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=-7.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 F0FAEC47404 for ; Fri, 4 Oct 2019 16:57:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2C11222BE for ; Fri, 4 Oct 2019 16:57:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="A0o11SDO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730112AbfJDQ5k (ORCPT ); Fri, 4 Oct 2019 12:57:40 -0400 Received: from mail-pg1-f194.google.com ([209.85.215.194]:34140 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725775AbfJDQ5j (ORCPT ); Fri, 4 Oct 2019 12:57:39 -0400 Received: by mail-pg1-f194.google.com with SMTP id y35so4102640pgl.1 for ; Fri, 04 Oct 2019 09:57:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ab3tBPQ6Pcp75EMdc8QMkmhS5pFStOh5Ri4sl4H0v0g=; b=A0o11SDOPotJTR39eKw+j9HVUoXBtR1ABbHLNkbmlRtwrujglMKYkhg8twvkc7P2Le v2sVc0UTrpSc9iYrgLn5vrVaUFCXXiixLD+9uRCODWkid05wuRaj4ErKxYecnjytS/uc fzc6e76CBTvg/DKxKhQRJuDGDwx1H1unSKBOc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ab3tBPQ6Pcp75EMdc8QMkmhS5pFStOh5Ri4sl4H0v0g=; b=muETvXk35cPiaeZDwJi0sPCqcPSlbsgvArSAejJhc+fPcA7guV71ltdXN09caKP9Ui FIGOTVqO+0ajOs/VOQL7z7Tti8CwDGdUNJGaTcZ7NnBjT/ZHcKzTthEKUQXhJvDkIIjf weps8xvQWcyMpt2eJ2Eg4em752j4WlzN098SOIa7CAbubhq2q9o2gfO6eqlydZ2G34Y7 x5mhHfJgIZu0zeorLRgjUdSa+EbutzM+JvdZl54ctdL7WSZfNd/Sou2E6wbqVHQEFiFr UVE5u8vq63AMy9dENOk0jRI90PLr87J/59Cyek/Xuv8PW6q2Qf63inoM3bNv1t7Q3/ie hKQw== X-Gm-Message-State: APjAAAXbATtQy9NitgdUjQDRc9QgJjTm96T2NSTa+Vnh8t2wr1x/8NUs Tf/TIY0DuieTDDj/XJTp4dXNhQF03gI= X-Google-Smtp-Source: APXvYqz7IVKm+JhSRuBZ3wUloItdZybc2Y5fUZoUGymqB8pch0UB1ERtNv0AZobl/w8oQOideEBk6A== X-Received: by 2002:aa7:8813:: with SMTP id c19mr18135534pfo.101.1570208257358; Fri, 04 Oct 2019 09:57:37 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id t125sm8906818pfc.80.2019.10.04.09.57.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Oct 2019 09:57:36 -0700 (PDT) Date: Fri, 4 Oct 2019 12:57:36 -0400 From: Joel Fernandes To: Dmitry Vyukov Cc: Marco Elver , kasan-dev , LKML , Andrey Konovalov , Alexander Potapenko , "Paul E. McKenney" , Paul Turner , Daniel Axtens , Anatol Pomazau , Will Deacon , Andrea Parri , Alan Stern , LKMM Maintainers -- Akira Yokosawa , Nicholas Piggin , Boqun Feng , Daniel Lustig , Jade Alglave , Luc Maranget Subject: Re: Kernel Concurrency Sanitizer (KCSAN) Message-ID: <20191004165736.GF253167@google.com> References: <20191001211948.GA42035@google.com> <20191004164859.GD253167@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Fri, Oct 04, 2019 at 06:52:49PM +0200, Dmitry Vyukov wrote: > On Fri, Oct 4, 2019 at 6:49 PM Joel Fernandes wrote: > > > > On Wed, Oct 02, 2019 at 09:51:58PM +0200, Marco Elver wrote: > > > Hi Joel, > > > > > > On Tue, 1 Oct 2019 at 23:19, Joel Fernandes wrote: > > > > > > > > On Fri, Sep 20, 2019 at 04:18:57PM +0200, Marco Elver wrote: > > > > > Hi all, > > > > > > > > > > We would like to share a new data-race detector for the Linux kernel: > > > > > Kernel Concurrency Sanitizer (KCSAN) -- > > > > > https://github.com/google/ktsan/wiki/KCSAN (Details: > > > > > https://github.com/google/ktsan/blob/kcsan/Documentation/dev-tools/kcsan.rst) > > > > > > > > > > To those of you who we mentioned at LPC that we're working on a > > > > > watchpoint-based KTSAN inspired by DataCollider [1], this is it (we > > > > > renamed it to KCSAN to avoid confusion with KTSAN). > > > > > [1] http://usenix.org/legacy/events/osdi10/tech/full_papers/Erickson.pdf > > > > > > > > > > In the coming weeks we're planning to: > > > > > * Set up a syzkaller instance. > > > > > * Share the dashboard so that you can see the races that are found. > > > > > * Attempt to send fixes for some races upstream (if you find that the > > > > > kcsan-with-fixes branch contains an important fix, please feel free to > > > > > point it out and we'll prioritize that). > > > > > > > > > > There are a few open questions: > > > > > * The big one: most of the reported races are due to unmarked > > > > > accesses; prioritization or pruning of races to focus initial efforts > > > > > to fix races might be required. Comments on how best to proceed are > > > > > welcome. We're aware that these are issues that have recently received > > > > > attention in the context of the LKMM > > > > > (https://lwn.net/Articles/793253/). > > > > > * How/when to upstream KCSAN? > > > > > > > > Looks exciting. I think based on our discussion at LPC, you mentioned > > > > one way of pruning is if the compiler generated different code with _ONCE > > > > annotations than what would have otherwise been generated. Is that still on > > > > the table, for the purposing of pruning the reports? > > > > > > This might be interesting at first, but it's not entirely clear how > > > feasible it is. It's also dangerous, because the real issue would be > > > ignored. It may be that one compiler version on a particular > > > architecture generates the same code, but any change in compiler or > > > architecture and this would no longer be true. Let me know if you have > > > any more ideas. > > > > My thought was this technique of looking at compiler generated code can be > > used for prioritization of the reports. Have you tested it though? I think > > without testing such technique, we could not know how much of benefit (or > > lack thereof) there is to the issue. > > > > In fact, IIRC, the compiler generating different code with _ONCE annotation > > can be given as justification for patches doing such conversions. > > > We also should not forget about "missed mutex" races (e.g. unprotected > radix tree), which are much worse and higher priority than a missed > atomic annotation. If we look at codegen we may discard most of them > as non important. Sure. I was not asking to look at codegen as the only signal. But to use the signal for whatever it is worth. thanks, - Joel