From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756148Ab2DQOLk (ORCPT ); Tue, 17 Apr 2012 10:11:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60530 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755605Ab2DQOLi (ORCPT ); Tue, 17 Apr 2012 10:11:38 -0400 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20120414021236.GB23393@redhat.com> References: <20120414021236.GB23393@redhat.com> <20120414021201.GA23385@redhat.com> To: Oleg Nesterov Cc: dhowells@redhat.com, Andrew Morton , Linus Torvalds , Thomas Gleixner , Alexander Gordeev , Chris Zankel , David Smith , "Frank Ch. Eigler" , Geert Uytterhoeven , Larry Woodman , Peter Zijlstra , Tejun Heo , linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/3] genirq: reimplement exit_irq_thread() hook via task_work_add() Date: Tue, 17 Apr 2012 15:11:18 +0100 Message-ID: <26830.1334671878@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov wrote: > 2. change irq_thread() to do task_queue_work(irq_thread_dtor) > at the start and task_work_cancel() before return. > > tracehook_notify_resume() can never play with kthreads, > only do_exit()->exit_task_work() can call the callback > and this is what we want. Hmmm... This seems wrong. You're now using the hook in two distinct ways: the primary use of that the hook is to detect that userspace is about to resume processing (via TIF_NOTIFY_RESUME) and then you're abusing the fact that the hook is also invoked via do_exit() to perform a clean up because we've got to get rid of it somehow under that circumstance. This only works for you because you're operating in a kernel thread which doesn't have a userspace (and so will never see TIF_NOTIFY_RESUME). However, if someone tries that in an ordinary thread, it is liable to malfunction as the record could be executed and deleted at some unpredictable point in the future. David