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Date: Fri, 19 Feb 2010 07:58:25 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Stephen Hemminger <shemminger@...tta.com>
Cc: Vlad Yasevich <vladislav.yasevich@...com>,
Sridhar Samudrala <sri@...ibm.com>,
"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
linux-sctp@...r.kernel.org
Subject: Re: [RFC 1/2] sctp: convert hash list to RCU
On Thu, Feb 18, 2010 at 09:55:21PM -0800, Stephen Hemminger wrote:
> This patch converts existing SCTP hash list to using RCU
> rather than reader/writer lock. Also, get rid of no longer used
> locking wrappers.
>
> In future, the SCTP hash locking should be broken out from the
> hash structure because of the wasted space for the hash locks
> and associated holes. A single lock per hashlist is sufficient
> now that RCU is used.
>
> Compile tested only. I can't think of an SCTP stress application.
>
> P.s: Some janitor ought to go through and remove the locking
> macros here.
One question below about what looks to be mixing of RCU and RCU-bh
read-side critical sections while waiting only for RCU grace periods.
Unless I am missing something, this can result in memory corruption.
Thanx, Paul
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
>
>
> --- a/include/net/sctp/sctp.h 2010-02-18 09:44:42.664390403 -0800
> +++ b/include/net/sctp/sctp.h 2010-02-18 09:52:48.004478538 -0800
> @@ -206,10 +206,6 @@ extern struct kmem_cache *sctp_bucket_ca
> #define sctp_local_bh_enable() local_bh_enable()
> #define sctp_spin_lock(lock) spin_lock(lock)
> #define sctp_spin_unlock(lock) spin_unlock(lock)
> -#define sctp_write_lock(lock) write_lock(lock)
> -#define sctp_write_unlock(lock) write_unlock(lock)
> -#define sctp_read_lock(lock) read_lock(lock)
> -#define sctp_read_unlock(lock) read_unlock(lock)
>
> /* sock lock wrappers. */
> #define sctp_lock_sock(sk) lock_sock(sk)
> @@ -649,6 +645,9 @@ static inline int sctp_vtag_hashfn(__u16
> #define sctp_for_each_hentry(epb, node, head) \
> hlist_for_each_entry(epb, node, head, node)
>
> +#define sctp_for_each_hentry_rcu(epb, node, head) \
> + hlist_for_each_entry_rcu(epb, node, head, node)
> +
> /* Is a socket of this style? */
> #define sctp_style(sk, style) __sctp_style((sk), (SCTP_SOCKET_##style))
> static inline int __sctp_style(const struct sock *sk, sctp_socket_type_t style)
> --- a/include/net/sctp/structs.h 2010-02-18 09:47:29.964390311 -0800
> +++ b/include/net/sctp/structs.h 2010-02-18 09:57:26.792896287 -0800
> @@ -111,7 +111,7 @@ struct sctp_bind_hashbucket {
>
> /* Used for hashing all associations. */
> struct sctp_hashbucket {
> - rwlock_t lock;
> + spinlock_t lock;
> struct hlist_head chain;
> } __attribute__((__aligned__(8)));
>
> @@ -1371,6 +1371,8 @@ struct sctp_endpoint {
> /* SCTP-AUTH: endpoint shared keys */
> struct list_head endpoint_shared_keys;
> __u16 active_key_id;
> +
> + struct rcu_head rcu;
> };
>
> /* Recover the outter endpoint structure. */
> --- a/net/sctp/endpointola.c 2010-02-18 09:43:22.868887786 -0800
> +++ b/net/sctp/endpointola.c 2010-02-18 10:00:55.807210206 -0800
> @@ -247,9 +247,9 @@ void sctp_endpoint_free(struct sctp_endp
> }
>
> /* Final destructor for endpoint. */
> -static void sctp_endpoint_destroy(struct sctp_endpoint *ep)
> +static void sctp_endpoint_destroy_rcu(struct rcu_head *rcu)
> {
> - SCTP_ASSERT(ep->base.dead, "Endpoint is not dead", return);
> + struct sctp_endpoint *ep = container_of(rcu, struct sctp_endpoint, rcu);
>
> /* Free up the HMAC transform. */
> crypto_free_hash(sctp_sk(ep->base.sk)->hmac);
