[Q] RCU usage in infiniband

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

Hi,

I've been randomly starting at infiniband code and noticed it uses
call_rcu() with a callback from its module. 

| drivers/infiniband/hw/mlx5/devx.c:         call_rcu(&event_sub->rcu, devx_free_subscription);
| drivers/infiniband/ulp/ipoib/ipoib_main.c: call_rcu(&neigh->rcu, ipoib_neigh_reclaim);

I don't see synchronize_rcu() and rcu_barrier() there so I've been
asking myself what ensures that the callback completes before module is
gone (via rmmod)? I would expect a rcu_barrier() in
ipoib_cleanup_module() for instance.

Is the unload path so "late" that the callbacks run before the module is
unmapped or is there something between the APIs that ensures this?

Sebastian