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hrtimer: Move unmarked hrtimers to soft interrupt expiry on RT 

On PREEMPT_RT not all hrtimers can be expired in hard interrupt context
even if that is perfectly fine on a PREEMPT_RT=n kernel, e.g. because they
take regular spinlocks. Also for latency reasons PREEMPT_RT tries to defer
most hrtimers' expiry into softirq context.

hrtimers marked with HRTIMER_MODE_HARD must be kept in hard interrupt
context expiry mode. Add the required logic.

No functional change for PREEMPT_RT=n kernels.

[ tglx: Split out of a larger combo patch. Added changelog ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190726185753.551967692@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2019-07-26 20:30:57 +02:00 committed by Thomas Gleixner
parent 902a9f9c50
commit f5c2f0215e
1 changed files with 11 additions and 1 deletions
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12
kernel/time/hrtimer.c
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@ -1275,8 +1275,17 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
enum hrtimer_mode mode)
{
bool softtimer = !!(mode & HRTIMER_MODE_SOFT);
int base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;
struct hrtimer_cpu_base *cpu_base;
int base;
/*
* On PREEMPT_RT enabled kernels hrtimers which are not explicitely
* marked for hard interrupt expiry mode are moved into soft
* interrupt context for latency reasons and because the callbacks
* can invoke functions which might sleep on RT, e.g. spin_lock().
*/
if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(mode & HRTIMER_MODE_HARD))
softtimer = true;
memset(timer, 0, sizeof(struct hrtimer));
@ -1290,6 +1299,7 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
if (clock_id == CLOCK_REALTIME && mode & HRTIMER_MODE_REL)
clock_id = CLOCK_MONOTONIC;
base = softtimer ? HRTIMER_MAX_CLOCK_BASES / 2 : 0;
base += hrtimer_clockid_to_base(clock_id);
timer->is_soft = softtimer;
timer->is_hard = !softtimer;