> @@ -286,6 +286,13 @@ static void sctp_endpoint_destroy(struct
> }
> }
>
> +static void sctp_endpoint_destroy(struct sctp_endpoint *ep)
> +{
> + SCTP_ASSERT(ep->base.dead, "Endpoint is not dead", return);
> + call_rcu(&ep->rcu, sctp_endpoint_destroy_rcu);
> +}
> +
> +
> /* Hold a reference to an endpoint. */
> void sctp_endpoint_hold(struct sctp_endpoint *ep)
> {
> @@ -338,8 +345,9 @@ static struct sctp_association *__sctp_e
>
> hash = sctp_assoc_hashfn(ep->base.bind_addr.port, rport);
> head = &sctp_assoc_hashtable[hash];
> - read_lock(&head->lock);
> - sctp_for_each_hentry(epb, node, &head->chain) {
> +
> + rcu_read_lock();
> + sctp_for_each_hentry_rcu(epb, node, &head->chain) {
> asoc = sctp_assoc(epb);
> if (asoc->ep != ep || rport != asoc->peer.port)
> goto next;
> @@ -352,7 +360,7 @@ static struct sctp_association *__sctp_e
> next:
> asoc = NULL;
> }
> - read_unlock(&head->lock);
> + rcu_read_unlock();
> return asoc;
> }
>
> --- a/net/sctp/input.c 2010-02-18 09:51:39.104889498 -0800
> +++ b/net/sctp/input.c 2010-02-18 10:02:42.972601804 -0800
> @@ -704,9 +704,9 @@ static void __sctp_hash_endpoint(struct
> epb->hashent = sctp_ep_hashfn(epb->bind_addr.port);
> head = &sctp_ep_hashtable[epb->hashent];
>
> - sctp_write_lock(&head->lock);
> - hlist_add_head(&epb->node, &head->chain);
> - sctp_write_unlock(&head->lock);
> + sctp_spin_lock(&head->lock);
> + hlist_add_head_rcu(&epb->node, &head->chain);
> + sctp_spin_unlock(&head->lock);
> }
>
> /* Add an endpoint to the hash. Local BH-safe. */
> @@ -732,9 +732,9 @@ static void __sctp_unhash_endpoint(struc
>
> head = &sctp_ep_hashtable[epb->hashent];
>
> - sctp_write_lock(&head->lock);
> - __hlist_del(&epb->node);
> - sctp_write_unlock(&head->lock);
> + sctp_spin_lock(&head->lock);
> + hlist_del_rcu(&epb->node);
> + sctp_spin_unlock(&head->lock);
> }
>
> /* Remove endpoint from the hash. Local BH-safe. */
> @@ -756,8 +756,8 @@ static struct sctp_endpoint *__sctp_rcv_
>
> hash = sctp_ep_hashfn(ntohs(laddr->v4.sin_port));
> head = &sctp_ep_hashtable[hash];
> - read_lock(&head->lock);
> - sctp_for_each_hentry(epb, node, &head->chain) {
> + rcu_read_lock();
> + sctp_for_each_hentry_rcu(epb, node, &head->chain) {
> ep = sctp_ep(epb);
> if (sctp_endpoint_is_match(ep, laddr))
> goto hit;
> @@ -767,7 +767,7 @@ static struct sctp_endpoint *__sctp_rcv_
>
> hit:
> sctp_endpoint_hold(ep);
> - read_unlock(&head->lock);
> + rcu_read_unlock();
> return ep;
> }
>
> @@ -784,9 +784,9 @@ static void __sctp_hash_established(stru
>
> head = &sctp_assoc_hashtable[epb->hashent];
>
> - sctp_write_lock(&head->lock);
> - hlist_add_head(&epb->node, &head->chain);
> - sctp_write_unlock(&head->lock);
> + sctp_spin_lock(&head->lock);
> + hlist_add_head_rcu(&epb->node, &head->chain);
> + sctp_spin_unlock(&head->lock);
> }
>
> /* Add an association to the hash. Local BH-safe. */
> @@ -813,9 +813,9 @@ static void __sctp_unhash_established(st
>
> head = &sctp_assoc_hashtable[epb->hashent];
>
> - sctp_write_lock(&head->lock);
> - __hlist_del(&epb->node);
> - sctp_write_unlock(&head->lock);
> + sctp_spin_lock(&head->lock);
> + hlist_del_rcu(&epb->node);
> + sctp_spin_unlock(&head->lock);
> }
>
> /* Remove association from the hash table. Local BH-safe. */
> @@ -847,22 +847,23 @@ static struct sctp_association *__sctp_l
> */
> hash = sctp_assoc_hashfn(ntohs(local->v4.sin_port), ntohs(peer->v4.sin_port));
> head = &sctp_assoc_hashtable[hash];
> - read_lock(&head->lock);
> - sctp_for_each_hentry(epb, node, &head->chain) {
> +
> + rcu_read_lock();
> + sctp_for_each_hentry_rcu(epb, node, &head->chain) {
> asoc = sctp_assoc(epb);
