[PATCH RT 10/32] hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration_base

Steven Rostedt
2020-01-17T17:41:38Z

From: Julien Grall <julien.grall@arm.com>

[ Upstream commit cef1b87f98823af923a386f3f69149acb212d4a1 ]

As tglx puts it:
|If base == migration_base then there is no point to lock soft_expiry_lock
|simply because the timer is not executing the callback in soft irq context
|and the whole lock/unlock dance can be avoided.

Furthermore, all the path leading to hrtimer_grab_expiry_lock() assumes
timer->base and timer->base->cpu_base are always non-NULL. So it is safe
to remove the NULL checks here.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908211557420.2223@nanos.tec.linutronix.de
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
[bigeasy: rewrite changelog]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/time/hrtimer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 49d20fe8570f..1a5167c68310 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -943,7 +943,7 @@ void hrtimer_grab_expiry_lock(const struct hrtimer *timer)
{
struct hrtimer_clock_base *base = READ_ONCE(timer->base);

- if (timer->is_soft && base && base->cpu_base) {
+ if (timer->is_soft && base != &migration_base) {
spin_lock(&base->cpu_base->softirq_expiry_lock);
spin_unlock(&base->cpu_base->softirq_expiry_lock);
}
--
2.24.1