[Ocfs2-devel] [PATCH] fix dead lock caused by ocfs2_defrag_extent

[Larry Chen]

Hi Joseph,

Thanks for your review, I'll remove it later.

Thanks,
Larry

On 08/28/2018 09:02 AM, Joseph Qi wrote:
> Hi Larry,
> 
> On 18/8/27 16:01, Larry Chen wrote:
>> ocfs2_defrag_extent may fall into dead lock.
>>
>> 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 back trace 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 dead lock
>> 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
>>
>> The ocfs2_lock_allocators_move_extents has been refered 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.
>>
> After this change, data_ac in ocfs2_lock_allocators_move_extents() is
> no longer used. So I'd prefer we also clean it up.
> 
> Thanks,
> Joseph
> 
>>
>>
>> Signed-off-by: Larry Chen <lchen at suse.com>
>> ---
>>   fs/ocfs2/move_extents.c | 13 ++++++-------
>>   1 file changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c
>> index 7eb3b0a6347e..064dedf40d74 100644
>> --- a/fs/ocfs2/move_extents.c
>> +++ b/fs/ocfs2/move_extents.c
>> @@ -192,13 +192,6 @@ 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);
>>   
>> @@ -283,6 +276,12 @@ static int ocfs2_defrag_extent(struct ocfs2_move_extents_context *context,
>>   		}
>>   	}
>>   
>> +	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);
>>
>