diff mbox series

[V2,net-next] rds: tcp: use rds_destroy_pending() to synchronize netns/module teardown and rds connection/workq management

Message ID 1517660811-181492-1-git-send-email-sowmini.varadhan@oracle.com
State Accepted, archived
Delegated to: David Miller
Headers show
Series [V2,net-next] rds: tcp: use rds_destroy_pending() to synchronize netns/module teardown and rds connection/workq management | expand

Commit Message

Sowmini Varadhan Feb. 3, 2018, 12:26 p.m. UTC 
An rds_connection can get added during netns deletion between lines 528
and 529 of

  506 static void rds_tcp_kill_sock(struct net *net)
  :
  /* code to pull out all the rds_connections that should be destroyed */
  :
  528         spin_unlock_irq(&rds_tcp_conn_lock);
  529         list_for_each_entry_safe(tc, _tc, &tmp_list, t_tcp_node)
  530                 rds_conn_destroy(tc->t_cpath->cp_conn);

Such an rds_connection would miss out the rds_conn_destroy()
loop (that cancels all pending work) and (if it was scheduled
after netns deletion) could trigger the use-after-free.

A similar race-window exists for the module unload path
in rds_tcp_exit -> rds_tcp_destroy_conns

Concurrency with netns deletion (rds_tcp_kill_sock()) must be handled
by checking check_net() before enqueuing new work or adding new
connections.

Concurrency with module-unload is handled by maintaining a module
specific flag that is set at the start of the module exit function,
and must be checked before enqueuing new work or adding new connections.

This commit refactors existing RDS_DESTROY_PENDING checks added by
commit 3db6e0d172c9 ("rds: use RCU to synchronize work-enqueue with
connection teardown") and consolidates all the concurrency checks
listed above into the function rds_destroy_pending().

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
v2: use check_net() for the netns delete case, as recommended on the list.
    refactor RDS_DESTROY_PENDING checks and consolidate into
    rds_destroy_pending()

 net/rds/cong.c        |    2 +-
 net/rds/connection.c  |   15 +++++++++------
 net/rds/ib.c          |   17 +++++++++++++++++
 net/rds/ib_cm.c       |    1 +
 net/rds/rds.h         |    7 +++++++
 net/rds/send.c        |   10 +++++-----
 net/rds/tcp.c         |   42 ++++++++++++++++++++++++++++++------------
 net/rds/tcp_connect.c |    2 +-
 net/rds/tcp_recv.c    |    2 +-
 net/rds/tcp_send.c    |    2 +-
 net/rds/threads.c     |    6 +++---
 11 files changed, 76 insertions(+), 30 deletions(-)

Comments

Santosh Shilimkar Feb. 5, 2018, 5:21 p.m. UTC | #1 
On 2/3/2018 4:26 AM, Sowmini Varadhan wrote:
> An rds_connection can get added during netns deletion between lines 528
> and 529 of
> 
>    506 static void rds_tcp_kill_sock(struct net *net)
>    :
>    /* code to pull out all the rds_connections that should be destroyed */
>    :
>    528         spin_unlock_irq(&rds_tcp_conn_lock);
>    529         list_for_each_entry_safe(tc, _tc, &tmp_list, t_tcp_node)
>    530                 rds_conn_destroy(tc->t_cpath->cp_conn);
> 
> Such an rds_connection would miss out the rds_conn_destroy()
> loop (that cancels all pending work) and (if it was scheduled
> after netns deletion) could trigger the use-after-free.
> 
> A similar race-window exists for the module unload path
> in rds_tcp_exit -> rds_tcp_destroy_conns
> 
> Concurrency with netns deletion (rds_tcp_kill_sock()) must be handled
> by checking check_net() before enqueuing new work or adding new
> connections.
> 
> Concurrency with module-unload is handled by maintaining a module
> specific flag that is set at the start of the module exit function,
> and must be checked before enqueuing new work or adding new connections.
> 
> This commit refactors existing RDS_DESTROY_PENDING checks added by
> commit 3db6e0d172c9 ("rds: use RCU to synchronize work-enqueue with
> connection teardown") and consolidates all the concurrency checks
> listed above into the function rds_destroy_pending().
> 
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
> ---
> v2: use check_net() for the netns delete case, as recommended on the list.
>      refactor RDS_DESTROY_PENDING checks and consolidate into
>      rds_destroy_pending()
> 
Thanks for the update. It looks inline as per off-list chat.

Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Sowmini Varadhan Feb. 8, 2018, 8:19 p.m. UTC | #2 
I was just checking the patchq for the fate of this patch and find
it marked "superseded" in http://patchwork.ozlabs.org/patch/868902/

I'm intrigued, superseded by what?

--Sowmini
David Miller Feb. 8, 2018, 8:23 p.m. UTC | #3 
From: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Date: Thu, 8 Feb 2018 15:19:05 -0500

> I was just checking the patchq for the fate of this patch and find
> it marked "superseded" in http://patchwork.ozlabs.org/patch/868902/
> 
> I'm intrigued, superseded by what?

My bad, I'll apply this.  I may have mis-clicked a button or something
like that.

Thanks.
diff mbox series

Patch

diff --git a/net/rds/cong.c b/net/rds/cong.c
index 8d19fd2..63da9d2 100644
--- a/net/rds/cong.c
+++ b/net/rds/cong.c
@@ -223,7 +223,7 @@  void rds_cong_queue_updates(struct rds_cong_map *map)
 
 		rcu_read_lock();
 		if (!test_and_set_bit(0, &conn->c_map_queued) &&
-		    !test_bit(RDS_DESTROY_PENDING, &cp->cp_flags)) {
+		    !rds_destroy_pending(cp->cp_conn)) {
 			rds_stats_inc(s_cong_update_queued);
 			/* We cannot inline the call to rds_send_xmit() here
 			 * for two reasons (both pertaining to a TCP transport):
diff --git a/net/rds/connection.c b/net/rds/connection.c
index b10c0ef..94e190f 100644
--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -220,8 +220,13 @@  static void __rds_conn_path_init(struct rds_connection *conn,
 				     is_outgoing);
 		conn->c_path[i].cp_index = i;
 	}
-	ret = trans->conn_alloc(conn, gfp);
+	rcu_read_lock();
+	if (rds_destroy_pending(conn))
+		ret = -ENETDOWN;
+	else
+		ret = trans->conn_alloc(conn, gfp);
 	if (ret) {
+		rcu_read_unlock();
 		kfree(conn->c_path);
 		kmem_cache_free(rds_conn_slab, conn);
 		conn = ERR_PTR(ret);
@@ -283,6 +288,7 @@  static void __rds_conn_path_init(struct rds_connection *conn,
 		}
 	}
 	spin_unlock_irqrestore(&rds_conn_lock, flags);
+	rcu_read_unlock();
 
 out:
 	return conn;
@@ -382,13 +388,10 @@  static void rds_conn_path_destroy(struct rds_conn_path *cp)
 {
 	struct rds_message *rm, *rtmp;
 
-	set_bit(RDS_DESTROY_PENDING, &cp->cp_flags);
-
 	if (!cp->cp_transport_data)
 		return;
 
 	/* make sure lingering queued work won't try to ref the conn */
-	synchronize_rcu();
 	cancel_delayed_work_sync(&cp->cp_send_w);
 	cancel_delayed_work_sync(&cp->cp_recv_w);
 
@@ -691,7 +694,7 @@  void rds_conn_path_drop(struct rds_conn_path *cp, bool destroy)
 	atomic_set(&cp->cp_state, RDS_CONN_ERROR);
 
