From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8CEE2C32750 for ; Fri, 2 Aug 2019 12:04:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5E497217D7 for ; Fri, 2 Aug 2019 12:04:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731420AbfHBMEM (ORCPT ); Fri, 2 Aug 2019 08:04:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41414 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731018AbfHBMEM (ORCPT ); Fri, 2 Aug 2019 08:04:12 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CD98330821A0; Fri, 2 Aug 2019 12:04:11 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.136]) by smtp.corp.redhat.com (Postfix) with SMTP id AC4DA5D704; Fri, 2 Aug 2019 12:04:08 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 2 Aug 2019 14:04:11 +0200 (CEST) Date: Fri, 2 Aug 2019 14:04:07 +0200 From: Oleg Nesterov To: Thomas Gleixner Cc: LKML , x86@kernel.org, Peter Zijlstra , Ingo Molnar , Sebastian Siewior , Anna-Maria Gleixner , Steven Rostedt , Julia Cartwright , Paul McKenney , Frederic Weisbecker , kvm@vger.kernel.org, Radim Krcmar , Paolo Bonzini , John Stultz , Andy Lutomirski , "Paul E. McKenney" Subject: Re: [patch 2/5] x86/kvm: Handle task_work on VMENTER/EXIT Message-ID: <20190802120407.GB20111@redhat.com> References: <20190801143250.370326052@linutronix.de> <20190801143657.887648487@linutronix.de> <20190801162451.GE31538@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Fri, 02 Aug 2019 12:04:12 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 08/01, Thomas Gleixner wrote: > > On Thu, 1 Aug 2019, Oleg Nesterov wrote: > > On 08/01, Thomas Gleixner wrote: > > > > > > @@ -8172,6 +8174,10 @@ static int vcpu_run(struct kvm_vcpu *vcp > > > ++vcpu->stat.signal_exits; > > > break; > > > } > > > + > > > + if (notify_resume_pending()) > > > + tracehook_handle_notify_resume(); > > > > shouldn't you drop kvm->srcu before tracehook_handle_notify_resume() ? > > > > I don't understand this code at all, but vcpu_run() does this even before > > cond_resched(). > > Yeah, I noticed that it's dropped around cond_resched(). > > My understanding is that for voluntary giving up the CPU via cond_resched() > it needs to be dropped. I am not sure it really needs, but this doesn't matter. tracehook_handle_notify_resume() can do "anything", say it can run the works queued by systemtap. I don't think it should delay synchronize_srcu(). And may be this is simply unsafe, even if I don't think a task_work can ever call synchronize_srcu(kvm->srcu) directly. Oleg.