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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,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 41E6CC43144 for ; Mon, 25 Jun 2018 08:28:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EB8F1255DF for ; Mon, 25 Jun 2018 08:28:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB8F1255DF Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lge.com 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 S1754423AbeFYI2e (ORCPT ); Mon, 25 Jun 2018 04:28:34 -0400 Received: from lgeamrelo11.lge.com ([156.147.23.51]:57531 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753154AbeFYI2c (ORCPT ); Mon, 25 Jun 2018 04:28:32 -0400 Received: from unknown (HELO lgemrelse6q.lge.com) (156.147.1.121) by 156.147.23.51 with ESMTP; 25 Jun 2018 17:28:31 +0900 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO X58A-UD3R) (10.177.222.33) by 156.147.1.121 with ESMTP; 25 Jun 2018 17:28:30 +0900 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Mon, 25 Jun 2018 17:28:24 +0900 From: Byungchul Park To: Joel Fernandes Cc: Steven Rostedt , "Paul E. McKenney" , Byungchul Park , jiangshanlai@gmail.com, josh@joshtriplett.org, Mathieu Desnoyers , linux-kernel@vger.kernel.org, kernel-team@lge.com, luto@kernel.org Subject: Re: [RFC 2/2] rcu: Remove ->dynticks_nmi_nesting from struct rcu_dynticks Message-ID: <20180625082824.GB21377@X58A-UD3R> References: <1529484440-20634-1-git-send-email-byungchul.park@lge.com> <1529484440-20634-2-git-send-email-byungchul.park@lge.com> <20180620145814.GQ3593@linux.vnet.ibm.com> <20180620164902.GW3593@linux.vnet.ibm.com> <20180622055659.GA255098@joelaf.mtv.corp.google.com> <20180622132843.GN3593@linux.vnet.ibm.com> <20180622181916.GA13628@joelaf.mtv.corp.google.com> <20180622143247.781028b1@gandalf.local.home> <20180622200548.GA114655@joelaf.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180622200548.GA114655@joelaf.mtv.corp.google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 22, 2018 at 01:05:48PM -0700, Joel Fernandes wrote: > On Fri, Jun 22, 2018 at 02:32:47PM -0400, Steven Rostedt wrote: > > On Fri, 22 Jun 2018 11:19:16 -0700 > > Joel Fernandes wrote: > > > > > Sure. So in a later thread you mentioned "usermode helpers". I took a closer > > > look at that subsystem, and it seems you can execute usermode helpers from > > > atomic sections with help of UMH_NO_WAIT flag. > > > > > > Then I checked where this flag is used and it turns out its from the > > > mce_work_trigger function in x86/kernel/cpu/mcheck/dev-mcelog.c which can be > > > called infact from an interrupt context (mce_notify_irq). > > > > > > Is this the usecase you remember causing this weird transitions to userspace? > > > > But this case still looks like it uses work queues, it just doesn't > > wait for the result. > > > > I'll have to look at the code from what it looked like back in 2011, to > > see if there was an actual issue here back then. > > Good point Steve. So I guess in the current kernel sources, there's no code > that uses UMH in IRQ context AFAICT. I'll go through the google group thread > Paul pointed as well to study the history of the problem a bit more. Me too. Good discussion we had thanks to you, Joel. > thanks, > > - Joel