Re: [PATCH v2] locking/mutex: Prevent lock starvation when spinning is enabled

[Waiman Long]

On 08/18/2016 10:14 AM, Peter Zijlstra wrote:
> On Wed, Aug 10, 2016 at 11:44:08AM -0700, Jason Low wrote:
> > diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> > index 2cb7531..5643a233 100644
> > --- a/include/linux/mutex.h
> > +++ b/include/linux/mutex.h
> > @@ -57,6 +57,8 @@ struct mutex {
> >   #endif
> >   #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
> >   	struct optimistic_spin_queue osq; /* Spinner MCS lock */
> > +#elif defined(CONFIG_SMP)
> > +	bool yield_to_waiter; /* Prevent starvation when spinning disabled */
> >   #endif
> >   #ifdef CONFIG_DEBUG_MUTEXES
> >   	void			*magic;
> Isn't this also possible on !SMP&&  PREEMPT ?

I don't think there is any realistic chance that starvation will happen 
on a uniprocessor system with preemptible kernel. So I don't think that 
is necessary.

Cheers,
Longman