On Sat, 2015-03-07 at 10:21 +0100, Peter Zijlstra wrote:
> On Fri, Mar 06, 2015 at 11:45:31PM -0800, Jason Low wrote:
> > static noinline
> > bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct
> > *owner)
> > {
> > long count;
> >
> > rcu_read_lock();
> > + while (sem->owner == owner) {
> > + /*
> > + * Ensure we emit the owner->on_cpu, dereference _after_
> > + * checking sem->owner still matches owner, if that fails,
> > + * owner might point to free()d memory, if it still matches,
> > + * the rcu_read_lock() ensures the memory stays valid.
> > + */
> > + barrier();
> > +
> > + /* abort spinning when need_resched or owner is not running */
> > + if (!owner->on_cpu || need_resched()) {
> > rcu_read_unlock();
> > return false;
> > }
>
> Thanks, looks good; do we want to change the mutex code (again) to more
> closely resemble this too? It still has the while (true) instead of the
> while(lock->owner != owner).
Yeah, I wondered about the same thing, though I wasn't sure if you
wanted an additional patch just for that change.
Guess you answered it for me :)
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