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=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 2BB39C18E5B for ; Tue, 10 Mar 2020 13:41:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 06A3C20663 for ; Tue, 10 Mar 2020 13:41:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=st.com header.i=@st.com header.b="I5UdkSdO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726952AbgCJNlN (ORCPT ); Tue, 10 Mar 2020 09:41:13 -0400 Received: from mx08-00178001.pphosted.com ([91.207.212.93]:21320 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726508AbgCJNlM (ORCPT ); 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Tue, 10 Mar 2020 14:41:06 +0100 Received: from euls16034.sgp.st.com (euls16034.sgp.st.com [10.75.44.20]) by beta.dmz-eu.st.com (STMicroelectronics) with ESMTP id E0836100038; Tue, 10 Mar 2020 14:41:01 +0100 (CET) Received: from Webmail-eu.st.com (sfhdag3node1.st.com [10.75.127.7]) by euls16034.sgp.st.com (STMicroelectronics) with ESMTP id CAC172B2B65; Tue, 10 Mar 2020 14:41:01 +0100 (CET) Received: from lmecxl0889.lme.st.com (10.75.127.44) by SFHDAG3NODE1.st.com (10.75.127.7) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 10 Mar 2020 14:41:00 +0100 Subject: Re: [PATCH v4 1/4] remoteproc: Traverse rproc_list under RCU read lock To: Bjorn Andersson , Andy Gross , Ohad Ben-Cohen CC: , , , Mathieu Poirier References: <20200310063817.3344712-1-bjorn.andersson@linaro.org> <20200310063817.3344712-2-bjorn.andersson@linaro.org> From: Arnaud POULIQUEN Message-ID: <87a14705-186d-01a4-e8a5-1844dab4ea14@st.com> Date: Tue, 10 Mar 2020 14:41:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200310063817.3344712-2-bjorn.andersson@linaro.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.75.127.44] X-ClientProxiedBy: SFHDAG6NODE2.st.com (10.75.127.17) To SFHDAG3NODE1.st.com (10.75.127.7) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-03-10_07:2020-03-10,2020-03-10 signatures=0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Bjorn, On 3/10/20 7:38 AM, Bjorn Andersson wrote: > In order to be able to traverse the mostly read-only rproc_list without > locking during panic migrate traversal to be done under rcu_read_lock(). > > Mutual exclusion for modifications of the list continues to be handled > by the rproc_list_mutex and a synchronization point is added before > releasing objects that are popped from the list. > > Signed-off-by: Bjorn Andersson > --- > > Change v3: > - New patch > > drivers/remoteproc/remoteproc_core.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c > index 097f33e4f1f3..f0a77c30c6b1 100644 > --- a/drivers/remoteproc/remoteproc_core.c > +++ b/drivers/remoteproc/remoteproc_core.c > @@ -1854,8 +1854,8 @@ struct rproc *rproc_get_by_phandle(phandle phandle) > if (!np) > return NULL; > > - mutex_lock(&rproc_list_mutex); > - list_for_each_entry(r, &rproc_list, node) { > + rcu_read_lock(); > + list_for_each_entry_rcu(r, &rproc_list, node) { > if (r->dev.parent && r->dev.parent->of_node == np) { > /* prevent underlying implementation from being removed */ > if (!try_module_get(r->dev.parent->driver->owner)) { > @@ -1868,7 +1868,7 @@ struct rproc *rproc_get_by_phandle(phandle phandle) > break; > } > } > - mutex_unlock(&rproc_list_mutex); > + rcu_read_unlock(); > > of_node_put(np); > > @@ -1925,7 +1925,7 @@ int rproc_add(struct rproc *rproc) > > /* expose to rproc_get_by_phandle users */ > mutex_lock(&rproc_list_mutex); > - list_add(&rproc->node, &rproc_list); > + list_add_rcu(&rproc->node, &rproc_list); > mutex_unlock(&rproc_list_mutex); > > return 0; > @@ -2140,9 +2140,12 @@ int rproc_del(struct rproc *rproc) > > /* the rproc is downref'ed as soon as it's removed from the klist */ > mutex_lock(&rproc_list_mutex); > - list_del(&rproc->node); > + list_del_rcu(&rproc->node); > mutex_unlock(&rproc_list_mutex); i'm not familiar with rcu but as rproc_panic_handler can be called in interrupt context, does mutex should be replaced by a spinlock? Regards, Arnaud > > + /* Ensure that no readers of rproc_list are still active */ > + synchronize_rcu(); > + > device_del(&rproc->dev); > > return 0; >