Re: UBIFS issues within kernel 4.14.69?

Re: UBIFS issues within kernel 4.14.69?

[Richard Weinberger]

Koen,

Am Dienstag, 11. September 2018, 16:26:34 CEST schrieb Koen Vandeputte:
> 
> On 2018-09-11 15:46, Koen Vandeputte wrote:
> > Hi Richard,
> ...
> 
> > I'm only seeing these issues on UBIFS enabled volumes.
> >
> > It seems it's related to one of your 5 commits, but I'm still in the 
> > process of bisecting to find the actual culprit.
> > As soon as I've found it, I'll let you know, but maybe you already 
> > have an idea here?
> >
> Reverting ("ubifs: xattr: Don't operate on deleted inodes") fixes the 
> weird issues.

Thanks for finding that bad commit!
I fear by fixing one bug I've uncovered another one.

So, I guess you are using overlayfs?
Which overlayfs features are you using?

Thanks,
//richard

Re: UBIFS issues within kernel 4.14.69?

[Richard Weinberger]

Koen,

Am Samstag, 15. September 2018, 09:13:09 CEST schrieb Richard Weinberger:
> Koen,
> 
> Am Dienstag, 11. September 2018, 16:26:34 CEST schrieb Koen Vandeputte:
> > 
> > On 2018-09-11 15:46, Koen Vandeputte wrote:
> > > Hi Richard,
> > ...
> > 
> > > I'm only seeing these issues on UBIFS enabled volumes.
> > >
> > > It seems it's related to one of your 5 commits, but I'm still in the 
> > > process of bisecting to find the actual culprit.
> > > As soon as I've found it, I'll let you know, but maybe you already 
> > > have an idea here?
> > >
> > Reverting ("ubifs: xattr: Don't operate on deleted inodes") fixes the 
> > weird issues.
> 
> Thanks for finding that bad commit!
> I fear by fixing one bug I've uncovered another one.
> 
> So, I guess you are using overlayfs?
> Which overlayfs features are you using?

I guess I've figured myself.
overlayfs is using temp files (O_TMPFILE), and a recent overlayfs
feature uses xattrs to indicate directory redirects.
So it can happen that a temp file, which has link count 0, gains
xattrs.

UBIFS models xattrs like regular files in directories. Since you cannot
add new files to a unlinked directory, UBIFS kind of enforced that for
xattrs too.
I say "kind of" because technically it works but can trigger an assertion
in UBIFS's journal code.
Recently I saw this assertion but failed to conclude that xattr operations on
unlinked files are perfectly fine and "fixed" the assert.

The right solution is reverting "ubifs: xattr: Don't operate on deleted inodes"
and removing the false positive asserts from UBIFS' journal code.

Sadly xfstests does not test for that, I'll prepare a new test case.
Maybe other file systems got this wrong too.

Thanks,
//richard

Re: UBIFS issues within kernel 4.14.69?

[Koen Vandeputte]

On 16-09-18 21:39, Richard Weinberger wrote:
> Koen,
>
> Am Samstag, 15. September 2018, 09:13:09 CEST schrieb Richard Weinberger:
>> Koen,
>>
>> Am Dienstag, 11. September 2018, 16:26:34 CEST schrieb Koen Vandeputte:
>>> On 2018-09-11 15:46, Koen Vandeputte wrote:
>>>> Hi Richard,
>>> ...
>>>
>>>> I'm only seeing these issues on UBIFS enabled volumes.
>>>>
>>>> It seems it's related to one of your 5 commits, but I'm still in the
>>>> process of bisecting to find the actual culprit.
>>>> As soon as I've found it, I'll let you know, but maybe you already
>>>> have an idea here?
>>>>
>>> Reverting ("ubifs: xattr: Don't operate on deleted inodes") fixes the
>>> weird issues.
>> Thanks for finding that bad commit!
>> I fear by fixing one bug I've uncovered another one.
>>
>> So, I guess you are using overlayfs?
>> Which overlayfs features are you using?
> I guess I've figured myself.
> overlayfs is using temp files (O_TMPFILE), and a recent overlayfs
> feature uses xattrs to indicate directory redirects.
> So it can happen that a temp file, which has link count 0, gains
> xattrs.
>
> UBIFS models xattrs like regular files in directories. Since you cannot
> add new files to a unlinked directory, UBIFS kind of enforced that for
> xattrs too.
> I say "kind of" because technically it works but can trigger an assertion
> in UBIFS's journal code.
> Recently I saw this assertion but failed to conclude that xattr operations on
> unlinked files are perfectly fine and "fixed" the assert.
>
> The right solution is reverting "ubifs: xattr: Don't operate on deleted inodes"
> and removing the false positive asserts from UBIFS' journal code.
>
> Sadly xfstests does not test for that, I'll prepare a new test case.
> Maybe other file systems got this wrong too.
>
> Thanks,
> //richard
>
Hi Richard,

Apologies for the late reply.
It was a busy weekend with the kids ..

I'm very pleased to read you already have a good idea of what is going 
on here.

Can I conclude you will provide a patch upstream to revert this specific 
commit?
Please keep me in CC in case you do, so I can backport it properly into 
OpenWrt on the next kernel bump. (until it is present in a future stable)

Once again, I highly appreciate you fast response in trying to get this 
fixed.

Thank you Richard,

Koen



Reported-by: Koen Vandeputte <koen.vandeputte@ncentric.com>

Re: UBIFS issues within kernel 4.14.69?

[Richard Weinberger]

Am Sonntag, 16. September 2018, 22:11:07 CEST schrieb Koen Vandeputte:
> Hi Richard,
> 
> Apologies for the late reply.
> It was a busy weekend with the kids ..
> 
> I'm very pleased to read you already have a good idea of what is going 
> on here.
> 
> Can I conclude you will provide a patch upstream to revert this specific 
> commit?

Correct.

> Please keep me in CC in case you do, so I can backport it properly into 
> OpenWrt on the next kernel bump. (until it is present in a future stable)

Done.

Thanks,
//richard