Re: [f2fs-dev] [PATCH v2 2/2] f2fs: Check write pointer consistency of non-open zones

[Chao Yu <yuchao0@huawei.com>]

On 2019/11/8 12:27, Shinichiro Kawasaki wrote:
> On Nov 05, 2019 / 20:22, Chao Yu wrote:
>> On 2019/10/28 14:58, Shin'ichiro Kawasaki wrote:
>>> To catch f2fs bugs in write pointer handling code for zoned block
>>> devices, check write pointers of non-open zones that current segments do
>>> not point to. Do this check at mount time, after the fsync data recovery
>>> and current segments' write pointer consistency fix. Check two items
>>> comparing write pointers with valid block maps in SIT.
>>>
>>> The first item is check for zones with no valid blocks. When there is no
>>> valid blocks in a zone, the write pointer should be at the start of the
>>> zone. If not, next write operation to the zone will cause unaligned write
>>> error. If write pointer is not at the zone start, make mount fail and ask
>>> users to run fsck.
>>>
>>> The second item is check between the write pointer position and the last
>>> valid block in the zone. It is unexpected that the last valid block
>>> position is beyond the write pointer. In such a case, report as the bug.
>>> Fix is not required for such zone, because the zone is not selected for
>>> next write operation until the zone get discarded.
>>>
>>> Also move a constant F2FS_REPORT_ZONE from super.c to f2fs.h to use it
>>> in segment.c also.
>>>
>>> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
>>> ---
>>>  fs/f2fs/f2fs.h    |   3 +
>>>  fs/f2fs/segment.c | 147 ++++++++++++++++++++++++++++++++++++++++++++++
>>>  fs/f2fs/super.c   |  11 ++--
>>>  3 files changed, 157 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 0216282c5b80..e8524be17852 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -3137,6 +3137,7 @@ int f2fs_lookup_journal_in_cursum(struct f2fs_journal *journal, int type,
>>>  			unsigned int val, int alloc);
>>>  void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc);
>>>  int f2fs_fix_curseg_write_pointer(struct f2fs_sb_info *sbi, bool check_only);
>>> +int f2fs_check_write_pointer(struct f2fs_sb_info *sbi);
>>>  int f2fs_build_segment_manager(struct f2fs_sb_info *sbi);
>>>  void f2fs_destroy_segment_manager(struct f2fs_sb_info *sbi);
>>>  int __init f2fs_create_segment_manager_caches(void);
>>> @@ -3610,6 +3611,8 @@ static inline bool f2fs_blkz_is_seq(struct f2fs_sb_info *sbi, int devi,
>>>  
>>>  	return test_bit(zno, FDEV(devi).blkz_seq);
>>>  }
>>> +
>>> +#define F2FS_REPORT_NR_ZONES   4096
>>>  #endif
>>>  
>>>  static inline bool f2fs_hw_should_discard(struct f2fs_sb_info *sbi)
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 2b6e637dd6d3..20ef5b3705e1 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -4333,6 +4333,131 @@ static int sanity_check_curseg(struct f2fs_sb_info *sbi)
>>>  
>>>  #ifdef CONFIG_BLK_DEV_ZONED
>>>  
>>> +static int check_zone_write_pointer(struct f2fs_sb_info *sbi,
>>> +				    struct f2fs_dev_info *fdev,
>>> +				    struct blk_zone *zone)
>>> +{
>>> +	unsigned int s, wp_segno, wp_blkoff, zone_secno, zone_segno, segno;
>>> +	block_t zone_block, wp_block, last_valid_block, b;
>>> +	unsigned int log_sectors_per_block = sbi->log_blocksize - SECTOR_SHIFT;
>>> +	int i;
>>> +	struct seg_entry *se;
>>> +
>>> +	wp_block = fdev->start_blk + (zone->wp >> log_sectors_per_block);
>>> +	wp_segno = GET_SEGNO(sbi, wp_block);
>>> +	wp_blkoff = wp_block - START_BLOCK(sbi, wp_segno);
>>> +	zone_block = fdev->start_blk + (zone->start >> log_sectors_per_block);
>>> +	zone_segno = GET_SEGNO(sbi, zone_block);
>>> +	zone_secno = GET_SEC_FROM_SEG(sbi, zone_segno);
>>> +
>>> +	if (zone_segno >= MAIN_SEGS(sbi))
>>> +		return 0;
>>> +
>>> +	/*
>>> +	 * If a curseg points to the zone, skip check because the zone
>>> +	 * may have fsync data that valid block map does not mark.
>>
>> None-curseg zone may also contain fsynced data as well? Maybe we can only verify
>> on clean image or recovered image?
> 
> Right. This function for none-curseg zones should be called after fsync data

