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

[Chao Yu]

Hi Sahitya,

Luckily, I can reproduce this issue with generic/269, and have sent another
patch for the issue, could you please check that one?

Thanks,

On 2019/8/7 22:06, 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.
> 
> 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 */
>>  
>>
> .
>