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Date:   Wed, 24 Mar 2021 16:49:47 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, chao@kernel.org
Subject: Re: [PATCH v2] f2fs: fix to avoid touching checkpointed data in
 get_victim()
Message-ID: <YFvQGxLbpmDjxEzR@google.com>
References: <20210324031828.67133-1-yuchao0@huawei.com>
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On 03/24, Chao Yu wrote:
> In CP disabling mode, there are two issues when using LFS or SSR | AT_SSR
> mode to select victim:
> 
> 1. LFS is set to find source section during GC, the victim should have
> no checkpointed data, since after GC, section could not be set free for
> reuse.
> 
> Previously, we only check valid chpt blocks in current segment rather
> than section, fix it.
> 
> 2. SSR | AT_SSR are set to find target segment for writes which can be
> fully filled by checkpointed and newly written blocks, we should never
> select such segment, otherwise it can cause panic or data corruption
> during allocation, potential case is described as below:
> 
>  a) target segment has 128 ckpt valid blocks
>  b) GC migrates 'n' (n < 512) valid blocks to other segment (segment is
>     still in dirty list)
>  c) GC migrates '512 - n' blocks to target segment (segment has 'n'
>     cp_vblocks and '512 - n' vblocks)
>  d) If GC selects target segment via {AT,}SSR allocator, however there
>     is no free space in targe segment.
> 
> Fixes: 4354994f097d ("f2fs: checkpoint disabling")
> Fixes: 093749e296e2 ("f2fs: support age threshold based garbage collection")
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
> v2:
> - fix to check checkpointed data in section rather than segment for
> LFS mode.
> - update commit title and message.
>  fs/f2fs/f2fs.h    |  1 +
>  fs/f2fs/gc.c      | 28 ++++++++++++++++++++--------
>  fs/f2fs/segment.c | 39 ++++++++++++++++++++++++---------------
>  fs/f2fs/segment.h | 14 +++++++++++++-
>  4 files changed, 58 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index eb154d9cb063..29e634d08a27 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -3387,6 +3387,7 @@ block_t f2fs_get_unusable_blocks(struct f2fs_sb_info *sbi);
>  int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable);
>  void f2fs_release_discard_addrs(struct f2fs_sb_info *sbi);
>  int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra);
> +bool segment_has_free_slot(struct f2fs_sb_info *sbi, int segno);
>  void f2fs_init_inmem_curseg(struct f2fs_sb_info *sbi);
>  void f2fs_save_inmem_curseg(struct f2fs_sb_info *sbi);
>  void f2fs_restore_inmem_curseg(struct f2fs_sb_info *sbi);
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index d96acc6531f2..4d9616373a4a 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -392,10 +392,6 @@ static void add_victim_entry(struct f2fs_sb_info *sbi,
>  		if (p->gc_mode == GC_AT &&
>  			get_valid_blocks(sbi, segno, true) == 0)
>  			return;
> -
> -		if (p->alloc_mode == AT_SSR &&
> -			get_seg_entry(sbi, segno)->ckpt_valid_blocks == 0)
> -			return;
>  	}
>  
>  	for (i = 0; i < sbi->segs_per_sec; i++)
> @@ -728,11 +724,27 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>  
>  		if (sec_usage_check(sbi, secno))
>  			goto next;
> +
>  		/* Don't touch checkpointed data */
> -		if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED) &&
> -					get_ckpt_valid_blocks(sbi, segno) &&
> -					p.alloc_mode == LFS))
> -			goto next;
> +		if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
> +			if (p.alloc_mode == LFS) {
> +				/*
> +				 * LFS is set to find source section during GC.
> +				 * The victim should have no checkpointed data.
> +				 */
> +				if (get_ckpt_valid_blocks(sbi, segno, true))
> +					goto next;
> +			} else {
> +				/*
> +				 * SSR | AT_SSR are set to find target segment
> +				 * for writes which can be full by checkpointed
> +				 * and newly written blocks.
