linux-kernel - Re: [PATCH] f2fs: fix to avoid data corruption by forbidding SSR overwrite

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Message-ID: <20190820010000.GA45681@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Mon, 19 Aug 2019 18:00:00 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: fix to avoid data corruption by forbidding SSR
 overwrite

On 08/19, Chao Yu wrote:
> On 2019/8/16 11:03, Chao Yu wrote:
> > There is one case can cause data corruption.
> > 
> > - write 4k to fileA
> > - fsync fileA, 4k data is writebacked to lbaA
> > - write 4k to fileA
> > - kworker flushs 4k to lbaB; dnode contain lbaB didn't be persisted yet
> > - write 4k to fileB
> > - kworker flush 4k to lbaA due to SSR
> > - SPOR -> dnode with lbaA will be recovered, however lbaA contains fileB's
> > data
> > 
> > One solution is tracking all fsynced file's block history, and disallow
> > SSR overwrite on newly invalidated block on that file.
> > 
> > However, during recovery, no matter the dnode is flushed or fsynced, all
> > previous dnodes until last fsynced one in node chain can be recovered,
> > that means we need to record all block change in flushed dnode, which
> > will cause heavy cost, so let's just use simple fix by forbidding SSR
> > overwrite directly.
> > 
> 
> Jaegeuk,
> 
> Please help to add below missed tag to keep this patch being merged in stable
> kernel.
> 
> Fixes: 5b6c6be2d878 ("f2fs: use SSR for warm node as well")

Done.

> 
> Thanks,
> 
> > Signed-off-by: Chao Yu <yuchao0@...wei.com>
> > ---
> >  fs/f2fs/segment.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 9d9d9a050d59..69b3b553ee6b 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -2205,9 +2205,11 @@ static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
> >  		if (!f2fs_test_and_set_bit(offset, se->discard_map))
> >  			sbi->discard_blks--;
> >  
> > -		/* don't overwrite by SSR to keep node chain */
> > -		if (IS_NODESEG(se->type) &&
> > -				!is_sbi_flag_set(sbi, SBI_CP_DISABLED)) {
> > +		/*
> > +		 * SSR should never reuse block which is checkpointed
> > +		 * or newly invalidated.
> > +		 */
> > +		if (!is_sbi_flag_set(sbi, SBI_CP_DISABLED)) {
> >  			if (!f2fs_test_and_set_bit(offset, se->ckpt_valid_map))
> >  				se->ckpt_valid_blocks++;
> >  		}
> >