From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] KVM: VMX: Do not overwrite vcpu->srcu_idx in vmx_vcpu_reset
Date: Thu, 14 Mar 2013 16:08:42 +0100
Message-ID: <5141E7FA.8060003@redhat.com>
References: <5141E41B.8080804@siemens.com> <20130314150004.GX11223@redhat.com> <5141E6BA.2060404@siemens.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Cc: Gleb Natapov <gleb@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	kvm <kvm@vger.kernel.org>
To: Jan Kiszka <jan.kiszka@siemens.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:46760 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1755847Ab3CNPIs (ORCPT <rfc822;kvm@vger.kernel.org>);
	Thu, 14 Mar 2013 11:08:48 -0400
In-Reply-To: <5141E6BA.2060404@siemens.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

Il 14/03/2013 16:03, Jan Kiszka ha scritto:
>> > vcpu->srcu_idx = srcu_read_lock()
>> >   idx = srcu_read_lock(&vcpu->kvm->srcu); 
>> >    srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
>> >    vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
>> >   srcu_read_unlock(&vcpu->kvm->srcu, idx);
>> > srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
>> > 
>> > Not sure this is valid.
> Grmbl, likely not.

It might be.

Isn't it the same as two different CPUs doing

CPU 1                                                 CPU 2
------------------------------------------------------------------------------------------------

vcpu->srcu_idx = srcu_read_lock()
                                                      idx = srcu_read_lock(&vcpu->kvm->srcu); 
srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
                                                      srcu_read_unlock(&vcpu->kvm->srcu, idx);
srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);

?

Paolo