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From: Julien Grall <julien.grall@arm.com>
Date: Wed, 21 Aug 2019 10:24:07 +0100
Subject: [PATCH 292/354] hrtimer: Use READ_ONCE to access timer->base in
hrimer_grab_expiry_lock()
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=633223e872d06689128bafec90d4f2454a3218c9
[ 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 089c74ff0511..648e41adf4ac 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -959,7 +959,7 @@ 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);
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