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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 07582C433DF for ; Thu, 21 May 2020 13:18:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC99020721 for ; Thu, 21 May 2020 13:18:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590067091; bh=ZJljZ6uIPIG3RU+2rBIuSdZVriwJ3EuVoA0eA8WQd10=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=HlsRUBWruG73r3O8e04NUkxlrMHpBPIad82mUIsTmUifhABAHtjvtAZILIH01s4W3 ctd/Pxs0De6JnDdQjUKYd710rcQkw7Vgw/fHkPUpKlV9rCfX+H9KwVCKRu+hp+RvY6 Ss6IdNopuR6RkiKGgpkd3le8vezL/rmeyE7tBHeU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729352AbgEUNSL (ORCPT ); Thu, 21 May 2020 09:18:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:57314 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727846AbgEUNSK (ORCPT ); Thu, 21 May 2020 09:18:10 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (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 B8A6B206B6; Thu, 21 May 2020 13:18:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590067089; bh=ZJljZ6uIPIG3RU+2rBIuSdZVriwJ3EuVoA0eA8WQd10=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MM5SHFs056yrBmf0QOycZMj8E/xE+B4HWHcEsMq10W3tp4EBHP8mQPZ+qgRSmg8xa l+W2c5utrU+hhQAspz1oBoWsKHc3ZPN9Ns+pRn6Nz+ig4QNZSkoHBTYrr2ZIKRpX82 zERKldt5Wuj4aOzId/i3A0kTvsLu28NuEq8c9a0I= Date: Thu, 21 May 2020 14:18:04 +0100 From: Will Deacon To: Marco Elver Cc: paulmck@kernel.org, dvyukov@google.com, glider@google.com, andreyknvl@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, clang-built-linux@googlegroups.com, bp@alien8.de Subject: Re: [PATCH -tip v2 03/11] kcsan: Support distinguishing volatile accesses Message-ID: <20200521131803.GA6608@willie-the-truck> References: <20200521110854.114437-1-elver@google.com> <20200521110854.114437-4-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200521110854.114437-4-elver@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 21, 2020 at 01:08:46PM +0200, Marco Elver wrote: > In the kernel, volatile is used in various concurrent context, whether > in low-level synchronization primitives or for legacy reasons. If > supported by the compiler, we will assume that aligned volatile accesses > up to sizeof(long long) (matching compiletime_assert_rwonce_type()) are > atomic. > > Recent versions Clang [1] (GCC tentative [2]) can instrument volatile > accesses differently. Add the option (required) to enable the > instrumentation, and provide the necessary runtime functions. None of > the updated compilers are widely available yet (Clang 11 will be the > first release to support the feature). > > [1] https://github.com/llvm/llvm-project/commit/5a2c31116f412c3b6888be361137efd705e05814 > [2] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html > > This patch allows removing any explicit checks in primitives such as > READ_ONCE() and WRITE_ONCE(). > > Signed-off-by: Marco Elver > --- > v2: > * Reword Makefile comment. > --- > kernel/kcsan/core.c | 43 ++++++++++++++++++++++++++++++++++++++++++ > scripts/Makefile.kcsan | 5 ++++- > 2 files changed, 47 insertions(+), 1 deletion(-) > > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c > index a73a66cf79df..15f67949d11e 100644 > --- a/kernel/kcsan/core.c > +++ b/kernel/kcsan/core.c > @@ -789,6 +789,49 @@ void __tsan_write_range(void *ptr, size_t size) > } > EXPORT_SYMBOL(__tsan_write_range); > > +/* > + * Use of explicit volatile is generally disallowed [1], however, volatile is > + * still used in various concurrent context, whether in low-level > + * synchronization primitives or for legacy reasons. > + * [1] https://lwn.net/Articles/233479/ > + * > + * We only consider volatile accesses atomic if they are aligned and would pass > + * the size-check of compiletime_assert_rwonce_type(). > + */ > +#define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \ > + void __tsan_volatile_read##size(void *ptr) \ > + { \ > + const bool is_atomic = size <= sizeof(long long) && \ > + IS_ALIGNED((unsigned long)ptr, size); \ > + if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ > + return; \ > + check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \ > + } \ > + EXPORT_SYMBOL(__tsan_volatile_read##size); \ > + void __tsan_unaligned_volatile_read##size(void *ptr) \ > + __alias(__tsan_volatile_read##size); \ > + EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ > + void __tsan_volatile_write##size(void *ptr) \ > + { \ > + const bool is_atomic = size <= sizeof(long long) && \ > + IS_ALIGNED((unsigned long)ptr, size); \ > + if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ > + return; \ > + check_access(ptr, size, \ > + KCSAN_ACCESS_WRITE | \ > + (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \ > + } \ > + EXPORT_SYMBOL(__tsan_volatile_write##size); \ > + void __tsan_unaligned_volatile_write##size(void *ptr) \ > + __alias(__tsan_volatile_write##size); \ > + EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) > + > +DEFINE_TSAN_VOLATILE_READ_WRITE(1); > +DEFINE_TSAN_VOLATILE_READ_WRITE(2); > +DEFINE_TSAN_VOLATILE_READ_WRITE(4); > +DEFINE_TSAN_VOLATILE_READ_WRITE(8); > +DEFINE_TSAN_VOLATILE_READ_WRITE(16); Having a 16-byte case seems a bit weird to me, but I guess clang needs this for some reason? Will