 	rcu_read_lock();
-	if (!destroy && test_bit(RDS_DESTROY_PENDING, &cp->cp_flags)) {
+	if (!destroy && rds_destroy_pending(cp->cp_conn)) {
 		rcu_read_unlock();
 		return;
 	}
@@ -714,7 +717,7 @@  void rds_conn_drop(struct rds_connection *conn)
 void rds_conn_path_connect_if_down(struct rds_conn_path *cp)
 {
 	rcu_read_lock();
-	if (test_bit(RDS_DESTROY_PENDING, &cp->cp_flags)) {
+	if (rds_destroy_pending(cp->cp_conn)) {
 		rcu_read_unlock();
 		return;
 	}
diff --git a/net/rds/ib.c b/net/rds/ib.c
index b2a5067..561dcc0 100644
--- a/net/rds/ib.c
+++ b/net/rds/ib.c
@@ -48,6 +48,7 @@ 
 static unsigned int rds_ib_mr_1m_pool_size = RDS_MR_1M_POOL_SIZE;
 static unsigned int rds_ib_mr_8k_pool_size = RDS_MR_8K_POOL_SIZE;
 unsigned int rds_ib_retry_count = RDS_IB_DEFAULT_RETRY_COUNT;
+static atomic_t rds_ib_unloading;
 
 module_param(rds_ib_mr_1m_pool_size, int, 0444);
 MODULE_PARM_DESC(rds_ib_mr_1m_pool_size, " Max number of 1M mr per HCA");
@@ -377,8 +378,23 @@  static void rds_ib_unregister_client(void)
 	flush_workqueue(rds_wq);
 }
 
+static void rds_ib_set_unloading(void)
+{
+	atomic_set(&rds_ib_unloading, 1);
+}
+
+static bool rds_ib_is_unloading(struct rds_connection *conn)
+{
+	struct rds_conn_path *cp = &conn->c_path[0];
+
+	return (test_bit(RDS_DESTROY_PENDING, &cp->cp_flags) ||
+		atomic_read(&rds_ib_unloading) != 0);
+}
+
 void rds_ib_exit(void)
 {
+	rds_ib_set_unloading();
+	synchronize_rcu();
 	rds_info_deregister_func(RDS_INFO_IB_CONNECTIONS, rds_ib_ic_info);
 	rds_ib_unregister_client();
 	rds_ib_destroy_nodev_conns();
@@ -412,6 +428,7 @@  struct rds_transport rds_ib_transport = {
 	.flush_mrs		= rds_ib_flush_mrs,
 	.t_owner		= THIS_MODULE,
 	.t_name			= "infiniband",
+	.t_unloading		= rds_ib_is_unloading,
 	.t_type			= RDS_TRANS_IB
 };
 
diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c
index 80fb6f6..eea1d86 100644
--- a/net/rds/ib_cm.c
+++ b/net/rds/ib_cm.c
@@ -117,6 +117,7 @@  void rds_ib_cm_connect_complete(struct rds_connection *conn, struct rdma_cm_even
 			  &conn->c_laddr, &conn->c_faddr,
 			  RDS_PROTOCOL_MAJOR(conn->c_version),
 			  RDS_PROTOCOL_MINOR(conn->c_version));
+		set_bit(RDS_DESTROY_PENDING, &conn->c_path[0].cp_flags);
 		rds_conn_destroy(conn);
 		return;
 	} else {
diff --git a/net/rds/rds.h b/net/rds/rds.h
index 374ae83..7301b9b 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -518,6 +518,7 @@  struct rds_transport {
 	void (*sync_mr)(void *trans_private, int direction);
 	void (*free_mr)(void *trans_private, int invalidate);
 	void (*flush_mrs)(void);
+	bool (*t_unloading)(struct rds_connection *conn);
 };
 
 struct rds_sock {
@@ -862,6 +863,12 @@  static inline void rds_mr_put(struct rds_mr *mr)
 		__rds_put_mr_final(mr);
 }
 
+static inline bool rds_destroy_pending(struct rds_connection *conn)
+{
+	return !check_net(rds_conn_net(conn)) ||
+	       (conn->c_trans->t_unloading && conn->c_trans->t_unloading(conn));
+}
+
 /* stats.c */
 DECLARE_PER_CPU_SHARED_ALIGNED(struct rds_statistics, rds_stats);
 #define rds_stats_inc_which(which, member) do {		\
diff --git a/net/rds/send.c b/net/rds/send.c
index d3e32d1..b1b0022 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -162,7 +162,7 @@  int rds_send_xmit(struct rds_conn_path *cp)
 		goto out;
 	}
 
