From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:43914)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1VlxOD-0005yM-7Y
	for qemu-devel@nongnu.org; Thu, 28 Nov 2013 03:56:07 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1VlxO7-0006sJ-8G
	for qemu-devel@nongnu.org; Thu, 28 Nov 2013 03:56:01 -0500
Received: from mx1.redhat.com ([209.132.183.28]:29392)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1VlxO6-0006sE-Uw
	for qemu-devel@nongnu.org; Thu, 28 Nov 2013 03:55:55 -0500
Message-ID: <5297050E.6000700@redhat.com>
Date: Thu, 28 Nov 2013 09:55:42 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
MIME-Version: 1.0
References: <D3E216785288A145B7BC975F83A2ED10448ADCCB@SZXEMA510-MBS.china.huawei.com>
	<52949847.6020908@redhat.com>
	<CAEbWaipAnmoa=gMbB1aNb=btU6LgYXhcnmQWHJ_89m4yvw6Dug@mail.gmail.com>
	<5294A68F.6060301@redhat.com>
	<CAF950W+-UiX6xv4vYmnxji9aWDU8ds2rnx7JugnbHQWJdCCD-Q@mail.gmail.com>
	<5294B461.5000405@redhat.com>
	<5294B634.4050801@cloudius-systems.com>
	<20131126150357.GA20352@redhat.com> <5294BC3B.6070902@redhat.com>
	<D3E216785288A145B7BC975F83A2ED10448BBAB3@SZXEMA510-MBS.china.huawei.com>
In-Reply-To: <D3E216785288A145B7BC975F83A2ED10448BBAB3@SZXEMA510-MBS.china.huawei.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [RFC] create a single workqueue for each vm to
 update vm irq routing table
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: "Zhanghaoyu (A)" <haoyu.zhang@huawei.com>
Cc: Avi Kivity <avi@cloudius-systems.com>, "Huangweidong (C)" <weidong.huang@huawei.com>, KVM <kvm@vger.kernel.org>, Gleb Natapov <gleb@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, Luonengjun <luonengjun@huawei.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Zanghongyong <zanghongyong@huawei.com>, Avi Kivity <avi.kivity@gmail.com>, "Jinxin (F)" <jinxin712@huawei.com>

Il 28/11/2013 07:27, Zhanghaoyu (A) ha scritto:
>> >Without synchronize_rcu you could have
>> >
>> >    VCPU writes to routing table
>> >                                       e = entry from IRQ routing table
>> >    kvm_irq_routing_update(kvm, new);
>> >    VCPU resumes execution
>> >                                       kvm_set_msi_irq(e, &irq);
>> >                                       kvm_irq_delivery_to_apic_fast();
>> >
>> >where the entry is stale but the VCPU has already resumed execution.
>> >
> If we use call_rcu()(Not consider the problem that Gleb pointed out temporarily) instead of synchronize_rcu(), should we still ensure this?

The problem is that we should ensure this, so using call_rcu is not
possible (even not considering the memory allocation problem).

Can you try using SRCU and synchronize_srcu?

Paolo