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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id B9D9FC433F5 for ; Thu, 14 Apr 2022 19:34:42 +0000 (UTC) Received: from localhost ([::1]:53634 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nf5En-0006Xc-CK for qemu-devel@archiver.kernel.org; Thu, 14 Apr 2022 15:34:41 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49022) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nf5E8-0005iH-8z for qemu-devel@nongnu.org; Thu, 14 Apr 2022 15:34:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:22093) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nf5E5-0003IG-NT for qemu-devel@nongnu.org; Thu, 14 Apr 2022 15:33:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1649964836; 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: in-reply-to:in-reply-to:references:references; bh=lJsp7rhn4Xcb3oRMfjIcQggDXI4RQVl9MUzPOMKG3i8=; b=HxqcYWX56nJXTMkG/zHZNJTmtO3l4FNLwDDIYzkFO+g6XBJOlXZ55SjFNmlXDra3IRoc2i cIPLQWyMM4PoH8U4AouPl5ztCHSo3xmHpO0hxNfxxNtZk4t+hOy3mCv8c1IBjfVMaUGjMr 6xWTiu3ylP3LK7ijjdLCb9gs0WaToj8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-418-sb9dhSQtOLC8z9CrjQ0nuw-1; Thu, 14 Apr 2022 15:33:53 -0400 X-MC-Unique: sb9dhSQtOLC8z9CrjQ0nuw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id AE0AB805A30; Thu, 14 Apr 2022 19:33:52 +0000 (UTC) Received: from redhat.com (unknown [10.2.17.149]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 510142024CB6; Thu, 14 Apr 2022 19:33:52 +0000 (UTC) Date: Thu, 14 Apr 2022 14:33:50 -0500 From: Eric Blake To: Paolo Bonzini Subject: Re: [PATCH v2 for-7.1 5/9] nbd: use a QemuMutex to synchronize yanking, reconnection and coroutines Message-ID: <20220414193350.3vbpn2isfpzzsovr@redhat.com> References: <20220414175756.671165-1-pbonzini@redhat.com> <20220414175756.671165-6-pbonzini@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220414175756.671165-6-pbonzini@redhat.com> User-Agent: NeoMutt/20211029-34-be16c3 X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: v.sementsov-og@mail.ru, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Apr 14, 2022 at 07:57:52PM +0200, Paolo Bonzini wrote: > The condition for waiting on the s->free_sema queue depends on > both s->in_flight and s->state. The latter is currently using > atomics, but this is quite dubious and probably wrong. > > Because s->state is written in the main thread too, for example by > the yank callback, it cannot be protected by a CoMutex. Introduce a > separate lock that can be used by nbd_co_send_request(); later on this > lock will also be used for s->state. There will not be any contention > on the lock unless there is a yank or reconnect, so this is not > performance sensitive. > > Signed-off-by: Paolo Bonzini > --- > block/nbd.c | 46 +++++++++++++++++++++++++++------------------- > 1 file changed, 27 insertions(+), 19 deletions(-) Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org