From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <4FF21C88.3060801@us.ibm.com> Date: Mon, 02 Jul 2012 15:11:20 -0700 From: John Stultz MIME-Version: 1.0 To: Thomas Gleixner CC: Linux Kernel , Prarit Bhargava , stable@vger.kernel.org Subject: Re: [PATCH 1/2] [RFC] Fix clock_was_set so it is safe to call from atomic References: <1341167401-31342-1-git-send-email-johnstul@us.ibm.com> <1341167401-31342-2-git-send-email-johnstul@us.ibm.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On 07/02/2012 01:53 AM, Thomas Gleixner wrote: > On Sun, 1 Jul 2012, John Stultz wrote: > >> NOTE:This is a prerequisite patch that's required to >> address the widely observed leap-second related futex/hrtimer >> issues. >> >> Currently clock_was_set() is unsafe to be called from atomic >> context, as it calls on_each_cpu(). This causes problems when >> we need to adjust the time from update_wall_time(). >> >> To fix this, introduce a work_struct so if we're in_atomic, >> we can schedule work to do the necessary update after we're >> out of the atomic section. > Shouldn't we queue a timer_list timer with expiry time jiffies + 0 > instead. We can call on_each_cpu() from softirq context. And that > ensures that the update happens right away, while a scheduled work > might be delayed arbitrary long. Thanks for the feedback. I've implemented this, but before I send it out, I'm trying to see if there's not a way to change hrtimers so it doesn't keep its own per-cpu sense of time. If I don't sort that out shortly, I'll go ahead and send your suggestion out for inclusion so the fix is committed and I can try to further improve it afterwards. thanks -john