linux-kernel - Re: [PATCH v3] f2fs: fix to force keeping write barrier for strict fsync mode

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Message-ID: <014d1b9d-0698-fda1-0765-cce81d915280@kernel.org>
Date:   Tue, 20 Jul 2021 09:19:10 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <chao.yu@...ux.dev>
Subject: Re: [PATCH v3] f2fs: fix to force keeping write barrier for strict
 fsync mode

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@...nel.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