Messages in this thread | | | Subject | Re: [PATCH v2] rwsem: Support optimistic spinning | From | Davidlohr Bueso <> | Date | Mon, 28 Apr 2014 20:05:08 -0700 |
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On Mon, 2014-04-28 at 17:50 -0700, Tim Chen wrote: > On Mon, 2014-04-28 at 16:10 -0700, Paul E. McKenney wrote: > > > > +#ifdef CONFIG_SMP > > > +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) > > > +{ > > > + int retval; > > > + struct task_struct *owner; > > > + > > > + rcu_read_lock(); > > > + owner = ACCESS_ONCE(sem->owner); > > > > OK, I'll bite... > > > > Why ACCESS_ONCE() instead of rcu_dereference()? > > We're using it as a speculative check on the sem->owner to see > if the owner is running on the cpu. The rcu_read_lock > is used for ensuring that the owner->on_cpu memory is > still valid.
Something worth documenting in the code, imho. I'll add it in an eventual v3.
Thanks, Davidlohr
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