From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-13.3 required=5.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI,SPF_HELO_NONE,SPF_NONE, USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id C3A3E7D90F for ; Fri, 15 Nov 2019 17:15:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727671AbfKORPC (ORCPT ); Fri, 15 Nov 2019 12:15:02 -0500 Received: from mail-oi1-f196.google.com ([209.85.167.196]:44073 "EHLO mail-oi1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727656AbfKORPB (ORCPT ); Fri, 15 Nov 2019 12:15:01 -0500 Received: by mail-oi1-f196.google.com with SMTP id s71so9212065oih.11 for ; Fri, 15 Nov 2019 09:15:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=OMJenj5JQASv6g4NovikQm2+Hb7lZX8x9WL40qMINts=; b=CBFLAcP+oKm5ozaC/dYCuIf8klMNXsh2hapTlsQCl2wIwMP890KgmIt8FubWjOJotW SBA0qHxfNEqf/6i9Jdz5242Bv3Qp2u6lAlduKS5V0Fuvapxf0kOztkzl27w0zsBtb8xX yTnmYMeItCp35Kq3H5eBWsRbw8ofmOm+ZBpYyFF12krdl0qWEAfg8Hcg7hzPswVqn1fN FwFNQRyyE3KBIFlaWKzS0W2mmgQ/hbL0TF60KX4gWFSxibKz0QDKtLPtOI4IrWzykGA8 7M2/Jp9d2h2Msqwj3bx5oQAdQZXvkYzLAGBZzJqyqk7VWIo6D482M+7RzUU3qO9b2Uly Fyqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=OMJenj5JQASv6g4NovikQm2+Hb7lZX8x9WL40qMINts=; b=CPOIve7UsE9VMOLjFirmx918R3Hbu/9/mKtO9hDSXeWYYrVSq6bDivsxylwESn/QdV TQJ7L/RuWm7VG8MG+yKKJwxAhr+FYsAX/xScPEyw4k5IC1ENIomuEjio6cpRlunVSzfH Dg70IYshI7TkRcAZBIYtcN3iZcfrbfidJPfLl4UExsRCAc/pli0vsLU4kGx+miZBU+Hd A8Nwpk3EdPahtucoVwJFcnWuLZh/HFkPn6DDzpfhQ2guJfmuMq1FDJNBiikEteENsaEl Bt1gUjDrT0Q4lvplfy7s1TmBcbup3M9wxP5a5vfTdENZsCWJK3JG4F0bMf2g1A84IEte d7HA== X-Gm-Message-State: APjAAAXlY9MT6aWx+JGj1tAbMrlRijCPrc441tC9wgT6Im85eSaezcDD iG6qGwoC47OL5tWi4EGnXstRuy4rRm7xLX9IKHTsMQ== X-Google-Smtp-Source: APXvYqxHWXVF03C+YdxtSxrgLxdL91oUGsi161YRDrFwzpCwmUgbv+aRRG2bYG5Q9dZzAnZnGy6OsSdj2lBrotybY3s= X-Received: by 2002:aca:4ec6:: with SMTP id c189mr8959788oib.70.1573838099466; Fri, 15 Nov 2019 09:14:59 -0800 (PST) MIME-Version: 1.0 References: <20191114180303.66955-1-elver@google.com> <20191114195046.GP2865@paulmck-ThinkPad-P72> <20191114213303.GA237245@google.com> <20191114221559.GS2865@paulmck-ThinkPad-P72> <20191115164159.GU2865@paulmck-ThinkPad-P72> In-Reply-To: <20191115164159.GU2865@paulmck-ThinkPad-P72> From: Marco Elver Date: Fri, 15 Nov 2019 18:14:46 +0100 Message-ID: Subject: Re: [PATCH v4 00/10] Add Kernel Concurrency Sanitizer (KCSAN) To: "Paul E. McKenney" Cc: LKMM Maintainers -- Akira Yokosawa , Alan Stern , Alexander Potapenko , Andrea Parri , Andrey Konovalov , Andy Lutomirski , Ard Biesheuvel , Arnd Bergmann , Boqun Feng , Borislav Petkov , Daniel Axtens , Daniel Lustig , Dave Hansen , David Howells , Dmitry Vyukov , "H. Peter Anvin" , Ingo Molnar , Jade Alglave , Joel Fernandes , Jonathan Corbet , Josh Poimboeuf , Luc Maranget , Mark Rutland , Nicholas Piggin , Peter Zijlstra , Thomas Gleixner , Will Deacon , Eric Dumazet , kasan-dev , linux-arch , "open list:DOCUMENTATION" , linux-efi@vger.kernel.org, Linux Kbuild mailing list , LKML , Linux Memory Management List , "the arch/x86 maintainers" Content-Type: text/plain; charset="UTF-8" Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Fri, 15 Nov 2019 at 17:42, Paul E. McKenney wrote: > > On Fri, Nov 15, 2019 at 01:02:08PM +0100, Marco Elver wrote: > > On Thu, 14 Nov 2019 at 23:16, Paul E. McKenney wrote: > > > > > > On Thu, Nov 14, 2019 at 10:33:03PM +0100, Marco Elver wrote: > > > > On Thu, 14 Nov 2019, Paul E. McKenney wrote: > > > > > > > > > On Thu, Nov 14, 2019 at 07:02:53PM +0100, Marco Elver wrote: > > > > > > This is the patch-series for the Kernel Concurrency Sanitizer (KCSAN). > > > > > > KCSAN is a sampling watchpoint-based *data race detector*. More details > > > > > > are included in **Documentation/dev-tools/kcsan.rst**. This patch-series > > > > > > only enables KCSAN for x86, but we expect adding support for other > > > > > > architectures is relatively straightforward (we are aware of > > > > > > experimental ARM64 and POWER support). > > > > > > > > > > > > To gather early feedback, we announced KCSAN