[OpenAFS] AFS-Cache hickups with Ubuntu and Kernel 6.17
Dave Botsch
botsch@cnf.cornell.edu
Tue, 10 Mar 2026 00:45:00 -0400
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What is the Linux kernel change so that we can check for this change bein=
g=20
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
>
> _______________________________________________
> OpenAFS-info mailing list
> OpenAFS-info@openafs.org
> https://lists.openafs.org/mailman/listinfo/openafs-info
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<div dir=3D"auto">
<div dir=3D"auto">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.</div><div dir=3D'auto'><br></div>
<div id=3D"aqm-original" style=3D"color: black;">
<div dir=3D"auto">On March 9, 2026 9:47:58 PM Cheyenne Wills <cwills@sin=
enomine.net> wrote:</div>
<div><br></div>
<blockquote type=3D"cite" class=3D"gmail_quote" style=3D"margin: 0 0 0 0.75=
ex; border-left: 1px solid #808080; padding-left: 0.75ex;">
<div dir=3D"auto">I believe that I found the problem that can result in sta=
le dentries.</div>
<div dir=3D"auto">The fix should be fairly simple. An old configure t=
est was masking a</div>
<div dir=3D"auto">change in the Linux kernel.</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">-- </div>
<div dir=3D"auto">Cheyenne Wills</div>
<div dir=3D"auto">cwills@sinenomine.net</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">On Mon, 9 Mar 2026 14:29:29 +0100</div>
<div dir=3D"auto">Gaja Sophie Peters <gaja.peters@math.uni-hamburg.de>=
; wrote:</div>
<blockquote type=3D"cite" class=3D"gmail_quote" style=3D"margin: 0 0 0 0.75=
ex; border-left: 1px solid #0099CC; padding-left: 0.75ex;">
<div dir=3D"auto">TLDR: OpenAFS on Ubuntu with kernel 6.17 is in certain ci=
rcumstances</div>
<div dir=3D"auto">not updating the Cache on file-deletion or file-creation =
happening on</div>
<div dir=3D"auto">a different machine, the only fix is: echo 3 >/proc/sy=
s/vm/drop_caches</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">Long version: We discovered a problem with the recent adv=
ent of the </div>
<div dir=3D"auto">kernel 6.17 as the newest "hardware enablement kernel" in=
Ubuntu</div>
<div dir=3D"auto">24.04. Basically the existence or non-existence of a file=
is not</div>
<div dir=3D"auto">correctly reflected by the AFS-Cache, when a file is dele=
ted or</div>
<div dir=3D"auto">created on another machine after the file was seen (or no=
t) on the</div>
<div dir=3D"auto">current machine.</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">### first test: file deletion not propagated</div>
<div dir=3D"auto">#this command on a different machine# echo X >test-afs=
</div>
<div dir=3D"auto">$ cat test-afs</div>
<div dir=3D"auto">X</div>
<div dir=3D"auto">#this command on the other machine# rm test-afs</div>
<div dir=3D"auto">$ cat test-afs</div>
<div dir=3D"auto">X</div>
<div dir=3D"auto">$ fs flushall</div>
<div dir=3D"auto">$ cat test-afs</div>
<div dir=3D"auto">cat: test-afs: Input/output error</div>
<div dir=3D"auto">#as root# echo 3 >/proc/sys/vm/drop_caches</div>
<div dir=3D"auto">$ cat test-afs</div>
<div dir=3D"auto">cat: test-afs: No such file or directory</div>
<div dir=3D"auto">### second test: file creation not propagated</div>
<div dir=3D"auto">#this command on a different machine# echo Y >test-afs=
</div>
<div dir=3D"auto">$ cat test-afs</div>
<div dir=3D"auto">cat: test-afs: No such file or directory</div>
<div dir=3D"auto">$ fs flushall</div>
<div dir=3D"auto">$ cat test-afs</div>
<div dir=3D"auto">cat: test-afs: No such file or directory</div>
<div dir=3D"auto">#as root# echo 3 >/proc/sys/vm/drop_caches</div>
<div dir=3D"auto">$ cat test-afs</div>
<div dir=3D"auto">Y</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">We haven't yet tried to pinpoint at which exact kernel-ve=
rsion that </div>
<div dir=3D"auto">problem got introduced, but the Ubuntu-kernels 6.8 and 6.=
14 are </div>
<div dir=3D"auto">unaffected, the Ubuntu-kernel 6.17 is affected (kAFS on 6=
.17 is </div>
<div dir=3D"auto">unaffected). It doesn't make a difference, if the OpenAFS=
-version is </div>
<div dir=3D"auto">1.8.14 with the Ubuntu-patches for Kernel 6.17 or if it i=
s OpenAFS</div>
<div dir=3D"auto">1.8.15</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">The file server hosting the volume was originally 1.8.13.=
2-1 from</div>
<div dir=3D"auto">Debian Trixie, but updating to 1.8.15 does not change any=
thing,</div>
<div dir=3D"auto">either.</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">Is this known? Any idea how to deal with it?</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">Greetings,</div>
<div dir=3D"auto">Gaja Peters</div>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">_______________________________________________</div>
<div dir=3D"auto">OpenAFS-info mailing list</div>
<div dir=3D"auto">OpenAFS-info@openafs.org</div>
<div dir=3D"auto">https://lists.openafs.org/mailman/listinfo/openafs-info</=
div>
</blockquote>
<div dir=3D"auto"><br></div>
<div dir=3D"auto">_______________________________________________</div>
<div dir=3D"auto">OpenAFS-info mailing list</div>
<div dir=3D"auto">OpenAFS-info@openafs.org</div>
<div dir=3D"auto">https://lists.openafs.org/mailman/listinfo/openafs-info</=
div>
</blockquote>
</div><div dir=3D"auto"><br></div>
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