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

[Waiman Long]

On 05/15/2018 02:05 PM, Amir Goldstein wrote:
> 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.

Yes, it is a good idea. I will do that.

-Longman