[OpenAFS-devel] Linux: inode freed while on LRU (change in d_splice_alias?)

[Marc Dionne]

On Fri, Dec 5, 2014 at 3:20 AM, Michael La=C3=9F <lass@mail.upb.de> wrote:
> Hi,
>
> an ArchLinux user reported an issue with OpenAFS on recent Linux kernels
> to me. When unmounting /afs after using it he gets the following error:
>
>> openafs: inode freed while on LRU
>> ------------[ cut here ]------------
>> kernel BUG at /var/lib/dkms/openafs/1.6.11pre1/build/src/libafs/MODLOAD-=
3.17.4-1-ARCH-SP/osi_vfsops.c:291!
>
> This happens using OpenAFS 1.6.10 (11549, 11550 applied on top) and
> 1.6.11pre1.
>
> It seems that this issue was introduced after Linux 3.17.2, so I had a
> look at the changes and found this one here introduced in 3.17.3:
> https://lkml.org/lkml/2014/11/11/1597
>
> If I understand this correctly the kernel now frees the inode reference
> that's still used in OpenAFS. Is that correct? If not, some further
> debugging might be necessary and the user will jump into this thread.
>
> Greetings,
> Michael

Thanks for the pointer, yes that kernel patch would cause a problem,
as in the case of an error from d_splice_alias we proceed to d_add an
inode to which we've lost our reference.  What probably needs to
happen is that we should grab an extra reference before calling
d_splice_alias, and we should drop it for the non error case, and for
the error case after checking that d_splice_alias has not already done
so.  I'll try to come up with a proposed fix.

Marc