From patchwork Tue Dec 6 19:12:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 13066224 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 C5EF2C352A1 for ; Tue, 6 Dec 2022 19:12:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229611AbiLFTMl (ORCPT ); Tue, 6 Dec 2022 14:12:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229616AbiLFTMj (ORCPT ); Tue, 6 Dec 2022 14:12:39 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D0C73B1F; Tue, 6 Dec 2022 11:12:34 -0800 (PST) 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 56EB9B81B2A; Tue, 6 Dec 2022 19:12:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 03B3FC433D6; Tue, 6 Dec 2022 19:12:32 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.96) (envelope-from ) id 1p2dMj-0004RL-33; Tue, 06 Dec 2022 14:12:29 -0500 Message-ID: <20221206191229.813199661@goodmis.org> User-Agent: quilt/0.66 Date: Tue, 06 Dec 2022 14:12:03 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Masami Hiramatsu , Andrew Morton , Karol Herbst , Pekka Paalanen , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "Paul E. McKenney" Subject: [PATCH 2/2] x86/mm/kmmio: Remove rcu_read_lock() References: <20221206191201.217838841@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org From: Steven Rostedt The mmiotrace tracer is "special". The purpose is to help reverse engineer binary drivers by removing the memory allocated by the driver and when the driver goes to access it, a fault occurs, the mmiotracer will record what the driver was doing and then do the work on its behalf by single stepping through the process. But to achieve this ability, it must do some special things. One is it take the rcu_read_lock() when the fault occurs, and then release it in the breakpoint that in the single stepping. This makes lockdep unhappy, as it changes the state of RCU from within an exception that is not contained in that exception, and we get a nasty splat from lockdep. As it also disables preemption everywhere rcu_read_lock() is taken, and enables preemption everywhere rcu_read_unlock(), and does not enable preemption in between, it is the same as synchronize_rcu_sched(). But as the RCU sched variant has the same grace period as normal RCU, there's no reason to take the rcu_read_lock(). Simply remove it. Cc: "Paul E. McKenney" Signed-off-by: Steven Rostedt Acked-by: Paul E. McKenney --- arch/x86/mm/kmmio.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c index edb486450158..e15e3aaaf94c 100644 --- a/arch/x86/mm/kmmio.c +++ b/arch/x86/mm/kmmio.c @@ -254,7 +254,6 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr) * again. */ preempt_disable(); - rcu_read_lock(); faultpage = get_kmmio_fault_page(page_base); if (!faultpage) { @@ -323,7 +322,6 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr) return 1; /* fault handled */ no_kmmio: - rcu_read_unlock(); preempt_enable_no_resched(); return ret; } @@ -363,7 +361,6 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs) /* These were acquired in kmmio_handler(). */ ctx->active--; BUG_ON(ctx->active); - rcu_read_unlock(); preempt_enable_no_resched(); /*