingly.
>>>
>>> I think we can't remove *clusters_to_move* from here as clusters can be reserved latter outsides this function, but we
>>> still have to reserve metadata(extents) in advance.
>>> So we need that argument.
>>>
>> I was not saying just remove it.
>> IIUC, clusters_to_move is for reserving data clusters (for meta_ac, we
> 
> Um...
> *cluster_to_move* is not only used for reserving data clusters.
> It is also an effecting input for calculating if existed extents still have enough free records for later
> tree operation like attaching clusters to extents.
> 
> Please refer to below code:
>   175         unsigned int max_recs_needed = 2 * extents_to_split + clusters_to_move;
>

IC. It is a bit odd that calculate it here but do the real reserve out.

> 
> 
>> mostly talk about blocks). Since we have moved data cluster reserve
>> logic out of ocfs2_lock_allocators_move_extents() now, then left
>> clusters_to_move related logic here is odd.
> 
> Like my preceding elaboration, it is used for telling if we need more extents.
> Anyway, I think we must keep *cluster_to_move* here as it used to. :-)
> 
> Thanks,
> Changwei
> 
> 
> 
> 
>>
>>>>>    					u32 extents_to_split,
>>>>>    					struct ocfs2_alloc_context **meta_ac,
>>>>> -					struct ocfs2_alloc_context **data_ac,
>>>>>    					int extra_blocks,
>>>>>    					int *credits)
>>>>>    {
>>>>> @@ -192,13 +188,6 @@ static int ocfs2_lock_allocators_move_extents(struct inode *inode,
>>>>>    		goto out;
>>>>>    	}
>>>>>    
>>>>> -	if (data_ac) {
>>>>> -		ret = ocfs2_reserve_clusters(osb, clusters_to_move, data_ac);
>>>>> -		if (ret) {
>>>>> -			mlog_errno(ret);
>>>>> -			goto out;
>>>>> -		}
>>>>> -	}
>>>>>    
>>>>>    	*credits += ocfs2_calc_extend_credits(osb->sb, et->et_root_el);
>>>>>    
>>>>> @@ -257,10 +246,10 @@ static int ocfs2_defrag_extent(struct ocfs2_move_extents_context *context,
>>>>>    		}
>>>>>    	}
>>>>>    
>>>>> -	ret = ocfs2_lock_allocators_move_extents(inode, &context->et, *len, 1,
>>>>> -						 &context->meta_ac,
>>>>> -						 &context->data_ac,
>>>>> -						 extra_blocks, &credits);
>>>>> +	ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et,
>>>>> +						*len, 1,
>>>>> +						&context->meta_ac,
>>>>> +						extra_blocks, &credits);
>>>>>    	if (ret) {
>>>>>    		mlog_errno(ret);
>>>>>    		goto out;
>>>>> @@ -283,6 +272,21 @@ static int ocfs2_defrag_extent(struct ocfs2_move_extents_context *context,
>>>>>    		}
>>>>>    	}
>>>>>    
>>>>> +	/*
>>>>> +	 * Make sure ocfs2_reserve_cluster is called after
>>>>> +	 * __ocfs2_flush_truncate_log, otherwise, dead lock may happen.
>>>>> +	 *
>>>>> +	 * If ocfs2_reserve_cluster is called
>>>>> +	 * before __ocfs2_flush_truncate_log, dead lock on global bitmap
>>>>> +	 * may happen.
>>>>> +	 *
>>>>> +	 */
>>>>> +	ret = ocfs2_reserve_clusters(osb, *len, &context->data_ac);
>>>>> +	if (ret) {
>>>>> +		mlog_errno(ret);
>>>>> +		goto out_unlock_mutex;
>>>>> +	}
>>>>> +
>>>>>    	handle = ocfs2_start_trans(osb, credits);
>>>>>    	if (IS_ERR(handle)) {
>>>>>    		ret = PTR_ERR(handle);
>>>>> @@ -600,9 +604,10 @@ static int ocfs2_move_extent(struct ocfs2_move_extents_context *context,
>>>>>    		}
>>>>>    	}
>>>>>    
>>>>> -	ret = ocfs2_lock_allocators_move_extents(inode, &context->et, len, 1,
>>>>> -						 &context->meta_ac,
>>>>> -						 NULL, extra_blocks, &credits);
>>>>> +	ret = ocfs2_lock_meta_allocator_move_extents(inode, &context->et,
>>>>> +						len, 1,
>>>>> +						&context->meta_ac,
>>>>> +						extra_blocks, &credits);
>>>>>    	if (ret) {
>>>>>    		mlog_errno(ret);
>>>>>    		goto out;
>>>>>
>>>>
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>>