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

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Date:   Mon, 19 Aug 2019 14:30:12 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <jaegeuk@...nel.org>
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 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")

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++;
>  		}
>