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SubjectRe: [PATCH v2 2/8] IB/core: Replace semaphore sm_sem with completion
On Tue, Oct 25, 2016 at 08:38:21PM +0530, Binoy Jayan wrote:
> On 25 October 2016 at 18:13, Jack Wang <xjtuwjp@gmail.com> wrote:
> > Hi Binoy,
> >
> > snip
> >>
> >> port->ib_dev = device;
> >> port->port_num = port_num;
> >> - sema_init(&port->sm_sem, 1);
> >> + init_completion(&port->sm_comp);
> >> + complete(&port->sm_comp);
> >
> > Why complete here?
> >
> >> mutex_init(&port->file_mutex);
> >> INIT_LIST_HEAD(&port->file_list);
> >>
> > KR,
> > Jinpu
>
>
> Hi Jack,
>
> ib_umad_sm_open() calls wait_for_completion_interruptible() which
> comes before ib_umad_sm_close() that calls complete(). In the
> initial open() there will not be anybody to signal the completion,
> so the complete is called to mark the initial state. I am not sure
> if this is the right way to do it, though.

Using a completion to model exclusive ownership seems convoluted to
me - is that a thing now? What about an atomic?

open:

while (true) {
wait_event_interruptible(priv->queue,test_bit(CLAIMED_BIT, &priv->flags));
if (!test_and_set_bit(CLAIMED_BIT, &priv->flags))
break;
}

close():

clear_bit(CLAIMED_BIT, &priv->flags)
wake_up(&priv->queue);

??

Jason

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