Regression in kernel 4.7 xenstore

Regression in kernel 4.7 xenstore

[Christoph Moench-Tegeder]

Hi,

I'm running Xen 4.4.1 as packaged in Debian 8.5 (jessie) with home-baked
kernels (that is, from kernel.org) (hardware is x86-64, in case that
matters).

After upgrading to kernel 4.7, xenstore-write is not able to set
the Dom0 name anymore (and no DomU can be started).
The journal shows:

Aug 20 23:36:09 dhcp-31 xenstored[683]: Checking store ...
Aug 20 23:36:09 dhcp-31 xenstored[683]: Checking store complete.
Aug 20 23:36:09 dhcp-31 xen[578]: Starting Xen daemons: xenfs xenstored xenconsoled init-dom0xenstore-write: could not write path /local/domain/0/name
Aug 20 23:36:09 dhcp-31 xen[578]: xenstore-write: could not write path /local/domain/0/domid
Aug 20 23:36:09 dhcp-31 xen[578]: .

(this is a test instance, therefore the hostname)
This problem exists in 4.7 and 4.7.2 (I checked just in case) (and
4.6.6+ but not 4.6.5 - that's history now anyways).
Backing out commit 0beef634b86a1350c31da5fcc2992f0d7c8a622b
  "xenbus: don't BUG() on user mode induced condition"
  https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/patch/?id=0beef634b86a1350c31da5fcc2992f0d7c8a622b
fixes this problem for me (but I've no idea how to fix the original
problem).

Am I looking at a bona fide regression, or did this change uncover
some misbehaviour in the (arguably not that recent) Xen 4.4 or even
in Debian's specific version?

In case you need more information or want a patch tested, I'll leave
this test system around for some time.

Regards,
Christoph

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Re: Regression in kernel 4.7 xenstore

[Jan Beulich]

>>> On 21.08.16 at 00:33, <cmt@burggraben.net> wrote:
> Hi,
> 
> I'm running Xen 4.4.1 as packaged in Debian 8.5 (jessie) with home-baked
> kernels (that is, from kernel.org) (hardware is x86-64, in case that
> matters).
> 
> After upgrading to kernel 4.7, xenstore-write is not able to set
> the Dom0 name anymore (and no DomU can be started).
> The journal shows:
> 
> Aug 20 23:36:09 dhcp-31 xenstored[683]: Checking store ...
> Aug 20 23:36:09 dhcp-31 xenstored[683]: Checking store complete.
> Aug 20 23:36:09 dhcp-31 xen[578]: Starting Xen daemons: xenfs xenstored 
> xenconsoled init-dom0xenstore-write: could not write path 
> /local/domain/0/name
> Aug 20 23:36:09 dhcp-31 xen[578]: xenstore-write: could not write path 
> /local/domain/0/domid
> Aug 20 23:36:09 dhcp-31 xen[578]: .
> 
> (this is a test instance, therefore the hostname)
> This problem exists in 4.7 and 4.7.2 (I checked just in case) (and
> 4.6.6+ but not 4.6.5 - that's history now anyways).
> Backing out commit 0beef634b86a1350c31da5fcc2992f0d7c8a622b
>   "xenbus: don't BUG() on user mode induced condition"
>   
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/patch/?id=0be 
> ef634b86a1350c31da5fcc2992f0d7c8a622b
> fixes this problem for me (but I've no idea how to fix the original
> problem).
> 
> Am I looking at a bona fide regression, or did this change uncover
> some misbehaviour in the (arguably not that recent) Xen 4.4 or even
> in Debian's specific version?
> 
> In case you need more information or want a patch tested, I'll leave
> this test system around for some time.

See https://patchwork.kernel.org/patch/9281193/.

Jan


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Re: Regression in kernel 4.7 xenstore

[Christoph Moench-Tegeder]

## Jan Beulich (JBeulich@suse.com):

> See https://patchwork.kernel.org/patch/9281193/.

Yes, that's it. Thanks, fix confirmed.

Regards,
Christoph

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