linux-kernel - Re: [PATCH] F2FS: invalidate META

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Message-ID: <9a0360922130485f4252970de4bb535667cc26e9.camel@samsung.com>
Date:   Mon, 01 Nov 2021 16:09:14 +0900
From:   Hyeong-Jun Kim <hj514.kim@...sung.com>
To:     Chao Yu <chao@...nel.org>, Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] F2FS: invalidate META_MAPPING before IPU/DIO write

On Mon, 2021-11-01 at 14:28 +0800, Chao Yu wrote:
> On 2021/11/1 13:42, Hyeong-Jun Kim wrote:
> > Encrypted pages during GC are read and cached in META_MAPPING.
> > However, due to cached pages in META_MAPPING, there is an issue
> > where
> > newly written pages are lost by IPU or DIO writes.
> > 
> > Thread A                              Thread B
> > - f2fs_gc(): blk 0x10 -> 0x20 (a)
> >                                        - IPU or DIO write on blk
> > 0x20 (b)
> > - f2fs_gc(): blk 0x20 -> 0x30 (c)
> > 
> > (a) page for blk 0x20 is cached in META_MAPPING and page for blk
> > 0x10
> >      is invalidated from META_MAPPING.
> > (b) write new data to blk 0x200 using IPU or DIO, but outdated data
> >      still remains in META_MAPPING.
> > (c) f2fs_gc() try to move blk from 0x20 to 0x30 using cached page
> > in
> >      META_MAPPING. In conclusion, the newly written data in (b) is
> > lost.
> 
> In c), f2fs_gc() will readahead encrypted block from disk via
> ra_data_block() anyway,
> not matter cached encrypted page of meta inode is uptodate or not, so
> it's safe, right?
Right, 
However, if DIO write is performed between phase 3 and phase 4 of
f2fs_gc(),
the cached page of meta_mapping will be out-dated, though it read data
from 
disk via ra_data_block() in phase 3.

What do you think?

Thanks,
> 
> Am I missing anything?
> 
> Thanks,
> 
> > To address this issue, invalidating pages in META_MAPPING before
> > IPU or
> > DIO write.
> > 
> > Signed-off-by: Hyeong-Jun Kim <
> > hj514.kim@...sung.com
> > >
> > ---
> >   fs/f2fs/data.c    | 2 ++
> >   fs/f2fs/segment.c | 3 +++
> >   2 files changed, 5 insertions(+)
> > 
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 74e1a350c1d8..9f754aaef558 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -1708,6 +1708,8 @@ int f2fs_map_blocks(struct inode *inode,
> > struct f2fs_map_blocks *map,
> >   		 */
> >   		f2fs_wait_on_block_writeback_range(inode,
> >   						map->m_pblk, map-
> > >m_len);
> > +		invalidate_mapping_pages(META_MAPPING(sbi),
> > +						map->m_pblk, map-
> > >m_pblk);
> >   
> >   		if (map->m_multidev_dio) {
> >   			block_t blk_addr = map->m_pblk;
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 526423fe84ce..f57c55190f9e 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -3652,6 +3652,9 @@ int f2fs_inplace_write_data(struct
> > f2fs_io_info *fio)
> >   		goto drop_bio;
> >   	}
> >   
> > +	invalidate_mapping_pages(META_MAPPING(fio->sbi),
> > +				fio->new_blkaddr, fio->new_blkaddr);
> > +
> >   	stat_inc_inplace_blocks(fio->sbi);
> >   
> >   	if (fio->bio && !(SM_I(sbi)->ipu_policy & (1 <<
> > F2FS_IPU_NOCACHE)))
> > 
> 
>