linux-kernel - Re: [PATCH] Fix preempt imbalance in kvm_timer

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Date:	Sun, 12 Dec 2010 11:28:10 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Thomas Meyer <thomas@...3r.de>
CC:	linux-kernel@...r.kernel.org, zamsden@...hat.com,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH] Fix preempt imbalance in kvm_timer_init()

On 12/09/2010 08:42 PM, Thomas Meyer wrote:
> Signed-off-by: Thomas Meyer<thomas@...3r.de>
> ---
>   arch/x86/kvm/x86.c |    5 +++--
>   1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index cdac9e5..2609c3d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4561,7 +4561,7 @@ static struct notifier_block kvmclock_cpu_notifier_block = {
>
>   static void kvm_timer_init(void)
>   {
> -	int cpu;
> +	int cpu = get_cpu();
>
>   	max_tsc_khz = tsc_khz;
>   	register_hotcpu_notifier(&kvmclock_cpu_notifier_block);

This eventually takes a mutex (in cpu_maps_update_begin()), so it can't 
be called with preemption disabled.

> @@ -4569,13 +4569,14 @@ static void kvm_timer_init(void)
>   #ifdef CONFIG_CPU_FREQ
>   		struct cpufreq_policy policy;
>   		memset(&policy, 0, sizeof(policy));
> -		cpufreq_get_policy(&policy, get_cpu());
> +		cpufreq_get_policy(&policy, cpu);
>   		if (policy.cpuinfo.max_freq)
>   			max_tsc_khz = policy.cpuinfo.max_freq;
>   #endif
>   		cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block,
>   					  CPUFREQ_TRANSITION_NOTIFIER);
>   	}
> +	put_cpu();
>   	pr_debug("kvm: max_tsc_khz = %ld\n", max_tsc_khz);
>   	for_each_online_cpu(cpu)
>   		smp_call_function_single(cpu, tsc_khz_changed, NULL, 1);


-- 
error compiling committee.c: too many arguments to function

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