pirmd., 2021. g. 22. marts, plkst. 02:25 — lietotājs Qu Wenruo
(<quwenruo.bt...@gmx.com>) rakstīja:
>
>
>
> On 2021/3/22 上午5:54, Dāvis Mosāns wrote:
> > sestd., 2021. g. 20. marts, plkst. 02:34 — lietotājs Qu Wenruo
> > (<quwenruo.bt...@gmx.com>) rakstīja:
> >>
> >>
> >>
> >> On 2021/3/19 下午11:34, Dāvis Mosāns wrote:
> >>> ceturtd., 2021. g. 18. marts, plkst. 01:49 — lietotājs Qu Wenruo
> >>> (<quwenruo.bt...@gmx.com>) rakstīja:
> >>>>
> >>>>
> >>>>
> >>>> On 2021/3/18 上午5:03, Dāvis Mosāns wrote:
> >>>>> trešd., 2021. g. 17. marts, plkst. 12:28 — lietotājs Qu Wenruo
> >>>>> (<quwenruo.bt...@gmx.com>) rakstīja:
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> On 2021/3/17 上午9:29, Dāvis Mosāns wrote:
> >>>>>>> trešd., 2021. g. 17. marts, plkst. 03:18 — lietotājs Dāvis Mosāns
> >>>>>>> (<davis...@gmail.com>) rakstīja:
> >>>>>>>>
> >>>>>>>> Currently if there's any corruption at all in extent tree
> >>>>>>>> (eg. even single bit) then mounting will fail with:
> >>>>>>>> "failed to read block groups: -5" (-EIO)
> >>>>>>>> It happens because we immediately abort on first error when
> >>>>>>>> searching in extent tree for block groups.
> >>>>>>>>
> >>>>>>>> Now with this patch if `ignorebadroots` option is specified
> >>>>>>>> then we handle such case and continue by removing already
> >>>>>>>> created block groups and creating dummy block groups.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Dāvis Mosāns <davis...@gmail.com>
> >>>>>>>> ---
> >>>>>>>> fs/btrfs/block-group.c | 14 ++++++++++++++
> >>>>>>>> fs/btrfs/disk-io.c | 4 ++--
> >>>>>>>> fs/btrfs/disk-io.h | 2 ++
> >>>>>>>> 3 files changed, 18 insertions(+), 2 deletions(-)
> >>>>>>>>
> >>>>>>>> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> >>>>>>>> index 48ebc106a606..827a977614b3 100644
> >>>>>>>> --- a/fs/btrfs/block-group.c
> >>>>>>>> +++ b/fs/btrfs/block-group.c
> >>>>>>>> @@ -2048,6 +2048,20 @@ int btrfs_read_block_groups(struct
> >>>>>>>> btrfs_fs_info *info)
> >>>>>>>> ret = check_chunk_block_group_mappings(info);
> >>>>>>>> error:
> >>>>>>>> btrfs_free_path(path);
> >>>>>>>> +
> >>>>>>>> + if (ret == -EIO && btrfs_test_opt(info, IGNOREBADROOTS)) {
> >>>>>>>> + btrfs_put_block_group_cache(info);
> >>>>>>>> + btrfs_stop_all_workers(info);
> >>>>>>>> + btrfs_free_block_groups(info);
> >>>>>>>> + ret = btrfs_init_workqueues(info, NULL);
> >>>>>>>> + if (ret)
> >>>>>>>> + return ret;
> >>>>>>>> + ret = btrfs_init_space_info(info);
> >>>>>>>> + if (ret)
> >>>>>>>> + return ret;
> >>>>>>>> + return fill_dummy_bgs(info);
> >>>>>>
> >>>>>> When we hit bad things in extent tree, we should ensure we're mounting
> >>>>>> the fs RO, or we can't continue.
> >>>>>>
> >>>>>> And we should also refuse to mount back to RW if we hit such case, so
> >>>>>> that we don't need anything complex, just ignore the whole extent tree
> >>>>>> and create the dummy block groups.
