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_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 9F458C04AB6 for ; Tue, 14 May 2019 11:35:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C64521530 for ; Tue, 14 May 2019 11:35:52 +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="eG6Qnz3D" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726254AbfENLfs (ORCPT ); Tue, 14 May 2019 07:35:48 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:57716 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725893AbfENLfs (ORCPT ); Tue, 14 May 2019 07:35:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=Hdo3J+SKgWMYdkmLex1ScT4QKrEl5Fkd2SvwQB3f/zU=; b=eG6Qnz3DL+iAnoIykPjWycQ24 XVA3G+osUl6uBIBNgtqHwidCwRHxK4E9/K0v2UHH4+oswQZYC5gpYwRC42f3z68fe9KUI63ivYlXy XmPckJkK3cfuX4iq7yxWqsecCrfMSd3yjuDodOmL79Hx1EHi9OqtTG1L8uw9npWO+E74yxREqK8RM FXCMz/eSYKCYVFQUiEKaWuaz2EtG+q3ZRXnqFL36QaGx1hrR014pGceOmHYXmNpRTIqvptgjFhnYk QwnnicyeLIGkbxUcyA37jw9S5joDPHb27g2VajMJV+lxF1fwlFaZMjmrguQEnZOCGxgsHnT6hwUln TWc5opcVw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hQVie-0000IC-M5; Tue, 14 May 2019 11:35:40 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 89F562029F877; Tue, 14 May 2019 13:35:38 +0200 (CEST) Date: Tue, 14 May 2019 13:35:38 +0200 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: minyard@acm.org, linux-rt-users@vger.kernel.org, Corey Minyard , linux-kernel@vger.kernel.org, tglx@linutronix.de, Steven Rostedt , Ingo Molnar Subject: Re: [PATCH RT v2] Fix a lockup in wait_for_completion() and friends Message-ID: <20190514113538.GL2589@hirez.programming.kicks-ass.net> References: <20190508205728.25557-1-minyard@acm.org> <20190509161925.kul66w54wpjcinuc@linutronix.de> <20190514084356.GJ2589@hirez.programming.kicks-ass.net> <20190514091219.nesriqe7qplk3476@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190514091219.nesriqe7qplk3476@linutronix.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Tue, May 14, 2019 at 11:12:19AM +0200, Sebastian Andrzej Siewior wrote: > On 2019-05-14 10:43:56 [+0200], Peter Zijlstra wrote: > > Now.. that will fix it, but I think it is also wrong. > > > > The problem being that it violates FIFO, something that might be more > > important on -RT than elsewhere. > > Wouldn't -RT be more about waking the task with the highest priority > instead the one that waited the longest? Possibly, but that's a far larger patch. Also, even with that completions do not avoid inversions and thus don't really make nice RT primitives anyway.