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Subject: Re: [f2fs-dev] [PATCH v3] f2fs: fix to force keeping write barrier
 for strict fsync mode
To:     Jaegeuk Kim <jaegeuk@kernel.org>
Cc:     Chao Yu <chao.yu@linux.dev>, linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
References: <20210720010329.3975-1-chao@kernel.org>
 <YPYjzAVq04LfUO2Y@google.com>
 <014d1b9d-0698-fda1-0765-cce81d915280@kernel.org>
From:   Chao Yu <chao@kernel.org>
Message-ID: <bdd499d9-1272-9fe3-8024-f53fbda458bc@kernel.org>
Date:   Thu, 29 Jul 2021 09:41:40 +0800
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Ping,

On 2021/7/20 9:19, Chao Yu wrote:
> On 2021/7/20 9:15, Jaegeuk Kim wrote:
>> Wasn't it supposed to be v1?
> 
> I skip IPU case for v1, and resend it as v3, is it fine to you?
> 
> Thanks,
> 
>>
>> On 07/20, Chao Yu wrote:
>>> [1] https://www.mail-archive.com/linux-f2fs-devel@lists.sourceforge.net/msg15126.html
>>>
>>> As [1] reported, if lower device doesn't support write barrier, in below
>>> case:
>>>
>>> - write page #0; persist
>>> - overwrite page #0
>>> - fsync
>>>    - write data page #0 OPU into device's cache
>>>    - write inode page into device's cache
>>>    - issue flush
>>>
>>> If SPO is triggered during flush command, inode page can be persisted
>>> before data page #0, so that after recovery, inode page can be recovered
>>> with new physical block address of data page #0, however there may
>>> contains dummy data in new physical block address.
>>>
>>> Then what user will see is: after overwrite & fsync + SPO, old data in
>>> file was corrupted, if any user do care about such case, we can suggest
>>> user to use STRICT fsync mode, in this mode, we will force to use atomic
>>> write sematics to keep write order in between data/node and last node,
>>> so that it avoids potential data corruption during fsync().
>>>
>>> Signed-off-by: Chao Yu <chao@kernel.org>
>>> ---
>>>    fs/f2fs/file.c | 12 ++++++++++++
>>>    1 file changed, 12 insertions(+)
>>>
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 6afd4562335f..00b45876eaa1 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -301,6 +301,18 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>>>    				f2fs_exist_written_data(sbi, ino, UPDATE_INO))
>>>    			goto flush_out;
>>>    		goto out;
>>> +	} else {
>>> +		/*
>>> +		 * for OPU case, during fsync(), node can be persisted before
>>> +		 * data when lower device doesn't support write barrier, result
>>> +		 * in data corruption after SPO.
>>> +		 * So for strict fsync mode, force to use atomic write sematics
>>> +		 * to keep write order in between data/node and last node to
>>> +		 * avoid potential data corruption.
>>> +		 */
>>> +		if (F2FS_OPTION(sbi).fsync_mode ==
>>> +				FSYNC_MODE_STRICT && !atomic)
>>> +			atomic = true;
>>>    	}
>>>    go_write:
>>>    	/*
>>> -- 
>>> 2.22.1
> 
> 
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