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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 91E3AC47404 for ; Mon, 7 Oct 2019 14:14:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 681CC206C2 for ; Mon, 7 Oct 2019 14:14:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nKBF67N0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728390AbfJGOOl (ORCPT ); Mon, 7 Oct 2019 10:14:41 -0400 Received: from mail-wr1-f67.google.com ([209.85.221.67]:42038 "EHLO mail-wr1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726334AbfJGOOk (ORCPT ); Mon, 7 Oct 2019 10:14:40 -0400 Received: by mail-wr1-f67.google.com with SMTP id n14so15474437wrw.9; Mon, 07 Oct 2019 07:14:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=eAFFgxm3qY/7LxpkZUrTWdSLnmn3UbQs0xpqBO+b2a4=; b=nKBF67N0rqnOTvG/Tl+oK7nJS0Wjo9edLmEGrRwKwpan0BzcwD+ej2m0C5PmxDvxwU 3YKV8uwKPt4z7oatfdCUCM92/SznZ5cciPpCQyHo0Cs7Fuxd5XmIiKmuPo54cxUSjT4v /FRhZRSVuv3dc4UBv518bNDDnVwGzq6JkrrP97ukTKw7sUEQpIAN9pQ42HC6bGLQY4iU C/gbdNlttA4PvQW+mLkdPU2ZlIlneJ/XQPaE/k195Ccc84M5Ol6m18X99ZvO5CV3XTSy shYjTDb5n9NQukgvS7HgpnVRSzpVcm2GB6sEorZ8K0+7oBmoCchblbaGd5gss3uLyFW8 5Geg== 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=eAFFgxm3qY/7LxpkZUrTWdSLnmn3UbQs0xpqBO+b2a4=; b=E26DYEZOxgFaLMoxpcuEboJFPy3z0OHUab3xYrCQFIJMv3+XGh0ihRBxAvmItb3QZR BTEoSrN7upILW7744JD03YB3AdAltDqpYpVPASrQNyLQcmb2ynx4XB2MhC77Me2mcQOj vbW0gxb5OMzTXKK72lczI+Bubap3povx24mqpDBn09jcbK6/z23r9MwDCa1gNoVr7oJL fu8szSZKsyHqiGBUfjaZEGMRzGN5o+BIQVvIAik5ET6wAIzZUvsb+uixrEwzki4TBPFM /mkFCvqcGA+bbCb1+BKVRlyQsYEH8NSYM5kH8sUme2MhLEur0NaR/n4aH9YSKyGPsDXe et7w== X-Gm-Message-State: APjAAAX0+hzYbYGKcJP66fGgnLKyspFgqKcTh+KhKnyCrW9YbRTq8y53 MQVtIJvtfwommxtISU40UL8= X-Google-Smtp-Source: APXvYqwapccFJ6OREAdhuMQJ4J1B+5o2iairGFJrhmlBACH5UaQdZWGbeLkf9Ag4sHZH/5WelSIa2Q== X-Received: by 2002:adf:fe11:: with SMTP id n17mr16300070wrr.221.1570457678013; Mon, 07 Oct 2019 07:14:38 -0700 (PDT) Received: from andrea.guest.corp.microsoft.com ([2a01:110:8012:1012:69a4:816:a2c:e717]) by smtp.gmail.com with ESMTPSA id a7sm33011934wra.43.2019.10.07.07.14.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Oct 2019 07:14:37 -0700 (PDT) Date: Mon, 7 Oct 2019 16:14:32 +0200 From: Andrea Parri To: Dmitry Vyukov Cc: Christian Brauner , bsingharora@gmail.com, Marco Elver , LKML , syzbot , syzkaller-bugs , stable Subject: Re: [PATCH v2] taskstats: fix data-race Message-ID: <20191007141432.GA22083@andrea.guest.corp.microsoft.com> References: <20191007104039.GA16085@andrea.guest.corp.microsoft.com> <20191007110117.1096-1-christian.brauner@ubuntu.com> <20191007131804.GA19242@andrea.guest.corp.microsoft.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 > > > static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk) > > > { > > > struct signal_struct *sig = tsk->signal; > > > - struct taskstats *stats; > > > + struct taskstats *stats_new, *stats; > > > > > > - if (sig->stats || thread_group_empty(tsk)) > > > - goto ret; > > > + /* Pairs with smp_store_release() below. */ > > > + stats = READ_ONCE(sig->stats); > > > > This pairing suggests that the READ_ONCE() is heading an address > > dependency, but I fail to identify it: what is the target memory > > access of such a (putative) dependency? > > I would assume callers of this function access *stats. So the > dependency is between loading stats and accessing *stats. AFAICT, the only caller of the function in 5.4-rc2 is taskstats_exit(), which 'casts' the return value to a boolean (so I really don't see how any address dependency could be carried over/relied upon here). Andrea