Re: [PATCH 1/3] jump_labels: fix concurrent static_key_enable/disable()

[Paolo Bonzini]

On 01/08/2017 18:45, Peter Zijlstra wrote:
> 
> Thanks for doing these patches, I hadn't come around to them yet.
> 
> On Tue, Aug 01, 2017 at 05:24:04PM +0200, Paolo Bonzini wrote:
>>  
>> +void static_key_enable(struct static_key *key)
>> +{
>> +	STATIC_KEY_CHECK_USE();
>> +	if (atomic_read(&key->enabled) > 0) {
>> +		WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
>> +		return;
>> +	}
>> +
>> +	cpus_read_lock();
>> +	jump_label_lock();
>> +	if (atomic_read(&key->enabled) == 0) {
>> +		atomic_set(&key->enabled, -1);
>> +		jump_label_update(key);
> 
> As per the previous discussion, should I do a patch adding barriers here
> (or using atomic_set_release()) such that we close the window where a
> concurrent inc/enable sees 1 but not all text changes?

Sure, and that applies to static_key_slow_inc as well.

Paolo

>> +		atomic_set(&key->enabled, 1);
>> +	}
>> +	jump_label_unlock();
>> +	cpus_read_unlock();
>> +}
>> +EXPORT_SYMBOL_GPL(static_key_enable);