CVE-2026-89535

In the Linux kernel, the following vulnerability has been resolved:

svcrdma: Reorder rpcrdma_rn_unregister before rdma_destroy_id

svc_rdma_free() caches rdma->sc_cm_id->device before teardown,
then calls rdma_destroy_id(sc_cm_id) which frees the cm_id.
rpcrdma_rn_unregister() follows, but between those two calls
the transport's sc_rn entry is still installed in the device's
rd_xa. A concurrent ib_unregister_device walk can dispatch
svc_rdma_xprt_done() against the now-freed sc_cm_id.

Move rpcrdma_rn_unregister() before rdma_destroy_id() so the
transport's notification entry is removed from the xarray before
the cm_id it references is destroyed.

Also guard the sc_cm_id dereference with a NULL check: the
following patches introduce paths that reach svc_rdma_free()
with sc_cm_id == NULL (listener create failure, ADDR_CHANGE
replacement failure).