linux-kernel - Re: [PATCH] F2FS: invalidate META

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Date:   Mon, 1 Nov 2021 15:12:57 +0800
From:   Chao Yu <chao@...nel.org>
To:     Hyeong-Jun Kim <hj514.kim@...sung.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] F2FS: invalidate META_MAPPING before IPU/DIO write

On 2021/11/1 15:09, Hyeong-Jun Kim wrote:
> On Mon, 2021-11-01 at 14:28 +0800, Chao Yu wrote:
>> On 2021/11/1 13:42, Hyeong-Jun Kim wrote:
>>> Encrypted pages during GC are read and cached in META_MAPPING.
>>> However, due to cached pages in META_MAPPING, there is an issue
>>> where
>>> newly written pages are lost by IPU or DIO writes.
>>>
>>> Thread A                              Thread B
>>> - f2fs_gc(): blk 0x10 -> 0x20 (a)
>>>                                         - IPU or DIO write on blk
>>> 0x20 (b)
>>> - f2fs_gc(): blk 0x20 -> 0x30 (c)
>>>
>>> (a) page for blk 0x20 is cached in META_MAPPING and page for blk
>>> 0x10
>>>       is invalidated from META_MAPPING.
>>> (b) write new data to blk 0x200 using IPU or DIO, but outdated data
>>>       still remains in META_MAPPING.
>>> (c) f2fs_gc() try to move blk from 0x20 to 0x30 using cached page
>>> in
>>>       META_MAPPING. In conclusion, the newly written data in (b) is
>>> lost.
>>
>> In c), f2fs_gc() will readahead encrypted block from disk via
>> ra_data_block() anyway,
>> not matter cached encrypted page of meta inode is uptodate or not, so
>> it's safe, right?
> Right,
> However, if DIO write is performed between phase 3 and phase 4 of
> f2fs_gc(),
> the cached page of meta_mapping will be out-dated, though it read data
> from
> disk via ra_data_block() in phase 3.
> 
> What do you think?

Due to i_gc_rwsem lock coverage, the race condition should not happen right now?

Thanks,

> 
> Thanks,
>>
>> Am I missing anything?
>>
>> Thanks,
>>
>>> To address this issue, invalidating pages in META_MAPPING before
>>> IPU or
>>> DIO write.
>>>
>>> Signed-off-by: Hyeong-Jun Kim <
>>> hj514.kim@...sung.com
>>>>
>>> ---
>>>    fs/f2fs/data.c    | 2 ++
>>>    fs/f2fs/segment.c | 3 +++
>>>    2 files changed, 5 insertions(+)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 74e1a350c1d8..9f754aaef558 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -1708,6 +1708,8 @@ int f2fs_map_blocks(struct inode *inode,
>>> struct f2fs_map_blocks *map,
>>>    		 */
>>>    		f2fs_wait_on_block_writeback_range(inode,
>>>    						map->m_pblk, map-
>>>> m_len);
>>> +		invalidate_mapping_pages(META_MAPPING(sbi),
>>> +						map->m_pblk, map-
>>>> m_pblk);
>>>    
>>>    		if (map->m_multidev_dio) {
>>>    			block_t blk_addr = map->m_pblk;
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 526423fe84ce..f57c55190f9e 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -3652,6 +3652,9 @@ int f2fs_inplace_write_data(struct
>>> f2fs_io_info *fio)
>>>    		goto drop_bio;
>>>    	}
>>>    
>>> +	invalidate_mapping_pages(META_MAPPING(fio->sbi),
>>> +				fio->new_blkaddr, fio->new_blkaddr);
>>> +
>>>    	stat_inc_inplace_blocks(fio->sbi);
>>>    
>>>    	if (fio->bio && !(SM_I(sbi)->ipu_policy & (1 <<
>>> F2FS_IPU_NOCACHE)))
>>>
>>
>>
>