From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756055Ab1HCXqP (ORCPT ); Wed, 3 Aug 2011 19:46:15 -0400 Received: from cantor2.suse.de ([195.135.220.15]:33306 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755924Ab1HCXZV (ORCPT ); Wed, 3 Aug 2011 19:25:21 -0400 X-Mailbox-Line: From gregkh@clark.kroah.org Wed Aug 3 15:12:45 2011 Message-Id: <20110803221245.667635348@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Wed, 03 Aug 2011 15:00:36 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Thomas Gleixner , John Stultz , Ingo Molnar Subject: [016/102] rtc: fix hrtimer deadlock In-Reply-To: <20110803221345.GA10346@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.0-stable review patch. If anyone has any objections, please let us know. ------------------ From: Thomas Gleixner commit b830ac1d9a2262093bb0f3f6a2fd2a1c8278daf5 upstream. Ben reported a lockup related to rtc. The lockup happens due to: CPU0 CPU1 rtc_irq_set_state() __run_hrtimer() spin_lock_irqsave(&rtc->irq_task_lock) rtc_handle_legacy_irq(); spin_lock(&rtc->irq_task_lock); hrtimer_cancel() while (callback_running); So the running callback never finishes as it's blocked on rtc->irq_task_lock. Use hrtimer_try_to_cancel() instead and drop rtc->irq_task_lock while waiting for the callback. Fix this for both rtc_irq_set_state() and rtc_irq_set_freq(). Signed-off-by: Thomas Gleixner Reported-by: Ben Greear Cc: John Stultz Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/rtc/interface.c | 56 +++++++++++++++++++++++++++++++----------------- 1 file changed, 37 insertions(+), 19 deletions(-) --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -636,6 +636,29 @@ void rtc_irq_unregister(struct rtc_devic } EXPORT_SYMBOL_GPL(rtc_irq_unregister); +static int rtc_update_hrtimer(struct rtc_device *rtc, int enabled) +{ + /* + * We unconditionally cancel the timer here, because otherwise + * we could run into BUG_ON(timer->state != HRTIMER_STATE_CALLBACK); + * when we manage to start the timer before the callback + * returns HRTIMER_RESTART. + * + * We cannot use hrtimer_cancel() here as a running callback + * could be blocked on rtc->irq_task_lock and hrtimer_cancel() + * would spin forever. + */ + if (hrtimer_try_to_cancel(&rtc->pie_timer) < 0) + return -1; + + if (enabled) { + ktime_t period = ktime_set(0, NSEC_PER_SEC / rtc->irq_freq); + + hrtimer_start(&rtc->pie_timer, period, HRTIMER_MODE_REL); + } + return 0; +} + /** * rtc_irq_set_state - enable/disable 2^N Hz periodic IRQs * @rtc: the rtc device @@ -651,24 +674,21 @@ int rtc_irq_set_state(struct rtc_device int err = 0; unsigned long flags; +retry: spin_lock_irqsave(&rtc->irq_task_lock, flags); if (rtc->irq_task != NULL && task == NULL) err = -EBUSY; if (rtc->irq_task != task) err = -EACCES; - if (err) - goto out; - - if (enabled) { - ktime_t period = ktime_set(0, NSEC_PER_SEC/rtc->irq_freq); - hrtimer_start(&rtc->pie_timer, period, HRTIMER_MODE_REL); - } else { - hrtimer_cancel(&rtc->pie_timer); + if (!err) { + if (rtc_update_hrtimer(rtc, enabled) < 0) { + spin_unlock_irqrestore(&rtc->irq_task_lock, flags); + cpu_relax(); + goto retry; + } + rtc->pie_enabled = enabled; } - rtc->pie_enabled = enabled; -out: spin_unlock_irqrestore(&rtc->irq_task_lock, flags); - return err; } EXPORT_SYMBOL_GPL(rtc_irq_set_state); @@ -690,20 +710,18 @@ int rtc_irq_set_freq(struct rtc_device * if (freq <= 0) return -EINVAL; - +retry: spin_lock_irqsave(&rtc->irq_task_lock, flags); if (rtc->irq_task != NULL && task == NULL) err = -EBUSY; if (rtc->irq_task != task) err = -EACCES; - if (err == 0) { + if (!err) { rtc->irq_freq = freq; - if (rtc->pie_enabled) { - ktime_t period; - hrtimer_cancel(&rtc->pie_timer); - period = ktime_set(0, NSEC_PER_SEC/rtc->irq_freq); - hrtimer_start(&rtc->pie_timer, period, - HRTIMER_MODE_REL); + if (rtc->pie_enabled && rtc_update_hrtimer(rtc, 1) < 0) { + spin_unlock_irqrestore(&rtc->irq_task_lock, flags); + cpu_relax(); + goto retry; } } spin_unlock_irqrestore(&rtc->irq_task_lock, flags);