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 44F80C43217 for ; Tue, 30 Nov 2021 11:47:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241180AbhK3LvG (ORCPT ); Tue, 30 Nov 2021 06:51:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45310 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241153AbhK3Ltj (ORCPT ); Tue, 30 Nov 2021 06:49:39 -0500 Received: from mail-wm1-x349.google.com (mail-wm1-x349.google.com [IPv6:2a00:1450:4864:20::349]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E9DD3C061757 for ; Tue, 30 Nov 2021 03:45:55 -0800 (PST) Received: by mail-wm1-x349.google.com with SMTP id g80-20020a1c2053000000b003331a764709so13625506wmg.2 for ; Tue, 30 Nov 2021 03:45:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=SnYVQxLC6YSHg0QBspCa3KEICf+BvvptqJyS2cHTmDQ=; b=YAPrqaSvFXPKIyChd2B9G/mC+V4Jc4D9Ysa+dt9+gyWoCPV+nRINqJd57Duo402ra3 fACCmxrugjWDUChLO48YEakWmtgKIBS2NenkgfzdEIUaFeOLMeRRLt3y3O0O8m42KVyP EYZTlGjECGMCo3XeJTyzQ9huKYBCMEUzAAG6gZ+6TrfzQbi+hkq/C1sNW9Osl71l2q00 KnvJkh1XBMAWo2p+iVXz1ZScDqJ9cYV8qalOkG24HTG/65Ii8z7IiAdL8qvRMC2Opkvc XOyIIRR2dMM8QMdcIa4mT34J5n4EmvIPm98FB4otkGxOdejNKSt9f8kvehv1Vt3mjuJX t2wA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=SnYVQxLC6YSHg0QBspCa3KEICf+BvvptqJyS2cHTmDQ=; b=FAe8YUyoHlXAo3KhtU2ycqDGP4QiFGt4iuQ7B6e0ymDRGstc2RI40IL5IGOHkUfnOi WEeVwb9GXuSrA3nsJG5TDkcWpCqjzPx/CdKKSKZDW3i80omBLWUqeyl2rwdCGNgFByfZ Xzk3suJX4eezSCP2dMmPIejNrpFMqGXp+Eq8o501BF6mgibYnC8txDfAwwCStXV84ouO bmJ4x0NcRKVBCNdolGXr5nFKRmC9fScb5Wuz9VNrLDnLBRoQO4Y9PsBvl3z42OHPg5eE CPLwArZ3JUX1ibhrmLCK3vEADFqy/6eT7Zvfu8dygAMlpMAjJnvdsLCp2sZmTDZOAYmW ek3A== X-Gm-Message-State: AOAM530k7NWyp4TjTIyWZ61GHyYtITo1nwhiajP0++VdgyGzfduKxx8n DyrcNcsTe1DpYCuZgSaEcbnc0BViOw== X-Google-Smtp-Source: ABdhPJy3VXvdk8vo/XrXiDkU+BIk+TJTbB/pqh504ouz3u8/5fsbp+KQ9JgMbQcOudhStkssJotFYNwe1A== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:86b7:11e9:7797:99f0]) (user=elver job=sendgmr) by 2002:a05:600c:4f0b:: with SMTP id l11mr626057wmq.0.1638272754116; Tue, 30 Nov 2021 03:45:54 -0800 (PST) Date: Tue, 30 Nov 2021 12:44:29 +0100 In-Reply-To: <20211130114433.2580590-1-elver@google.com> Message-Id: <20211130114433.2580590-22-elver@google.com> Mime-Version: 1.0 References: <20211130114433.2580590-1-elver@google.com> X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH v3 21/25] sched, kcsan: Enable memory barrier instrumentation From: Marco Elver To: elver@google.com, "Paul E. McKenney" Cc: Alexander Potapenko , Boqun Feng , Borislav Petkov , Dmitry Vyukov , Ingo Molnar , Mark Rutland , Peter Zijlstra , Thomas Gleixner , Waiman Long , Will Deacon , kasan-dev@googlegroups.com, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, x86@kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org There's no fundamental reason to disable KCSAN for scheduler code, except for excessive noise and performance concerns (instrumenting scheduler code is usually a good way to stress test KCSAN itself). However, several core sched functions imply memory barriers that are invisible to KCSAN without instrumentation, but are required to avoid false positives. Therefore, unconditionally enable instrumentation of memory barriers in scheduler code. Also update the comment to reflect this and be a bit more brief. Signed-off-by: Marco Elver --- kernel/sched/Makefile | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile index c7421f2d05e1..c83b37af155b 100644 --- a/kernel/sched/Makefile +++ b/kernel/sched/Makefile @@ -11,11 +11,10 @@ ccflags-y += $(call cc-disable-warning, unused-but-set-variable) # that is not a function of syscall inputs. E.g. involuntary context switches. KCOV_INSTRUMENT := n -# There are numerous data races here, however, most of them are due to plain accesses. -# This would make it even harder for syzbot to find reproducers, because these -# bugs trigger without specific input. Disable by default, but should re-enable -# eventually. +# Disable KCSAN to avoid excessive noise and performance degradation. To avoid +# false positives ensure barriers implied by sched functions are instrumented. KCSAN_SANITIZE := n +KCSAN_INSTRUMENT_BARRIERS := y ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y) # According to Alan Modra , the -fno-omit-frame-pointer is -- 2.34.0.rc2.393.gf8c9666880-goog