On Mon, Apr 28, 2014 at 03:09:01PM -0700, Davidlohr Bueso wrote:
> +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
> +{
> + int retval;
> + struct task_struct *owner;
> +
> + rcu_read_lock();
> + owner = ACCESS_ONCE(sem->owner);
> +
> + /* Spin only if active writer running */
> + if (owner)
> + retval = owner->on_cpu;
> + else {
> + /*
> + * When the owner is not set, the sem owner may have just
> + * acquired it and not set the owner yet, or the sem has
> + * been released, or reader active.
> + */
> + retval = false;
> + }
> + rcu_read_unlock();
> +
> + return retval;
> +}
Also, the mutex case has a need_resched() test in there; any particular
reason you didn't mirror that?
See 46af29e479cc0 ("locking/mutexes: Return false if task need_resched() in
mutex_can_spin_on_owner()")
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