From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Date: Tue, 18 Feb 2020 11:15:30 -0500 (EST) Message-ID: <1841874582.7975.1582042530726.JavaMail.zimbra@efficios.com> References: <20200213211930.GG170680@google.com> <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> <20200218161231.GD2935@paulmck-ThinkPad-P72> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Received: from mail.efficios.com ([167.114.26.124]:42580 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726360AbgBRQPc (ORCPT ); Tue, 18 Feb 2020 11:15:32 -0500 In-Reply-To: <20200218161231.GD2935@paulmck-ThinkPad-P72> Sender: linux-arch-owner@vger.kernel.org List-ID: To: paulmck , Masami Hiramatsu Cc: rostedt , "Joel Fernandes, Google" , Peter Zijlstra , linux-kernel , linux-arch , Ingo Molnar , Greg Kroah-Hartman , "Gustavo A. R. Silva" , Thomas Gleixner , Josh Triplett , Lai Jiangshan ----- On Feb 18, 2020, at 11:12 AM, paulmck paulmck@kernel.org wrote: > 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. ;-) I suspect this kind of comment would belong in a new Documentation/features/kprobes/annotations.txt or something similar. You might want to look at other "features" files to see the expected layout. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com