Re: [PATCH v3] f2fs: Fix indefinite loop in f2fs_gc()

[Sahitya Tummala]

Hi Chao,

On Wed, Aug 07, 2019 at 05:29:24PM +0800, Chao Yu wrote:
> On 2019/8/7 16:52, Sahitya Tummala wrote:
> > Policy - Foreground GC, LFS and greedy GC mode.
> > 
> > Under this policy, f2fs_gc() loops forever to GC as it doesn't have
> > enough free segements to proceed and thus it keeps calling gc_more
> > for the same victim segment.  This can happen if the selected victim
> > segment could not be GC'd due to failed blkaddr validity check i.e.
> > is_alive() returns false for the blocks set in current validity map.
> > 
> > Fix this by keeping track of such invalid segments and skip those
> > segments for selection in get_victim_by_default() to avoid endless
> > GC loop under such error scenarios.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
> > ---
> > v3: address Chao's comments and also add logic to clear invalid_segmap
> 
> Hi Sahitya,
> 
> I meant we could cover all invalid_segmap related codes w/ CONFIG_F2FS_CHECK_FS
> in upstream code, like we did for sit_info.sit_bitmap_mir. In private code
> (qualconn or others), if this issue happens frequently, we can enable it by
> default before it is fixed.
> 
> How do you think?
> 
Sure, we can do it that way.

> Btw, still no fsck log on broken image?
>
I have requested customers to provide this log next time when the issue is
reproduced again. I will update you once I get the log.

Thanks,

> Thanks,
> 
> > 
> >  fs/f2fs/gc.c      | 25 +++++++++++++++++++++++--
> >  fs/f2fs/segment.c | 10 +++++++++-
> >  fs/f2fs/segment.h |  3 +++
> >  3 files changed, 35 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index 8974672..f7b9602 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
> >  			nsearched++;
> >  		}
> >  
> > +		/*
> > +		 * skip selecting the invalid segno (that is failed due to block
> > +		 * validity check failure during GC) to avoid endless GC loop in
> > +		 * such cases.
> > +		 */
> > +		if (test_bit(segno, sm->invalid_segmap))
> > +			goto next;
> > +
> >  		secno = GET_SEC_FROM_SEG(sbi, segno);
> >  
> >  		if (sec_usage_check(sbi, secno))
> > @@ -602,8 +610,13 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >  {
> >  	struct page *node_page;
> >  	nid_t nid;
> > -	unsigned int ofs_in_node;
> > +	unsigned int ofs_in_node, segno;
> >  	block_t source_blkaddr;
> > +	unsigned long offset;
> > +	struct sit_info *sit_i = SIT_I(sbi);
> > +
> > +	segno = GET_SEGNO(sbi, blkaddr);
> > +	offset = GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
> >  
> >  	nid = le32_to_cpu(sum->nid);
> >  	ofs_in_node = le16_to_cpu(sum->ofs_in_node);
> > @@ -627,8 +640,16 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >  	source_blkaddr = datablock_addr(NULL, node_page, ofs_in_node);
> >  	f2fs_put_page(node_page, 1);
> >  
> > -	if (source_blkaddr != blkaddr)
> > +	if (source_blkaddr != blkaddr) {
> > +		if (unlikely(check_valid_map(sbi, segno, offset))) {
> > +			if (!test_and_set_bit(segno, sit_i->invalid_segmap)) {
> > +				f2fs_err(sbi, "mismatched blkaddr %u (source_blkaddr %u) in seg %u\n",
> > +						blkaddr, source_blkaddr, segno);
> > +				f2fs_bug_on(sbi, 1);
> > +			}
> > +		}
> >  		return false;
> > +	}
> >  	return true;
> >  }
> >  
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index a661ac3..c3ba9e7 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -806,6 +806,7 @@ static void __remove_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
> >  		enum dirty_type dirty_type)
> >  {
> >  	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
> > +	struct sit_info *sit_i = SIT_I(sbi);
> >  
> >  	if (test_and_clear_bit(segno, dirty_i->dirty_segmap[dirty_type]))
> >  		dirty_i->nr_dirty[dirty_type]--;
> > @@ -817,9 +818,11 @@ static void __remove_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno,
> >  		if (test_and_clear_bit(segno, dirty_i->dirty_segmap[t]))
> >  			dirty_i->nr_dirty[t]--;
> >  
> > -		if (get_valid_blocks(sbi, segno, true) == 0)
> > +		if (get_valid_blocks(sbi, segno, true) == 0) {
> >  			clear_bit(GET_SEC_FROM_SEG(sbi, segno),
> >  						dirty_i->victim_secmap);
> > +			clear_bit(segno, sit_i->invalid_segmap);
> > +		}
> >  	}
> >  }
> >  
> > @@ -4017,6 +4020,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
> >  		return -ENOMEM;
> >  #endif
> >  
> > +	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
> > +	if (!sit_i->invalid_segmap)
> > +		return -ENOMEM;
> > +
> >  	/* init SIT information */
> >  	sit_i->s_ops = &default_salloc_ops;
> >  
> > @@ -4518,6 +4525,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
> >  #ifdef CONFIG_F2FS_CHECK_FS
> >  	kvfree(sit_i->sit_bitmap_mir);
> >  #endif
> > +	kvfree(sit_i->invalid_segmap);
> >  	kvfree(sit_i);
> >  }
> >  
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index b746028..3918155c 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -246,6 +246,9 @@ struct sit_info {
> >  	unsigned long long min_mtime;		/* min. modification time */
> >  	unsigned long long max_mtime;		/* max. modification time */
> >  
> > +	/* bitmap of segments to be ignored by GC in case of errors */
> > +	unsigned long *invalid_segmap;
> > +
> >  	unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
> >  };
> >  
> > 

-- 
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