linux-kernel - Re: [PATCH v4 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY

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Date:   Fri, 18 May 2018 09:02:58 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Oleg Nesterov <oleg@...hat.com>,
        Amir Goldstein <amir73il@...il.com>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v4 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED
 flag


* Matthew Wilcox <willy@...radead.org> wrote:

> On Tue, May 15, 2018 at 05:49:50PM -0400, Waiman Long wrote:
> > @@ -357,11 +357,8 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
> >  
> >  	rcu_read_lock();
> >  	owner = READ_ONCE(sem->owner);
> > -	if (!rwsem_owner_is_writer(owner)) {
> > -		/*
> > -		 * Don't spin if the rwsem is readers owned.
> > -		 */
> > -		ret = !rwsem_owner_is_reader(owner);
> > +	if (!owner || !is_rwsem_owner_spinnable(owner)) {
> > +		ret = !owner;	/* !owner is spinnable */
> >  		goto done;
> >  	}
> 
> This is confusingly written.  I think you mean ...
> 
> 	if (!owner)
> 		goto done;
> 	if (!is_rwsem_owner_spinnable(owner)) {
> 		ret = false;
> 		goto done;
> 	}

Yes, that's cleaner. Waiman, mind sending a followup patch that cleans this up?

Thanks,

	Ingo