Re: [PATCH v4 08/16] locking/rwsem: Make rwsem_spin_on_owner() return owner state

[Peter Zijlstra]

On Wed, Apr 17, 2019 at 02:29:02PM -0400, Waiman Long wrote:
> On 04/17/2019 08:47 AM, Peter Zijlstra wrote:
> >>
> >> enum owner_state {
> >> 	OWNER_NULL		= 1 << 0,
> >> 	OWNER_WRITER		= 1 << 1,
> >> 	OWNER_READER		= 1 << 2,
> >> 	OWNER_NONSPINNABLE	= 1 << 3,
> >> };
> >> #define OWNER_SPINNABLE		(OWNER_NULL | OWNER_WRITER)
> > Hmm, we should not spin on OWNER_NULL. Or at least not mixed in with the
> > patch that changes the shape of all this. That should go in the RT
> > thingy patch, which comes after this.
> 
> We do spin on OWNER_NULL right now, not in rwsem_spin_on_owner() but in
> the main rwsem_optimistic_spin() function.
> 
> RT task will quit if owner is NULL.

Yeah, I figured it out eventually :-)