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SubjectRe: [PATCH 1/3] [RFC] hrtimer: Fix clock_was_set so it is safe to call from irq context


On 07/04/2012 02:21 AM, 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 irq
> context, as it calls on_each_cpu(). This causes problems when
> we need to adjust the time from update_wall_time().
>
> To fix this, if clock_was_set is called when irqs are
> disabled, we schedule a timer to fire for immedately after
> we're out of interrupt context to then notify the hrtimer
> subsystem.
>
> CC: Prarit Bhargava <prarit@redhat.com>
> CC: stable@vger.kernel.org
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: linux@openhuawei.org
> Reported-by: Jan Engelhardt <jengelh@inai.de>
> Signed-off-by: John Stultz <johnstul@us.ibm.com>
> ---
> kernel/hrtimer.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index ae34bf5..d730678 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -746,7 +746,7 @@ static inline void retrigger_next_event(void *arg) { }
> * resolution timer interrupts. On UP we just disable interrupts and
> * call the high resolution interrupt code.
> */
> -void clock_was_set(void)
> +static void do_clock_was_set(unsigned long data)
> {
> #ifdef CONFIG_HIGH_RES_TIMERS
> /* Retrigger the CPU local events everywhere */
> @@ -755,6 +755,21 @@ void clock_was_set(void)
> timerfd_clock_was_set();
> }
>
> +static DEFINE_TIMER(clock_was_set_timer, do_clock_was_set , 0, 0);
> +
> +void clock_was_set(void)
> +{
> + /*
> + * We can't call on_each_cpu() from irq context,
> + * so if irqs are disabled , schedule the clock_was_set
> + * via a timer_list timer for right after.
> + */
> + if (irqs_disabled())

I was wondering about this in earlier versions of the patchset. I thought it
was supposed to be irqs_disabled. Thanks for changing this.

Acked-by: Prarit Bhargava <prarit@redhat.com>

P.


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