Re: [PATCH rc] RDMA/cma: Ensure rdma_addr_cancel() happens before issuing more requests

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Sep 23, 2021 at 09:15:44PM +0300, Leon Romanovsky wrote:
> On Thu, Sep 23, 2021 at 08:45:57AM -0300, Jason Gunthorpe wrote:
> > On Thu, Sep 23, 2021 at 08:49:06AM +0300, Leon Romanovsky wrote:
> > > On Wed, Sep 22, 2021 at 11:41:19AM -0300, Jason Gunthorpe wrote:
> > > > On Wed, Sep 22, 2021 at 11:01:39AM +0300, Leon Romanovsky wrote:
> > > > 
> > > > > > +			/* The FSM can return back to RDMA_CM_ADDR_BOUND after
> > > > > > +			 * rdma_resolve_ip() is called, eg through the error
> > > > > > +			 * path in addr_handler. If this happens the existing
> > > > > > +			 * request must be canceled before issuing a new one.
> > > > > > +			 */
> > > > > > +			if (id_priv->used_resolve_ip)
> > > > > > +				rdma_addr_cancel(&id->route.addr.dev_addr);
> > > > > > +			else
> > > > > > +				id_priv->used_resolve_ip = 1;
> > > > > 
> > > > > Why don't you never clear this field?
> > > > 
> > > > The only case where it can be cleared is if we have called
> > > > rdma_addr_cancel(), and since this is the only place that does it and
> > > > immediately calls rdma_resolve_ip() again, there is no reason to ever
> > > > clear it.
> > > 
> > > IMHO, it is better to clear instead to rely on "the only place" semantic.
> > 
> > Then the code looks really silly:
> > 
> > 	if (id_priv->used_resolve_ip) {
> > 		rdma_addr_cancel(&id->route.addr.dev_addr);
> >                 id_priv->used_resolve_ip = 0;
> >         }
> >         id_priv->used_resolve_ip = 1;
> 
> So write comment why you don't need to clear used_resolve_ip, but don't
> leave it as it is now, where readers need to guess.
>

I think it is a bit wordy, but I put this:

			/*
			 * The FSM can return back to RDMA_CM_ADDR_BOUND after
			 * rdma_resolve_ip() is called, eg through the error
			 * path in addr_handler(). If this happens the existing
			 * request must be canceled before issuing a new one.
			 * Since canceling a request is a bit slow and this
			 * oddball path is rare, keep track once a request has
			 * been issued. The track turns out to be a permanent
			 * state since this is the only cancel as it is
			 * immediately before rdma_resolve_ip().
			 */

And into for-rc

Jason