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

[Anand Jain]

On 03/16/2018 10:02 PM, Greg Kroah-Hartman wrote:
> 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.

 Thanks ! Sorry for the mess.

-Anand

> greg k-h
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