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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 EA190CA9EAF for ; Mon, 21 Oct 2019 13:47:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B9994214AE for ; Mon, 21 Oct 2019 13:47:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Suol0hHw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729035AbfJUNrK (ORCPT ); Mon, 21 Oct 2019 09:47:10 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:25792 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728083AbfJUNrK (ORCPT ); Mon, 21 Oct 2019 09:47:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1571665629; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6rO/O10MdAqoNhorXBny5B06tfBtdVmzTbFkBdZmSP0=; b=Suol0hHwnaUwaFkCA7s2RO64mT/qhfui0zPBaYrVp2rqU7Q49ojJO3VKyxBq1dX5qvDaxg rJfzNlYEk0SFnylRC/Y6y4O5vOHHzkTy1JK+UlHpmUQPRt/jIpFQ3JXcxsnU0lcEJ2jvuI qZS/en1BsfY37pwllrJp48k1A7hZ4As= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-181-sQlMYvpEPQusM1aD1O9A0A-1; Mon, 21 Oct 2019 09:47:05 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DD173800D41; Mon, 21 Oct 2019 13:47:03 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.44]) by smtp.corp.redhat.com (Postfix) with SMTP id 711855C207; Mon, 21 Oct 2019 13:47:01 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 21 Oct 2019 15:47:03 +0200 (CEST) Date: Mon, 21 Oct 2019 15:47:00 +0200 From: Oleg Nesterov To: Marco Elver Cc: Christian Brauner , syzbot , Andrew Morton , Arnd Bergmann , christian@brauner.io, deepa.kernel@gmail.com, ebiederm@xmission.com, guro@fb.com, LKML , syzkaller-bugs@googlegroups.com, Will Deacon Subject: Re: KCSAN: data-race in exit_signals / prepare_signal Message-ID: <20191021134659.GA1339@redhat.com> References: <0000000000003b1e8005956939f1@google.com> <20191021111920.frmc3njkha4c3a72@wittgenstein> <20191021120029.GA24935@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: sQlMYvpEPQusM1aD1O9A0A-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/21, Marco Elver wrote: > > On Mon, 21 Oct 2019 at 14:00, Oleg Nesterov wrote: > > > > I think this is WONTFIX. > > If taking the spinlock is unnecessary (which AFAIK it probably is) and > there are no other writers to this flag, you will still need a > WRITE_ONCE(tsk->flags, tsk->flags | PF_EXITING) to avoid the > data-race. Or even WRITE_ONCE(tsk->flags, READ_ONCE(tsk->flags) | PF_EXITING) in theory. But in practice, I do not think compiler can turn =09curent->flags |=3D PF_EXITING; into something which temporary clears another flag, say, PF_KTHREAD. > However, if it is possible that there are concurrent writers setting > other bits in flags, No, only current taks should change its ->flags. Oleg.