Re: [PATCH 3/5] can: af_can.c use rcu_barrier() on module unload.

Paul E. McKenney
2009-06-08T16:13:29Z

On Mon, Jun 08, 2009 at 03:11:38PM +0200, Jesper Dangaard Brouer wrote:
> This module uses rcu_call() thus it should use rcu_barrier()
> on module unload.

This does appear to make things better!!!

However, I don't understand why it is safe to do the following in
can_exit():

hlist_for_each_entry_safe(d, n, next, &can_rx_dev_list, list) {
hlist_del(&d->list);
kfree(d);
}

Given that this list is scanned by RCU readers, shouldn't this kfree()
be something like "call_rcu(&d->rcu, can_rx_delete_device);"?

Also, what frees up the "struct receiver" structures?

Thanx, Paul

> Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
> ---
>
> net/can/af_can.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/net/can/af_can.c b/net/can/af_can.c
> index 10f0528..e733725 100644
> --- a/net/can/af_can.c
> +++ b/net/can/af_can.c
> @@ -903,6 +903,8 @@ static __exit void can_exit(void)
> }
> spin_unlock(&can_rcvlists_lock);
>
> + rcu_barrier(); /* Wait for completion of call_rcu()'s */
> +
> kmem_cache_destroy(rcv_cache);
> }
>
>