Re: [Xen-devel] Regression in kernel 4.7 xenstore

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.08.16 at 00:33, <cmt@xxxxxxxxxxxxxx> 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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