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

[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
By "UBIFS error" I mean:
[   14.308125] UBIFS error (ubi0:1 pid 628): ubifs_add_orphan: orphaned twice


1) 3a1e819b4e80~1
(one commit before regression)
Corruption: NO
UBIFS error: YES

2) 3a1e819b4e80~1 + cherry-pick of 32fe905c17f0
(one commit before regression + ubifs fix)
Corruption: NO
UBIFS error: NO

3) 3a1e819b4e80
(regressing commit)
Corruption: YES
UBIFS error: YES

4) 3a1e819b4e80 + cherry-pick of 32fe905c17f0
(regressing commit + ubifs fix)
Corruption: YES
UBIFS error: NO

5) 4.12.14
Corruption: YES
UBIFS error: NO

6) 4.12.14 + ovl_set_origin() made nop
Corruption: NO
UBIFS error: NO


It proves that:
1) UBIFS error is not related to this file system corruption and can be ignored
2) 3a1e819b4e80 and ovl_set_origin() are definitely responsible for
the regression and file system corruption

-- 
Rafał

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