Re: [PATCH] F2FS: invalidate META_MAPPING before IPU/DIO write

[Chao Yu]

On 2021/11/1 15:09, Hyeong-Jun Kim wrote:
> 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 (b) write new data to blk 0x200 using IPU or DIO, but outdated data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?

Due to i_gc_rwsem lock coverage, the race condition should not happen right now?

Thanks,

> 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@xxxxxxxxxxx
> > > >
> > > ---
> > >    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)))