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,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 55BFAC1975A for ; Thu, 12 Mar 2020 18:04:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2CDD9206B1 for ; Thu, 12 Mar 2020 18:04:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584036257; bh=3ebw41AAR7jI7zrpwYlbI0uq+8obGDWDf1Wk8w7lo2I=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=XUj6GY0qMn/kKZT2dpBCrzNn5b+vOax0dw3uxC1ypFV0kqeK9ohhEPjgl9KXCjgRQ wTQNV9CuYYGbb3RrdCCF+Fm8xnsnrZ+GlfG/xoHiK18a7BIJ0SYOAcLLwnzzboWLdS i3DsQ+FiyZNh0hTzNc91EGCOVNiaJ51GRrXJYY+g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726513AbgCLSEQ (ORCPT ); Thu, 12 Mar 2020 14:04:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:49934 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbgCLSEP (ORCPT ); Thu, 12 Mar 2020 14:04:15 -0400 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 C54BB20663; Thu, 12 Mar 2020 18:04:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584036254; bh=3ebw41AAR7jI7zrpwYlbI0uq+8obGDWDf1Wk8w7lo2I=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=YCrpA8y6jsj2G11HLAf/BGvq/T4nIdgUaGy7cYtXTezOk0/nXGNWM5pZCSizozQlJ xo68a7VfZsVBRCkpRssDwlT1sTjeI8Mq6ezhW8d0PLjWBYXx7McqnGnxH4tuquNEIE wx4ohNlFML2QVuuE5pRQP4ZJ1fSFzqnU05rg44Ss= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id A0F9435226D0; Thu, 12 Mar 2020 11:04:14 -0700 (PDT) Date: Thu, 12 Mar 2020 11:04:14 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, kernel-team@fb.com, mingo@kernel.org Cc: elver@google.com, andreyknvl@google.com, glider@google.com, dvyukov@google.com, cai@lca.pw, boqun.feng@gmail.com Subject: Re: [PATCH kcsan 27/32] kcsan: Add option to allow watcher interruptions Message-ID: <20200312180414.GA8024@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200309190359.GA5822@paulmck-ThinkPad-P72> <20200309190420.6100-27-paulmck@kernel.org> <20200312180328.GA4772@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200312180328.GA4772@paulmck-ThinkPad-P72> 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 Thu, Mar 12, 2020 at 11:03:28AM -0700, Paul E. McKenney wrote: > On Mon, Mar 09, 2020 at 12:04:15PM -0700, paulmck@kernel.org wrote: > > From: Marco Elver > > > > Add option to allow interrupts while a watchpoint is set up. This can be > > enabled either via CONFIG_KCSAN_INTERRUPT_WATCHER or via the boot > > parameter 'kcsan.interrupt_watcher=1'. > > > > Note that, currently not all safe per-CPU access primitives and patterns > > are accounted for, which could result in false positives. For example, > > asm-generic/percpu.h uses plain operations, which by default are > > instrumented. On interrupts and subsequent accesses to the same > > variable, KCSAN would currently report a data race with this option. > > > > Therefore, this option should currently remain disabled by default, but > > may be enabled for specific test scenarios. > > > > To avoid new warnings, changes all uses of smp_processor_id() to use the > > raw version (as already done in kcsan_found_watchpoint()). The exact SMP > > processor id is for informational purposes in the report, and > > correctness is not affected. > > > > Signed-off-by: Marco Elver > > Signed-off-by: Paul E. McKenney > > And I get silent hangs that bisect to this patch when running the > following rcutorture command, run in the kernel source tree on a > 12-hardware-thread laptop: > > bash tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 12 --duration 10 --kconfig "CONFIG_DEBUG_INFO=y CONFIG_KCSAN=y CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC=n CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000 CONFIG_KCSAN_VERBOSE=y CONFIG_KCSAN_INTERRUPT_WATCHER=y" --configs TREE03 > > It works fine on some (but not all) of the other rcutorture test > scenarios. It fails on TREE01, TREE02, TREE03, TREE09. The common thread > is that these are the TREE scenarios are all PREEMPT=y. So are RUDE01, > SRCU-P, TASKS01, and TASKS03, but these scenarios are not hammering > on Tree RCU, and thus have far less interrupt activity and the like. > Given that it is an interrupt-related feature being added by this commit, > this seems like expected (mis)behavior. > > Can you reproduce this? If not, are there any diagnostics I can add to > my testing? Or a diagnostic patch I could apply? I should hasten to add that this feature was quite helpful in recent work! Thanx, Paul