Re: [PATCH rdma-next 4/4] RDMA/uverbs: Expose the new GID query API to user space

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Sep 16, 2020 at 03:44:29PM +0300, Leon Romanovsky wrote:
> On Wed, Sep 16, 2020 at 09:04:40AM -0300, Jason Gunthorpe wrote:
> > On Wed, Sep 16, 2020 at 01:37:10PM +0300, Leon Romanovsky wrote:
> > > It depends on how you want to treat errors from rdma_read_gid_attr_ndev_rcu().
> > > Current check allows us to ensure that any error returned by this call is
> > > handled.
> > >
> > > Otherwise we will find ourselves with something like this:
> > > ndev = rdma_read_gid_attr_ndev_rcu(gid_attr);
> > > if (IS_ERR(ndev)) {
> > > 	if (rdma_protocol_roce())
> > > 		goto error;
> > > 	if (ERR_PTR(ndev) != -ENODEV)
> > > 	        goto error;
> > > }
> >
> > Isn't it just
> >
> > if (IS_ERR(ndev)) {
> >    if (ERR_PTR(ndev) != -ENODEV)
> >         goto error;
> >    index = -1;
> > }
> >
> > Which seems fine and clear enough
> 
> It is a problem if roce device returned -ENODEV.

Can it happen? RCU I suppose, but I think this is an issue in
rdma_read_gid_attr_ndev_rcu() - it should not return ENODEV if the RCU
shows the gid_attr is being concurrently destroyed

Jason