From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [question] bug in cpu_schedule_up?
Date: Wed, 18 Jan 2012 08:38:55 +0000
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To: Kai Huang <mail.kai.huang@gmail.com>
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On Wed, 2012-01-18 at 08:13 +0000, Kai Huang wrote:
> Hi,
> 
> I see below code in cpu_schedule_up in xen-unstable hg repository
> (xen/common/schedule.c).
> 
>     if ( idle_vcpu[cpu] == NULL )
>         alloc_vcpu(idle_vcpu[0]->domain, cpu, cpu);
>     if ( idle_vcpu[cpu] == NULL )
>         return -ENOMEM;
> 
> Seems it's a bug? Should be like this?
> 
>     if ( idle_vcpu[cpu] == NULL )
>         idle_vcpu[cpu] = alloc_vcpu(idle_vcpu[0]->domain, cpu, cpu);
>     if ( idle_vcpu[cpu] == NULL )
>         return -ENOMEM;

alloc_vcpu will set idle_vcpu[0]->domain->vcpu[cpu] to the newly
allocated vcpu. idle_vcpu[0]->domain == idle_domain and
idle_vcpu[0]->domain->vcpu == idle_vcpu (both are by construction in
scheduler_init). Therefore idle_vcpu[cpu] is already being set inside
alloc_vcpu.

The return value of alloc_vcpu is to save code which wants a local
handle on the newly allocated vcpu to perform further setup from doing
the lookup itself.

Ian.