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Message-ID: <20150811074454.GI16853@twins.programming.kicks-ass.net>
Date: Tue, 11 Aug 2015 09:44:54 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Larry Finger <Larry.Finger@...inger.net>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: Kernel crashes in VirtualBox module after commit 2ecd9d29abb1
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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