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=-9.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 3F475C43461 for ; Fri, 11 Sep 2020 11:42:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CB8BA221E7 for ; Fri, 11 Sep 2020 11:42:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="RNqqoHer" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725839AbgIKLmF (ORCPT ); Fri, 11 Sep 2020 07:42:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725779AbgIKLlt (ORCPT ); Fri, 11 Sep 2020 07:41:49 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B418C061757 for ; Fri, 11 Sep 2020 04:41:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=uGxhjmqGos/FmWn6COOVwZ2sqJ6ts5j539p0PpxlONM=; b=RNqqoHerAdj/UNFERk7iyQDLbJ wqCD50BZ13LuMybml6khgghWKGQKM4yQf9pr3CjzJ9pIk8dkNldiHC8Qtgth+8XhwOi9VNzlmspYg engVZ59087aaH7FavIOn3V/BRKidOH5YlV1idhs2cv5sexGOsmvCV6QWpNo1VejZRvclFXyIyIWIC 0jORXE8HEGjJ/XB+SmMAuXhVGCrcXM1MxVVs8f1ENbUts+pzE0aZVJPiP8dy88K2AuqsGjMfVEipV JqzP7nMhAk5hi3AIubwhjKm5tG3uz7sHm+xvBJrXrGfRW7B5ZCZYErq1g7t4jMffFhji4RJhMUhTv GGjJyNmA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kGhQu-0005gA-Gj; Fri, 11 Sep 2020 11:41:36 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id B93D73003D8; Fri, 11 Sep 2020 13:41:32 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 737382B08276B; Fri, 11 Sep 2020 13:41:32 +0200 (CEST) Date: Fri, 11 Sep 2020 13:41:32 +0200 From: peterz@infradead.org To: Adrian Hunter Cc: rostedt@goodmis.org, mingo@redhat.com, mhiramat@kernel.org, mbenes@suse.cz, linux-kernel@vger.kernel.org, Paul McKenney Subject: Re: [PATCH] ftrace: Fix missing synchronize_rcu() removing trampoline from kallsyms Message-ID: <20200911114132.GH1362448@hirez.programming.kicks-ass.net> References: <20200901091617.31837-1-adrian.hunter@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200901091617.31837-1-adrian.hunter@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 01, 2020 at 12:16:17PM +0300, Adrian Hunter wrote: > Add synchronize_rcu() after list_del_rcu() in > ftrace_remove_trampoline_from_kallsyms() to protect readers of > ftrace_ops_trampoline_list (in ftrace_get_trampoline_kallsym) > which is used when kallsyms is read. > > Fixes: fc0ea795f53c8d ("ftrace: Add symbols for ftrace trampolines") > Signed-off-by: Adrian Hunter > --- > kernel/trace/ftrace.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 275441254bb5..4e64367c9774 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -2782,6 +2782,7 @@ static void ftrace_remove_trampoline_from_kallsyms(struct ftrace_ops *ops) > { > lockdep_assert_held(&ftrace_lock); > list_del_rcu(&ops->list); > + synchronize_rcu(); > } Hurmph, we've just done a ton of that: ftrace_shutdown() synchronize_rcu_tasks_rude() ftrace_trampoline_free() ftrace_remove_trampoline_from_kallsyms() So would it not be better to move that call before the existing synchronize_rcu_tasks stuff rather than adding another synchronize_rcu() call?