[openib-general] [PATCH] ib_mad: In ib_mad_complete_recv, decrement agent refcount when not fully reassembled and when no request found

Mon Oct 25 10:14:15 PDT 2004

On Sun, 24 Oct 2004 13:38:01 -0400
Hal Rosenstock <halr at voltaire.com> wrote:

> ib_mad: In ib_mad_complete_recv, decrement agent reference count when
> receive is not fully reassembled, and also when solicited and no
> matching request is found. This allows deregistration to complete rather
> than waiting for an event which never occurs.
> ... 
>     /* Fully reassemble receive before processing */
>     recv = reassemble_recv(mad_agent_priv, recv);
> -   if (!recv)
> +   if (!recv) {
> +           atomic_dec(&mad_agent_priv->refcount);
>             return;
> +   }

I'm not sure about this.  If we just start assembling a MAD, we're probably going to want to maintain a reference on the MAD agent while the reassembly is occurring, in order to handle timeouts.  We'll have a better idea of what the RMPP code will do once it's actually written however, so that reference could be a different one.  If we do keep this code, it should probably be an atomic_dec_and_test, followed by a wake_up.

>         /* Complete corresponding request */
>     if (solicited) {
> @@ -884,6 +886,7 @@
>             if (!mad_send_wr) {
>                     spin_unlock_irqrestore(&mad_agent_priv->lock, flags);
>                     ib_free_recv_mad(&recv->header.recv_wc);
> +                   atomic_dec(&mad_agent_priv->refcount);
>                     return;

I think that we want this to be atomic_dec_and_test().  (Similar to the call near the end of this function.)  If a match is found, we can get away with a simple atomic_dec, since the send will still hold a reference on the mad agent.  But if no match is found, then I think this may be the last reference being held.