RDMA/cm: Remove a race freeing timewait_info

RDMA/cm: Remove a race freeing timewait_info

When creating a cm_id during REQ the id immediately becomes visible to the
other MAD handlers, and shortly after the state is moved to IB_CM_REQ_RCVD

This allows cm_rej_handler() to run concurrently and free the work:

        CPU 0                                CPU1
 cm_req_handler()
  ib_create_cm_id()
  cm_match_req()
    id_priv->state = IB_CM_REQ_RCVD
                                       cm_rej_handler()
                                         cm_acquire_id()
                                         spin_lock(&id_priv->lock)
                                         switch (id_priv->state)
  					   case IB_CM_REQ_RCVD:
                                            cm_reset_to_idle()
                                             kfree(id_priv->timewait_info);
   goto destroy
  destroy:
    kfree(id_priv->timewait_info);
                                             id_priv->timewait_info = NULL

Causing a double free or worse.

Do not free the timewait_info without also holding the
id_priv->lock. Simplify this entire flow by making the free unconditional
during cm_destroy_id() and removing the confusing special case error
unwind during creation of the timewait_info.

This also fixes a leak of the timewait if cm_destroy_id() is called in
IB_CM_ESTABLISHED with an XRC TGT QP. The state machine will be left in
ESTABLISHED while it needed to transition through IB_CM_TIMEWAIT to
release the timewait pointer.

Also fix a leak of the timewait_info if the caller mis-uses the API and
does ib_send_cm_reqs().

Fixes: a977049dacde ("[PATCH] IB: Add the kernel CM implementation")
Link: https://lore.kernel.org/r/20200310092545.251365-4-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>