From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756793AbcBEUuM (ORCPT ); Fri, 5 Feb 2016 15:50:12 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:49744 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931AbcBEUuK (ORCPT ); Fri, 5 Feb 2016 15:50:10 -0500 Date: Fri, 5 Feb 2016 12:50:08 -0800 From: Andrew Morton To: Kees Cook Cc: John Stultz , lkml , Ruchi Kandoi , Arjan van de Ven , Thomas Gleixner , Oren Laadan , Rom Lemarchand , Android Kernel Team Subject: Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread. Message-Id: <20160205125008.15ccbdbe82afc3521a8ee381@linux-foundation.org> In-Reply-To: References: <1454695723-4393-1-git-send-email-john.stultz@linaro.org> <20160205121353.63d65c6b33a153bd9f863d8b@linux-foundation.org> <20160205123230.bd8bd228a0f3798a281266eb@linux-foundation.org> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; 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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 5 Feb 2016 12:44:04 -0800 Kees Cook wrote: > On Fri, Feb 5, 2016 at 12:39 PM, John Stultz wrote: > > On Fri, Feb 5, 2016 at 12:32 PM, Andrew Morton > > wrote: > >> On Fri, 5 Feb 2016 12:23:13 -0800 John Stultz wrote: > >>> On Fri, Feb 5, 2016 at 12:13 PM, Andrew Morton > >>> wrote: > >>>> > >>>> IOW, it would be more consistent to add sys_set_timer_slack()? > >>> > >>> I'm fine with moving this way. > >>> > >>> Ruchi/Rom: Any objections to that idea? > >>> > >>> Thomas/Arjan: Any other functionality we should consider including > >>> when adding a syscall to tweak timer slack? > >> > >> A syscall is quite a bit more fuss - implement it on x86_64, provide a > >> no-op default in sys_ni.c, add a test suite into > >> tools/testing/selftests (mainly for arch maintainers), wait for the > >> various arch maintainers to wire it up. > > > > Yea. It is. And I'm not excited to start over on this, but this > > functionality has already run into trouble in the Android tree, as the > > PR_SET_TIMERSLACK_PID value has hit multiple collisions over time. So > > this functionality upstream would help resolve that pain. > > > >> Fortunately the build system now emits little messages which tell > >> maintainers that there's a new syscall which needs looking at. > >> > >> And a manpage will be needed, but a prctl manpage patch would have been > >> needed anyway. > > > > Yea. > > Could this be exposed as a writable /proc entry instead? Like the oom_* stuff? /proc//timer_slack_ns, guarded by ptrace_may_access(), documented under Documentation/? Yup, that would work. It's there for all architectures from day one and there is precedent. It's not as nice, but /proc nasties will always be with us.