Re: [PATCH 4.14 024/110] btrfs: use proper endianness accessors for super_copy

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Mar 16, 2018 at 02:22:02PM +0100, David Sterba wrote:
> 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.

Now reverted, thanks.

greg k-h