Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751697AbaGaTH6 (ORCPT ); Thu, 31 Jul 2014 15:07:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26856 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751322AbaGaTHy (ORCPT ); Thu, 31 Jul 2014 15:07:54 -0400 Date: Thu, 31 Jul 2014 21:05:18 +0200 From: Oleg Nesterov To: Frederic Weisbecker Cc: Andy Lutomirski , "Paul E. McKenney" , LKML , Kees Cook , Will Drewry , the arch/x86 maintainers , "" , Linux MIPS Mailing List , "linux-arch@vger.kernel.org" , LSM List , Alexei Starovoitov , "H. Peter Anvin" Subject: Re: TIF_NOHZ can escape nonhz mask? (Was: [PATCH v3 6/8] x86: Split syscall_trace_enter into two phases) Message-ID: <20140731190518.GA21938@redhat.com> References: <20140728192209.GA26017@localhost.localdomain> <20140729175414.GA3289@redhat.com> <20140730163516.GC18158@localhost.localdomain> <20140730174630.GA30862@redhat.com> <20140731003034.GA32078@localhost.localdomain> <20140731160353.GA14772@redhat.com> <20140731171329.GD7842@localhost.localdomain> <20140731181230.GA18695@redhat.com> <20140731184729.GA12296@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/31, Frederic Weisbecker wrote: > > 2014-07-31 20:47 GMT+02:00 Frederic Weisbecker : > > On Thu, Jul 31, 2014 at 08:12:30PM +0200, Oleg Nesterov wrote: > >> On 07/31, Frederic Weisbecker wrote: > > No, because preempt_schedule_irq() does the ctx_state save and restore with > > exception_enter/exception_exit. > > Similar thing happens with schedule_user(). > > preempt_schedule_irq() handles kernel preemption and schedule_user() > the user preemption. On both cases we save and restore the context > tracking state. > > This might be the missing piece you were missing :) YYYYYEEEEESSSS, thanks!! And in fact I was going to suggest to add this logic into preempt schedule paths to improve the situation if we can't make TIF_NOHZ per-cpu. But Frederic, perhaps I'll return here tomorrow with another question, it is too late for me now ;) Thanks! Oleg. -- 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/