linux-kernel - Re: [f2fs-dev] [PATCH v2] f2fs: update dirty status for CURSEG as well

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Date:   Sat, 14 Oct 2017 08:14:35 +0800
From:   Chao Yu <chao@...nel.org>
To:     Yunlong Song <yunlong.song@...wei.com>, jaegeuk@...nel.org,
        yuchao0@...wei.com, yunlong.song@...oud.com
Cc:     linux-fsdevel@...r.kernel.org, miaoxie@...wei.com,
        linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: update dirty status for CURSEG as
 well

On 2017/10/13 21:21, Yunlong Song wrote:
> Without this patch, it will cause all the free segments using up in some
> corner case. For example, there are 100 segments, and 20 of them are
> reserved for ovp. If 79 segments are full of data, segment 80 becomes
> CURSEG segment, write 512 blocks and then delete 511 blocks. Since it is
> CURSEG segment, the __locate_dirty_segment will not update its dirty
> status. Then the dirty_segments(sbi) is 0, f2fs_gc will fail to
> get_victim, and f2fs_balance_fs will fail to trigger gc action. After
> f2fs_balance_fs returns, f2fs can continue to write data to segment 81.
> Again, segment 81 becomes CURSEG segment, write 512 blocks and delete
> 511 blocks, the dirty_segments(sbi) is 0 and f2fs_gc fail again. This
> can finally use up all the free segments and cause panic.

Look into this patch again, I found refresh_sit_entry is called after
->allocate_segment, so if all 512 blocks were allocated, log header should
have been moved to another segment, so locate_dirty_segment in
refresh_sit_entry should update dirty status of previous segment correctly,
anything I'm missing?

Thanks,

> 
> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
> ---
>  fs/f2fs/segment.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index bfbcff8..0fce076 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -687,7 +687,7 @@ static void __locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
>  	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
>  
>  	/* need not be added */
> -	if (IS_CURSEG(sbi, segno))
> +	if (IS_CURSEG(sbi, segno) && dirty_type == PRE)
>  		return;
>  
>  	if (!test_and_set_bit(segno, dirty_i->dirty_segmap[dirty_type]))
> @@ -737,7 +737,7 @@ static void locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno)
>  	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
>  	unsigned short valid_blocks;
>  
> -	if (segno == NULL_SEGNO || IS_CURSEG(sbi, segno))
> +	if (segno == NULL_SEGNO)
>  		return;
>  
>  	mutex_lock(&dirty_i->seglist_lock);
>