Re: Cannot mount or recover btrfs

[Raviu <raviu@protonmail.com>]

I've restored over 90% of the data using restore command, and reformatted disk before I got the email.
But I can confirm that I'd RAM corruption, I've done memtest per your recommendation and found that the 1st module of the two modules is bad.
Corruption was severe and repetitive, I just exclaim how did this server corruption went without notice from the linux kernel other than random rare lockups. I'm really amazed how apps and kernel was functioning! Data is really changed on ram.
I've upgraded to vanilla kernel 5.4.6 before doing the memtest, so the latest kernel was not panic about this bad RAM.

Isn't this something that should be fixed?


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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Monday, December 30, 2019 7:38 AM, Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:

> On 2019/12/29 下午11:05, Raviu wrote:
>
> > Hi,
> > My system suddenly crashed, after reboot I cannot mount /home any more.
> > `uname -a`
> > Linux moonIk80 4.12.14-lp151.28.36-default #1 SMP Fri Dec 6 13:50:27 UTC 2019 (8f4a495) x86_64 x86_64 x86_64 GNU/Linux
> > btrfs-progs v5.4
> > `btrfs fi show`
> > Label: none uuid: 378faa6e-8af0-415e-93f7-68b31fb08a29
> > Total devices 1 FS bytes used 194.99GiB
> > devid 1 size 232.79GiB used 231.79GiB path /dev/mapper/cr_sda4
> > The device cannot be mounted.
> > [ 188.649876] BTRFS info (device dm-1): disk space caching is enabled
> > [ 188.649878] BTRFS info (device dm-1): has skinny extents
> > [ 188.656364] BTRFS critical (device dm-1): corrupt leaf: root=2 block=294640566272 slot=104, unexpected item end, have 42739 expect 9971
>
> As Hugo has already pointed out, this looks very like a bit flip.
> Thus a memtest is highly recommended.
>
> Also, your kernel is a little old. I'm not sure if the distro (I guess
> it's openSUSE or SLE?) had all the backports, but starts from v5.2, we
> had newer write-time tree-checker to even prevent such bitflip written
> back to disk, thus we could catch them earlier.
>
> This is extent tree, in theory you can always salvage the data using
> `btrfs-restore`.
>
> But that's the last resort method.
>
> > [ 188.656374] BTRFS error (device dm-1): failed to read block groups: -5
> > [ 188.700088] BTRFS error (device dm-1): open_ctree failed
> > `btrfs check /dev/mapper/cr_sda4`
> > Opening filesystem to check...
> > incorrect offsets 9971 42739
> > incorrect offsets 9971 42739
> > incorrect offsets 9971 42739
> > ERROR: failed to read block groups: Operation not permitted
> > ERROR: cannot open file system
>
> If you can re-compile btrfs-progs, you can try this branch:
> https://github.com/adam900710/btrfs-progs/tree/dirty_fix_for_raviu
>
> Then use the compiled btrfs-corrupt-block (I know it's a terrible name)
> to fix the fs:
>
> ./btrfs-corrupt-block -X /dev/dm-1
>
> ===================================
>
> It should output what it fixed if it found anything.
>
> Thanks,
> Qu