Re: [RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[John Stultz]

On Thu, Jul 21, 2016 at 12:24 PM, Nicolai Stange  wrote:
> John Stultz  writes:
>
>> On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange  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 
>>> ---
>>>  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(_lock, flags);
>>> ret = __clockevents_update_freq(dev, freq);
>>> -   local_irq_restore(flags);
>>> +   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
>>> +   raw_spin_lock_irqsave(_broadcast_lock, flags);
>>> ret = __clockevents_update_freq(dev, freq);
>>> -   raw_spin_unlock(_broadcast_lock);
>>> +   raw_spin_unlock_irqrestore(_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

Re: [RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[John Stultz]

On Thu, Jul 21, 2016 at 12:24 PM, Nicolai Stange  wrote:
> John Stultz  writes:
>
>> On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange  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 
>>> ---
>>>  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(_lock, flags);
>>> ret = __clockevents_update_freq(dev, freq);
>>> -   local_irq_restore(flags);
>>> +   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
>>> +   raw_spin_lock_irqsave(_broadcast_lock, flags);
>>> ret = __clockevents_update_freq(dev, freq);
>>> -   raw_spin_unlock(_broadcast_lock);
>>> +   raw_spin_unlock_irqrestore(_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

Re: [RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[Nicolai Stange]

John Stultz  writes:

> On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange  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 
>> ---
>>  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(_lock, flags);
>> ret = __clockevents_update_freq(dev, freq);
>> -   local_irq_restore(flags);
>> +   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
>> +   raw_spin_lock_irqsave(_broadcast_lock, flags);
>> ret = __clockevents_update_freq(dev, freq);
>> -   raw_spin_unlock(_broadcast_lock);
>> +   raw_spin_unlock_irqrestore(_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

Re: [RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[Nicolai Stange]

John Stultz  writes:

> On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange  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 
>> ---
>>  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(_lock, flags);
>> ret = __clockevents_update_freq(dev, freq);
>> -   local_irq_restore(flags);
>> +   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
>> +   raw_spin_lock_irqsave(_broadcast_lock, flags);
>> ret = __clockevents_update_freq(dev, freq);
>> -   raw_spin_unlock(_broadcast_lock);
>> +   raw_spin_unlock_irqrestore(_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

Re: [RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[John Stultz]

On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange  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 
> ---
>  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(_lock, flags);
> ret = __clockevents_update_freq(dev, freq);
> -   local_irq_restore(flags);
> +   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
> +   raw_spin_lock_irqsave(_broadcast_lock, flags);
> ret = __clockevents_update_freq(dev, freq);
> -   raw_spin_unlock(_broadcast_lock);
> +   raw_spin_unlock_irqrestore(_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

Re: [RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[John Stultz]

On Wed, Jul 13, 2016 at 6:00 AM, Nicolai Stange  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 
> ---
>  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(_lock, flags);
> ret = __clockevents_update_freq(dev, freq);
> -   local_irq_restore(flags);
> +   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
> +   raw_spin_lock_irqsave(_broadcast_lock, flags);
> ret = __clockevents_update_freq(dev, freq);
> -   raw_spin_unlock(_broadcast_lock);
> +   raw_spin_unlock_irqrestore(_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

[RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[Nicolai Stange]

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 
---
 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(_lock, flags);
ret = __clockevents_update_freq(dev, freq);
-   local_irq_restore(flags);
+   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
+   raw_spin_lock_irqsave(_broadcast_lock, flags);
ret = __clockevents_update_freq(dev, freq);
-   raw_spin_unlock(_broadcast_lock);
+   raw_spin_unlock_irqrestore(_broadcast_lock, flags);
}
return ret;
 }
-- 
2.9.0

[RFC v3 2/3] kernel/time/clockevents: make setting of ->mult and ->mult_mono atomic

[Nicolai Stange]

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 
---
 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(_lock, flags);
ret = __clockevents_update_freq(dev, freq);
-   local_irq_restore(flags);
+   raw_spin_unlock_irqrestore(_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(_broadcast_lock);
+   raw_spin_lock_irqsave(_broadcast_lock, flags);
ret = __clockevents_update_freq(dev, freq);
-   raw_spin_unlock(_broadcast_lock);
+   raw_spin_unlock_irqrestore(_broadcast_lock, flags);
}
return ret;
 }
-- 
2.9.0