> >>>>>>
> >>>>>
> >>>>> That's what we're doing here, `ignorebadroots` implies RO mount and
> >>>>> without specifying it doesn't mount at all.
> >>>>>
> >>>>>>>
> >>>>>>> This isn't that nice, but I don't really know how to properly clean up
> >>>>>>> everything related to already created block groups so this was easiest
> >>>>>>> way. It seems to work fine.
> >>>>>>> But looks like need to do something about replay log aswell because if
> >>>>>>> it's not disabled then it fails with:
> >>>>>>>
> >>>>>>> [ 1397.246869] BTRFS info (device sde): start tree-log replay
> >>>>>>> [ 1398.218685] BTRFS warning (device sde): sde checksum verify failed
> >>>>>>> on 21057127661568 wanted 0xd1506ed9 found 0x22ab750a level 0
> >>>>>>> [ 1398.218803] BTRFS warning (device sde): sde checksum verify failed
> >>>>>>> on 21057127661568 wanted 0xd1506ed9 found 0x7dd54bb9 level 0
> >>>>>>> [ 1398.218813] BTRFS: error (device sde) in __btrfs_free_extent:3054:
> >>>>>>> errno=-5 IO failure
> >>>>>>> [ 1398.218828] BTRFS: error (device sde) in
> >>>>>>> btrfs_run_delayed_refs:2124: errno=-5 IO failure
> >>>>>>> [ 1398.219002] BTRFS: error (device sde) in btrfs_replay_log:2254:
> >>>>>>> errno=-5 IO failure (Failed to recover log tree)
> >>>>>>> [ 1398.229048] BTRFS error (device sde): open_ctree failed
> >>>>>>
> >>>>>> This is because we shouldn't allow to do anything write to the fs if we
> >>>>>> have anything wrong in extent tree.
> >>>>>>
> >>>>>
> >>>>> This is happening when mounting read-only. My assumption is that it
> >>>>> only tries to replay in memory without writing anything to disk.
> >>>>>
> >>>>
> >>>> We lacks the check on log tree.
> >>>>
> >>>> Normally for such forced RO mount, log replay is not allowed.
> >>>>
> >>>> We should output a warning to prompt user to use nologreplay, and reject
> >>>> the mount.
> >>>>
> >>>
> >>> I'm not familiar with log replay but couldn't there be something
> >>> useful (ignoring ref counts) that would still be worth replaying in
> >>> memory?
> >>>
> >> Log replay means metadata write.
> >>
> >> Any write needs a valid extent tree to find out free space for new
> >> metadata/data.
> >>
> >> So no, we can't do anything but completely ignoring the log.
> >>
> >
> > I see, updated patch. But even then it seems it could be possible to
> > add new ramdisk and make allocations there (eg. create new extent tree
> > there) thus allowing replay.
>
> The problem here is, since the extent tree is corrupted, we won't know
> which range has metadata already.
> While metadata CoW, just like its name, needs to CoW, which means it
> can't writeback (even just in memory) to anywhere we have metadata.
>
> The worst case is, we choose a bytenr for the new metadata to be (in
> memory), but it turns out later read needs to read metadata from the
> exactly same location.
>
The idea is if we add new disk then we would put it after last bytenr
(which isn't mapped to any existing disks) thus there wouldn't be any
overlap.
>
> BTW, I'm curious what's your test cases? As it seems you're using
> log-replay but if we hit anything wrong for the replayed data, it means
> btrfs kernel module has something wrong.
> Did you add extra corruption for the replayed data, or it's some bug
> unexposed?
Basically I've a corrupted btrfs due to HBA card fault and before I
nuke it I want to copy as much usable data as possible. So I was
thinking if whatever is in replay log could be restored. The replay
tree log itself is perfectly fine with valid checksum and there isn't
any issues regarding that. I looked at it with `btrfs inspect
dump-tree` and saw that there isn't anything important so it's fine
ignoring it.
