Re: [PATCH v8 14/19] locking/rwsem: Enable time-based spinning on reader-owned rwsem

[Waiman Long]

On 6/4/19 5:03 AM, Peter Zijlstra wrote:
> On Mon, May 20, 2019 at 04:59:13PM -0400, Waiman Long wrote:
>> +static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
>> +{
>> +	long owner = atomic_long_read(&sem->owner);
>> +
>> +	while (owner & RWSEM_READER_OWNED) {
>> +		if (owner & RWSEM_NONSPINNABLE)
>> +			break;
>> +		owner = atomic_long_cmpxchg(&sem->owner, owner,
>> +					    owner | RWSEM_NONSPINNABLE);
>> +	}
>> +}
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -206,12 +206,13 @@ static inline void rwsem_set_nonspinnabl
>  {
>  	long owner = atomic_long_read(&sem->owner);
>  
> -	while (owner & RWSEM_READER_OWNED) {
> +	do {
> +		if (!(owner & RWSEM_READER_OWNED))
> +			break;
>  		if (owner & RWSEM_NONSPINNABLE)
>  			break;
> -		owner = atomic_long_cmpxchg(&sem->owner, owner,
> -					    owner | RWSEM_NONSPINNABLE);
> -	}
> +	} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
> +					  owner | RWSEM_NONSPINNABLE));
>  }
>  
>  /*

Sure.

Thanks,
Longman