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, 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 0FDC2C34026 for ; Tue, 18 Feb 2020 16:12:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C708C24649 for ; Tue, 18 Feb 2020 16:12:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582042353; bh=awLNWgK3jSpoYCcHsbDIpFWZ3TfC+77EIQEyj8YiqW0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=w5EZ3s7CsZ+Jk2OJZhukN2MJJCZFdLgVO5w+luKtMVidm3VVBQ1R9iWHga0nBPR5A VXL8KISjtrLF4kw8yxSWdpFCrsCLNTPyeiCaPwh24wyV2+7Jwqwzzd9k1+d/T5k9AG o5RrturLRogmk0GmTqBBxNqhSo0bMOtfHhwHEfxY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726681AbgBRQMc (ORCPT ); Tue, 18 Feb 2020 11:12:32 -0500 Received: from mail.kernel.org ([198.145.29.99]:48756 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726411AbgBRQMc (ORCPT ); Tue, 18 Feb 2020 11:12:32 -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 7EDB821D56; Tue, 18 Feb 2020 16:12:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582042351; bh=awLNWgK3jSpoYCcHsbDIpFWZ3TfC+77EIQEyj8YiqW0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=0X7a46sIOjECzRz0gSgsb45lVTD4LoFMqM8lAfqw5BBMjeunTIzosKnnh8wvwOgmn dw1c7kHiv4rK+byDki53gflxLqjmyJwI0xy2GTrvm88GH9/2CTmZIfyfhZOwUmQG1E e9w4sDNTWeU7FtqiUtCsTrU+lkaMLAEg8LsZnMpY= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4A93D3520365; Tue, 18 Feb 2020 08:12:31 -0800 (PST) Date: Tue, 18 Feb 2020 08:12:31 -0800 From: "Paul E. McKenney" To: Masami Hiramatsu Cc: Steven Rostedt , Joel Fernandes , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Message-ID: <20200218161231.GD2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200213211930.GG170680@google.com> <20200213163800.5c51a5f1@gandalf.local.home> <20200213215004.GM2935@paulmck-ThinkPad-P72> <20200213170451.690c4e5c@gandalf.local.home> <20200213223918.GN2935@paulmck-ThinkPad-P72> <20200214151906.b1354a7ed6b01fc3bf2de862@kernel.org> <20200215145934.GD2935@paulmck-ThinkPad-P72> <20200217175519.12a694a969c1a8fb2e49905e@kernel.org> <20200217163112.GM2935@paulmck-ThinkPad-P72> <20200218133335.c87d7b2399ee6532bf28b74a@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218133335.c87d7b2399ee6532bf28b74a@kernel.org> 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 Tue, Feb 18, 2020 at 01:33:35PM +0900, Masami Hiramatsu wrote: > On Mon, 17 Feb 2020 08:31:12 -0800 > "Paul E. McKenney" wrote: > > > > > BTW, if you consider the x86 specific code is in the generic file, > > > we can move NOKPROBE_SYMBOL() in arch/x86/kernel/traps.c. > > > (Sorry, I've hit this idea right now) > > > > Might this affect other architectures with NMIs and probe-like things? > > If so, it might make sense to leave it where it is. > > Yes, git grep shows that arm64 is using rcu_nmi_enter() in > debug_exception_enter(). > OK, let's keep it, but maybe it is good to update the comment for > arm64 too. What about following? > > +/* > + * All functions in do_int3() on x86, do_debug_exception() on arm64 must be > + * marked NOKPROBE before kprobes handler is called. > + * ist_enter() on x86 and debug_exception_enter() on arm64 which is called > + * before kprobes handle happens to call rcu_nmi_enter() which means > + * that rcu_nmi_enter() must be marked NOKRPOBE. > + */ Would it work to describe the general problem, then give x86 details as a specific example, as follows? /* * On some architectures, certain exceptions prohibit use of kprobes until * the exception code path reaches a certain point. For example, on x86 all * functions called by do_int3() must be marked NOKPROBE. However, once * kprobe_int3_handler() is called, kprobing is permitted. Specifically, * ist_enter() is called in do_int3() before kprobe_int3_handle(). * Furthermore, ist_enter() calls rcu_nmi_enter(), which means that * rcu_nmi_enter() must be marked NOKRPOBE. */ That way, I don't feel like I need to update the commment each time a new architecture adds this capability. ;-) Thanx, Paul