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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 DBB47C43144 for ; Fri, 22 Jun 2018 18:32:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8D6CB2473E for ; Fri, 22 Jun 2018 18:32:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8D6CB2473E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org 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 S934214AbeFVScv (ORCPT ); Fri, 22 Jun 2018 14:32:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:36812 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933869AbeFVScu (ORCPT ); Fri, 22 Jun 2018 14:32:50 -0400 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 25AEE2473E; Fri, 22 Jun 2018 18:32:49 +0000 (UTC) Date: Fri, 22 Jun 2018 14:32:47 -0400 From: Steven Rostedt To: Joel Fernandes Cc: "Paul E. McKenney" , Byungchul Park , 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: <20180622143247.781028b1@gandalf.local.home> In-Reply-To: <20180622181916.GA13628@joelaf.mtv.corp.google.com> 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> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Steve