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=-17.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 1AC72C433B4 for ; Wed, 7 Apr 2021 14:37:42 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 D2945610F8 for ; Wed, 7 Apr 2021 14:37:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D2945610F8 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.106713.204047 (Exim 4.92) (envelope-from ) id 1lU9JG-0000NE-3M; Wed, 07 Apr 2021 14:37:34 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 106713.204047; Wed, 07 Apr 2021 14:37:34 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lU9JF-0000N7-Vj; Wed, 07 Apr 2021 14:37:33 +0000 Received: by outflank-mailman (input) for mailman id 106713; Wed, 07 Apr 2021 14:37:33 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lU9JF-0000Mx-D2 for xen-devel@lists.xenproject.org; Wed, 07 Apr 2021 14:37:33 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 9663923e-363a-4c8c-8c8b-6169e901c5ff; Wed, 07 Apr 2021 14:37:32 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 74DBEB034; Wed, 7 Apr 2021 14:37:31 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 9663923e-363a-4c8c-8c8b-6169e901c5ff X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617806251; h=from:from:reply-to: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=VS4wzz4JN1F6uBq2W5fhu7rrdUSiDdslm/RtnI7Yyw0=; b=V+qWN/caw4IVWpZnWxOfPRmNweRh3TWDlswo2itZariZbCfk8clHdAwL66wTavooDRgCfv tLoYX/24ibzLiOg94lE2cc3L9HyZY89UXXs0X4V4ci7zA1goVy2AvSiStjTKTzJEWfN6nm SK8Izn6jcRFuiKggP1VBfL5WPxrgOAE= Subject: [PATCH 2/3] xen-pciback: reconfigure also from backend watch handler From: Jan Beulich To: "xen-devel@lists.xenproject.org" Cc: Juergen Gross , Boris Ostrovsky , Konrad Wilk References: Message-ID: <74955b48-80b1-3436-06b4-d8569260aa65@suse.com> Date: Wed, 7 Apr 2021 16:37:31 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit When multiple PCI devices get assigned to a guest right at boot, libxl incrementally populates the backend tree. The writes for the first of the devices trigger the backend watch. In turn xen_pcibk_setup_backend() will set the XenBus state to Initialised, at which point no further reconfigures would happen unless a device got hotplugged. Arrange for reconfigure to also get triggered from the backend watch handler. Signed-off-by: Jan Beulich Cc: stable@vger.kernel.org --- I will admit that this isn't entirely race-free (with the guest actually attaching in parallel), but from the looks of it such a race ought to be benign (not the least thanks to the mutex). Ideally the tool stack wouldn't write num_devs until all devices had their information populated. I tried doing so in libxl, but xen_pcibk_setup_backend() calling xenbus_dev_fatal() when not being able to read that node prohibits such an approach (or else libxl and driver changes would need to go into use in lock-step). I wonder why what is being watched isn't just the num_devs node. Right now the watch triggers quite frequently without anything relevant actually having changed (I suppose in at least some cases in response to writes by the backend itself). --- a/drivers/xen/xen-pciback/xenbus.c +++ b/drivers/xen/xen-pciback/xenbus.c @@ -359,7 +359,8 @@ out: return err; } -static int xen_pcibk_reconfigure(struct xen_pcibk_device *pdev) +static int xen_pcibk_reconfigure(struct xen_pcibk_device *pdev, + enum xenbus_state state) { int err = 0; int num_devs; @@ -374,8 +375,7 @@ static int xen_pcibk_reconfigure(struct mutex_lock(&pdev->dev_lock); /* Make sure we only reconfigure once */ - if (xenbus_read_driver_state(pdev->xdev->nodename) != - XenbusStateReconfiguring) + if (xenbus_read_driver_state(pdev->xdev->nodename) != state) goto out; err = xenbus_scanf(XBT_NIL, pdev->xdev->nodename, "num_devs", "%d", @@ -500,6 +500,9 @@ static int xen_pcibk_reconfigure(struct } } + if (state != XenbusStateReconfiguring) + goto out; + err = xenbus_switch_state(pdev->xdev, XenbusStateReconfigured); if (err) { xenbus_dev_fatal(pdev->xdev, err, @@ -525,7 +528,7 @@ static void xen_pcibk_frontend_changed(s break; case XenbusStateReconfiguring: - xen_pcibk_reconfigure(pdev); + xen_pcibk_reconfigure(pdev, XenbusStateReconfiguring); break; case XenbusStateConnected: @@ -664,6 +667,10 @@ static void xen_pcibk_be_watch(struct xe xen_pcibk_setup_backend(pdev); break; + case XenbusStateInitialised: + xen_pcibk_reconfigure(pdev, XenbusStateInitialised); + break; + default: break; }