From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 26 Jul 2019 20:30:57 +0200
Subject: hrtimer: Move unmarked hrtimers to soft interrupt expiry on RT
Patch-mainline: v5.4-rc1
Git-commit: f5c2f0215e36d76fbb9605283dd7535af09f5770
References: bsc#1162702
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
Acked-by: Daniel Wagner <dwagner@suse.de>
---
kernel/time/hrtimer.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 0ace301a56f4..90dcc4d95e91 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -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;
--
2.16.4