Re: Kernel crashes in VirtualBox module after commit 2ecd9d29abb1

[Peter Zijlstra]

On Mon, Aug 10, 2015 at 04:49:49PM -0500, Larry Finger wrote:
> A problem with the VirtualBox kernel module vboxdrv.ko has been bisected to
> commit 2ecd9d29abb1 "sched, preempt_notifier: separate notifier registration
> from static_key inc/dec".  The affected kernels crash is various ways. The
> most instructive includes a warning issued at kernel/sched/core.c:2342 in
> prempt_notifier_register() for "registering prempt_notifier while notifiers
> disabled" The call from vboxdrv is as follows:
> 
>         /*
>          * Register the callback.
>          */
>         preempt_disable();
>         pThis->fEnabled = true;
>         preempt_notifier_register(&pThis->LnxPreemptNotifier);
>         preempt_enable();
> 
> As I have no reason to suspect the kernel after this patch, I would like
> some suggestions regarding the best method to patch/fix the VirtualBox code.

You have to call preempt_notifier_inc() when creating your virtual box
instance _before_ creating your vCPU threads which will register the
preempt_notifiers.

You also have to call a matching preempt_notifier_dec() when destroying
your virtual box instance.

The patch you refer adds these calls in
kvm_create_vm()/kvm_destroy_vm(). Mirror that and things should work
again.
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