Re: [PATCH v3 2/2] locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN

[Matthew Wilcox]

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.