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

[Amir Goldstein]

On Tue, May 15, 2018 at 9:02 PM, Waiman Long <longman@xxxxxxxxxx> wrote:
> On 05/15/2018 01:58 PM, 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 am just trying not to expose internal working of rwsem, but I can
> document that one of the bits is the real deal without specifying which one.
>

BUILD_BUG_ON(!rwsem_has_anonymous_owner(RWSEM_OWNER_UNKNOWN))
inside rwsem.c and comment above to explain it.

Thanks,
Amir.