Messages in this thread | | | Subject | Re: [PATCH 4.14 024/110] btrfs: use proper endianness accessors for super_copy | From | Anand Jain <> | Date | Sat, 17 Mar 2018 00:21:04 +0800 |
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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 >
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