Re: [PATCH 4/5] sctp: protocol.c call rcu_barrier() on unload.

Vlad Yasevich
2009-06-09T16:26:25Z

Paul E. McKenney wrote:
> On Tue, Jun 09, 2009 at 11:44:23AM -0400, Vlad Yasevich wrote:
>> Paul E. McKenney wrote:
>>> On Mon, Jun 08, 2009 at 03:11:43PM +0200, Jesper Dangaard Brouer wrote:
>>>> On module unload call rcu_barrier(), this is needed as synchronize_rcu()
>>>> is not strong enough. The kmem_cache_destroy() does invoke
>>>> synchronize_rcu() but it does not provide same protection.
>>> Good, looks like sctp_v4_del_protocol() invokes call_rcu(), which the
>>> rcu_barrier() would then wait for. And it looks like sctp_v6_del_protocol()
>>> does the same for IPv6.
>>>
>>> Reviewed_by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>>>
>>>> Signed-off-by: Jesper Dangaard Brouer <hawk-4UpuNZONu4c@public.gmane.org>
>>>> ---
>>>>
>>>> net/sctp/protocol.c | 2 ++
>>>> 1 files changed, 2 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
>>>> index cb2c50d..79cbd47 100644
>>>> --- a/net/sctp/protocol.c
>>>> +++ b/net/sctp/protocol.c
>>>> @@ -1370,6 +1370,8 @@ SCTP_STATIC __exit void sctp_exit(void)
>>>> sctp_proc_exit();
>>>> cleanup_sctp_mibs();
>>>>
>>>> + rcu_barrier(); /* Wait for completion of call_rcu()'s */
>>>> +
>>>> kmem_cache_destroy(sctp_chunk_cachep);
>>>> kmem_cache_destroy(sctp_bucket_cachep);
>>>> }
>> Shouldn't the rcu_barrier call be before sctp_free_local_addr_list()?
>
> Hmmm... What sequence of events would lead to a failure if
> rcu_barrier() is after sctp_free_local_addr_list()?
>
> Thanx, Paul
>

I thought that the notifier could could potentially execute at the
same time as the unregister(), but I see that's protected. So, I guess
it doesn't really matter then where the barrier is.

Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>

-vlad