Messages in this thread Patch in this message | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] hrtimer: Interrupt storm on clock_settime | Date | Fri, 05 Feb 2021 16:45:42 +0100 |
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On Thu, Jan 28 2021 at 15:02, Mikael Beckius wrote:
> During clock_settime absolute realtime timers may get updated to expire > sooner in absolute monotonic time but if hrtimer_force_reprogram is > called as part of a clock_settime and the next hard hrtimer expires > before the next soft hrtimer softirq_expires_next will not be updated > to reflect this change (assuming the realtime timer is a soft timer). > > This means that if the next soft hrtimer expires before > softirq_expires_next but after now no soft hrtimer interrupt will be > raised in hrtimer_interrupt which will instead retry tick_program_event > three times before forcing a tick_program_event using a very short delay > entering hrtimer_interrupt again almost immediately repeating the > process over and over again until now exceeds softirq_expires_next and a > soft hrtimer interrupt is finally raised.
Duh.
> This patch aims to solve this by always updating softirq_expires_next if > a soft hrtimer exists.
git grep 'This patch' Documentation/process/
> Signed-off-by: Mikael Beckius <mikael.beckius@windriver.com> > --- > kernel/time/hrtimer.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c > index 743c852e10f2..e4c233f404b1 100644 > --- a/kernel/time/hrtimer.c > +++ b/kernel/time/hrtimer.c > @@ -633,7 +633,7 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) > */ > expires_next = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_ALL); > > - if (cpu_base->next_timer && cpu_base->next_timer->is_soft) { > + if (cpu_base->softirq_next_timer) {
> /* > * When the softirq is activated, hrtimer has to be > * programmed with the first hard hrtimer because soft > @@ -643,7 +643,8 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) > expires_next = __hrtimer_get_next_event(cpu_base, > HRTIMER_ACTIVE_HARD); > else > - cpu_base->softirq_expires_next = expires_next; > + cpu_base->softirq_expires_next = __hrtimer_get_next_event(cpu_base, > + HRTIMER_ACTIVE_SOFT);
That works, but we can spare the double scan completely and make the code understandable. See below.
Thanks,
tglx ---
--- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -626,26 +626,25 @@ static inline int hrtimer_hres_active(vo static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) { - ktime_t expires_next; + ktime_t expires_next, soft = KTIME_MAX; /* - * Find the current next expiration time. + * If soft interrupt has already been activated, ignore the soft + * base. It will be handled in the already raised soft interrupt. */ - expires_next = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_ALL); - - if (cpu_base->next_timer && cpu_base->next_timer->is_soft) { + if (!cpu_base->softirq_activated) { + soft = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_SOFT); /* - * When the softirq is activated, hrtimer has to be - * programmed with the first hard hrtimer because soft - * timer interrupt could occur too late. + * Update the soft expiry time. clock_settime() might have + * affected it. */ - if (cpu_base->softirq_activated) - expires_next = __hrtimer_get_next_event(cpu_base, - HRTIMER_ACTIVE_HARD); - else - cpu_base->softirq_expires_next = expires_next; + cpu_base->softirq_expires_next = soft; } + expires_next = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_HARD); + if (expires_next > soft) + expires_next = soft; + if (skip_equal && expires_next == cpu_base->expires_next) return;
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