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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 7C4FCC54FD0 for ; Mon, 20 Apr 2020 21:44:56 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4094320724 for ; Mon, 20 Apr 2020 21:44:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ck05UatT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4094320724 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:42902 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jQeDn-0007nb-F8 for qemu-devel@archiver.kernel.org; Mon, 20 Apr 2020 17:44:55 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45056) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jQeDC-0007Od-Go for qemu-devel@nongnu.org; Mon, 20 Apr 2020 17:44:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.90_1) (envelope-from ) id 1jQeDC-0000L5-3Q for qemu-devel@nongnu.org; Mon, 20 Apr 2020 17:44:18 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:39261 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jQeDB-0000K4-NQ for qemu-devel@nongnu.org; Mon, 20 Apr 2020 17:44:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587419056; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ur0LRAuxFc8ulkjog3Q2fNWV1PxOzVt4euylp8ZQYZc=; b=ck05UatTOnI72kqmySPa2OmQjUeu67MDnMLXbJs/55aTFwfs/d5VwiBAlERmKXAVKneees 35oFDqX3cvge7ROPmXxaH9Qs0KRctpTmDVzyeCs4pJ2QioJ63OWHViQDco3MXzYTpFMdwQ 4f63vwDUutaOWMKiW08XmtCVTzr+B6E= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-296-aK5xk8tEMP6Z1DZINUe-0w-1; Mon, 20 Apr 2020 17:44:14 -0400 X-MC-Unique: aK5xk8tEMP6Z1DZINUe-0w-1 Received: by mail-wr1-f69.google.com with SMTP id y10so1300391wrn.5 for ; Mon, 20 Apr 2020 14:44:14 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=Ur0LRAuxFc8ulkjog3Q2fNWV1PxOzVt4euylp8ZQYZc=; b=WOVfLZdSJlIergN3DJ2hxqgifVq6GpvBGxQsyKftd6GrZOj0hBD14+H7Yn4uEevq4Z 7l3dEbvZ/QOmNWxhbjsen0b7ORcUuwtOZf4zqGN9g5DPrK1MrelqhQYiWQ50RB9m/JMa 9QopItOvtzwJl3aqhPxhErE/XbsDfWMrT5zLHmub7+8RXC0L8C63E9rbgtcMnjT5xh4+ kMuQqpLxlwDjLaoLNa5+uSrG68qerw2u9YindeQuEQjsGksCWcrpZLzBr+iII7cAeVJT jHuFdiISnzfEArmPmvMm7PODXvIpDEbSNilIIeciFreP0ha81iuYj2IQpBaDPjAAH3mg Lyhg== X-Gm-Message-State: AGi0Pub2M9jMwQ7fmlFis/iPFO6pGhLazl273fWTFcwQyJlHgIuCMIJk fmcn+lWBUC6bDc+22VBxS71DhYqkzJDSxV20kX99rVM4e78/V88XHkBW+sBwHsW1EktreQNpcvI 6VOb7llCcQy6CBhQ= X-Received: by 2002:a5d:6607:: with SMTP id n7mr22214758wru.150.1587419053336; Mon, 20 Apr 2020 14:44:13 -0700 (PDT) X-Google-Smtp-Source: APiQypLNXTIpjLTeHIKxCQLIk/ESjsWkGUdDZmBxuKMCpLoxw+y4BHYykyalNPxezsRFxMHqaTq7sA== X-Received: by 2002:a5d:6607:: with SMTP id n7mr22214744wru.150.1587419053093; Mon, 20 Apr 2020 14:44:13 -0700 (PDT) Received: from ?IPv6:2001:b07:6468:f312:5c18:5523:c13e:fa9f? ([2001:b07:6468:f312:5c18:5523:c13e:fa9f]) by smtp.gmail.com with ESMTPSA id r2sm945287wmg.2.2020.04.20.14.44.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Apr 2020 14:44:12 -0700 (PDT) Subject: Re: Question on memory commit during MR finalize() To: Peter Xu References: <20200420210049.GA420399@xz-x1> From: Paolo Bonzini Message-ID: Date: Mon, 20 Apr 2020 23:44:11 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200420210049.GA420399@xz-x1> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/20 17:00:59 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Markus Armbruster , QEMU Devel Mailing List Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 20/04/20 23:00, Peter Xu wrote: > > I'm still uncertain how the dirty ring branch can easily trigger this, however > the backtrace looks really odd to me in that we're going to do memory commit > and even sending KVM ioctls during finalize(), especially in the RCU thread... > I never expected that. Short answer: it is really hard to not trigger finalize() from an RCU callback, and it's the reason why the RCU thread takes the big QEMU lock. However, instead of memory_region_transaction_commit, memory_region_finalize probably should do something like --memory_region_transaction_depth; assert (memory_region_transaction_depth || (!memory_region_update_pending && !ioeventfd_update_pending)); Paolo