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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,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 C16EEC35242 for ; Fri, 14 Feb 2020 23:40:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 95C1622314 for ; Fri, 14 Feb 2020 23:40:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581723607; bh=P3PrqY8rGU0zQljxzqKpqhR6KHKcyTeu6sKBhqLMeR8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=ZepAMrHD1jsnIVot/qoF0srxSdIR5AV+MgR9bVeJZ1qCQB8z/BIxBuk8lRlgu1cdV pVoNPK7E8jCOP//6Mt2qoWm4YLYCPYlW8XSsQlziyOc6U/bilM5nPEJFqSqcDLV3Hb 7sS6bQgi4knSpJBYTucUuAq8yhe16f+wefXixTa0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728556AbgBNXkG (ORCPT ); Fri, 14 Feb 2020 18:40:06 -0500 Received: from mail.kernel.org ([198.145.29.99]:60746 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727983AbgBNXkG (ORCPT ); Fri, 14 Feb 2020 18:40:06 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [62.84.152.189]) (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 B078E2187F; Fri, 14 Feb 2020 23:40:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581723605; bh=P3PrqY8rGU0zQljxzqKpqhR6KHKcyTeu6sKBhqLMeR8=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=ZoJanWRXUKxRt9zUSLc6Vh8940BKILbjXhvzhIxo+lsp3tVu1BmoITDnwbDD13msK 9nPdOOXLYrYeW2X/3W0U6AyO16dgv+CQf17Nk6v3T/x7j73J6uRM5wV9+U8fEpCMIh UC/QEEYqUCRQ3VUp27ocIsRIrGBtsYaKrTynr0Zo= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 4A98E3520D46; Fri, 14 Feb 2020 15:40:04 -0800 (PST) Date: Fri, 14 Feb 2020 15:40:04 -0800 From: "Paul E. McKenney" To: Marco Elver Cc: andreyknvl@google.com, glider@google.com, dvyukov@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, rostedt@goodmis.org, mingo@redhat.com, x86@kernel.org, Qian Cai Subject: Re: [PATCH v2] kcsan, trace: Make KCSAN compatible with tracing Message-ID: <20200214234004.GT2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200214211035.209972-1-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200214211035.209972-1-elver@google.com> 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 Fri, Feb 14, 2020 at 10:10:35PM +0100, Marco Elver wrote: > Previously the system would lock up if ftrace was enabled together with > KCSAN. This is due to recursion on reporting if the tracer code is > instrumented with KCSAN. > > To avoid this for all types of tracing, disable KCSAN instrumentation > for all of kernel/trace. > > Furthermore, since KCSAN relies on udelay() to introduce delay, we have > to disable ftrace for udelay() (currently done for x86) in case KCSAN is > used together with lockdep and ftrace. The reason is that it may corrupt > lockdep IRQ flags tracing state due to a peculiar case of recursion > (details in Makefile comment). > > Signed-off-by: Marco Elver > Reported-by: Qian Cai > Cc: Paul E. McKenney > Cc: Steven Rostedt Queued for review and further testing, thank you! Qian, does this also fix things for you? Thanx, Paul > --- > v2: > * Fix KCSAN+lockdep+ftrace compatibility. > --- > arch/x86/lib/Makefile | 5 +++++ > kernel/kcsan/Makefile | 2 ++ > kernel/trace/Makefile | 3 +++ > 3 files changed, 10 insertions(+) > > diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile > index 432a077056775..6110bce7237bd 100644 > --- a/arch/x86/lib/Makefile > +++ b/arch/x86/lib/Makefile > @@ -8,6 +8,11 @@ KCOV_INSTRUMENT_delay.o := n > > # KCSAN uses udelay for introducing watchpoint delay; avoid recursion. > KCSAN_SANITIZE_delay.o := n > +ifdef CONFIG_KCSAN > +# In case KCSAN+lockdep+ftrace are enabled, disable ftrace for delay.o to avoid > +# lockdep -> [other libs] -> KCSAN -> udelay -> ftrace -> lockdep recursion. > +CFLAGS_REMOVE_delay.o = $(CC_FLAGS_FTRACE) > +endif > > # Early boot use of cmdline; don't instrument it > ifdef CONFIG_AMD_MEM_ENCRYPT > diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile > index df6b7799e4927..d4999b38d1be5 100644 > --- a/kernel/kcsan/Makefile > +++ b/kernel/kcsan/Makefile > @@ -4,6 +4,8 @@ KCOV_INSTRUMENT := n > UBSAN_SANITIZE := n > > CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE) > +CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE) > +CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE) > > CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \ > $(call cc-option,-fno-stack-protector,) > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile > index f9dcd19165fa2..6b601d88bf71e 100644 > --- a/kernel/trace/Makefile > +++ b/kernel/trace/Makefile > @@ -6,6 +6,9 @@ ifdef CONFIG_FUNCTION_TRACER > ORIG_CFLAGS := $(KBUILD_CFLAGS) > KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS)) > > +# Avoid recursion due to instrumentation. > +KCSAN_SANITIZE := n > + > ifdef CONFIG_FTRACE_SELFTEST > # selftest needs instrumentation > CFLAGS_trace_selftest_dynamic.o = $(CC_FLAGS_FTRACE) > -- > 2.25.0.265.gbab2e86ba0-goog >