Re: Ran into "invalid block group size" bug, unclear how to proceed.

[Mike Javorski <mike.javorski@gmail.com>]

On Tue, Dec 4, 2018 at 2:18 AM Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
>
>
>
> On 2018/12/4 上午11:32, Mike Javorski wrote:
> > Need a bit of advice here ladies / gents. I am running into an issue
> > which Qu Wenruo seems to have posted a patch for several weeks ago
> > (see https://patchwork.kernel.org/patch/10694997/).
> >
> > Here is the relevant dmesg output which led me to Qu's patch.
> > ----
> > [   10.032475] BTRFS critical (device sdb): corrupt leaf: root=2
> > block=24655027060736 slot=20 bg_start=13188988928 bg_len=10804527104,
> > invalid block group size, have 10804527104 expect (0, 10737418240]
> > [   10.032493] BTRFS error (device sdb): failed to read block groups: -5
> > [   10.053365] BTRFS error (device sdb): open_ctree failed
> > ----
>
> Exactly the same symptom.
>
> >
> > This server has a 16 disk btrfs filesystem (RAID6) which I boot
> > periodically to btrfs-send snapshots to. This machine is running
> > ArchLinux and I had just updated  to their latest 4.19.4 kernel
> > package (from 4.18.10 which was working fine). I've tried updating to
> > the 4.19.6 kernel that is in testing, but that doesn't seem to resolve
> > the issue. From what I can see on kernel.org, the patch above is not
> > pushed to stable or to Linus' tree.
> >
> > At this point the question is what to do. Is my FS toast?
>
> If there is no other problem at all, your fs is just fine.
> It's my original patch too sensitive (the excuse for not checking chunk
> allocator carefully enough).
>
> But since you have the down time, it's never a bad idea to run a btrfs
> check --readonly to see if your fs is really OK.
>

After running for 4 hours...

UUID: 25b16375-b90b-408e-b592-fb07ed116d58
[1/7] checking root items
[2/7] checking extents
[3/7] checking free space cache
[4/7] checking fs roots
[5/7] checking only csums items (without verifying data)
[6/7] checking root refs
[7/7] checking quota groups
found 24939616169984 bytes used, no error found
total csum bytes: 24321980768
total tree bytes: 41129721856
total fs tree bytes: 9854648320
total extent tree bytes: 737804288
btree space waste bytes: 7483785005
file data blocks allocated: 212883520618496
 referenced 212876546314240

So things appear good to go. I will keep an eye out for the patch to
land before upgrading the kernel again.

> > Could I
> > revert to the 4.18.10 kernel and boot safely?
>
> If your btrfs check --readonly doesn't report any problem, then you're
> completely fine to do so.
> Although I still recommend to go RAID10 other than RAID5/6.

I understand the risk, but don't have the funds to buy sufficient
disks to operate in RAID10. The data is mostly large files and
activity is predominantly reads, so risk is currently acceptable given
the backup server. All super critical data is backed up to (very slow)
cloud storage.

>
> Thanks,
> Qu
>
> > I don't know if the 4.19
> > boot process may have flipped some bits which would make reverting
> > problematic.
> >
> > Thanks much,
> >
> > - mike
> >
>