On 3/17/25 18:16, Chunhai Guo wrote:
> During a checkpoint, the current active segment X may not be handled
> properly. This occurs when segment X has 0 valid blocks and a non-zero
> number of discard blocks, for the following reasons:
>
> locate_dirty_segment() does not mark any active segment as a prefree
> segment. As a result, segment X is not included in dirty_segmap[PRE], and
> f2fs_clear_prefree_segments() skips it when handling prefree segments.
>
> add_discard_addrs() skips any segment with 0 valid blocks, so segment X is
> also skipped.
>
> Consequently, no `struct discard_cmd` is actually created for segment X.
> However, the ckpt_valid_map and cur_valid_map of segment X are synced by
> seg_info_to_raw_sit() during the current checkpoint process. As a result,
> it cannot find the missing discard bits even in subsequent checkpoints.
> Consequently, the value of sbi->discard_blks remains non-zero. Thus, when
> f2fs is umounted, CP_TRIMMED_FLAG will not be set due to the non-zero
> sbi->discard_blks.
>
> Relevant code process:
>
> f2fs_write_checkpoint()
> f2fs_flush_sit_entries()
> list_for_each_entry_safe(ses, tmp, head, set_list) {
> for_each_set_bit_from(segno, bitmap, end) {
> ...
> add_discard_addrs(sbi, cpc, false); // skip segment X due to
> its 0 valid blocks
> ...
> seg_info_to_raw_sit(); // sync ckpt_valid_map with
> cur_valid_map for segment X
> ...
> }
> }
> f2fs_clear_prefree_segments(); // segment X is not included in
> dirty_segmap[PRE] and is skipped
>
> This issue is easy to reproduce with the following operations:
>
> root # mkfs.f2fs -f /dev/f2fs_dev
> root # mount -t f2fs /dev/f2fs_dev /mnt_point
> root # dd if=/dev/blk_dev of=/mnt_point/1.bin bs=4k count=256
> root # sync
> root # rm /mnt_point/1.bin
> root # umount /mnt_point
> root # dump.f2fs /dev/f2fs_dev | grep "checkpoint state"
> Info: checkpoint state = 45 : crc compacted_summary unmount ---- 'trimmed'
> flag is missing
>
> Since add_discard_addrs() can handle active segments with non-zero valid
> blocks, it is reasonable to fix this issue by allowing it to also handle
> active segments with 0 valid blocks.
>
> Fixes: b29555505d81 ("f2fs: add key functions for small discards")
> Signed-off-by: Chunhai Guo <guochun...@vivo.com>
Reviewed-by: Chao Yu <c...@kernel.org>
Thanks,
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