Re: [f2fs-dev] [PATCH v4] f2fs: Fix indefinite loop in f2fs_gc()

[Jaegeuk Kim]

On 08/07, Chao Yu wrote:
> On 2019-8-7 21:40, 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. Currently, add this logic under
> > CONFIG_F2FS_CHECK_FS to be able to root cause the issue in debug
> > version.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
> > ---
> > v4: Cover all logic with CONFIG_F2FS_CHECK_FS
> > 
> >  fs/f2fs/gc.c      | 31 +++++++++++++++++++++++++++++--
> >  fs/f2fs/segment.c | 14 +++++++++++++-
> >  fs/f2fs/segment.h |  3 +++
> >  3 files changed, 45 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index 8974672..cbcacbd 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -382,6 +382,16 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
> >  			nsearched++;
> >  		}
> >  
> > +#ifdef CONFIG_F2FS_CHECK_FS
> > +		/*
> > +		 * 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;
> > +#endif
> > +
> >  		secno = GET_SEC_FROM_SEG(sbi, segno);
> >  
> >  		if (sec_usage_check(sbi, secno))
> > @@ -602,8 +612,15 @@ 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;
> > +#ifdef CONFIG_F2FS_CHECK_FS
> > +	struct sit_info *sit_i = SIT_I(sbi);
> > +#endif
> > +
> > +	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 +644,18 @@ 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) {
> > +#ifdef CONFIG_F2FS_CHECK_FS
> 
> 		unsigned int segno = GET_SEGNO(sbi, blkaddr);
> 		unsigned int offset = GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
> 
> Should be local, otherwise it looks good to me, I think Jaegeuk can help to fix
> this while merging.

Fixed a bit, and merged.
Thanks~

> 
> Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
> 
> Thanks,
> 
> > +		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);
> > +			}
> > +		}
> > +#endif
> >  		return false;
> > +	}
> >  	return true;
> >  }
> >  
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index a661ac3..ee795b1 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -806,6 +806,9 @@ 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);
> > +#ifdef CONFIG_F2FS_CHECK_FS
> > +	struct sit_info *sit_i = SIT_I(sbi);
> > +#endif
> >  
> >  	if (test_and_clear_bit(segno, dirty_i->dirty_segmap[dirty_type]))
> >  		dirty_i->nr_dirty[dirty_type]--;
> > @@ -817,9 +820,13 @@ 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);
> > +#ifdef CONFIG_F2FS_CHECK_FS
> > +			clear_bit(segno, sit_i->invalid_segmap);
> > +#endif
> > +		}
> >  	}
> >  }
> >  
> > @@ -4015,6 +4022,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
> >  	sit_i->sit_bitmap_mir = kmemdup(src_bitmap, bitmap_size, GFP_KERNEL);
> >  	if (!sit_i->sit_bitmap_mir)
> >  		return -ENOMEM;
> > +
> > +	sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
> > +	if (!sit_i->invalid_segmap)
> > +		return -ENOMEM;
> >  #endif
> >  
> >  	/* init SIT information */
> > @@ -4517,6 +4528,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
> >  	kvfree(sit_i->sit_bitmap);
> >  #ifdef CONFIG_F2FS_CHECK_FS
> >  	kvfree(sit_i->sit_bitmap_mir);
> > +	kvfree(sit_i->invalid_segmap);
> >  #endif
> >  	kvfree(sit_i);
> >  }
> > diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> > index b746028..9370d53 100644
> > --- a/fs/f2fs/segment.h
> > +++ b/fs/f2fs/segment.h
> > @@ -229,6 +229,9 @@ struct sit_info {
> >  	char *sit_bitmap;		/* SIT bitmap pointer */
> >  #ifdef CONFIG_F2FS_CHECK_FS
> >  	char *sit_bitmap_mir;		/* SIT bitmap mirror */
> > +
> > +	/* bitmap of segments to be ignored by GC in case of errors */
> > +	unsigned long *invalid_segmap;
> >  #endif
> >  	unsigned int bitmap_size;	/* SIT bitmap size */
> >  
> >