Re: Oops and somewhat borked filesystem after btrfs-convert and image removal

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On Tue, Oct 27, 2009 at 3:09 AM, Nuutti Kotivuori <naked@xxxxxx> wrote:
> Hello,
>
> I managed to get an oops and a somewhat borked btrfs filesystem after
> using btrfs-convert and then removing the image file. I will explain the
> full sequence of actions below (as I remember it):
>
>  - In the beginning, I have an ext3 filesystem that I'd like to convert
>   to btrfs
>
>  - I run btrfs-convert on the filesystem, forgetting to do fsck before
>   it - however, I have done a full fsck recently on the filesystem, and
>   it was cleanly unmounted (no journal replay necessary)
>
>  - Conversion runs smoothly
>
>  - I boot the newly converted filesystem as a root filesystem for my
>   computer, and everything looks good. "df" reports proper free space.
>
>  - I mount the subvolume with the ext2 filesystem under /mnt, while
>   having the btrfs main volume as my root filesystem:
>
>     mount -t btrfs -o subvol=ext2_saved /dev/mapper/perspire-root /mnt
>
>  - I remove the image file from the subvolume:
>
>     rm /mnt/image
>
>  - At this time, during or immediately after the removal, I get a
>   notification of a kernel oops, which is here:
>
>     http://www.kerneloops.org/submitresult.php?number=823167

This is a known bug in btrfs kernel driver, it's fixed in 2.6.32-rcX.

>
>  - I unmount the subvolume:
>
>     umount /mnt
>
>  - I reboot the computer, after which I check "df":
>
>     /dev/mapper/perspire-root 7245824 -73786976294826385180 -4575460 100% /

This is a known bug in btrfs-progs 0.19, it's fixed in btrfs-progs-untable tree.

>
>   (Sizes in 1K-blocks, used space being the hugely negative number, and
>   available being the somewhat less huge number.)
>
>  - Btrfsck reports:
>
>     root 5 inode 453339 errors 2
>     root 5 inode 453343 errors 2
>     root 5 inode 453347 errors 2
>     root 5 inode 453356 errors 2
>     root 5 inode 466532 errors 2
>     root 5 inode 466537 errors 2
>     root 5 inode 466540 errors 2
>     root 5 inode 466544 errors 2
>     found 5867835392 bytes used err is 1
>     total csum bytes: 5477992
>     total tree bytes: 258371584
>     total fs tree bytes: 228814848
>     btree space waste bytes: 71477071
>     file data blocks allocated: 8317644800
>      referenced 5582884864
>     Btrfs Btrfs v0.19

These errors are not critical. Some inodes' link counts are zero,
but they aren't marked as orphan inodes. I have no idea how this
can happen. Did you run btrfsck on mounted FS?

>
>  - Otherwise the filesystem seems to be in perfect working order, no
>   problems that I can see. I have been using it for several days after
>   the incident now.
>
> Then, useful info:
>
>  - Kernel: 2.6.31-trunk-686 (debian experimental)
>  - Btrfs utilities: 0.19-5 (debian package)
>  - Hardware: Acer Aspire One, with 8 Gb SSD
>
> Please let me know if you have any further questions, or want the
> btrfs-debug-tree output of the filesystem or something similar. I will
> not be reading the list, so please e-mail me directly as well.
>
> Also, I am wondering, how am I supposed to fix this situation? I see
> conflicting info if btrfsck can be run on a mounted filesystem (I did
> run it on a mounted filesystem above, as can be seen) - but is it
> supposed to be able to fix this kind of corruption?
>
> (In this case, the data on the drive is not crucial, I can fix it by
> reinstalling or just copying files out and in, but that's obviously not
> good enough solution for a stable release.)

Copying files out and in is the simplest and safest solution.
Sorry for the inconvenience.

Yan, Zheng
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