On Fri, Mar 16, 2018 at 01:30:49PM +0100, Greg Kroah-Hartman wrote: > On Thu, Mar 15, 2018 at 07:55:42PM +0100, 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. > > > > 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. > > That sucks. Can you test Linus's tree to verify the problem is there? > I'll gladly revert this if Linus's tree also gets the revert, I don't > want you to hit this when you upgrade to a newer kernel. I'll push a fix for the upcoming rc but I think it would be better to remove the broken patch from stable kernels ASAP, so I'd recommend to revert it now.