linux-kernel - Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem

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Message-ID: <20180515140043.GH31599@bombadil.infradead.org>
Date:   Tue, 15 May 2018 07:00:43 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        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: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as
 non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 09:57:44AM -0400, Waiman Long wrote:
> > Afaict the whole .owner=NULL thing in release already stops the spinners
> > dead, and the above 'fixes' the debug splat. And this avoids exposing
> > that horrible interface and keeps the mucking private to
> > rwsem/percpu_rwsem.
> 
> Actually setting owner to NULL does not stop spinning. The code just
> assume that the lock is going to be freed and spin in the outer loop. We
> need some special value to indicate that spinning should be stopped. How
> about just exposing a special value for that in linux/rwsem.h? Any
> suggestion for a good name?

RWSEM_NO_OWNER