back in September, and have > > > > > > integrated the feedback where possible: > > > > > > http://lkml.kernel.org/r/CANpmjNPJ_bHjfLZCAPV23AXFfiPiyXXqqu72n6TgWzb2Gnu1eA@mail.gmail.com > > > > > > > > > > > > The current list of known upstream fixes for data races found by KCSAN > > > > > > can be found here: > > > > > > https://github.com/google/ktsan/wiki/KCSAN#upstream-fixes-of-data-races-found-by-kcsan > > > > > > > > > > > > We want to point out and acknowledge the work surrounding the LKMM, > > > > > > including several articles that motivate why data races are dangerous > > > > > > [1, 2], justifying a data race detector such as KCSAN. > > > > > > > > > > > > [1] https://lwn.net/Articles/793253/ > > > > > > [2] https://lwn.net/Articles/799218/ > > > > > > > > > > I queued this and ran a quick rcutorture on it, which completed > > > > > successfully with quite a few reports. > > > > > > > > Great. Many thanks for queuing this in -rcu. And regarding merge window > > > > you mentioned, we're fine with your assumption to targeting the next > > > > (v5.6) merge window. > > > > > > > > I've just had a look at linux-next to check what a future rebase > > > > requires: > > > > > > > > - There is a change in lib/Kconfig.debug and moving KCSAN to the > > > > "Generic Kernel Debugging Instruments" section seems appropriate. > > > > - bitops-instrumented.h was removed and split into 3 files, and needs > > > > re-inserting the instrumentation into the right places. > > > > > > > > Otherwise there are no issues. Let me know what you recommend. > > > > > > Sounds good! > > > > > > I will be rebasing onto v5.5-rc1 shortly after it comes out. My usual > > > approach is to fix any conflicts during that rebasing operation. > > > Does that make sense, or would you prefer to send me a rebased stack at > > > that point? Either way is fine for me. > > > > That's fine with me, thanks! To avoid too much additional churn on > > your end, I just replied to the bitops patch with a version that will > > apply with the change to bitops-instrumented infrastructure. > > My first thought was to replace 8/10 of the previous version of your > patch in -rcu (047ca266cfab "asm-generic, kcsan: Add KCSAN instrumentation > for bitops"), but this does not apply. So I am guessing that I instead > do this substitution when a rebase onto -rc1.. > > Except... > > > Also considering the merge window, we had a discussion and there are > > some arguments for targeting the v5.5 merge window: > > - we'd unblock ARM and POWER ports; > > - we'd unblock people wanting to use the data_race macro; > > - we'd unblock syzbot just tracking upstream; > > Unless there are strong reasons to not target v5.5, I leave it to you > > if you think it's appropriate. > > My normal process is to send the pull request shortly after -rc5 comes > out, but you do call out some benefits of getting it in sooner, so... > > What I will do is to rebase your series onto (say) -rc7, test it, and > see about an RFC pull request. > > One possible complication is the new 8/10 patch. But maybe it will > apply against -rc7? > > Another possible complication is this: > > scripts/kconfig/conf --syncconfig Kconfig > * > * Restart config... > * > * > * KCSAN: watchpoint-based dynamic data race detector > * > KCSAN: watchpoint-based dynamic data race detector (KCSAN) [N/y/?] (NEW) > > Might be OK in this case because it is quite obvious what it is doing. > (Avoiding pain from this is the reason that CONFIG_RCU_EXPERT exists.) > > But I will just mention this in the pull request. > > If there is a -rc8, there is of course a higher probability of making it > into the next merge window. > > Fair enough? Totally fine with that, sounds like a good plan, thanks! If it helps, in theory we can also drop and delay the bitops instrumentation patch until the new bitops instrumentation infrastructure is in 5.5-rc1. There won't be any false positives if this is missing, we might just miss a few data races until we have it. Thanks, -- Marco