Re: rdma provider module references

Roland Dreier
2010-12-15T17:09:12Z

> I notice that if I have a user rdma application running that has an
> rdma connection using iw_cxgb3, then the iw_cxgb3 module reference
> count is bumped and thus it cannot be unloaded. However when I have
> an NFSRDMA connection that utilizes iw_cxgb3, the module reference
> count is not bumped, and iw_cxgb3 can erroneously be unloaded while
> the NFSRDMA connection is still active, causing a crash.

What is supposed to happen is that as the HW driver is unloading, it
calls ib_unregister_device() first, and this calls each client's
.remove() method to have it release everything related to that device.

However I guess NFS/RDMA is behind the RDMA CM, which is supposed to
handle device removal. In that code it seems to end up in
cma_process_remove(), which appears at first glance to do the right
things to destroy all connections etc.

The idea is that RDMA devices should be like net devices, ie you can
remove them even if they're in use -- things should just clean up,
rather than blocking the module removal. The uverbs case is a bit of a
hack because we don't have a way to handle revoking the mmap regions
etc yet.

What goes wrong with NFS/RDMA in this scheme? It looks like it should work.

- R.