From: Julien Grall Date: Wed, 21 Aug 2019 10:24:07 +0100 Subject: [PATCH 292/353] 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=5817dd3ce58d48f4407ab82766339582745ff505 [ 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 Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt (VMware) --- 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 92ee6cf49c24..a868444c6154 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);