[Xenial SRU/Yakkety]: Regression warning about 4.4.17+18 / 4.6.7 / 4.7+ and Xen

[Stefan Bader]

On 22.08.2016 12:07, Stefan Bader wrote:
> There has been a recent (maybe not that recent, it was in 4.7) kernel regression
> for Xen which made its way back to several stable trees[1]:
> 
>   xenbus: don't BUG() on user mode induced condition
> 
> It appears there is a fix on patchworks[2] but as of today was not included, yet
> in upstream Linux.
> 
> For Yakkety the regression is part of the 4.6.0-11 unstable package. For Xenial
> it is part of the pending next SRU cycle (master-next). I did a quick test with
> the proposed patch on top of 4.6 in yakkety/master-next and it allowed me to
> starts VMs again. Not sure whether we want to pick that additional patch or back
> out the stable change introducing the problem. But either way the master-next
> branches of both Xenial and Yakkety will cause a Xen regression as they are now.
> 
> The effect is that tools like xenstore-ls or xenstore-write no longer work and
> it is no longer possible to start any VMs.

The commit went upstream as of today. The attached patch uses the tracking bug
of the commit that would introduce the regression (upstream stable update
4.4.18). Mind that for Yakkety 4.6 based kernels currently also have the
regression and would need this patch until everything moves to 4.8...

-Stefan

> 
> -Stefan
> 
> [1] https://lists.xenproject.org/archives/html/xen-devel/2016-08/msg02496.html
> [2] https://patchwork.kernel.org/patch/9281193/
> 

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