From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753563Ab2HTPrE (ORCPT ); Mon, 20 Aug 2012 11:47:04 -0400 Received: from merlin.infradead.org ([205.233.59.134]:42423 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752846Ab2HTPrD convert rfc822-to-8bit (ORCPT ); Mon, 20 Aug 2012 11:47:03 -0400 Message-ID: <1345477609.23018.61.camel@twins> Subject: Re: lockdep trace from posix timers From: Peter Zijlstra To: Oleg Nesterov Cc: Dave Jones , Linux Kernel , Thomas Gleixner , rostedt , dhowells , Al Viro Date: Mon, 20 Aug 2012 17:46:49 +0200 In-Reply-To: <20120820153225.GA20258@redhat.com> References: <20120724203613.GA9637@redhat.com> <1345140478.29668.54.camel@twins> <20120817151447.GA7918@redhat.com> <1345446957.23018.14.camel@twins> <1345463081.23018.34.camel@twins> <20120820145919.GB18499@redhat.com> <1345475434.23018.48.camel@twins> <1345476436.23018.54.camel@twins> <20120820153225.GA20258@redhat.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-08-20 at 17:32 +0200, Oleg Nesterov wrote: > > I guess we could steal the entire list and requeue it afterwards and > > lift TIF_NOTIFY_RESUME along with it.. > > We can't. This can race with exit_task_work(). And this can break > fput(), the task can return to the userspace without __fput(). So we could put that spinlock back around cancel and run and leave add lockless. That'd solve my immediate problem but its not something I'm proud of. All schemes I can come up with end up being broken or effectively the same as the above proposal.