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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 415BAC35254 for ; Wed, 5 Feb 2020 13:19:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1C9BD217F4 for ; Wed, 5 Feb 2020 13:19:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728052AbgBENT2 (ORCPT ); Wed, 5 Feb 2020 08:19:28 -0500 Received: from mail.kernel.org ([198.145.29.99]:36672 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726822AbgBENT2 (ORCPT ); Wed, 5 Feb 2020 08:19:28 -0500 Received: from oasis.local.home (unknown [212.187.182.165]) (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 D349A217BA; Wed, 5 Feb 2020 13:19:25 +0000 (UTC) Date: Wed, 5 Feb 2020 08:19:21 -0500 From: Steven Rostedt To: "Paul E. McKenney" Cc: Joel Fernandes , Amol Grover , Ingo Molnar , linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, Madhuparna Bhowmik Subject: Re: [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu Message-ID: <20200205081921.34b19d9a@oasis.local.home> In-Reply-To: <20200205081409.4550aa67@oasis.local.home> References: <20200201072703.17330-1-frextrite@gmail.com> <20200203163301.GB85781@google.com> <20200204200116.479f0c60@oasis.local.home> <20200205131110.GT2935@paulmck-ThinkPad-P72> <20200205081409.4550aa67@oasis.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 5 Feb 2020 08:14:09 -0500 Steven Rostedt wrote: > On Wed, 5 Feb 2020 05:11:10 -0800 > "Paul E. McKenney" wrote: > > > I strongly recommend a comment stating why disabling preemption prevents > > ftrace_graph_hash from going away. I see the synchronize_rcu() after > > the rcu_assign_pointer() in ftrace_graph_release(), but I don't see > > anything that waits on CPUs that RCU is not watching. > > > > Of course, event tracing -makes- RCU watch when needed, but if that > > was set up, then lockdep would not have complained. > > > > So what am I missing? > > Keep looking in your INBOX and look at the patch I asked you to ack or > complain about ;-) Actually, looking at the code myself, it appears to be missing the ftrace_sync. Thus, this is a bug, and requires the ftrace sync, as synchronize_rcu() is not strong enough here. Patch in process! -- Steve 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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 13CB9C35254 for ; Wed, 5 Feb 2020 13:19:32 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CE578217BA for ; Wed, 5 Feb 2020 13:19:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CE578217BA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linux-kernel-mentees-bounces@lists.linuxfoundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id B09EB8783F; Wed, 5 Feb 2020 13:19:31 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 4vgQG+dLHY-3; Wed, 5 Feb 2020 13:19:29 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id B1E8A874BA; Wed, 5 Feb 2020 13:19:29 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id A4E14C0175; Wed, 5 Feb 2020 13:19:29 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 86F20C0174 for ; Wed, 5 Feb 2020 13:19:28 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 6F1F6816F9 for ; Wed, 5 Feb 2020 13:19:28 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id EqIlozHKo5QG for ; Wed, 5 Feb 2020 13:19:27 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by whitealder.osuosl.org (Postfix) with ESMTPS id B0ECF816D2 for ; Wed, 5 Feb 2020 13:19:27 +0000 (UTC) Received: from oasis.local.home (unknown [212.187.182.165]) (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 D349A217BA; Wed, 5 Feb 2020 13:19:25 +0000 (UTC) Date: Wed, 5 Feb 2020 08:19:21 -0500 From: Steven Rostedt To: "Paul E. McKenney" Message-ID: <20200205081921.34b19d9a@oasis.local.home> In-Reply-To: <20200205081409.4550aa67@oasis.local.home> References: <20200201072703.17330-1-frextrite@gmail.com> <20200203163301.GB85781@google.com> <20200204200116.479f0c60@oasis.local.home> <20200205131110.GT2935@paulmck-ThinkPad-P72> <20200205081409.4550aa67@oasis.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Cc: linux-kernel@vger.kernel.org, Madhuparna Bhowmik , Ingo Molnar , Joel Fernandes , linux-kernel-mentees@lists.linuxfoundation.org Subject: Re: [Linux-kernel-mentees] [PATCH] tracing: Annotate ftrace_graph_hash pointer with __rcu X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Sender: "Linux-kernel-mentees" On Wed, 5 Feb 2020 08:14:09 -0500 Steven Rostedt wrote: > On Wed, 5 Feb 2020 05:11:10 -0800 > "Paul E. McKenney" wrote: > > > I strongly recommend a comment stating why disabling preemption prevents > > ftrace_graph_hash from going away. I see the synchronize_rcu() after > > the rcu_assign_pointer() in ftrace_graph_release(), but I don't see > > anything that waits on CPUs that RCU is not watching. > > > > Of course, event tracing -makes- RCU watch when needed, but if that > > was set up, then lockdep would not have complained. > > > > So what am I missing? > > Keep looking in your INBOX and look at the patch I asked you to ack or > complain about ;-) Actually, looking at the code myself, it appears to be missing the ftrace_sync. Thus, this is a bug, and requires the ftrace sync, as synchronize_rcu() is not strong enough here. Patch in process! -- Steve _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees