On Thu, Jul 21, 2016 at 12:24 PM, Nicolai Stange <[email protected]> wrote: > John Stultz <[email protected]> writes: > >> On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange <[email protected]> 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 <[email protected]> >>> --- >>> 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.
Ah. Thanks, that bit didn't stick out to me. -john
