Re: [PATCH] f2fs: avoid GC causing encrypted file corrupted

[Yunlong Song]

On 2018/9/19 2:17, Jaegeuk Kim wrote:
> On 09/18, Yunlong Song wrote:
> > The encrypted file may be corrupted by GC in following case:
> >
> > Time 1: | segment 1 blkaddr = A |  GC -> | segment 2 blkaddr = B |
> > Encrypted block 1 is moved from blkaddr A of segment 1 to blkaddr B of
> > segment 2,
> >
> > Time 2: | segment 1 blkaddr = B |  GC -> | segment 3 blkaddr = C |
>              segment 2 blkaddr = B?
Sorry for typing error.
Yes.
> > Before page 1 is written back and if segment 2 become a victim, then
> > page 1 is moved from blkaddr B of segment 2 to blkaddr Cof segment 3,
>                                                           C of ?
Yes.
> > during the GC process of Time 2, f2fs should wait for page 1 written back
> > before reading it, or move_data_block will read a garbage block from
> > blkaddr B since page is not written back to blkaddr B yet.
> move_data_block() checks PageUptodate() so it won't get garbage, yes?
> So, does ra_data_block need to check PageUptodate?
You mean if page 1 is read from blkaddr B before it is written back to 
blkaddr B, then
the page will become non-uptodate status, why? Is it because 
__read_end_io checks
"(bio->bi_status || PageError(page))" and ClearPageUptodate(page)?

> > Commit 6aa58d8a ("f2fs: readahead encrypted block during GC") introduce
> > ra_data_block to read encrypted block, but it forgets to add
> > f2fs_wait_on_page_writeback to avoid racing between GC and flush.
> >
> > Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
> > ---
> >   fs/f2fs/gc.c | 10 ++++++++++
> >   1 file changed, 10 insertions(+)
> >
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index a4c1a41..c55fb62 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -641,6 +641,14 @@ static int ra_data_block(struct inode *inode, pgoff_t index)
> >   	fio.page = page;
> >   	fio.new_blkaddr = fio.old_blkaddr = dn.data_blkaddr;
> >   
> > +	/*
> > +	 * don't cache encrypted data into meta inode until previous dirty
> > +	 * data were writebacked to avoid racing between GC and flush.
> > +	 */
> > +	f2fs_wait_on_page_writeback(page, DATA, true);
> > +
> > +	f2fs_wait_on_block_writeback(inode, dn.data_blkaddr);
> > +
> >   	fio.encrypted_page = f2fs_pagecache_get_page(META_MAPPING(sbi),
> >   					dn.data_blkaddr,
> >   					FGP_LOCK | FGP_CREAT, GFP_NOFS);
> > @@ -723,6 +731,8 @@ static void move_data_block(struct inode *inode, block_t bidx,
> >   	 */
> >   	f2fs_wait_on_page_writeback(page, DATA, true);
> >   
> > +	f2fs_wait_on_block_writeback(inode, dn.data_blkaddr);
> > +
> >   	err = f2fs_get_node_info(fio.sbi, dn.nid, &ni);
> >   	if (err)
> >   		goto put_out;
> > --
> > 1.8.5.2
> .

--
Thanks,
Yunlong Song