Re: [f2fs-dev] [PATCH 1/2] f2fs: avoid deadlock caused by lock order of page and lock_op

[Chao Yu <chao@kernel.org>]

On 2017/7/1 22:27, Jaegeuk Kim wrote:
> On 07/01, Chao Yu wrote:
>> On 2017/7/1 15:28, Jaegeuk Kim wrote:
>>> On 06/26, Chao Yu wrote:
>>>> Hi Jaegeuk,
>>>>
>>>> On 2017/6/26 22:54, Jaegeuk Kim wrote:
>>>>> Hi Chao,
>>>>>
>>>>> On 06/26, Chao Yu wrote:
>>>>>> Hi Jaegeuk,
>>>>>>
>>>>>> On 2017/6/25 0:25, Jaegeuk Kim wrote:
>>>>>>> - punch_hole
>>>>>>>  - fill_zero
>>>>>>>   - f2fs_lock_op
>>>>>>>   - get_new_data_page
>>>>>>>    - lock_page
>>>>>>>
>>>>>>> - f2fs_write_data_pages
>>>>>>>  - lock_page
>>>>>>>  - do_write_data_page
>>>>>>>   - f2fs_lock_op
>>>>>>
>>>>>> Good catch!
>>>>>>
>>>>>> With this implementation, page writeback can fail due to concurrent checkpoint,
>>>>>> this will make fsync/atomic_commit which trigger synchronous write failed randomly.
>>>>>>
>>>>>> How about unifying the lock order in punch_hole as one in writepages for regular
>>>>>> inode? We can add one more parameter in get_new_data_page to indicate whether
>>>>>> callee needs to lock cp_rwsem.
>>>>>
>>>>> Currently, there would be some places to keep cp_rwsem -> page.lock, which seems
>>>>> not simple to change the lock order with page.lock -> cp_rwsem. IMO, we can retry
>>>>> flushing data in f2fs_sync_file, once it gets -EAGAIN.
>>>>>
>>>>> Any thoughts?
>>>>
>>>> What about adding inode_lock in f2fs_sync_file to exclude other
>>>> foreground operation which have reversed lock order? Atomic_commit is OK
>>>> since it has inode_lock in its path.
>>>
>>> I have concerned about performance regression, if we do that.
>>
>> I think fsync vs write or fsync vs fsync scenarios are unusual, so is
>> there any usecase?
> 
> Well, that'd be common to call multiple fsync calls at the same time.
> Like dbench or tiotest?

Do you have test numbers of dbench/tiotest with inode:lock in fsync?

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>>
>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>>>>>> ---
>>>>>>>  fs/f2fs/data.c | 5 +++--
>>>>>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>>>> index 7d3af48d34a9..9141bd19a902 100644
>>>>>>> --- a/fs/f2fs/data.c
>>>>>>> +++ b/fs/f2fs/data.c
>>>>>>> @@ -1404,8 +1404,9 @@ int do_write_data_page(struct f2fs_io_info *fio)
>>>>>>>  		}
>>>>>>>  	}
>>>>>>>  
>>>>>>> -	if (fio->need_lock == LOCK_REQ)
>>>>>>> -		f2fs_lock_op(fio->sbi);
>>>>>>> +	/* Deadlock due to between page->lock and f2fs_lock_op */
>>>>>>> +	if (fio->need_lock == LOCK_REQ && !f2fs_trylock_op(fio->sbi))
>>>>>>> +		return -EAGAIN;
>>>>>>>  
>>>>>>>  	err = get_dnode_of_data(&dn, page->index, LOOKUP_NODE);
>>>>>>>  	if (err)
>>>>>>>
>>>>>
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