[OpenWrt-Devel] Regression in handling power cuts since 3a1e819b4e80 ("ovl: store file handle of lower inode on copy up")

[Amir Goldstein]

On Mon, Oct 22, 2018 at 11:26 AM Richard Weinberger <richard at nod.at> wrote:
>
> Am Montag, 22. Oktober 2018, 09:14:08 CEST schrieb Rafał Miłecki:
> > On Fri, 19 Oct 2018 at 14:31, Rafał Miłecki <zajec5 at gmail.com> wrote:
> > > Since OpenWrt switch from kernel 4.9 to 4.14 users started randomly
> > > reporting file system corruptions. OpenWrt uses overlay(fs) with
> > > squashfs as lowerdir and ubifs as upperdir. Russell managed to isolate
> > > & describe test case for reproducing corruption when doing a power cut
> > > after first boot.
> > >
> > > (...)
> > >
> > > Can I ask you to check if there is something possibly wrong with the
> > > above ovl commit? Or does it expose some problem with the ubifs? Or
> > > maybe the whole UBI?
> > >
> > > FWIW testing above commit (and one before it) always results in single
> > > error in the kernel log:
> > > [   14.250184] UBIFS error (ubi0:1 pid 637): ubifs_add_orphan: orphaned twice
> > >
> > > That UBIFS error doesn't occur with 4.12.14. Unfortunately it's
> > > impossible to cleanly revert 3a1e819b4e80 from the top of 4.12.14.
> >
> > Let me provide a summary of all relevant commits & tests:
> >
> > By "Corruption" I mean file system corruption after power cut
>
> Well, is the filesystem not consistent anymore?
> From what Russel explained to me, I thought the main problem is that no write back happens.
> IOW the inode is present, has correct length, but no content is there (all zeros).
>
> Just like the typical case where userspace does not fsync.
> But in your case sooner or later write back should have happened because the writeback timer
> fires at some point.
>

For the records overlayfs does:
- open(O_TMPFILE)
- setxattr() [with 3a1e819b4e80]
- write to tmpfile
- fsync tmpfile
- link tmpfile

I suggest that you try the same from user space on ubifs.

Thanks,
Amir.

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