Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752648AbbBSREZ (ORCPT ); Thu, 19 Feb 2015 12:04:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40927 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751568AbbBSREY (ORCPT ); Thu, 19 Feb 2015 12:04:24 -0500 Date: Thu, 19 Feb 2015 11:03:53 -0600 From: Josh Poimboeuf To: Vojtech Pavlik Cc: Peter Zijlstra , Andrew Morton , Ingo Molnar , Jiri Kosina , Seth Jennings , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] sched: add sched_task_call() Message-ID: <20150219170353.GB15980@treble.redhat.com> References: <20150217141211.GC11861@treble.redhat.com> <20150217181541.GP5029@twins.programming.kicks-ass.net> <20150217212532.GJ11861@treble.redhat.com> <20150218152100.GZ5029@twins.programming.kicks-ass.net> <20150218171256.GA28553@treble.hsd1.ky.comcast.net> <20150219002058.GD5029@twins.programming.kicks-ass.net> <20150219041753.GA13423@treble.redhat.com> <20150219101607.GG5029@twins.programming.kicks-ass.net> <20150219162429.GA15980@treble.redhat.com> <20150219163359.GA25438@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150219163359.GA25438@suse.cz> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 973 Lines: 25 On Thu, Feb 19, 2015 at 05:33:59PM +0100, Vojtech Pavlik wrote: > On Thu, Feb 19, 2015 at 10:24:29AM -0600, Josh Poimboeuf wrote: > > > > No, these tasks will _never_ make syscalls. So you need to guarantee > > > they don't accidentally enter the kernel while you flip them. Something > > > like so should do. > > > > > > You set TIF_ENTER_WAIT on them, check they're still in userspace, flip > > > them then clear TIF_ENTER_WAIT. > > > > Ah, that's a good idea. But how do we check if they're in user space? > > I don't see the benefit in holding them in a loop - you can just as well > flip them from the syscall code as kGraft does. But we were talking specifically about HPC tasks which never make syscalls. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/