linux-kernel - Re: [PATCH 3/6] sched_ext: Make @rf optional for dispatch_to_local

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Message-ID: <20240710114142.GY27299@noisy.programming.kicks-ass.net>
Date: Wed, 10 Jul 2024 13:41:42 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrea Righi <righi.andrea@...il.com>
Cc: Tejun Heo <tj@...nel.org>, void@...ifault.com,
	linux-kernel@...r.kernel.org, kernel-team@...a.com,
	schatzberg.dan@...il.com, mingo@...hat.com, changwoo@...lia.com
Subject: Re: [PATCH 3/6] sched_ext: Make @rf optional for
 dispatch_to_local_dsq()

On Wed, Jul 10, 2024 at 10:59:29AM +0200, Andrea Righi wrote:
> On Tue, Jul 09, 2024 at 11:21:09AM -1000, Tejun Heo wrote:
> ...
> > @@ -2052,17 +2052,20 @@ static bool move_task_to_local_dsq(struct rq *rq, struct task_struct *p,
> >  static void dispatch_to_local_dsq_lock(struct rq *rq, struct rq_flags *rf,
> >  				       struct rq *src_rq, struct rq *dst_rq)
> >  {
> > -	rq_unpin_lock(rq, rf);
> > +	if (rf)
> > +		rq_unpin_lock(rq, rf);
> >  
> >  	if (src_rq == dst_rq) {
> >  		raw_spin_rq_unlock(rq);
> >  		raw_spin_rq_lock(dst_rq);
> >  	} else if (rq == src_rq) {
> >  		double_lock_balance(rq, dst_rq);
> > -		rq_repin_lock(rq, rf);
> > +		if (rf)
> > +			rq_repin_lock(rq, rf);
> >  	} else if (rq == dst_rq) {
> >  		double_lock_balance(rq, src_rq);
> > -		rq_repin_lock(rq, rf);
> > +		if (rf)
> > +			rq_repin_lock(rq, rf);
> >  	} else {
> >  		raw_spin_rq_unlock(rq);
> >  		double_rq_lock(src_rq, dst_rq);
> 
> Not a blocker, but would it make sense to provide some wrappers for
> rq_unpin_lock() / rq_repin_lock() to simply return if rf == NULL?

There are very limited contexts where unpin is sound. I have no idea if
this is one of them or not.