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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 C3895C34056 for ; Wed, 19 Feb 2020 17:42:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9CA9120801 for ; Wed, 19 Feb 2020 17:42:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582134133; bh=vIgg2+36Ua5x8HLBjl9/8lcExSUzV+uuuacH+jPaAXU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=WQxh5vU2YrVdxdSRdTwkZ2bgV0+ci+QnzbO9164VMkjn4lGBoo3dZLhR1NLsGPMlD nxuf1j0aCmLeeyi583OKt7DoSWgsI2Ta7uFoe0HaX4wa/JtobpprGGeGsbLfT5lQiD FtLVKjlANS8+oyb3y/+pjSR5TfuxXslmdFVtaljk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726683AbgBSRmM (ORCPT ); Wed, 19 Feb 2020 12:42:12 -0500 Received: from mail.kernel.org ([198.145.29.99]:48352 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726518AbgBSRmM (ORCPT ); Wed, 19 Feb 2020 12:42:12 -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 33950206DB; Wed, 19 Feb 2020 17:42:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582134131; bh=vIgg2+36Ua5x8HLBjl9/8lcExSUzV+uuuacH+jPaAXU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=nAIpKrpFowh8AD0faMeogIAyLpP8hxzgnzmFYS81QqfDCsn+lJvzjeUAE0wD8YPsu c+gcGvF4qhq+TM2ofGgTVpgDlhogxD1pEPMSa8mId/A0cP+wHbiEzpKWUFOZDcJf4V K1IiVYU1t6nm2uPfnXU4/iGlfM2i03Ngxmut/IAw= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 0FCBF35209B0; Wed, 19 Feb 2020 09:42:11 -0800 (PST) Date: Wed, 19 Feb 2020 09:42:11 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org Subject: Re: [PATCH v3 05/22] rcu: Make RCU IRQ enter/exit functions rely on in_nmi() Message-ID: <20200219174211.GL2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200219144724.800607165@infradead.org> <20200219150744.661923520@infradead.org> <20200219163156.GY2935@paulmck-ThinkPad-P72> <20200219163700.GK18400@hirez.programming.kicks-ass.net> <20200219170304.GG14946@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200219170304.GG14946@hirez.programming.kicks-ass.net> 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 19, 2020 at 06:03:04PM +0100, Peter Zijlstra wrote: > On Wed, Feb 19, 2020 at 05:37:00PM +0100, Peter Zijlstra wrote: > > On Wed, Feb 19, 2020 at 08:31:56AM -0800, Paul E. McKenney wrote: > > > > Here is the latest version of that comment, posted by Steve Rostedt. > > > > > > Thanx, Paul > > > > > > /* > > > * 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. > > > */ > > > > Oh right, let me stick that in a separate patch. Best we not loose that > > I suppose ;-) > > Having gone over the old thread, I ended up with the below. Anyone > holler if I got it wrong somehow. Looks good to me! Thanx, Paul > --- > Subject: rcu: Provide comment for NOKPROBE() on rcu_nmi_enter() > From: Steven Rostedt > > From: Steven Rostedt > > The rcu_nmi_enter() function was marked NOKPROBE() by commit > c13324a505c77 ("x86/kprobes: Prohibit probing on functions before > kprobe_int3_handler()") because the do_int3() call kprobe code must > not be invoked before kprobe_int3_handler() is called. It turns out > that ist_enter() (in do_int3()) calls rcu_nmi_enter(), hence the > marking NOKPROBE() being added to rcu_nmi_enter(). > > This commit therefore adds a comment documenting this line of > reasoning. > > Signed-off-by: Steven Rostedt > Reviewed-by: Masami Hiramatsu > Signed-off-by: Paul E. McKenney > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/rcu/tree.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -842,6 +842,14 @@ void rcu_nmi_enter(void) > { > rcu_nmi_enter_common(false); > } > +/* > + * 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. > + */ > NOKPROBE_SYMBOL(rcu_nmi_enter); > > /**