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SubjectRe: [PATCH v4 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED flag

* Oleg Nesterov <oleg@redhat.com> wrote:

> 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.

That looks good to me too - mind sending a patch on top of latest -tip?

Thanks,

Ingo

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