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Date:   Wed, 24 Mar 2021 18:51:07 -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: <YFvsi3r3DPSVARWz@google.com>
References: <20210324031828.67133-1-yuchao0@huawei.com>
 <YFvQGxLbpmDjxEzR@google.com>
 <8fd71953-05a9-61e4-2fb0-e1dcd65bbaa0@huawei.com>
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On 03/25, Chao Yu wrote:
> On 2021/3/25 7:49, Jaegeuk Kim wrote:
> > 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
> 
> Oh, correct.
> 
> BTW, could you please add 'f2fs_' prefix for segment_has_free_slot()
> like we did for other non-static symbols?

Added.

> 
> Thanks,
> 
> > 
> > > +	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
> > .
> >