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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 8E31EC3F2D2 for ; Fri, 28 Feb 2020 11:49:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B79E246AA for ; Fri, 28 Feb 2020 11:49:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726579AbgB1LtF (ORCPT ); Fri, 28 Feb 2020 06:49:05 -0500 Received: from lhrrgout.huawei.com ([185.176.76.210]:2478 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725536AbgB1LtF (ORCPT ); Fri, 28 Feb 2020 06:49:05 -0500 Received: from lhreml709-cah.china.huawei.com (unknown [172.18.7.108]) by Forcepoint Email with ESMTP id 3EA0F548ADD1CC5E62CD; Fri, 28 Feb 2020 11:49:03 +0000 (GMT) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by lhreml709-cah.china.huawei.com (10.201.108.32) with Microsoft SMTP Server (TLS) id 14.3.408.0; Fri, 28 Feb 2020 11:49:02 +0000 Received: from [127.0.0.1] (10.202.226.45) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.1713.5; Fri, 28 Feb 2020 11:49:02 +0000 Subject: Re: [PATCH] ipmi: Fix RCU list lockdep debugging warnings To: Amol Grover , Corey Minyard , "Arnd Bergmann" , Greg Kroah-Hartman CC: , , , Joel Fernandes , Madhuparna Bhowmik , "Paul E . Mckenney" References: <20200228081731.18149-1-frextrite@gmail.com> From: John Garry Message-ID: Date: Fri, 28 Feb 2020 11:49:01 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <20200228081731.18149-1-frextrite@gmail.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.202.226.45] X-ClientProxiedBy: lhreml708-chm.china.huawei.com (10.201.108.57) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/02/2020 08:17, Amol Grover wrote: > It is completely safe to traverse ipmi_interfaces and > intf->users under SRCU read lock using list_for_each_entry_rcu(). > Tell lockdep about it as well else it will show false-positive > warnings as the one below. > > Fixes the following false-positive warning and others that may follow. > > [ 29.772408] ============================= > [ 29.776863] WARNING: suspicious RCU usage > [ 29.780915] 5.6.0-rc3-00001-g907305ae6618-dirty #1755 Not tainted > [ 29.787046] ----------------------------- > [ 29.791100] drivers/char/ipmi/ipmi_msghandler.c:744 RCU-list traversed in > non-reader section!! > > Reported-by: John Garry > Suggested-by: Paul E. McKenney > Signed-off-by: Amol Grover Tested-by: John Garry Thanks, the warnings have gone away with this > --- > drivers/char/ipmi/ipmi_msghandler.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c > index cad9563f8f48..d202022c69de 100644 > --- a/drivers/char/ipmi/ipmi_msghandler.c > +++ b/drivers/char/ipmi/ipmi_msghandler.c > @@ -741,7 +741,8 @@ int ipmi_smi_watcher_register(struct ipmi_smi_watcher *watcher) > list_add(&watcher->link, &smi_watchers); > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > int intf_num = READ_ONCE(intf->intf_num); > > if (intf_num == -1) > @@ -1188,7 +1189,8 @@ int ipmi_create_user(unsigned int if_num, > return -ENOMEM; > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > if (intf->intf_num == if_num) > goto found; > } > @@ -1241,7 +1243,8 @@ int ipmi_get_smi_info(int if_num, struct ipmi_smi_info *data) > struct ipmi_smi *intf; > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > if (intf->intf_num == if_num) > goto found; > } > @@ -4098,7 +4101,8 @@ static int handle_read_event_rsp(struct ipmi_smi *intf, > * getting events. > */ > index = srcu_read_lock(&intf->users_srcu); > - list_for_each_entry_rcu(user, &intf->users, link) { > + list_for_each_entry_rcu(user, &intf->users, link, > + srcu_read_lock_held(&intf->users_srcu)) { > if (!user->gets_events) > continue; > > @@ -4453,7 +4457,8 @@ static void handle_new_recv_msgs(struct ipmi_smi *intf) > int index; > > index = srcu_read_lock(&intf->users_srcu); > - list_for_each_entry_rcu(user, &intf->users, link) { > + list_for_each_entry_rcu(user, &intf->users, link, > + srcu_read_lock_held(&intf->users_srcu)) { > if (user->handler->ipmi_watchdog_pretimeout) > user->handler->ipmi_watchdog_pretimeout( > user->handler_data); > @@ -4746,7 +4751,8 @@ static void ipmi_timeout(struct timer_list *unused) > return; > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > if (atomic_read(&intf->event_waiters)) { > intf->ticks_to_req_ev--; > if (intf->ticks_to_req_ev == 0) { >