linux-kernel - Re: [PATCH 2/5 V5] Add functions to check if the host has stopped the vm

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Message-ID: <4EDF78C5.8060908@redhat.com>
Date:	Wed, 07 Dec 2011 16:31:33 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Eric B Munson <emunson@...bm.net>
CC:	mingo@...hat.com, hpa@...or.com, arnd@...db.de,
	ryanh@...ux.vnet.ibm.com, aliguori@...ibm.com, mtosatti@...hat.com,
	jeremy.fitzhardinge@...rix.com, levinsasha928@...il.com,
	Jan Kiszka <jan.kiszka@...mens.com>, kvm@...r.kernel.org,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5 V5] Add functions to check if the host has stopped
 the vm

On 12/05/2011 10:19 PM, Eric B Munson wrote:
> When a host stops or suspends a VM it will set a flag to show this.  The
> watchdog will use these functions to determine if a softlockup is real, or the
> result of a suspended VM.
>  
> +bool kvm_check_and_clear_guest_paused(int cpu)
> +{
> +	bool ret = false;
> +	struct pvclock_vcpu_time_info *src;
> +
> +	/*
> +	 * per_cpu() is safe here because this function is only called from
> +	 * timer functions where preemption is already disabled.
> +	 */
> +	WARN_ON(!in_atomic());
> +	src = &per_cpu(hv_clock, cpu);

__get_cpu_var(); drop the cpu argument

> +	if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
> +		src->flags = src->flags & (~PVCLOCK_GUEST_STOPPED);

Isn't this racy?  Between reading and writing src->flags, we can exit to
the hypervisor and add/remove new flags.  The write then overrides those
new flags.

> +		ret = true;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(kvm_check_and_clear_guest_paused);
> +
>  static struct clocksource kvm_clock = {
>  	.name = "kvm-clock",
>  	.read = kvm_clock_get_cycles,


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

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