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SubjectRe: [PATCH v4 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED flag
On 05/18, Ingo Molnar wrote:
>
>
> * Matthew Wilcox <willy@infradead.org> wrote:
>
> > This is confusingly written. I think you mean ...
> >
> > if (!owner)
> > goto done;
> > if (!is_rwsem_owner_spinnable(owner)) {
> > ret = false;
> > goto done;
> > }
>
> Yes, that's cleaner. Waiman, mind sending a followup patch that cleans this up?

Or simply

static inline bool owner_on_cpu(struct task_struct *owner)
{
return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
}

static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *owner;
bool ret = true;

if (need_resched())
return false;

rcu_read_lock();
owner = READ_ONCE(sem->owner);
if (owner) {
ret = is_rwsem_owner_spinnable(owner) &&
owner_on_cpu(owner);
}
rcu_read_unlock();
return ret;
}

note that rwsem_spin_on_owner() can use the new owner_on_cpu() helper too,

if (need_resched() || !owner_on_cpu(owner)) {
rcu_read_unlock();
return false;
}

looks a bit better than the current code:

if (!owner->on_cpu || need_resched() ||
vcpu_is_preempted(task_cpu(owner))) {
rcu_read_unlock();
return false;
}

Oleg.

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