From nobody Mon Feb 9 11:05:51 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; envelope-from=xen-devel-bounces@lists.xenproject.org; helo=lists.xenproject.org; Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; dmarc=pass(p=quarantine dis=none) header.from=suse.com ARC-Seal: i=1; a=rsa-sha256; t=1617806268; cv=none; d=zohomail.com; s=zohoarc; b=T6W9DqXCaMuvbjZROHqFps/xAxA2mx+bRVKxDzh2OazbpacjDYQYngCmYIYZ/n9pj3f3BTiQkOGsiMNbkvA+m5053zbmCEoz7KDfQVAjhLNcwH187yt9ZjTubRQ1OsvmiBhtrb3dMCR6mQkx99TOjDfsf3sPw6Cs7QUXbmN7cvw= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1617806268; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To; bh=VS4wzz4JN1F6uBq2W5fhu7rrdUSiDdslm/RtnI7Yyw0=; b=bmnbHCvKHnSLi+c1xCl69a1kDX+Esj8BFDmpm/Hy4S5FU5PjERk1NEW3Y53UJrPQAtORKmI6hROmiehsjjb4U0bE9LexEeWu5Ax1okAjJtM4tK2nvh64vGVxGMphz40s5FZlV1r+COaV2f3Zqc6PXufhmVkQLS0Ad++eGRGuhKo= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org; dmarc=pass header.from= (p=quarantine dis=none) header.from= Return-Path: Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) by mx.zohomail.com with SMTPS id 1617806268777666.5347829422144; Wed, 7 Apr 2021 07:37:48 -0700 (PDT) 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 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-Outflank-Mailman: Message body and most headers restored to incoming version 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-Language: en-US Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @suse.com) Content-Type: text/plain; charset="utf-8" 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; } =20 -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 =3D 0; int num_devs; @@ -374,8 +375,7 @@ static int xen_pcibk_reconfigure(struct =20 mutex_lock(&pdev->dev_lock); /* Make sure we only reconfigure once */ - if (xenbus_read_driver_state(pdev->xdev->nodename) !=3D - XenbusStateReconfiguring) + if (xenbus_read_driver_state(pdev->xdev->nodename) !=3D state) goto out; =20 err =3D xenbus_scanf(XBT_NIL, pdev->xdev->nodename, "num_devs", "%d", @@ -500,6 +500,9 @@ static int xen_pcibk_reconfigure(struct } } =20 + if (state !=3D XenbusStateReconfiguring) + goto out; + err =3D 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; =20 case XenbusStateReconfiguring: - xen_pcibk_reconfigure(pdev); + xen_pcibk_reconfigure(pdev, XenbusStateReconfiguring); break; =20 case XenbusStateConnected: @@ -664,6 +667,10 @@ static void xen_pcibk_be_watch(struct xe xen_pcibk_setup_backend(pdev); break; =20 + case XenbusStateInitialised: + xen_pcibk_reconfigure(pdev, XenbusStateInitialised); + break; + default: break; }