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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT 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 BD711C04ABB for ; Tue, 11 Sep 2018 11:44:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 67FF920839 for ; Tue, 11 Sep 2018 11:44:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="HbST/1CF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 67FF920839 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726863AbeIKQnw (ORCPT ); Tue, 11 Sep 2018 12:43:52 -0400 Received: from merlin.infradead.org ([205.233.59.134]:59994 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726554AbeIKQnw (ORCPT ); Tue, 11 Sep 2018 12:43:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=YyviicP+lTpBCPn/WgAStSGu/SbAo4yVeTel1oh4zLI=; b=HbST/1CFOQ3I9Ifcj0cDPUO2z 6bGp1TLfmK8nmtJUw1OA9NMsksbtiUE/mxORwFenquCGkWmIZG7IPPFuJMJRIRrhvcwOQ5VxEKg0Z CEf5i/yPuau8IAuHf9t0LMnqL99ioaGp8NHCI0wnaiBP9YnGt7de0zrtm+0RtEfKvxxxyN7UJiUkD BvuqtSovjn97DOWonDp0H65tfdoeeZgY4n6qbSueyAS31+8lmQVMSzW94G7EigwuG2si+Cdz33aZa hHOGVErR/Seks74uE+JcRbpYzFXusugA4zhwFlUGNPbBWJuXArSSC3LjYmiq6XDS3bu0yjCumhogs WPP5L1rSg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fzh5q-0005gP-PT; Tue, 11 Sep 2018 11:44:30 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 934692057F833; Tue, 11 Sep 2018 13:44:29 +0200 (CEST) Date: Tue, 11 Sep 2018 13:44:29 +0200 From: Peter Zijlstra To: Sergey Senozhatsky Cc: Dmitry Safonov , linux-kernel@vger.kernel.org, Dmitry Safonov <0x7f454c46@gmail.com>, Daniel Axtens , Dmitry Vyukov , Michael Neuling , Mikulas Patocka , Nathan March , Pasi =?iso-8859-1?Q?K=E4rkk=E4inen?= , Peter Hurley , "Rong, Chen" , Tan Xiaojun , Tetsuo Handa , stable@vger.kernel.org, Greg Kroah-Hartman , Jiri Slaby , "Paul E. McKenney" Subject: Re: [PATCHv3 2/6] tty/ldsem: Update waiter->task before waking up reader Message-ID: <20180911114429.GT24106@hirez.programming.kicks-ass.net> References: <20180911014821.26286-1-dima@arista.com> <20180911014821.26286-3-dima@arista.com> <20180911050449.GB4065@jagdpanzerIV> <20180911054129.GC4065@jagdpanzerIV> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180911054129.GC4065@jagdpanzerIV> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 11, 2018 at 02:41:29PM +0900, Sergey Senozhatsky wrote: > On (09/11/18 14:04), Sergey Senozhatsky wrote: > > > for (;;) { > > > set_current_state(TASK_UNINTERRUPTIBLE); > > > > I think that set_current_state() also executes memory barrier. Just > > because it accesses task state. > > > > > - if (!waiter.task) > > > + if (!READ_ONCE(waiter.task)) > > > break; > > > if (!timeout) > > > break; > > This READ_ONCE(waiter.task) looks interesting. Maybe could be moved > to a loop condition > > while (!READ_ONCE(waiter.task)) { > ... > } No, it must be after set_current_state(). See that same comment.