From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH] ARM: timer: Shutdown clock event device when stopping local timer Date: Mon, 01 Apr 2013 02:06:17 +0200 Message-ID: <5158CF79.2060702@linaro.org> References: <1364549049-29278-1-git-send-email-ning.n.jiang@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <1364549049-29278-1-git-send-email-ning.n.jiang@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: ning.n.jiang@gmail.com 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 List-Id: linux-arm-msm@vger.kernel.org On 03/29/2013 10:24 AM, ning.n.jiang@gmail.com wrote: > From: Ning Jiang >=20 > 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. >=20 > 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. >=20 > 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. >=20 > 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 =3D *((int *)arg); list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) { if (cpumask_test_cpu(cpu, dev->cpumask) && cpumask_weight(dev->cpumask) =3D=3D 1 && !tick_is_broadcast_device(dev)) { BUG_ON(dev->mode !=3D CLOCK_EVT_MODE_UNUSED); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ list_del(&dev->list); } } break; ... } This is called triggered from hrtimer_cpu_notify with the CPU_DEAD even= t. --=20 Linaro.org =E2=94=82 Open source software for= ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog From mboxrd@z Thu Jan 1 00:00:00 1970 From: daniel.lezcano@linaro.org (Daniel Lezcano) Date: Mon, 01 Apr 2013 02:06:17 +0200 Subject: [PATCH] ARM: timer: Shutdown clock event device when stopping local timer In-Reply-To: <1364549049-29278-1-git-send-email-ning.n.jiang@gmail.com> References: <1364549049-29278-1-git-send-email-ning.n.jiang@gmail.com> Message-ID: <5158CF79.2060702@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 03/29/2013 10:24 AM, ning.n.jiang at 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. -- Linaro.org ? Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog