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Date: Thu, 06 Dec 2012 13:35:49 -0500
From: Vlad Yasevich <vyasevich@...il.com>
To: Thomas Graf <tgraf@...g.ch>
CC: linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH] sctp: Add RCU protection to assoc->transport_addr_list
On 12/06/2012 01:15 PM, Thomas Graf wrote:
> peer.transport_addr_list is currently only protected by sk_sock
> which is inpractical to acquire for procfs dumping purposes.
>
> This patch adds RCU protection allowing for the procfs readers to
> enter RCU read-side critical sections.
>
> Modification of the list continues to be serialized via sk_lock.
>
> Cc: Vlad Yasevich <vyasevich@...il.com>
> Cc: Neil Horman <nhorman@...driver.com>
> Signed-off-by: Thomas Graf <tgraf@...g.ch>
> ---
> include/net/sctp/structs.h | 2 ++
> net/sctp/associola.c | 4 ++--
> net/sctp/proc.c | 8 ++++++--
> net/sctp/transport.c | 18 +++++++++++++-----
> 4 files changed, 23 insertions(+), 9 deletions(-)
>
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 64158aa..5d6987b 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -948,6 +948,8 @@ struct sctp_transport {
>
> /* 64-bit random number sent with heartbeat. */
> __u64 hb_nonce;
> +
> + struct rcu_head rcu;
> };
>
> struct sctp_transport *sctp_transport_new(struct net *, const union sctp_addr *,
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index b1ef3bc..c826bb8 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -565,7 +565,7 @@ void sctp_assoc_rm_peer(struct sctp_association *asoc,
> sctp_assoc_update_retran_path(asoc);
>
> /* Remove this peer from the list. */
> - list_del(&peer->transports);
> + list_del_rcu(&peer->transports);
>
> /* Get the first transport of asoc. */
> pos = asoc->peer.transport_addr_list.next;
> @@ -765,7 +765,7 @@ struct sctp_transport *sctp_assoc_add_peer(struct sctp_association *asoc,
> peer->state = peer_state;
>
> /* Attach the remote transport to our asoc. */
> - list_add_tail(&peer->transports, &asoc->peer.transport_addr_list);
> + list_add_tail_rcu(&peer->transports, &asoc->peer.transport_addr_list);
> asoc->peer.transport_count++;
>
> /* If we do not yet have a primary path, set one. */
> diff --git a/net/sctp/proc.c b/net/sctp/proc.c
> index ec9b0c8..36a3f9d 100644
> --- a/net/sctp/proc.c
> +++ b/net/sctp/proc.c
> @@ -159,7 +159,8 @@ static void sctp_seq_dump_remote_addrs(struct seq_file *seq, struct sctp_associa
> struct sctp_af *af;
>
> primary = &assoc->peer.primary_addr;
> - list_for_each_entry(transport, &assoc->peer.transport_addr_list,
> + rcu_read_lock();
> + list_for_each_entry_rcu(transport, &assoc->peer.transport_addr_list,
> transports) {
> addr = &transport->ipaddr;
> af = sctp_get_af_specific(addr->sa.sa_family);
> @@ -168,6 +169,7 @@ static void sctp_seq_dump_remote_addrs(struct seq_file *seq, struct sctp_associa
> }
> af->seq_dump_addr(seq, addr);
> }
> + rcu_read_unlock();
> }
>
> static void * sctp_eps_seq_start(struct seq_file *seq, loff_t *pos)
> @@ -438,11 +440,12 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
> head = &sctp_assoc_hashtable[hash];
> sctp_local_bh_disable();
> read_lock(&head->lock);
> + rcu_read_lock();
> sctp_for_each_hentry(epb, node, &head->chain) {
> if (!net_eq(sock_net(epb->sk), seq_file_net(seq)))
> continue;
> assoc = sctp_assoc(epb);
> - list_for_each_entry(tsp, &assoc->peer.transport_addr_list,
> + list_for_each_entry_rcu(tsp, &assoc->peer.transport_addr_list,
> transports) {
> /*
> * The remote address (ADDR)
> @@ -489,6 +492,7 @@ static int sctp_remaddr_seq_show(struct seq_file *seq, void *v)
> }
> }
>
> + rcu_read_unlock();
> read_unlock(&head->lock);
> sctp_local_bh_enable();
>
> diff --git a/net/sctp/transport.c b/net/sctp/transport.c
> index 206cf52..1295aec 100644
> --- a/net/sctp/transport.c
> +++ b/net/sctp/transport.c
> @@ -163,13 +163,11 @@ void sctp_transport_free(struct sctp_transport *transport)
> sctp_transport_put(transport);
> }
>
> -/* Destroy the transport data structure.
> - * Assumes there are no more users of this structure.
> - */
> -static void sctp_transport_destroy(struct sctp_transport *transport)
> +static void sctp_transport_destroy_rcu(struct rcu_head *head)
> {
> - SCTP_ASSERT(transport->dead, "Transport is not dead", return);
> + struct sctp_transport *transport;
>
> + transport = container_of(head, struct sctp_transport, rcu);
> if (transport->asoc)
> sctp_association_put(transport->asoc);
>
> @@ -180,6 +178,16 @@ static void sctp_transport_destroy(struct sctp_transport *transport)
> SCTP_DBG_OBJCNT_DEC(transport);
> }
>
> +/* Destroy the transport data structure.
> + * Assumes there are no more users of this structure.
> + */
> +static void sctp_transport_destroy(struct sctp_transport *transport)
> +{
> + SCTP_ASSERT(transport->dead, "Transport is not dead", return);
> +
> + call_rcu(&transport->rcu, sctp_transport_destroy_rcu);
> +}
> +
> /* Start T3_rtx timer if it is not already running and update the heartbeat
> * timer. This routine is called every time a DATA chunk is sent.
> */
>
We may want to mark transports as dead sooner. Probably right about the
time we pull them off the list. When displaying, we may want to
look at transport->dead, and skip them. It will reduce the probability
that we would be looking at a transport that's about to go away.
Otherwise, looks very nice.
-vlad
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