[OpenAFS] AFS-Cache hickups with Ubuntu and Kernel 6.17

[Cheyenne Wills]

The problem was introduced in 6.17 with the Linux commit: 
    'new helper: set_default_d_op()' (05fb0e666495c)

This changed the s_d_op member in the super_block to a private member
and requires the use of the helper function.

The OpenAFS autoconf test for s_d_op failed which caused a fallback to
an older way of setting the dentry_operations for a dentry, but this
could lead to stale dentries.

I have a fix that is being reviewed and will be posted to gerrit soon.

-- 
Cheyenne Wills
cwills@sinenomine.net



On Tue, 10 Mar 2026 00:45:00 -0400
Dave Botsch <botsch@cnf.cornell.edu> wrote:
> What is the Linux kernel change so that we can check for this change
> being back ported into other kernels that have a lesser version
> number? Thanks.
> 
> On March 9, 2026 9:47:58 PM Cheyenne Wills <cwills@sinenomine.net>
> wrote:
> 
> > I believe that I found the problem that can result in stale
> > dentries. The fix should be fairly simple.  An old configure test
> > was masking a change in the Linux kernel.
> >
> > --
> > Cheyenne Wills
> > cwills@sinenomine.net
> >
> >
> >
> > On Mon, 9 Mar 2026 14:29:29 +0100
> > Gaja Sophie Peters <gaja.peters@math.uni-hamburg.de> wrote:
> >> TLDR: OpenAFS on Ubuntu with kernel 6.17 is in certain
> >> circumstances not updating the Cache on file-deletion or
> >> file-creation happening on a different machine, the only fix is:
> >> echo 3 >/proc/sys/vm/drop_caches
> >>
> >>
> >> Long version: We discovered a problem with the recent advent of the
> >> kernel 6.17 as the newest "hardware enablement kernel" in Ubuntu
> >> 24.04. Basically the existence or non-existence of a file is not
> >> correctly reflected by the AFS-Cache, when a file is deleted or
> >> created on another machine after the file was seen (or not) on the
> >> current machine.
> >>
> >> ### first test: file deletion not propagated
> >>      #this command on a different machine# echo X >test-afs
> >>      $ cat test-afs
> >>      X
> >>      #this command on the other machine# rm test-afs
> >>      $ cat test-afs
> >>      X
> >>      $ fs flushall
> >>      $ cat test-afs
> >>      cat: test-afs: Input/output error
> >>      #as root# echo 3 >/proc/sys/vm/drop_caches
> >>      $ cat test-afs
> >>      cat: test-afs: No such file or directory
> >> ### second test: file creation not propagated
> >>      #this command on a different machine# echo Y >test-afs
> >>      $ cat test-afs
> >>      cat: test-afs: No such file or directory
> >>      $ fs flushall
> >>      $ cat test-afs
> >>      cat: test-afs: No such file or directory
> >>      #as root# echo 3 >/proc/sys/vm/drop_caches
> >>      $ cat test-afs
> >>      Y
> >>
> >> We haven't yet tried to pinpoint at which exact kernel-version that
> >> problem got introduced, but the Ubuntu-kernels 6.8 and 6.14 are
> >> unaffected, the Ubuntu-kernel 6.17 is affected (kAFS on 6.17 is
> >> unaffected). It doesn't make a difference, if the OpenAFS-version
> >> is 1.8.14 with the Ubuntu-patches for Kernel 6.17 or if it is
> >> OpenAFS 1.8.15
> >>
> >> The file server hosting the volume was originally 1.8.13.2-1 from
> >> Debian Trixie, but updating to 1.8.15 does not change anything,
> >> either.
> >>
> >> Is this known? Any idea how to deal with it?
> >>
> >> Greetings,
> >> Gaja Peters
> >>
> >> _______________________________________________
> >> OpenAFS-info mailing list
> >> OpenAFS-info@openafs.org
> >> https://lists.openafs.org/mailman/listinfo/openafs-info
> >
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