From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752757AbcIAWtW (ORCPT ); Thu, 1 Sep 2016 18:49:22 -0400 Received: from merlin.infradead.org ([205.233.59.134]:50250 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751494AbcIAWtS (ORCPT ); Thu, 1 Sep 2016 18:49:18 -0400 Date: Thu, 1 Sep 2016 20:09:02 +0200 From: Peter Zijlstra To: Oleg Nesterov Cc: Ingo Molnar , Al Viro , Bart Van Assche , Johannes Weiner , Linus Torvalds , Neil Brown , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] sched/wait: abort_exclusive_wait() should pass TASK_NORMAL to wake_up() Message-ID: <20160901180902.GD10153@twins.programming.kicks-ass.net> References: <20160826124453.GA28894@redhat.com> <20160826124528.GA28904@redhat.com> <20160901113919.GI10138@twins.programming.kicks-ass.net> <20160901172658.GA14456@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160901172658.GA14456@redhat.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 01, 2016 at 07:26:58PM +0200, Oleg Nesterov wrote: > On 09/01, Peter Zijlstra wrote: > > > > So mixing INTERRUPTIBLE and UNINTERRUPTIBLE and then not using > > TASK_NORMAL for wakeups is a mis-feature/abuse of waitqueues IMO. > > Heh, agreed. When I was doing this fix I suddenly realize that I do > not understand why do we have, say, wake_up_interruptible(). > > I mean, I can't imagine the "real" use-case when you actually want > to wake up only the INTERRUPTIBLE tasks and leave the UNINTERRUPTIBLE > sleeping. Exclusive or not. > > It seems that wake_up_interruptible() is mostly used simply because > the caller knows that UNINTERRUPTIBLE waiters are not possible, this > is often the case. I suspect the same. > Actually, I think that TASK_NORMAL should be used even if wq mixes > UNINTERRUPTIBLE and KILLABLE waiters. The fact that TASK_KILLABLE > includes TASK_UNINTERRUPTIBLE is just "implementation detail" even > if I do not think this will be ever changed. I think its a fairly fundamental thing, its part of the semantics of TASK_KILLABLE. Namely its UNINTERRUPTIBLE, except you can interrupt it with fatal. A TASK_NORMAL wake should very much wake a TASK_KILLABLE sleep, and for that to happen they need to share a bit, namely UNINTERRUPTIBLE. But I agree with you, all waitqueue wakeups _should_ simply be TASK_NORMAL. Like said, I don't see it ever makes sense to play games with it. Now, let me try and get back to making sense of your abort abortion ;-)