linux/debian/patches-rt/0294-hrtimer-Use-READ_ONCE-to-access-timer-base-in-hrimer.patch

From e7c83855d0557c416f5940cc7c57095b166f993f Mon Sep 17 00:00:00 2001
From: Julien Grall <julien.grall@arm.com>
Date: Wed, 21 Aug 2019 10:24:07 +0100
Subject: [PATCH 294/325] hrtimer: Use READ_ONCE to access timer->base in
 hrimer_grab_expiry_lock()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.115-rt48.tar.xz

[ Upstream commit 2c8fdbe7ef0ad06c1a326886c5954e117b5657d6 ]

The update to timer->base is protected by the base->cpu_base->lock().
However, hrtimer_grab_expirty_lock() does not access it with the lock.

So it would theorically be possible to have timer->base changed under
our feet. We need to prevent the compiler to refetch timer->base so the
check and the access is performed on the same base.

Other access of timer->base are either done with a lock or protected
with READ_ONCE(). So use READ_ONCE() in hrtimer_grab_expirty_lock().

Signed-off-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 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 94d97eae0a46..d6026c170c2d 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -941,7 +941,7 @@ EXPORT_SYMBOL_GPL(hrtimer_forward);
 
 void hrtimer_grab_expiry_lock(const struct hrtimer *timer)
 {
-	struct hrtimer_clock_base *base = timer->base;
+	struct hrtimer_clock_base *base = READ_ONCE(timer->base);
 
 	if (base && base->cpu_base) {
 		spin_lock(&base->cpu_base->softirq_expiry_lock);
-- 
2.25.1