Re: [PATCH 12/14] sched: Add shared runqueue locking to __task_rq_lock()

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Sep 12, 2025 at 01:54:59PM +0200, Peter Zijlstra wrote:
> On Thu, Sep 11, 2025 at 02:19:57PM -1000, Tejun Heo wrote:
> > Hello,
> > 
> > On Wed, Sep 10, 2025 at 05:44:21PM +0200, Peter Zijlstra wrote:
> > > @@ -703,17 +703,24 @@ void double_rq_lock(struct rq *rq1, stru
> > >  struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
> > >  	__acquires(rq->lock)
> > >  {
> > > +	raw_spinlock_t *slock;
> > >  	struct rq *rq;
> > >  
> > >  	lockdep_assert_held(&p->pi_lock);
> > >  
> > >  	for (;;) {
> > >  		rq = task_rq(p);
> > > +		slock = p->srq_lock;
> > >  		raw_spin_rq_lock(rq);
> > > -		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
> > > +		if (slock)
> > > +			raw_spin_lock(slock);
> > > +		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p) &&
> > > +			   (!slock || p->srq_lock == slock))) {
> > >  			rq_pin_lock(rq, rf);
> > >  			return rq;
> > >  		}
> 
> Yeah, I think that needs to change a little. Perhaps something like:
> 
> 	slock2 = p->srq_lock;
> 	if (... && (!slock2 || slock2 == slock))

I'm being stupid, all that wants is: && (p->srq_lock == slock). If there
is a mis-match, unlock and re-try.