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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 4F478C35254 for ; Wed, 5 Feb 2020 13:29:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E2CB217F4 for ; Wed, 5 Feb 2020 13:29:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580909362; bh=q3GH23a1FDWaFVRhUTNliOpuwo1wF6ZsFejI9M8tSQ0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=iDiD3I+EHv6yueiF57DhJ/V/MG3Q54ZE23cUx/uLCuMN+SRervNjaDMkDVTrJxsm9 0BmN86Vr4cDO8ZQWxYu+rs0VjDuPEibgD+BWiTFR+M977Ju4I6h3Q+iaHMh9JS7XZ6 Y94GMo4yh//LJhemDHC+Xqb2g4lnAD8Zu4kdTMHI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727561AbgBEN3V (ORCPT ); Wed, 5 Feb 2020 08:29:21 -0500 Received: from mail.kernel.org ([198.145.29.99]:40144 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726748AbgBEN3U (ORCPT ); Wed, 5 Feb 2020 08:29:20 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 0FB7F2072B; Wed, 5 Feb 2020 13:29:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580909360; bh=q3GH23a1FDWaFVRhUTNliOpuwo1wF6ZsFejI9M8tSQ0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=ofwCmh1sIX/qbPu2BPDWAM8+n1bBJRtfpk57yQ5E3gpnTb1ouvryIAWv1mX68b7+V asnILCtTNG4d18fkKGdPX0/wEEH9JMoUTOeLLVzuWrJ4NExqkhMf2bNqoCf0SNipV1 0qXXPXGEiLt76+qPSL7164BVlu3fifDR8dPG4HNc= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id D16FD35227F3; Wed, 5 Feb 2020 05:29:19 -0800 (PST) Date: Wed, 5 Feb 2020 05:29:19 -0800 From: "Paul E. McKenney" To: Steven Rostedt 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: <20200205132919.GU2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org 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> <20200205081921.34b19d9a@oasis.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200205081921.34b19d9a@oasis.local.home> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 05, 2020 at 08:19:21AM -0500, Steven Rostedt wrote: > 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 ;-) Not yet seeing it, but... > 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! Thank you for chasing it down! Thanx, Paul