From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755373AbcBEUNz (ORCPT ); Fri, 5 Feb 2016 15:13:55 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:34421 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751798AbcBEUNy (ORCPT ); Fri, 5 Feb 2016 15:13:54 -0500 Date: Fri, 5 Feb 2016 12:13:53 -0800 From: Andrew Morton To: John Stultz Cc: lkml , Ruchi Kandoi , Arjan van de Ven , Thomas Gleixner , Oren Laadan , Rom Lemarchand , Kees Cook , Android Kernel Team Subject: Re: [PATCH] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread. Message-Id: <20160205121353.63d65c6b33a153bd9f863d8b@linux-foundation.org> In-Reply-To: <1454695723-4393-1-git-send-email-john.stultz@linaro.org> References: <1454695723-4393-1-git-send-email-john.stultz@linaro.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 10:08:43 -0800 John Stultz wrote: > From: Ruchi Kandoi > > This allows power/performance management software to set timer > slack for other threads according to its policy for the thread > (such as when the thread is designated foreground vs. background > activity) > > Second argument is similar to PR_SET_TIMERSLACK, if non-zero > then the slack is set to that value otherwise sets it to the > default for the thread. > > Takes PID of the thread as the third argument. > > This interface checks that the calling task has permissions to > to use PTRACE_MODE_ATTACH on the target task, so that we can > ensure arbitrary apps do not change the timer slack for other > apps. > > Additional fixes from Ruchi and Micha Kalfon > have been folded into this patch to make it easier to reivew. > > ... > > @@ -2218,6 +2222,27 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > case PR_GET_TID_ADDRESS: > error = prctl_get_tid_address(me, (int __user **)arg2); > break; > + case PR_SET_TIMERSLACK_PID: > + rcu_read_lock(); > + tsk = find_task_by_vpid((pid_t)arg3); hm, as far as I can tell this is the first instance in which prctl() is used to play with a task other than "current". Maybe this isn't a good precedent. If you look at all the other diddle-other-task functions in kernel/sys.c, you'll see that they are standalone syscalls. What you've done here is just a bit lazy: added what is effectively a new standalone syscall, only it has been hidden within the prctl() switch statement. I don't see a practical problem with this - we could have implemented all those other syscalls as prctl submodes as well. But we didn't... IOW, it would be more consistent to add sys_set_timer_slack()?