From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Date: Tue, 18 Feb 2020 12:18:06 -0800 Message-ID: <20200218201806.GI2935@paulmck-ThinkPad-P72> References: <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> <20200218124609.1a33f868@gandalf.local.home> Reply-To: paulmck@kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.kernel.org ([198.145.29.99]:53236 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726384AbgBRUSH (ORCPT ); Tue, 18 Feb 2020 15:18:07 -0500 Content-Disposition: inline In-Reply-To: <20200218124609.1a33f868@gandalf.local.home> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Steven Rostedt Cc: Masami Hiramatsu , 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 On Tue, Feb 18, 2020 at 12:46:09PM -0500, Steven Rostedt wrote: > On Tue, 18 Feb 2020 13:33:35 +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. > > + */ > > > > Ah, why don't we just say... > > /* > * All functions called in the breakpoint trap handler (e.g. do_int3() > * on x86), must not allow kprobes until the kprobe breakpoint handler > * is called, otherwise it can cause an infinite recursion. > * On some archs, rcu_nmi_enter() is called in the breakpoint handler > * before the kprobe breakpoint handler is called, thus it must be > * marked as NOKPROBE. > */ > > And that way we don't make this an arch specific comment. That looks good to me. Masami, does this work for you? Thanx, Paul