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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0ADE1C433FE for ; Mon, 4 Oct 2021 13:39:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCB8E60F58 for ; Mon, 4 Oct 2021 13:39:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237413AbhJDNlE (ORCPT ); Mon, 4 Oct 2021 09:41:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:53180 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238617AbhJDNiu (ORCPT ); Mon, 4 Oct 2021 09:38:50 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 35B356324B; Mon, 4 Oct 2021 13:18:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1633353481; bh=1MLeZklQqxtUfQ7JboQfwHPWxFjt2Oe4JLxtf++UOGk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=njNWONOlmSCVg+LKKRF3cVFFDNZBxyda04Xm2zny2ekPp9YVRtPF694lrV+i++o15 aIRF6/C9PBK+paJxi/T3dZOGOvZ5+ZAcdAOm33ew4YCt3HFawDA0cv8ZW9mPudvTq4 NIggtNF5L1kipb5/XdznZECtcnVu3TcBVC72Vfqw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Marek Szyprowski , Saravana Kannan Subject: [PATCH 5.14 146/172] driver core: fw_devlink: Improve handling of cyclic dependencies Date: Mon, 4 Oct 2021 14:53:16 +0200 Message-Id: <20211004125049.685211278@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20211004125044.945314266@linuxfoundation.org> References: <20211004125044.945314266@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Saravana Kannan commit 2de9d8e0d2fe3a1eb632def2245529067cb35db5 upstream. When we have a dependency of the form: Device-A -> Device-C Device-B Device-C -> Device-B Where, * Indentation denotes "child of" parent in previous line. * X -> Y denotes X is consumer of Y based on firmware (Eg: DT). We have cyclic dependency: device-A -> device-C -> device-B -> device-A fw_devlink current treats device-C -> device-B dependency as an invalid dependency and doesn't enforce it but leaves the rest of the dependencies as is. While the current behavior is necessary, it is not sufficient if the false dependency in this example is actually device-A -> device-C. When this is the case, device-C will correctly probe defer waiting for device-B to be added, but device-A will be incorrectly probe deferred by fw_devlink waiting on device-C to probe successfully. Due to this, none of the devices in the cycle will end up probing. To fix this, we need to go relax all the dependencies in the cycle like we already do in the other instances where fw_devlink detects cycles. A real world example of this was reported[1] and analyzed[2]. [1] - https://lore.kernel.org/lkml/0a2c4106-7f48-2bb5-048e-8c001a7c3fda@samsung.com/ [2] - https://lore.kernel.org/lkml/CAGETcx8peaew90SWiux=TyvuGgvTQOmO4BFALz7aj0Za5QdNFQ@mail.gmail.com/ Fixes: f9aa460672c9 ("driver core: Refactor fw_devlink feature") Cc: stable Reported-by: Marek Szyprowski Tested-by: Marek Szyprowski Signed-off-by: Saravana Kannan Link: https://lore.kernel.org/r/20210915170940.617415-2-saravanak@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/base/core.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -1790,14 +1790,21 @@ static int fw_devlink_create_devlink(str * be broken by applying logic. Check for these types of cycles and * break them so that devices in the cycle probe properly. * - * If the supplier's parent is dependent on the consumer, then - * the consumer-supplier dependency is a false dependency. So, - * treat it as an invalid link. + * If the supplier's parent is dependent on the consumer, then the + * consumer and supplier have a cyclic dependency. Since fw_devlink + * can't tell which of the inferred dependencies are incorrect, don't + * enforce probe ordering between any of the devices in this cyclic + * dependency. Do this by relaxing all the fw_devlink device links in + * this cycle and by treating the fwnode link between the consumer and + * the supplier as an invalid dependency. */ sup_dev = fwnode_get_next_parent_dev(sup_handle); if (sup_dev && device_is_dependent(con, sup_dev)) { - dev_dbg(con, "Not linking to %pfwP - False link\n", - sup_handle); + dev_info(con, "Fixing up cyclic dependency with %pfwP (%s)\n", + sup_handle, dev_name(sup_dev)); + device_links_write_lock(); + fw_devlink_relax_cycle(con, sup_dev); + device_links_write_unlock(); ret = -EINVAL; } else { /*