From: "Paul E. McKenney" Subject: Re: [PATCH 3/5] can: af_can.c use rcu_barrier() on module unload. Date: Mon, 8 Jun 2009 09:13:29 -0700 Message-ID: <20090608161329.GD6961@linux.vnet.ibm.com> References: <20090608130959.10052.54590.stgit@localhost> <20090608131138.10052.5408.stgit@localhost> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "David S. Miller" , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, urs.thuermann@volkswagen.de, oliver.hartkopp@volkswagen.de, wg@grandegger.com, vladislav.yasevich@hp.com, sri@us.ibm.com, linux-sctp@vger.kernel.org, Trond.Myklebust@netapp.com, linux-nfs@vger.kernel.org, netfilter-devel@vger.kernel.org To: Jesper Dangaard Brouer Return-path: In-Reply-To: <20090608131138.10052.5408.stgit@localhost> Sender: netfilter-devel-owner@vger.kernel.org List-ID: 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 > --- > > 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); > } > >