Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756093Ab3DACFI (ORCPT ); Sun, 31 Mar 2013 22:05:08 -0400 Received: from mail-vc0-f181.google.com ([209.85.220.181]:56471 "EHLO mail-vc0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754983Ab3DACFF (ORCPT ); Sun, 31 Mar 2013 22:05:05 -0400 MIME-Version: 1.0 In-Reply-To: <5158CF79.2060702@linaro.org> References: <1364549049-29278-1-git-send-email-ning.n.jiang@gmail.com> <5158CF79.2060702@linaro.org> Date: Mon, 1 Apr 2013 10:05:03 +0800 Message-ID: Subject: Re: [PATCH] ARM: timer: Shutdown clock event device when stopping local timer From: Ning Jiang To: Daniel Lezcano Cc: linux@arm.linux.org.uk, kgene.kim@samsung.com, davidb@codeaurora.org, dwalker@fifo99.com, bryanh@codeaurora.org, john.stultz@linaro.org, tglx@linutronix.de, linus.walleij@linaro.org, shawn.guo@linaro.org, rob.herring@calxeda.com, arnd@arndb.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-arm-msm@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3290 Lines: 86 2013/4/1 Daniel Lezcano : > On 03/29/2013 10:24 AM, ning.n.jiang@gmail.com wrote: >> From: Ning Jiang >> >> Currently there are two problems when we try to stop local timer. >> First, it calls set_mode function directly so mode state is not >> updated for the clock event device. Second, it makes the device >> unused instead of shutdown. >> >> A subtle error will happen because of it. When a cpu is plugged out >> it will stop the local timer. It will call tick_nohz_idle_enter() >> in idle thread afterwards. It will cancel the sched timer and try >> to reprogram the next event. This is wrong since the local timer >> is supposed to be stopped. >> >> The right way to stop the local timer is to shutdown it by calling >> clockevents_set_mode(). Thus when we try to reprogram the clock >> event device, it will return directly without doing anything since >> the clock mode is CLOCK_EVT_MODE_SHUTDOWN. >> >> Signed-off-by: Ning Jiang >> --- > > > Don't you see a kernel BUG with this patch ? > > In the clockevents code, there is: > > /** > * clockevents_notify - notification about relevant events > */ > void clockevents_notify(unsigned long reason, void *arg) > { > ... > case CLOCK_EVT_NOTIFY_CPU_DEAD: > ... > cpu = *((int *)arg); > list_for_each_entry_safe(dev, tmp, &clockevent_devices, > list) { > if (cpumask_test_cpu(cpu, dev->cpumask) && > cpumask_weight(dev->cpumask) == 1 && > !tick_is_broadcast_device(dev)) { > BUG_ON(dev->mode != > CLOCK_EVT_MODE_UNUSED); > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > list_del(&dev->list); > } > } > break; > ... > } > > This is called triggered from hrtimer_cpu_notify with the CPU_DEAD event. > The clockevents_do_notify() in clockevents_notify() will call tick_notify() which will call tick_shutdown() in turn. tick_shutdown() will set clock event device mode to UNUSED. So no panic afterwards. void clockevents_notify(unsigned long reason, void *arg) { ... clockevents_do_notify(reason, arg); switch (reason) { case CLOCK_EVT_NOTIFY_CPU_DEAD: ... list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) { if (cpumask_test_cpu(cpu, dev->cpumask) && cpumask_weight(dev->cpumask) == 1 && !tick_is_broadcast_device(dev)) { BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED); list_del(&dev->list); } } .... } raw_spin_unlock_irqrestore(&clockevents_lock, flags); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/