Re: [PATCH v3 2/2] locking/percpu-rwsem: Annotate rwsem ownership transfer by setting RWSEM_OWNER_UNKNOWN
From: Waiman Long
Date: Tue May 15 2018 - 14:35:45 EST
On 05/15/2018 02:05 PM, Peter Zijlstra wrote:
> On Tue, May 15, 2018 at 02:02:00PM -0400, Waiman Long 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.
> Thing is, you don't want someone changing this without knowing about
> that one magic bit. It doesn't hurt to be explicit here.
> Also, do we want -1L instead of a -1 literal?
Yes, I should -1L instead.