John Stultz <john.stu...@linaro.org> writes:
> On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange <nicsta...@gmail.com> wrote:
>> In order to avoid races between setting a struct clock_event_device's
>> ->mult_mono in clockevents_update_freq() and yet to be implemented updates
>> triggered from the timekeeping core, the setting of ->mult and ->mult_mono
>> should be made atomic.
>>
>> Protect the update in clockevents_update_freq() by locking the
>> clockevents_lock spinlock. Frequency updates are expected to be done
>> seldomly and thus, taking this subsystem lock should not have any impact
>> on performance.
>>
>> Use a raw_spin_lock_irq_save()/raw_spin_unlock_irq_restore() pair for
>> locking/unlocking the clockevents_lock spinlock.
>> Purge the now redundant local_irq_save()/local_irq_restore() pair from
>> clockevents_update_freq(). Since the call to tick_broadcast_update_freq()
>> isn't done with interrupts disabled anymore, its
>> raw_spin_lock()/raw_spin_unlock() pair must be converted to
>> raw_spin_lock_irq_save()/raw_spin_unlock_irq_restore().
>>
>> Signed-off-by: Nicolai Stange <nicsta...@gmail.com>
>> ---
>> kernel/time/clockevents.c | 7 ++++---
>> kernel/time/tick-broadcast.c | 5 +++--
>> 2 files changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
>> index ba7fea4..ec01375 100644
>> --- a/kernel/time/clockevents.c
>> +++ b/kernel/time/clockevents.c
>> @@ -589,11 +589,12 @@ int clockevents_update_freq(struct clock_event_device
>> *dev, u32 freq)
>> unsigned long flags;
>> int ret;
>>
>> - local_irq_save(flags);
>> ret = tick_broadcast_update_freq(dev, freq);
>> - if (ret == -ENODEV)
>> + if (ret == -ENODEV) {
>> + raw_spin_lock_irqsave(&clockevents_lock, flags);
>> ret = __clockevents_update_freq(dev, freq);
>> - local_irq_restore(flags);
>> + raw_spin_unlock_irqrestore(&clockevents_lock, flags);
>> + }
>> return ret;
>> }
>>
>> diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
>> index f6aae79..9c94c41 100644
>> --- a/kernel/time/tick-broadcast.c
>> +++ b/kernel/time/tick-broadcast.c
>> @@ -125,11 +125,12 @@ int tick_is_broadcast_device(struct clock_event_device
>> *dev)
>> int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq)
>> {
>> int ret = -ENODEV;
>> + unsigned long flags;
>>
>> if (tick_is_broadcast_device(dev)) {
>> - raw_spin_lock(&tick_broadcast_lock);
>> + raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
>> ret = __clockevents_update_freq(dev, freq);
>> - raw_spin_unlock(&tick_broadcast_lock);
>> + raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
>> }
>
>
> So not necessarily part of your change, but this makes using
> tick_broadcast_update_freq() seem strange.
>
> We call it and if dev is a broadcast_device we call
> __clockevents_update_freq(), and if not, it fails and we then just
> call __clockevents_update_freq() again?
Yes, but the first call is made under a different lock than the second
one.
>
> Why bother calling tick_broadcast_update_freq here, and instead just
> call __clockevents_update_freq() directly the first time?
Thanks,
Nicolai