If so, any place to check recovery is done? You know, user can choose to skip
recovery by using disable_roll_forward/norecovery mount option.

> recovery. I think my comment above is confusing. The point is that this
> function is for none-curseg zones, and other function covers check for curseg
> zones. Let me revise the comment as follows:
> 
>      Skip check of zones cursegs point to, since fix_curseg_write_pointer()
>      checks them.
> 
>>
>>> +	 */
>>> +	for (i = 0; i < NO_CHECK_TYPE; i++)
>>> +		if (zone_secno == GET_SEC_FROM_SEG(sbi,
>>> +						   CURSEG_I(sbi, i)->segno))
>>> +			return 0;
>>> +
>>> +	/*
>>> +	 * Get last valid block of the zone.
>>> +	 */
>>> +	last_valid_block = zone_block - 1;
>>> +	for (s = 0; s < sbi->segs_per_sec; s++) {
>>> +		segno = zone_segno + s;
>>> +		se = get_seg_entry(sbi, segno);
>>> +		for (b = 0; b < sbi->blocks_per_seg; b++)
>>> +			if (f2fs_test_bit(b, se->cur_valid_map))
>>> +				last_valid_block = START_BLOCK(sbi, segno) + b;
>>> +	}
>>
>> We search bitmap table reversedly.
> 
> Yes, will reverse the loops in the next post.
> 
>>
>>> +
>>> +	/*
>>> +	 * If last valid block is beyond the write pointer, report the
>>> +	 * inconsistency. This inconsistency does not cause write error
>>> +	 * because the zone will not be selected for write operation until
>>> +	 * it get discarded. Just report it.
>>> +	 */
>>> +	if (last_valid_block >= wp_block) {
>>> +		f2fs_notice(sbi, "Valid block beyond write pointer: "
>>> +			    "valid block[0x%x,0x%x] wp[0x%x,0x%x]",
>>> +			    GET_SEGNO(sbi, last_valid_block),
>>> +			    GET_BLKOFF_FROM_SEG0(sbi, last_valid_block),
>>> +			    wp_segno, wp_blkoff);
>>> +		return 0;
>>> +	}
>>> +
>>> +	/*
>>> +	 * If there is no valid block in the zone and if write pointer is
>>> +	 * not at zone start, report the error to run fsck and mark the
>>> +	 * zone as used.
>>> +	 */
>>> +	if (last_valid_block + 1 == zone_block && zone->wp != zone->start) {
>>> +		f2fs_notice(sbi,
>>> +			    "Zone without valid block has non-zero write "
>>> +			    "pointer, run fsck to fix: wp[0x%x,0x%x]",
>>> +			    wp_segno, wp_blkoff);
>>> +		__set_inuse(sbi, zone_segno);
>>
>> Why do we need to set it inused? if this is necessary, we need to call this
>> under free_i->segmap_lock.
> 
> I once thought that I need to set inconsistent zones in use, because I observed
> that write operation happened after zone consistency check failure (in
> fill_super() after free_meta label). It caused unaligned writer error. To avoid
> it, I added __set_inuse() to keep inconsistent zones not selected for the write
> target.
> 
> But that write operation happened because the write pointer fix curseg was done
> out of the SBI_POR_DOING protection. Now I learned SBI_POR_DOING can protect
> write operation, and I don't think set in use for the inconsistent zones is
> required. Will remove __set_inuse() calls from this patch and the first patch.

Also f2fs_stop_checkpoint() will stop any data/node/meta writeback, so it'd be
safe here.

Thanks,

> 
> Thanks!
> 
> --
> Best Regards,
> Shin'ichiro Kawasaki.
> 


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