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SubjectRe: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin()
On Fri, 12 Feb 2016, Peter Zijlstra wrote:

>On Fri, Feb 12, 2016 at 12:32:12PM -0500, Waiman Long wrote:
>> static bool mutex_optimistic_spin(struct mutex *lock,
>> + struct ww_acquire_ctx *ww_ctx,
>> + const bool use_ww_ctx, int waiter)
>> {
>> struct task_struct *task = current;
>> + bool acquired = false;
>>
>> + if (!waiter) {
>> + if (!mutex_can_spin_on_owner(lock))
>> + goto done;
>
>Why doesn't the waiter have to check mutex_can_spin_on_owner() ?

afaict because mutex_can_spin_on_owner() fails immediately when the counter
is -1, which is a nono for the waiters case.

Thanks,
Davidlohr

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