linux-kernel - Re: [f2fs-dev] [PATCH v2 RFC] f2fs: fix to force keeping write barrier for strict fsync mode

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Date:   Tue, 8 Jun 2021 07:32:52 +0800
From:   Chao Yu <chao@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>, jaegeuk@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2 RFC] f2fs: fix to force keeping write
 barrier for strict fsync mode

Still no time to check this?

Thanks,

On 2021/6/4 0:00, Chao Yu wrote:
> Jaegeuk,
> 
> Any comments on this patch?
> 
> On 2021/6/1 18:10, 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 trigger
>> preflush command to persist data in device cache in prior to node
>> writeback, it avoids potential data corruption during fsync().
>>
>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>> ---
>> v2:
>> - fix this by adding additional preflush command rather than using
>> atomic write flow.
>>   fs/f2fs/file.c | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 7d5311d54f63..238ca2a733ac 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -301,6 +301,20 @@ 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 trigger preflush to keep
>> +         * data/node write order to avoid potential data corruption.
>> +         */
>> +        if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_STRICT &&
>> +                                !atomic) {
>> +            ret = f2fs_issue_flush(sbi, inode->i_ino);
>> +            if (ret)
>> +                goto out;
>> +        }
>>       }
>>   go_write:
>>       /*
>>
> 
> 
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