From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [RFC] create a single workqueue for each vm to update
 vm irq routing table
Date: Thu, 28 Nov 2013 09:55:42 +0100
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Cc: Gleb Natapov <gleb@redhat.com>,
	Avi Kivity <avi@cloudius-systems.com>,
	Avi Kivity <avi.kivity@gmail.com>,
	"Huangweidong (C)" <weidong.huang@huawei.com>,
	KVM <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>,
	"Jinxin (F)" <jinxin712@huawei.com>,
	Luonengjun <luonengjun@huawei.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	Zanghongyong <zanghongyong@huawei.com>
To: "Zhanghaoyu (A)" <haoyu.zhang@huawei.com>
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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