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

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Date:   Mon, 26 Jun 2017 23:42:21 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: avoid deadlock caused by lock order
 of page and lock_op

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.

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.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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