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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 132EDC43381 for ; Wed, 13 Mar 2019 09:08:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E19672147C for ; Wed, 13 Mar 2019 09:08:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727335AbfCMJIa (ORCPT ); Wed, 13 Mar 2019 05:08:30 -0400 Received: from Mailgw01.mediatek.com ([1.203.163.78]:13728 "EHLO mailgw01.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726163AbfCMJIa (ORCPT ); Wed, 13 Mar 2019 05:08:30 -0400 X-UUID: 6ab37ab9377f46f4a1e5c820377e028a-20190313 X-UUID: 6ab37ab9377f46f4a1e5c820377e028a-20190313 Received: from mtkcas35.mediatek.inc [(172.27.4.253)] by mailgw01.mediatek.com (envelope-from ) (mailgw01.mediatek.com ESMTP with TLS) with ESMTP id 2093687650; Wed, 13 Mar 2019 17:08:25 +0800 Received: from MTKCAS32.mediatek.inc (172.27.4.184) by MTKMBS31N2.mediatek.inc (172.27.4.87) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Wed, 13 Mar 2019 17:08:23 +0800 Received: from [10.17.3.153] (172.27.4.253) by MTKCAS32.mediatek.inc (172.27.4.170) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Wed, 13 Mar 2019 17:08:23 +0800 Message-ID: <1552468103.7433.11.camel@mhfsdcap03> Subject: Re: [PATCH 02/13] driver core: Remove the link if there is no driver with AUTO flag From: Yong Wu To: Evan Green CC: Matthias Brugger , Joerg Roedel , Greg Kroah-Hartman , "Rob Herring" , Robin Murphy , "Tomasz Figa" , Will Deacon , , , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , LKML , , , Arnd Bergmann , , , Nicolas Boichat Date: Wed, 13 Mar 2019 17:08:23 +0800 In-Reply-To: References: <1546318276-18993-1-git-send-email-yong.wu@mediatek.com> <1546318276-18993-3-git-send-email-yong.wu@mediatek.com> <1551278000.17917.50.camel@mhfsdcap03> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit MIME-Version: 1.0 X-MTK: N Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2019-03-12 at 16:17 -0700, Evan Green wrote: > On Tue, Mar 12, 2019 at 7:21 AM Matthias Brugger wrote: > > > > > > > > On 05/03/2019 20:03, Evan Green wrote: > > > On Wed, Feb 27, 2019 at 6:33 AM Yong Wu wrote: > > >> > > >> On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > > >>> On Mon, Dec 31, 2018 at 8:52 PM Yong Wu wrote: > > >>>> > > >>>> DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > >>>> automatically on consumer/supplier driver unbind", that means we should > > >>>> remove whole the device_link when there is no this driver no matter what > > >>>> the ref_count of the link is. > > >>>> > > >>>> CC: Greg Kroah-Hartman > > >>>> Signed-off-by: Yong Wu > > >>>> --- > > >>>> The ref_count of our device_link normally is over 1. When the consumer > > >>>> device driver is removed, whole the device_link should be removed. > > >>>> Thus, I add this patch. > > >>>> --- > > >>> > > >>> I will admit to reading about device links for the first time while > > >>> reviewing this patch, but I don't really get this. Why use a kref at > > >>> all if we're just going to ignore its value? For instance, I see that > > >>> if you call device_link_add() with the same supplier and consumer, it > > >>> uses the kref to return the same link. That machinery is broken with > > >>> your change. Although I don't see any uses of it, you might also > > >>> expect a supplier or consumer could do a kref_get() on the link it got > > >>> back from device_link_add(), and have a reasonable expectation that > > >>> the link wouldn't be freed out from under it. This would also be > > >>> broken. > > >>> > > >>> Can you explain why your device_links normally have a reference count > > >>>> 1, > > >> > > >> I use device link between the smi-larb device and the iommu-consumer > > >> device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this > > >> patchset, we use device_link to link the VDEC device and the smi-larb1 > > >> device in the function(mtk_iommu_config). since there are 4 ports, it > > >> will call device_link_add 4 times. > > >> > > >>> > > >>> and why those additional references can't be cleaned up in an > > >>> orderly fashion? > > >> > > >> If the iommu-consume device(like VDEC above) is removed, It should enter > > >> device_links_driver_cleanup which only ref_put one time. I guess whole > > >> the link should be removed at that time. > > > > > > It seems like Robin had some suggestions about using > > > mtk_iommu_add_device() rather than the attach_dev() to set the links > > > up, and then track them for removal in the corresponding > > > remove_device() callback. Then you wouldn't need this change, right? Hi Evan, sorry for reply you so late. I have not got time to try this(Put it in the add_device), But I guess it works. At that time the ref_cnt here should be 1, then this patch is unnecessary. > > > > > > > FYI, Evan the patch is queued for v5.1-rc1 as > > 0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO flag") > > > > So if you think there is something wrong with it, then please provide a fix or > > raise awareness :) > > Oh. Thanks for the heads-up Matthias. It's pretty weird that we have > the kref there whose count we just completely ignore. I'll try to find > some time to submit a patch. Thanks very much if you improve this. > -Evan