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

[Chao Yu]

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@xxxxxxxxxxxxxxxxxxxxx/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@xxxxxxxxxx>
> > ---
> >   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