linux-kernel - Re: [PATCH] remove static declaration from wall clock version

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Message-Id: <200902262050.27555.arnd@arndb.de>
Date:	Thu, 26 Feb 2009 20:50:26 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com
Subject: Re: [PATCH] remove static declaration from wall clock version

On Thursday 26 February 2009, Glauber Costa wrote:
> @@ -548,15 +548,13 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
>  
>  static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
>  {
> -       static int version;
> +       int version = 1;
>         struct pvclock_wall_clock wc;
>         struct timespec now, sys, boot;
>  
>         if (!wall_clock)
>                 return;
>  
> -       version++;
> -
>         kvm_write_guest(kvm, wall_clock, &version, sizeof(version));
>  
>         /*

Doesn't this mean that kvm_write_guest now writes an uninitialized value
to the guest?

I think what you need here is a 'static atomic_t version;' so you can
do an atomic_inc instead of the ++.

	Arnd <><
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