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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 B02BBC433DF for ; Thu, 9 Jul 2020 09:35:31 +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 6F865206C3 for ; Thu, 9 Jul 2020 09:35:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UC/DfTHW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F865206C3 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]:37616 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jtSxm-0000Qa-Jh for qemu-devel@archiver.kernel.org; Thu, 09 Jul 2020 05:35:30 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45246) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jtSxB-0008JC-Oq for qemu-devel@nongnu.org; Thu, 09 Jul 2020 05:34:53 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:31581 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 1jtSxA-0001IN-0d for qemu-devel@nongnu.org; Thu, 09 Jul 2020 05:34:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594287290; 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=95m+vveXFqdFSJz1YEHUha3bRVCC5LtbQKgAMro6tp8=; b=UC/DfTHWTnOrodTM84a587zGnaZ+c4w3SHs7CoiRaUZ3mPIJZ+HpfMwbpdE5S+uuV1HUuc C9UV0dsVPM1Dx4pxgCzcdCYaT5xP+cVBIAZ94HxY9wW8qkn3iVgDgEtYOtZlGDM9gvM/TL D6jV++2eZh0vAalm1Sze7039alf57d0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-294-agGgjExyMRuvHTp8DCC8mA-1; Thu, 09 Jul 2020 05:34:47 -0400 X-MC-Unique: agGgjExyMRuvHTp8DCC8mA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 302DB108BD09; Thu, 9 Jul 2020 09:34:46 +0000 (UTC) Received: from starship (unknown [10.35.206.232]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0C0345D9DD; Thu, 9 Jul 2020 09:34:40 +0000 (UTC) Message-ID: Subject: Re: [PATCH v2 2/7] Implement drain_call_rcu and use it in hmp_device_del From: Maxim Levitsky To: Stefan Hajnoczi Date: Thu, 09 Jul 2020 12:34:39 +0300 In-Reply-To: <20200527131148.GH29137@stefanha-x1.localdomain> References: <20200511160951.8733-1-mlevitsk@redhat.com> <20200511160951.8733-3-mlevitsk@redhat.com> <20200527131148.GH29137@stefanha-x1.localdomain> User-Agent: Evolution 3.34.4 (3.34.4-1.fc31) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com 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=mlevitsk@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/09 04:20:09 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Fam Zheng , "Daniel P. =?ISO-8859-1?Q?Berrang=E9?=" , Eduardo Habkost , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 2020-05-27 at 14:11 +0100, Stefan Hajnoczi wrote: > On Mon, May 11, 2020 at 07:09:46PM +0300, Maxim Levitsky wrote: > > /* The operands of the minus operator must have the same type, > > * which must be the one that we specify in the cast. > > diff --git a/qdev-monitor.c b/qdev-monitor.c > > index 56cee1483f..70877840a2 100644 > > --- a/qdev-monitor.c > > +++ b/qdev-monitor.c > > @@ -812,6 +812,8 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp) > > return; > > } > > dev = qdev_device_add(opts, &local_err); > > + drain_call_rcu(); > > Please include comments explaining what each drain waits for. Without > comments we'll quickly lose track of why drain_call_rcu() calls are > necessary (similar to documenting memory barrier or refcount inc/dec > pairing). > > > diff --git a/util/rcu.c b/util/rcu.c > > index 60a37f72c3..e8b1c4d6c5 100644 > > --- a/util/rcu.c > > +++ b/util/rcu.c > > @@ -293,6 +293,39 @@ void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node)) > > qemu_event_set(&rcu_call_ready_event); > > } > > > > + > > +struct rcu_drain { > > + struct rcu_head rcu; > > + QemuEvent drain_complete_event; > > +}; > > + > > +static void drain_rcu_callback(struct rcu_head *node) > > +{ > > + struct rcu_drain *event = (struct rcu_drain *)node; > > + qemu_event_set(&event->drain_complete_event); > > A comment would be nice explaining that callbacks are invoked in > sequence so we're sure that all previously scheduled callbacks have > completed when drain_rcu_callback() is invoked. > > > +} > > + > > +void drain_call_rcu(void) > > Please document that the main loop mutex is dropped if it's held. This > will prevent surprises and allow callers to think about thread-safety > across this call. Done. > > Aside from the comment requests: > Reviewed-by: Stefan Hajnoczi Best regards, Maxim levitsky