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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 0AF4FC433E5 for ; Thu, 25 Mar 2021 01:22:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C4CA861A1A for ; Thu, 25 Mar 2021 01:22:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239621AbhCYBWB (ORCPT ); Wed, 24 Mar 2021 21:22:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:53094 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239566AbhCYBVN (ORCPT ); Wed, 24 Mar 2021 21:21:13 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4596E61A14; Thu, 25 Mar 2021 01:20:19 +0000 (UTC) Date: Wed, 24 Mar 2021 21:20:17 -0400 From: Steven Rostedt To: Li Huafei Cc: , , , , , Subject: Re: [PATCH 1/2] ftrace: Update ftrace_ops->next pointer with rcu_assign_pointer() Message-ID: <20210324212017.0cd11e7e@oasis.local.home> In-Reply-To: <20210317102529.226734-2-lihuafei1@huawei.com> References: <20210317102529.226734-1-lihuafei1@huawei.com> <20210317102529.226734-2-lihuafei1@huawei.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 17 Mar 2021 18:25:28 +0800 Li Huafei wrote: > The unregistered ftrace_ops may be freed by the caller, so we should use > rcu_assign_pointer() in remove_ftrace_ops() to remove the ftrace_ops, > which ensures that no more users will reference the ftrace_ops after > synchronize_rcu() is called. The patch is fine, but we don't use synchronize_rcu() to protect the list. We use synchronize_rcu_tasks(). -- Steve > > Signed-off-by: Li Huafei > --- > kernel/trace/ftrace.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 4d8e35575549..2e315a145d20 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -282,7 +282,7 @@ static int remove_ftrace_ops(struct ftrace_ops __rcu **list, > lockdep_is_held(&ftrace_lock)) == ops && > rcu_dereference_protected(ops->next, > lockdep_is_held(&ftrace_lock)) == &ftrace_list_end) { > - *list = &ftrace_list_end; > + rcu_assign_pointer(*list, &ftrace_list_end); > return 0; > } > > @@ -293,7 +293,7 @@ static int remove_ftrace_ops(struct ftrace_ops __rcu **list, > if (*p != ops) > return -1; > > - *p = (*p)->next; > + rcu_assign_pointer(*p, (*p)->next); > return 0; > } >