-	if (test_bit(RDS_DESTROY_PENDING, &cp->cp_flags)) {
+	if (rds_destroy_pending(cp->cp_conn)) {
 		release_in_xmit(cp);
 		ret = -ENETUNREACH; /* dont requeue send work */
 		goto out;
@@ -444,7 +444,7 @@  int rds_send_xmit(struct rds_conn_path *cp)
 			if (batch_count < send_batch_count)
 				goto restart;
 			rcu_read_lock();
-			if (test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
+			if (rds_destroy_pending(cp->cp_conn))
 				ret = -ENETUNREACH;
 			else
 				queue_delayed_work(rds_wq, &cp->cp_send_w, 1);
@@ -1162,7 +1162,7 @@  int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
 	else
 		cpath = &conn->c_path[0];
 
-	if (test_bit(RDS_DESTROY_PENDING, &cpath->cp_flags)) {
+	if (rds_destroy_pending(conn)) {
 		ret = -EAGAIN;
 		goto out;
 	}
@@ -1209,7 +1209,7 @@  int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
 	if (ret == -ENOMEM || ret == -EAGAIN) {
 		ret = 0;
 		rcu_read_lock();
-		if (test_bit(RDS_DESTROY_PENDING, &cpath->cp_flags))
+		if (rds_destroy_pending(cpath->cp_conn))
 			ret = -ENETUNREACH;
 		else
 			queue_delayed_work(rds_wq, &cpath->cp_send_w, 1);
@@ -1295,7 +1295,7 @@  int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
 
 	/* schedule the send work on rds_wq */
 	rcu_read_lock();
-	if (!test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
+	if (!rds_destroy_pending(cp->cp_conn))
 		queue_delayed_work(rds_wq, &cp->cp_send_w, 1);
 	rcu_read_unlock();
 
diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 9920d2f..44c4652 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -49,6 +49,7 @@ 
 /* Track rds_tcp_connection structs so they can be cleaned up */
 static DEFINE_SPINLOCK(rds_tcp_conn_lock);
 static LIST_HEAD(rds_tcp_conn_list);
+static atomic_t rds_tcp_unloading = ATOMIC_INIT(0);
 
 static struct kmem_cache *rds_tcp_conn_slab;
 
@@ -274,14 +275,13 @@  static int rds_tcp_laddr_check(struct net *net, __be32 addr)
 static void rds_tcp_conn_free(void *arg)
 {
 	struct rds_tcp_connection *tc = arg;
-	unsigned long flags;
 
 	rdsdebug("freeing tc %p\n", tc);
 
-	spin_lock_irqsave(&rds_tcp_conn_lock, flags);
+	spin_lock_bh(&rds_tcp_conn_lock);
 	if (!tc->t_tcp_node_detached)
 		list_del(&tc->t_tcp_node);
-	spin_unlock_irqrestore(&rds_tcp_conn_lock, flags);
+	spin_unlock_bh(&rds_tcp_conn_lock);
 
 	kmem_cache_free(rds_tcp_conn_slab, tc);
 }
@@ -296,7 +296,7 @@  static int rds_tcp_conn_alloc(struct rds_connection *conn, gfp_t gfp)
 		tc = kmem_cache_alloc(rds_tcp_conn_slab, gfp);
 		if (!tc) {
 			ret = -ENOMEM;
-			break;
+			goto fail;
 		}
 		mutex_init(&tc->t_conn_path_lock);
 		tc->t_sock = NULL;
@@ -306,14 +306,19 @@  static int rds_tcp_conn_alloc(struct rds_connection *conn, gfp_t gfp)
 
 		conn->c_path[i].cp_transport_data = tc;
 		tc->t_cpath = &conn->c_path[i];
+		tc->t_tcp_node_detached = true;
 
