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Subject[PATCH RT 4/9] kernel/hrtimer: dont wakeup a process while holding the hrtimer base lock
4.4.102-rt117-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

We must not wake any process (and thus acquire the pi->lock) while
holding the hrtimer's base lock. This does not happen usually because
the hrtimer-callback is invoked in IRQ-context and so
raise_softirq_irqoff() does not wakeup a process.
However during CPU-hotplug it might get called from hrtimers_dead_cpu()
which would wakeup the thread immediately.

Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/time/hrtimer.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 759913626eec..78066f7ea2a2 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1461,7 +1461,7 @@ static inline int hrtimer_rt_defer(struct hrtimer *timer) { return 0; }

static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer);

-static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
+static int __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
{
struct hrtimer_clock_base *base = cpu_base->clock_base;
unsigned int active = cpu_base->active_bases;
@@ -1511,8 +1511,7 @@ static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
raise = 1;
}
}
- if (raise)
- raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+ return raise;
}

#ifdef CONFIG_HIGH_RES_TIMERS
@@ -1526,6 +1525,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
ktime_t expires_next, now, entry_time, delta;
int retries = 0;
+ int raise;

BUG_ON(!cpu_base->hres_active);
cpu_base->nr_events++;
@@ -1544,7 +1544,7 @@ retry:
*/
cpu_base->expires_next.tv64 = KTIME_MAX;

- __hrtimer_run_queues(cpu_base, now);
+ raise = __hrtimer_run_queues(cpu_base, now);

/* Reevaluate the clock bases for the next expiry */
expires_next = __hrtimer_get_next_event(cpu_base);
@@ -1555,6 +1555,8 @@ retry:
cpu_base->expires_next = expires_next;
cpu_base->in_hrtirq = 0;
raw_spin_unlock(&cpu_base->lock);
+ if (raise)
+ raise_softirq_irqoff(HRTIMER_SOFTIRQ);

/* Reprogramming necessary ? */
if (!tick_program_event(expires_next, 0)) {
@@ -1634,6 +1636,7 @@ void hrtimer_run_queues(void)
{
struct hrtimer_cpu_base *cpu_base = this_cpu_ptr(&hrtimer_bases);
ktime_t now;
+ int raise;

if (__hrtimer_hres_active(cpu_base))
return;
@@ -1652,8 +1655,10 @@ void hrtimer_run_queues(void)

raw_spin_lock(&cpu_base->lock);
now = hrtimer_update_base(cpu_base);
- __hrtimer_run_queues(cpu_base, now);
+ raise = __hrtimer_run_queues(cpu_base, now);
raw_spin_unlock(&cpu_base->lock);
+ if (raise)
+ raise_softirq_irqoff(HRTIMER_SOFTIRQ);
}

/*
--
2.13.2

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