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? Why bother calling tick_broadcast_update_freq here, and instead just call __clockevents_update_freq() directly the first time? thanks -john