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Date: Tue, 15 May 2018 11:02:19 -0700
From: Matthew Wilcox <willy@infradead.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: [PATCH v3 2/2] locking/percpu-rwsem: Annotate rwsem ownership
 transfer by setting RWSEM_OWNER_UNKNOWN
Message-ID: <20180515180219.GA6612@bombadil.infradead.org>
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On Tue, May 15, 2018 at 07:58:05PM +0200, Peter Zijlstra wrote:
> On Tue, May 15, 2018 at 01:38:04PM -0400, Waiman Long wrote:
> > +/*
> > + * Owner value to indicate the rwsem's owner is not currently known.
> > + */
> > +#define RWSEM_OWNER_UNKNOWN	((struct task_struct *)-1)
> 
> It might be nice to comment that this works and relies on having that
> ANON_OWNER bit set.

I'd rather change the definition to be ((struct task_struct *)2)
otherwise this is both reader-owned and anonymously-owned which doesn't
make much sense.