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SubjectRe: [PATCH] Prevent clockevent event_handler ending up handler_noop
On Tue, 2 Sep 2008, Venki Pallipadi wrote:
> There is a ordering related problem with clockevents code, due to which
> clockevents_register_device() called after tickless/highres switch
> will not work. The new clockevent ends up with clockevents_handle_noop as
> event handler, resulting in no timer activity.
>
> The problematic path seems to be
>
> * old device already has hrtimer_interrupt as the event_handler
> * new clockevent device registers with a higher rating
> * tick_check_new_device() is called
> * clockevents_exchange_device() gets called
> * old->event_handler is set to clockevents_handle_noop
> * tick_setup_device() is called for the new device
> * which sets new->event_handler using the old->event_handler which is noop.
>
> Change the ordering so that new device inherits the proper handler.
>
> This does not have any issue in normal case as most likely all the clockevent
> devices are setup before the highres switch. But, can potentially be affecting
> some corner case where HPET force detect happens after the highres switch.
> This was a problem with HPET in MSI mode code that we have been experimenting
> with.
>
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>

Acked-by: Thomas Gleixner <tglx@linutronix.de>

Should go into stable as well.

/me looks for a brown paperbag

Thanks,

tglx

> ---
> include/linux/clockchips.h | 2 ++
> kernel/time/clockevents.c | 3 +--
> kernel/time/tick-common.c | 1 +
> 3 files changed, 4 insertions(+), 2 deletions(-)
>
> Index: tip/kernel/time/clockevents.c
> ===================================================================
> --- tip.orig/kernel/time/clockevents.c 2008-09-02 13:26:35.000000000 -0700
> +++ tip/kernel/time/clockevents.c 2008-09-02 15:24:13.000000000 -0700
> @@ -177,7 +177,7 @@ void clockevents_register_device(struct
> /*
> * Noop handler when we shut down an event device
> */
> -static void clockevents_handle_noop(struct clock_event_device *dev)
> +void clockevents_handle_noop(struct clock_event_device *dev)
> {
> }
>
> @@ -199,7 +199,6 @@ void clockevents_exchange_device(struct
> * released list and do a notify add later.
> */
> if (old) {
> - old->event_handler = clockevents_handle_noop;
> clockevents_set_mode(old, CLOCK_EVT_MODE_UNUSED);
> list_del(&old->list);
> list_add(&old->list, &clockevents_released);
> Index: tip/kernel/time/tick-common.c
> ===================================================================
> --- tip.orig/kernel/time/tick-common.c 2008-09-02 13:26:35.000000000 -0700
> +++ tip/kernel/time/tick-common.c 2008-09-02 15:24:13.000000000 -0700
> @@ -161,6 +161,7 @@ static void tick_setup_device(struct tic
> } else {
> handler = td->evtdev->event_handler;
> next_event = td->evtdev->next_event;
> + td->evtdev->event_handler = clockevents_handle_noop;
> }
>
> td->evtdev = newdev;
> Index: tip/include/linux/clockchips.h
> ===================================================================
> --- tip.orig/include/linux/clockchips.h 2008-09-02 13:26:34.000000000 -0700
> +++ tip/include/linux/clockchips.h 2008-09-02 15:24:13.000000000 -0700
> @@ -127,6 +127,8 @@ extern int clockevents_register_notifier
> extern int clockevents_program_event(struct clock_event_device *dev,
> ktime_t expires, ktime_t now);
>
> +extern void clockevents_handle_noop(struct clock_event_device *dev);
> +
> #ifdef CONFIG_GENERIC_CLOCKEVENTS
> extern void clockevents_notify(unsigned long reason, void *arg);
> #else
> --
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