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

[Chao Yu]

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.

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 */
>  
>