netdev - Re: [PATCH 4/5] sctp: protocol.c call rcu

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Message-ID: <20090609155011.GD6789@linux.vnet.ibm.com>
Date:	Tue, 9 Jun 2009 08:50:11 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Vlad Yasevich <vladislav.yasevich@...com>
Cc:	Jesper Dangaard Brouer <hawk@...x.dk>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, urs.thuermann@...kswagen.de,
	oliver.hartkopp@...kswagen.de, wg@...ndegger.com, sri@...ibm.com,
	linux-sctp@...r.kernel.org, Trond.Myklebust@...app.com,
	linux-nfs@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 4/5] sctp: protocol.c call rcu_barrier() on unload.

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@...ux.vnet.ibm.com>
> > 
> >> Signed-off-by: Jesper Dangaard Brouer <hawk@...x.dk>
> >> ---
> >>
> >>  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
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