Re: [f2fs-dev] [PATCH v2 3/4] fsck.f2fs: Check write pointer consistency with current segments

[Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On Aug 27, 2019 / 10:13, Chao Yu wrote:
> On 2019/8/27 10:01, Chao Yu wrote:
> > On 2019/8/21 12:48, Shin'ichiro Kawasaki wrote:
> >> On sudden f2fs shutdown, zoned block device status and f2fs current
> >> segment positions in meta data can be inconsistent. When f2fs shutdown
> >> happens before write operations completes, write pointers of zoned block
> >> devices can go further but f2fs meta data keeps current segments at
> >> positions before the write operations. After remounting the f2fs, the
> >> inconsistency causes write operations not at write pointers and
> >> "Unaligned write command" error is reported. This error was observed when
> >> xfstests test case generic/388 was run with f2fs on a zoned block device.
> >>
> >> To avoid the error, have f2fs.fsck check consistency between each current
> >> segment's position and the write pointer of the zone the current segment
> >> points to. If the write pointer goes advance from the current segment,
> >> fix the current segment position setting at same as the write pointer
> >> position. In case the write pointer is behind the current segment, write
> >> zero data at the write pointer position to make write pointer position at
> >> same as the current segment.
> >>
> >> When inconsistencies are found, turn on c.bug_on flag in fsck_verify() to
> >> ask users to fix them or not. When inconsistencies get fixed, turn on
> >> 'force' flag in fsck_verify() to enforce fixes in following checks. This
> >> position fix is done at the beginning of do_fsck() function so that other
> >> checks reflect the current segment modification.
> >>
> >> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> >> ---
> >>  fsck/fsck.c | 133 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  fsck/fsck.h |   3 ++
> >>  fsck/main.c |   2 +
> >>  3 files changed, 138 insertions(+)
> >>
> >> diff --git a/fsck/fsck.c b/fsck/fsck.c
> >> index 8953ca1..21a06ac 100644
> >> --- a/fsck/fsck.c
> >> +++ b/fsck/fsck.c
> >> @@ -2574,6 +2574,125 @@ out:
> >>  	return cnt;
> >>  }
> >>  
> >> +struct write_pointer_check_data {
> >> +	struct f2fs_sb_info *sbi;
> >> +	struct device_info *dev;
> >> +};
> >> +
> >> +#define SECTOR_SHIFT 9
> >> +
> >> +static int fsck_chk_write_pointer(int i, struct blk_zone *blkz, void *opaque)
> >> +{
> >> +	struct write_pointer_check_data *wpd = opaque;
> >> +	struct f2fs_sb_info *sbi = wpd->sbi;
> >> +	struct device_info *dev = wpd->dev;
> >> +	struct f2fs_fsck *fsck = F2FS_FSCK(sbi);
> >> +	block_t zone_block, wp_block, wp_blkoff, cs_block, b;
> >> +	unsigned int zone_segno, wp_segno;
> >> +	struct seg_entry *se;
> >> +	struct curseg_info *cs;
> >> +	int cs_index, ret;
> >> +	int log_sectors_per_block = sbi->log_blocksize - SECTOR_SHIFT;
> >> +	unsigned int segs_per_zone = sbi->segs_per_sec * sbi->secs_per_zone;
> >> +	void *zero_blk;
> >> +
> >> +	if (blk_zone_conv(blkz))
> >> +		return 0;
> >> +
> >> +	zone_block = dev->start_blkaddr
> >> +		+ (blk_zone_sector(blkz) >> log_sectors_per_block);
> >> +	zone_segno = GET_SEGNO(sbi, zone_block);
> >> +	wp_block = dev->start_blkaddr
> >> +		+ (blk_zone_wp_sector(blkz) >> log_sectors_per_block);
> >> +	wp_segno = GET_SEGNO(sbi, wp_block);
> >> +	wp_blkoff = wp_block - START_BLOCK(sbi, wp_segno);
> >> +
> >> +	/* find the curseg which points to the zone */
> >> +	for (cs_index = 0; cs_index < NO_CHECK_TYPE; cs_index++) {
> >> +		cs = &SM_I(sbi)->curseg_array[cs_index];
> >> +		if (zone_segno <= cs->segno &&
> >> +		    cs->segno < zone_segno + segs_per_zone)
> >> +			break;
> >> +	}
> > 
> > Will this happen?
> > 
> > - write checkpoint
> > - curseg points zone A
> > - write large number of data
> > - curseg points zone B, write pointer > 0
> > - sudden power cut, curseg will be reset to zone A
> > 
> > zone B's write pointer won't be verified due to curseg points to zone A?
> 
> IIUC, we are trying fix such condition in a separated PATCH 4/4.
> 
> Reviewed-by: Chao Yu <yuchao0@huawei.com>

Yes, that's the failure scenario that PATCH 4/4 tried to address. As I
responded separately, I would like to drop PATCH 4/4 at this moment.

Will add your reviewed-by tag to this PATCH 3/4 in the next version.
Thanks!

--
Best Regards,
Shin'ichiro Kawasaki

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