From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751502AbdFGNFW (ORCPT ); Wed, 7 Jun 2017 09:05:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33882 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751203AbdFGNFV (ORCPT ); Wed, 7 Jun 2017 09:05:21 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com C4665C0587DC Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx08.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=pbonzini@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com C4665C0587DC Subject: Re: [PATCH] KVM: async_pf: Fix rcu_irq_enter/exit() usage To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li References: <1496837040-8200-1-git-send-email-wanpeng.li@hotmail.com> From: Paolo Bonzini Message-ID: <1733800e-2547-39dc-f3c8-9002ea42539e@redhat.com> Date: Wed, 7 Jun 2017 15:05:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0 MIME-Version: 1.0 In-Reply-To: <1496837040-8200-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 07 Jun 2017 13:05:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/06/2017 14:04, Wanpeng Li wrote: > From: Wanpeng Li > > Commit 9b132fbe5419 (Add rcu user eqs exception hooks for async page fault) > adds rcu_irq_enter/exit() to kvm_async_pf_task_wait() to exit cpu idle eqs > when needed, to protect the code that needs use rcu. There is no need to call > this pairs if async page fault is not triggered from idle task. > > This patch fixes it by rcu irq exit if it is not triggered from idle task to > avoid rcu hang after schedule() in the for loop. How does the bug manifest? Paolo > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Signed-off-by: Wanpeng Li > --- > arch/x86/kernel/kvm.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 43e10d6..e70ed72 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -141,6 +141,8 @@ void kvm_async_pf_task_wait(u32 token) > n.token = token; > n.cpu = smp_processor_id(); > n.halted = is_idle_task(current) || preempt_count() > 1; > + if (!n.halted) > + rcu_irq_exit(); > init_swait_queue_head(&n.wq); > hlist_add_head(&n.link, &b->list); > raw_spin_unlock(&b->lock); > @@ -167,8 +169,9 @@ void kvm_async_pf_task_wait(u32 token) > } > if (!n.halted) > finish_swait(&n.wq, &wait); > + else > + rcu_irq_exit(); > > - rcu_irq_exit(); > return; > }