From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751280Ab3LJW6b (ORCPT ); Tue, 10 Dec 2013 17:58:31 -0500 Received: from mga02.intel.com ([134.134.136.20]:59898 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750787Ab3LJW63 (ORCPT ); Tue, 10 Dec 2013 17:58:29 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.93,867,1378882800"; d="scan'208";a="450152315" Message-ID: <1386716299.3685.99.camel@dvhart-mobl4.amr.corp.intel.com> Subject: Re: process 'stuck' at exit. From: Darren Hart To: Linus Torvalds Cc: Thomas Gleixner , Dave Jones , Oleg Nesterov , Andrea Arcangeli , Linux Kernel Mailing List , Peter Zijlstra , Mel Gorman Date: Tue, 10 Dec 2013 14:58:19 -0800 In-Reply-To: References: <20131210154724.GA30020@redhat.com> <20131210203559.GA1209@redhat.com> <20131210204925.GB27373@redhat.com> <20131210213431.GA6342@redhat.com> <20131210214143.GG27373@redhat.com> Organization: Intel Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5 (3.8.5-2.fc19) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2013-12-10 at 14:48 -0800, Linus Torvalds wrote: > On Tue, Dec 10, 2013 at 2:42 PM, Thomas Gleixner wrote: > > > > And yes, I remember that we do not do an extra check for the fshared > > case, because get_user_pages_fast() should do it for us already. If > > not we are fubared not only in the futex code. > > Yeah. It turns out we do do the access check indirectly - by looking > at the PAGE_USER bit, even if we don't necessarily check the actual > limits. So get_user_pages_fast() is fine. > > > But there is a subtle detail: > > Yup, see my email from ten minutes ago, we found the same thing. And > that would seem to explain the endless loop, and also the timing > (since Dave mentions he started doing large-pages lately). > > So I think the "__get_user_pages_fast(address, 1, !ro, &page)" thing > should work. > > Dave, can you re-create that trinity run and test that patch? I think > we've got this, but it might be nice to leave the hung machine up and > running until it's verified.. Although I don't really see what else we > could need or get out of it, so.. Would it be possible to limit the options to only pass FUTEX_CMP_REQUEUE and a read-only uaddr? That should improve confidence when it doesn't fail :-) -- Darren Hart Intel Open Source Technology Center Yocto Project - Linux Kernel