-		spin_lock_irq(&rds_tcp_conn_lock);
-		tc->t_tcp_node_detached = false;
-		list_add_tail(&tc->t_tcp_node, &rds_tcp_conn_list);
-		spin_unlock_irq(&rds_tcp_conn_lock);
 		rdsdebug("rds_conn_path [%d] tc %p\n", i,
 			 conn->c_path[i].cp_transport_data);
 	}
+	spin_lock_bh(&rds_tcp_conn_lock);
+	for (i = 0; i < RDS_MPATH_WORKERS; i++) {
+		tc = conn->c_path[i].cp_transport_data;
+		tc->t_tcp_node_detached = false;
+		list_add_tail(&tc->t_tcp_node, &rds_tcp_conn_list);
+	}
+	spin_unlock_bh(&rds_tcp_conn_lock);
+fail:
 	if (ret) {
 		for (j = 0; j < i; j++)
 			rds_tcp_conn_free(conn->c_path[j].cp_transport_data);
@@ -332,6 +337,16 @@  static bool list_has_conn(struct list_head *list, struct rds_connection *conn)
 	return false;
 }
 
+static void rds_tcp_set_unloading(void)
+{
+	atomic_set(&rds_tcp_unloading, 1);
+}
+
+static bool rds_tcp_is_unloading(struct rds_connection *conn)
+{
+	return atomic_read(&rds_tcp_unloading) != 0;
+}
+
 static void rds_tcp_destroy_conns(void)
 {
 	struct rds_tcp_connection *tc, *_tc;
@@ -370,6 +385,7 @@  struct rds_transport rds_tcp_transport = {
 	.t_type			= RDS_TRANS_TCP,
 	.t_prefer_loopback	= 1,
 	.t_mp_capable		= 1,
+	.t_unloading		= rds_tcp_is_unloading,
 };
 
 static unsigned int rds_tcp_netid;
@@ -513,7 +529,7 @@  static void rds_tcp_kill_sock(struct net *net)
 
 	rtn->rds_tcp_listen_sock = NULL;
 	rds_tcp_listen_stop(lsock, &rtn->rds_tcp_accept_w);
-	spin_lock_irq(&rds_tcp_conn_lock);
+	spin_lock_bh(&rds_tcp_conn_lock);
 	list_for_each_entry_safe(tc, _tc, &rds_tcp_conn_list, t_tcp_node) {
 		struct net *c_net = read_pnet(&tc->t_cpath->cp_conn->c_net);
 
@@ -526,7 +542,7 @@  static void rds_tcp_kill_sock(struct net *net)
 			tc->t_tcp_node_detached = true;
 		}
 	}
-	spin_unlock_irq(&rds_tcp_conn_lock);
+	spin_unlock_bh(&rds_tcp_conn_lock);
 	list_for_each_entry_safe(tc, _tc, &tmp_list, t_tcp_node)
 		rds_conn_destroy(tc->t_cpath->cp_conn);
 }
@@ -574,7 +590,7 @@  static void rds_tcp_sysctl_reset(struct net *net)
 {
 	struct rds_tcp_connection *tc, *_tc;
 
-	spin_lock_irq(&rds_tcp_conn_lock);
+	spin_lock_bh(&rds_tcp_conn_lock);
 	list_for_each_entry_safe(tc, _tc, &rds_tcp_conn_list, t_tcp_node) {
 		struct net *c_net = read_pnet(&tc->t_cpath->cp_conn->c_net);
 
@@ -584,7 +600,7 @@  static void rds_tcp_sysctl_reset(struct net *net)
 		/* reconnect with new parameters */
 		rds_conn_path_drop(tc->t_cpath, false);
 	}
-	spin_unlock_irq(&rds_tcp_conn_lock);
+	spin_unlock_bh(&rds_tcp_conn_lock);
 }
 
 static int rds_tcp_skbuf_handler(struct ctl_table *ctl, int write,
@@ -607,6 +623,8 @@  static int rds_tcp_skbuf_handler(struct ctl_table *ctl, int write,
 
