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SubjectRe: [PATCH v8 14/19] locking/rwsem: Enable time-based spinning on reader-owned rwsem
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));
}

/*
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