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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BD63FC433F5 for ; Mon, 3 Oct 2022 12:37:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229482AbiJCMhd (ORCPT ); Mon, 3 Oct 2022 08:37:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229572AbiJCMh2 (ORCPT ); Mon, 3 Oct 2022 08:37:28 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 59BA02AE34; Mon, 3 Oct 2022 05:37:27 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 158ADB80DD6; Mon, 3 Oct 2022 12:37:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 67987C433D6; Mon, 3 Oct 2022 12:37:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664800644; bh=O3QAvL8OdjeWpq50dRv5DNuegtUnsx+x5jpFskeJUI4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=C4xclOPw1kbHF2toKSXWJ4agg3HyE0w4RO7TNYCaG0O9Aajx/jJw9A9vAlSttiYGk fPU9hsGZAnCAll2NtreE11U6a25PgUoa8ueqwWhr9yGb+PTi/OsJyMXMXJKxxtMbpN o5ReRpCHdqHPoyOCkUlh0Koa95J3TxuONhCHXNNV84YJnFBlpx7wqft61HBpPfxavV YfntqOzA2FA0Q7cF67hwzgEl16d2cRkaEFFgoD606b5xTqjjDaQlLvvtnOTWyKuIEi zfwuEunJRocm7Rjb3jxvs1DVdHWlTANf5gJgCVVlBUC0GWKxaJmq9GE7F637cERNkh Db1odr2qNVOog== Date: Mon, 3 Oct 2022 14:37:21 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, Thomas Gleixner , John Ogness , Petr Mladek Subject: Re: [PATCH RFC v2 rcu 3/8] srcu: Check for consistent per-CPU per-srcu_struct NMI safety Message-ID: <20221003123721.GA304426@lothringen> References: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1> <20220929180731.2875722-3-paulmck@kernel.org> <20221002220619.GA298433@lothringen> <20221002235103.GW4196@paulmck-ThinkPad-P17-Gen-1> <20221003101331.GA304186@lothringen> <20221003115718.GY4196@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221003115718.GY4196@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 03, 2022 at 04:57:18AM -0700, Paul E. McKenney wrote: > On Mon, Oct 03, 2022 at 12:13:31PM +0200, Frederic Weisbecker wrote: > > On Sun, Oct 02, 2022 at 04:51:03PM -0700, Paul E. McKenney wrote: > > > On Mon, Oct 03, 2022 at 12:06:19AM +0200, Frederic Weisbecker wrote: > > > > On Thu, Sep 29, 2022 at 11:07:26AM -0700, Paul E. McKenney wrote: > > > > > This commit adds runtime checks to verify that a given srcu_struct uses > > > > > consistent NMI-safe (or not) read-side primitives on a per-CPU basis. > > > > > > > > > > Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/ > > > > > > > > > > Signed-off-by: Paul E. McKenney > > > > > Cc: Thomas Gleixner > > > > > Cc: John Ogness > > > > > Cc: Petr Mladek > > > > > --- > > > > > include/linux/srcu.h | 4 ++-- > > > > > include/linux/srcutiny.h | 4 ++-- > > > > > include/linux/srcutree.h | 9 +++++++-- > > > > > kernel/rcu/srcutree.c | 38 ++++++++++++++++++++++++++++++++------ > > > > > 4 files changed, 43 insertions(+), 12 deletions(-) > > > > > > > > > > diff --git a/include/linux/srcu.h b/include/linux/srcu.h > > > > > index 2cc8321c0c86..565f60d57484 100644 > > > > > --- a/include/linux/srcu.h > > > > > +++ b/include/linux/srcu.h > > > > > @@ -180,7 +180,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp > > > > > int retval; > > > > > > > > > > if (IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) > > > > > - retval = __srcu_read_lock_nmisafe(ssp); > > > > > + retval = __srcu_read_lock_nmisafe(ssp, true); > > > > > else > > > > > retval = __srcu_read_lock(ssp); > > > > > > > > Shouldn't it be checked also when CONFIG_NEED_SRCU_NMI_SAFE=n ? > > > > > > You are asking why there is no "true" argument to __srcu_read_lock()? > > > That is because it checks unconditionally. > > > > It checks unconditionally but it always assumes not to be called as nmisafe. > > > > For example on x86/arm64/loongarch, the same ssp used with both srcu_read_lock() and > > srcu_read_lock_nmisafe() won't report an issue. But on powerpc it will. > > > > My point is that strong archs should warn as well on behalf of others, to detect > > mistakes early. > > Good point, especially given that x86_64 and arm64 are a rather large > fraction of the uses. Not critically urgent, but definitely nice to have. No indeed. > > Did you by chance have a suggestion for a nice way to accomplish this? This could be like this: enum srcu_nmi_flags { SRCU_NMI_UNKNOWN = 0x0, SRCU_NMI_UNSAFE = 0x1, SRCU_NMI_SAFE = 0x2 }; #ifdef CONFIG_NEED_SRCU_NMI_SAFE static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, enum srcu_nmi_flags flags) { int idx; struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); idx = READ_ONCE(ssp->srcu_idx) & 0x1; atomic_long_inc(&sdp->srcu_lock_count[idx]); smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical section. */ srcu_check_nmi_safety(ssp, flags); return idx; } #else static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, enum srcu_nmi_flags flags) { srcu_check_nmi_safety(ssp, flags); return __srcu_read_lock(ssp); } #endif static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) { return __srcu_read_lock_nmisafe(ssp, SRCU_NMI_SAFE); } // An __srcu_read_lock() caller in kernel/rcu/tasks.h must be // taken care of as well static inline int srcu_read_lock(struct srcu_struct *ssp) { srcu_check_nmi_safety(ssp, SRCU_NMI_UNSAFE); return __srcu_read_lock(ssp); } And then you can call __srcu_read_lock_nmisafe(ssp, SRCU_NMI_UNKNOWN) from initializers of gp.