Messages in this thread | | | Subject | Re: [PATCH v2 RFC] f2fs: fix to force keeping write barrier for strict fsync mode | From | Chao Yu <> | Date | Fri, 2 Jul 2021 23:49:25 +0800 |
| |
On 2021/7/2 9:32, Jaegeuk Kim wrote: > On 07/02, Chao Yu wrote: >> On 2021/7/2 1:10, Jaegeuk Kim wrote: >>> On 06/01, 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 >>> >>> Well, we have preflush for node writes, so I don't think this is the case. >>> >>> fio.op_flags |= REQ_PREFLUSH | REQ_FUA; >> >> This is only used for atomic write case, right? >> >> I mean the common case which is called from f2fs_issue_flush() in >> f2fs_do_sync_file(). > > How about adding PREFLUSH when writing node blocks aligned to the above set?
You mean implementation like v1 as below?
https://lore.kernel.org/linux-f2fs-devel/20200120100045.70210-1-yuchao0@huawei.com/
Thanks,
> >> >> And please see do_checkpoint(), we call f2fs_flush_device_cache() and >> commit_checkpoint() separately to keep persistence order of CP datas. >> >> See commit 46706d5917f4 ("f2fs: flush cp pack except cp pack 2 page at first") >> for details. >> >> Thanks, >> >>> >>>> >>>> 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@huawei.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: >>>> /* >>>> -- >>>> 2.29.2
| |