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

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

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
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.

Thanks!

--
Best Regards,
Shin'ichiro Kawasaki

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