> +				 */
> +				if (!segment_has_free_slot(sbi, segno))
> +					goto next;
> +			}
> +		}
> +
>  		if (gc_type == BG_GC && test_bit(secno, dirty_i->victim_secmap))
>  			goto next;
>  
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 6e1a5f5657bf..f6a30856ceda 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -865,7 +865,7 @@ static void locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno)
>  	mutex_lock(&dirty_i->seglist_lock);
>  
>  	valid_blocks = get_valid_blocks(sbi, segno, false);
> -	ckpt_valid_blocks = get_ckpt_valid_blocks(sbi, segno);
> +	ckpt_valid_blocks = get_ckpt_valid_blocks(sbi, segno, false);
>  
>  	if (valid_blocks == 0 && (!is_sbi_flag_set(sbi, SBI_CP_DISABLED) ||
>  		ckpt_valid_blocks == usable_blocks)) {
> @@ -950,7 +950,7 @@ static unsigned int get_free_segment(struct f2fs_sb_info *sbi)
>  	for_each_set_bit(segno, dirty_i->dirty_segmap[DIRTY], MAIN_SEGS(sbi)) {
>  		if (get_valid_blocks(sbi, segno, false))
>  			continue;
> -		if (get_ckpt_valid_blocks(sbi, segno))
> +		if (get_ckpt_valid_blocks(sbi, segno, false))
>  			continue;
>  		mutex_unlock(&dirty_i->seglist_lock);
>  		return segno;
> @@ -2643,6 +2643,26 @@ static void __refresh_next_blkoff(struct f2fs_sb_info *sbi,
>  		seg->next_blkoff++;
>  }
>  
> +bool segment_has_free_slot(struct f2fs_sb_info *sbi, int segno)
> +{
> +	struct sit_info *sit = SIT_I(sbi);
> +	struct seg_entry *se = get_seg_entry(sbi, segno);
> +	int entries = SIT_VBLOCK_MAP_SIZE / sizeof(unsigned long);
> +	unsigned long *target_map = SIT_I(sbi)->tmp_map;
> +	unsigned long *ckpt_map = (unsigned long *)se->ckpt_valid_map;
> +	unsigned long *cur_map = (unsigned long *)se->cur_valid_map;
> +	int i, pos;
> +
> +	down_write(&sit->sentry_lock);

Should remove this lock.
https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev

> +	for (i = 0; i < entries; i++)
> +		target_map[i] = ckpt_map[i] | cur_map[i];
> +
> +	pos = __find_rev_next_zero_bit(target_map, sbi->blocks_per_seg, 0);
> +	up_write(&sit->sentry_lock);
> +
> +	return pos < sbi->blocks_per_seg;
> +}
> +
>  /*
>   * This function always allocates a used segment(from dirty seglist) by SSR
>   * manner, so it should recover the existing segment information of valid blocks
> @@ -2913,19 +2933,8 @@ static void __allocate_new_segment(struct f2fs_sb_info *sbi, int type,
>  		get_valid_blocks(sbi, curseg->segno, new_sec))
>  		goto alloc;
>  
> -	if (new_sec) {
> -		unsigned int segno = START_SEGNO(curseg->segno);
> -		int i;
> -
> -		for (i = 0; i < sbi->segs_per_sec; i++, segno++) {
> -			if (get_ckpt_valid_blocks(sbi, segno))
> -				goto alloc;
> -		}
> -	} else {
> -		if (!get_ckpt_valid_blocks(sbi, curseg->segno))
> -			return;
> -	}
> -
> +	if (!get_ckpt_valid_blocks(sbi, curseg->segno, new_sec))
> +		return;
>  alloc:
>  	old_segno = curseg->segno;
>  	SIT_I(sbi)->s_ops->allocate_segment(sbi, type, true);
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 144980b62f9e..dab87ecba2b5 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -359,8 +359,20 @@ static inline unsigned int get_valid_blocks(struct f2fs_sb_info *sbi,
>  }
>  
>  static inline unsigned int get_ckpt_valid_blocks(struct f2fs_sb_info *sbi,
> -				unsigned int segno)
> +				unsigned int segno, bool use_section)
>  {
> +	if (use_section && __is_large_section(sbi)) {
> +		unsigned int start_segno = START_SEGNO(segno);
> +		unsigned int blocks = 0;
> +		int i;
> +
> +		for (i = 0; i < sbi->segs_per_sec; i++, start_segno++) {
> +			struct seg_entry *se = get_seg_entry(sbi, start_segno);
> +
> +			blocks += se->ckpt_valid_blocks;
> +		}
> +		return blocks;
> +	}
>  	return get_seg_entry(sbi, segno)->ckpt_valid_blocks;
>  }
>  
> -- 
> 2.29.2