> transport = sctp_assoc_is_match(asoc, local, peer);
> if (transport)
> goto hit;
> }
>
> - read_unlock(&head->lock);
> + rcu_read_unlock();
>
> return NULL;
>
> hit:
> *pt = transport;
> sctp_association_hold(asoc);
> - read_unlock(&head->lock);
> + rcu_read_unlock();
> return asoc;
> }
>
> --- a/net/sctp/protocol.c 2010-02-18 09:42:04.556389428 -0800
> +++ b/net/sctp/protocol.c 2010-02-18 09:53:03.360663641 -0800
> @@ -1204,7 +1204,7 @@ SCTP_STATIC __init int sctp_init(void)
> goto err_ahash_alloc;
> }
> for (i = 0; i < sctp_assoc_hashsize; i++) {
> - rwlock_init(&sctp_assoc_hashtable[i].lock);
> + spin_lock_init(&sctp_assoc_hashtable[i].lock);
> INIT_HLIST_HEAD(&sctp_assoc_hashtable[i].chain);
> }
>
> @@ -1218,7 +1218,7 @@ SCTP_STATIC __init int sctp_init(void)
> goto err_ehash_alloc;
> }
> for (i = 0; i < sctp_ep_hashsize; i++) {
> - rwlock_init(&sctp_ep_hashtable[i].lock);
> + spin_lock_init(&sctp_ep_hashtable[i].lock);
> INIT_HLIST_HEAD(&sctp_ep_hashtable[i].chain);
> }
>
> --- a/net/sctp/proc.c 2010-02-18 10:03:50.428764115 -0800
> +++ b/net/sctp/proc.c 2010-02-18 10:05:09.961659526 -0800
> @@ -208,9 +208,9 @@ static int sctp_eps_seq_show(struct seq_
> return -ENOMEM;
>
> head = &sctp_ep_hashtable[hash];
> - sctp_local_bh_disable();
> - read_lock(&head->lock);
> - sctp_for_each_hentry(epb, node, &head->chain) {
> +
> + rcu_read_lock_bh();
Why _bh() here instead of just rcu_read_lock()? Either way, we would
need a call_rcu_bh() to wait for this particular RCU read-side critical
section -- call_rcu() won't necessarily do it because and RCU grace
period is not guaranteed to wait for RCU-bh read-side critical sections.
If we do need _bh() here, one approach would be to do call_rcu(), and
make the callback do call_rcu_bh(), and the _bh callback could then do
the free. This approach would be guaranteed to wait for both RCU and
RCU-bh read-side critical sections.
> + sctp_for_each_hentry_rcu(epb, node, &head->chain) {
> ep = sctp_ep(epb);
> sk = epb->sk;
> seq_printf(seq, "%8p %8p %-3d %-3d %-4d %-5d %5d %5lu ", ep, sk,
> @@ -221,8 +221,7 @@ static int sctp_eps_seq_show(struct seq_
> sctp_seq_dump_local_addrs(seq, epb);
> seq_printf(seq, "\n");
> }
> - read_unlock(&head->lock);
> - sctp_local_bh_enable();
> + rcu_read_unlock_bh();
>
> return 0;
> }
> @@ -312,9 +311,9 @@ static int sctp_assocs_seq_show(struct s
> return -ENOMEM;
>
> head = &sctp_assoc_hashtable[hash];
> - sctp_local_bh_disable();
> - read_lock(&head->lock);
> - sctp_for_each_hentry(epb, node, &head->chain) {
> +
> + rcu_read_lock_bh();
> + sctp_for_each_hentry_rcu(epb, node, &head->chain) {
> assoc = sctp_assoc(epb);
> sk = epb->sk;
> seq_printf(seq,
> @@ -339,8 +338,7 @@ static int sctp_assocs_seq_show(struct s
> assoc->rtx_data_chunks);
> seq_printf(seq, "\n");
> }
> - read_unlock(&head->lock);
> - sctp_local_bh_enable();
> + rcu_read_unlock_bh();
>
> return 0;
> }
> @@ -425,9 +423,9 @@ static int sctp_remaddr_seq_show(struct
> return -ENOMEM;
>
> head = &sctp_assoc_hashtable[hash];
> - sctp_local_bh_disable();
> - read_lock(&head->lock);
> - sctp_for_each_hentry(epb, node, &head->chain) {
> +
> + rcu_read_lock_bh();
> + sctp_for_each_hentry_rcu(epb, node, &head->chain) {
> assoc = sctp_assoc(epb);
> list_for_each_entry(tsp, &assoc->peer.transport_addr_list,
> transports) {
> @@ -475,9 +473,7 @@ static int sctp_remaddr_seq_show(struct
> seq_printf(seq, "\n");
> }
> }
> -
> - read_unlock(&head->lock);
> - sctp_local_bh_enable();
> + rcu_read_unlock_bh();
>
> return 0;
>
>
> --
>
--
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