On 2019-8-28 19:53, Shinichiro Kawasaki wrote:
> On Aug 27, 2019 / 10:25, Chao Yu wrote:
>> On 2019/8/21 12:48, Shin'ichiro Kawasaki wrote:
>>> When sudden f2fs shutdown happens on zoned block devices, write
>>> pointers can be inconsistent with valid blocks counts in meta data.
>>> The failure scenario is as follows:
>>>
>>> - Just before a sudden shutdown, a new segment in a new zone is selected
>>> for a current segment. Write commands were executed to the segment.
>>> and the zone has a write pointer not at zone start.
>>> - Before the write commands complete, shutdown happens. Meta data is
>>> not updated and still keeps zero valid blocks count for the zone.
>>> - After next mount of the file system, the zone is selected for the next
>>> write target because it has zero valid blocks count. However, it has
>>> the write pointer not at zone start. Then "Unaligned write command"
>>> error happens.
>>>
>>> To avoid this potential error path, reset write pointers if the zone
>>> does not have a current segment, the write pointer is not at the zone
>>> start and the zone has no valid blocks.
>>>
>>> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawas...@wdc.com>
>>> ---
>>> fsck/fsck.c | 30 +++++++++++++++++++++++++++++-
>>> 1 file changed, 29 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fsck/fsck.c b/fsck/fsck.c
>>> index 21a06ac..cc9bbc0 100644
>>> --- a/fsck/fsck.c
>>> +++ b/fsck/fsck.c
>>> @@ -2595,6 +2595,7 @@ static int fsck_chk_write_pointer(int i, struct
>>> blk_zone *blkz, void *opaque)
>>> 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;
>>> + block_t zone_valid_blocks = 0;
>>>
>>> if (blk_zone_conv(blkz))
>>> return 0;
>>> @@ -2615,8 +2616,35 @@ static int fsck_chk_write_pointer(int i, struct
>>> blk_zone *blkz, void *opaque)
>>> break;
>>> }
>>>
>>> - if (cs_index >= NR_CURSEG_TYPE)
>>> + if (cs_index >= NR_CURSEG_TYPE) {
>>> + for (b = zone_block; b < zone_block + c.zone_blocks &&
>>> + IS_VALID_BLK_ADDR(sbi, b); b += c.blks_per_seg) {
>>> + se = get_seg_entry(sbi, GET_SEGNO(sbi, b));
>>> + zone_valid_blocks += se->valid_blocks;
>>> + }
>>> + if (wp_block == zone_block || zone_valid_blocks)
>>> + return 0;
>>> +
>>> + /*
>>> + * The write pointer is not at zone start but there is no valid
>>> + * block in the zone. Segments in the zone can be selected for
>>> + * next write. Need to reset the write pointer to avoid
>>> + * unaligned write command error.
>>
>> In SPOR (sudden power-off recovery) of kernel side, we may revalidate blocks
>> belong to fsynced file in such zone within range of [0, write pointer], if we
>> just reset zone, will we lose those data for ever?
>
> Yes. This patch resets zone and the data will be lost. I walked through
> fs/f2fs/recovery.c and learned that nodes with fsync mark are recovered at
> remount. Such fsync recovery cannot be done after zone reset. To avoid the
> data loss, I would like to drop this fourth patch at this moment.
>
> Later on, I will consider safer approach not to reset the zone, but to set
> next
> write target block at the write pointer. I guess this approach will need
> kernel
> side patch to change block selection logic.
I guess below commit can help to recognize fsynced data in unclean umounted
image, maybe we can skip invalidating those data during zone write pointer
recovery.
f2fs-tools: fix to skip block allocation for fsynced data
https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git/commit/?h=dev-test&id=a50cfc89e56ce8c022e295bf4de619af070fabe9
>
>>
>> BTW, how you think enabling f2fs kernel module to recover incorrect write
>> pointer of zone? Once f2fs-tools doesn't upgrade, however kernel does...
>
> Current f2fs allows to mount zoned block devices even when they have
> inconsistency with f2fs meta data. This is not good. Then I believe kernel
> side
> needs the feature to check write pointer inconsistency at mount time and fix
> it.
>
> As you indicate, fix by kernel is more handy than notice to run fsck,
> especially
> when users do not have latest f2fs-tools. Still fix by fsck is needed when
> users
> use the kernel without the fix feature. I think both approaches are required:
> fix by kernel and fix by fsck.
Agreed, let's try to fix in both side.
Thanks,
>
> --
> Best Regards,
> Shin'ichiro Kawasaki
>
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