On 03/16/2018 02:55 AM, Christoph Biedl wrote:
Greg Kroah-Hartman wrote...
4.14-stable review patch. If anyone has any objections, please let me know.
commit 3c181c12c431fe33b669410d663beb9cceefcd1b upstream.
(...)
If the filesystem is always used on a same endian host, this will not be a problem.
From my observations I cannot quite subscribe to that.
On big-endian systems, this change intruduces severe corruption, resulting in complete loss of the data on the used block device.
Thanks for the report.
That's really bad, my mistake. I am digging to know how it happened. Our on-disk root bytenr are little-endian compatible. So using the cpu_to_le for write on a big-endian arch is a correct thing to do. If it fails, certainly there is something which I have overlooked. I am digging to know. Thanks for the report again.
Fsck won't be able to figure out the correct on-disk btyenr either.
If there isn't any backup we could try to find out the correct pointers manually. However, restore from the backup approach is much better.
-Anand
Steps to reproduce (tested on ppc/powerpc and parisc/hppa):
# mkfs.btrfs $DEV # mount $DEV /mnt/tmp/ # umount /mnt/tmp/
This simple umount corrupts the file system:
# mount $DEV /mnt/tmp/ mount: /mnt/tmp: wrong fs type, bad option, bad superblock on $DEV, missing codepage or helper program, or other error.
# dmesg: BTRFS critical (device <dev>): unable to find logical 4294967296 length 4096 BTRFS critical (device <dev>): unable to find logical 4294967296 length 4096 BTRFS critical (device <dev>): unable to find logical 18102363734671360 length 16384 BTRFS error (device <dev>): failed to read chunk root BTRFS error (device <dev>): open_ctree failed
Also fsck is of no help:
# btrfsck $DEV Couldn't map the block 18102363734671360 No mapping for 18102363734671360-18102363734687744 Couldn't map the block 18102363734671360 bytenr mismatch, want=18102363734671360, have=0 ERROR: cannot read chunk root ERROR: cannot open file system
Trying mount or fsck on a little-endian system does not help either. So I consider the data on that device lost - luckily I use btrfs only for files where a backup exists all the time.
Reverting that change restored the previous error-free behaviour. I didn't check HEAD, i.e. v4.16-rc5, since the upstream commt was the last that affected these files. Still I could give this a try if anybody wishes so.
Cheers,
Christoph