 static void rds_tcp_exit(void)
 {
+	rds_tcp_set_unloading();
+	synchronize_rcu();
 	rds_info_deregister_func(RDS_INFO_TCP_SOCKETS, rds_tcp_tc_info);
 	unregister_pernet_subsys(&rds_tcp_net_ops);
 	if (unregister_netdevice_notifier(&rds_tcp_dev_notifier))
diff --git a/net/rds/tcp_connect.c b/net/rds/tcp_connect.c
index 534c67a..d999e70 100644
--- a/net/rds/tcp_connect.c
+++ b/net/rds/tcp_connect.c
@@ -170,7 +170,7 @@  void rds_tcp_conn_path_shutdown(struct rds_conn_path *cp)
 		 cp->cp_conn, tc, sock);
 
 	if (sock) {
-		if (test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
+		if (rds_destroy_pending(cp->cp_conn))
 			rds_tcp_set_linger(sock);
 		sock->ops->shutdown(sock, RCV_SHUTDOWN | SEND_SHUTDOWN);
 		lock_sock(sock->sk);
diff --git a/net/rds/tcp_recv.c b/net/rds/tcp_recv.c
index dd707b9..b9fbd2e 100644
--- a/net/rds/tcp_recv.c
+++ b/net/rds/tcp_recv.c
@@ -323,7 +323,7 @@  void rds_tcp_data_ready(struct sock *sk)
 
 	if (rds_tcp_read_sock(cp, GFP_ATOMIC) == -ENOMEM) {
 		rcu_read_lock();
-		if (!test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
+		if (!rds_destroy_pending(cp->cp_conn))
 			queue_delayed_work(rds_wq, &cp->cp_recv_w, 0);
 		rcu_read_unlock();
 	}
diff --git a/net/rds/tcp_send.c b/net/rds/tcp_send.c
index 16f6574..7df869d 100644
--- a/net/rds/tcp_send.c
+++ b/net/rds/tcp_send.c
@@ -204,7 +204,7 @@  void rds_tcp_write_space(struct sock *sk)
 
 	rcu_read_lock();
 	if ((refcount_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf &&
-	    !test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
+	    !rds_destroy_pending(cp->cp_conn))
 		queue_delayed_work(rds_wq, &cp->cp_send_w, 0);
 	rcu_read_unlock();
 
diff --git a/net/rds/threads.c b/net/rds/threads.c
index eb76db1..c52861d 100644
--- a/net/rds/threads.c
+++ b/net/rds/threads.c
@@ -88,7 +88,7 @@  void rds_connect_path_complete(struct rds_conn_path *cp, int curr)
 	cp->cp_reconnect_jiffies = 0;
 	set_bit(0, &cp->cp_conn->c_map_queued);
 	rcu_read_lock();
-	if (!test_bit(RDS_DESTROY_PENDING, &cp->cp_flags)) {
+	if (!rds_destroy_pending(cp->cp_conn)) {
 		queue_delayed_work(rds_wq, &cp->cp_send_w, 0);
 		queue_delayed_work(rds_wq, &cp->cp_recv_w, 0);
 	}
@@ -138,7 +138,7 @@  void rds_queue_reconnect(struct rds_conn_path *cp)
 	if (cp->cp_reconnect_jiffies == 0) {
 		cp->cp_reconnect_jiffies = rds_sysctl_reconnect_min_jiffies;
 		rcu_read_lock();
-		if (!test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
+		if (!rds_destroy_pending(cp->cp_conn))
 			queue_delayed_work(rds_wq, &cp->cp_conn_w, 0);
 		rcu_read_unlock();
 		return;
@@ -149,7 +149,7 @@  void rds_queue_reconnect(struct rds_conn_path *cp)
 		 rand % cp->cp_reconnect_jiffies, cp->cp_reconnect_jiffies,
 		 conn, &conn->c_laddr, &conn->c_faddr);
 	rcu_read_lock();
-	if (!test_bit(RDS_DESTROY_PENDING, &cp->cp_flags))
+	if (!rds_destroy_pending(cp->cp_conn))
 		queue_delayed_work(rds_wq, &cp->cp_conn_w,
 				   rand % cp->cp_reconnect_jiffies);
 	rcu_read_unlock();