fs: dlm: make connection hash lockless
There are some problems with the connections_lock. During my experiements I saw sometimes circular dependencies with sock_lock. The reason here might be code parts which runs nodeid2con() before or after sock_lock is acquired. Another issue are missing locks in for_conn() iteration. Maybe this works fine because for_conn() is running in a context where connection_hash cannot be manipulated by others anymore. However this patch changes the connection_hash to be protected by sleepable rcu. The hotpath function __find_con() is implemented lockless as it is only a reader of connection_hash and this hopefully fixes the circular locking dependencies. The iteration for_conn() will still call some sleepable functionality, that's why we use sleepable rcu in this case. This patch removes the kmemcache functionality as I think I need to make some free() functionality via call_rcu(). However allocation time isn't here an issue. The dlm_allow_con will not be protected by a lock anymore as I think it's enough to just set and flush workqueues afterwards. Signed-off-by: Alexander Aring <aahringo@redhat.com> Signed-off-by: David Teigland <teigland@redhat.com>
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@ -4,6 +4,7 @@ menuconfig DLM
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depends on INET
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depends on SYSFS && CONFIGFS_FS && (IPV6 || IPV6=n)
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select IP_SCTP
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select SRCU
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help
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A general purpose distributed lock manager for kernel or userspace
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applications.
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@ -126,6 +126,7 @@ struct connection {
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struct work_struct rwork; /* Receive workqueue */
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struct work_struct swork; /* Send workqueue */
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wait_queue_head_t shutdown_wait; /* wait for graceful shutdown */
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struct rcu_head rcu;
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};
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#define sock2con(x) ((struct connection *)(x)->sk_user_data)
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@ -167,8 +168,8 @@ static struct workqueue_struct *recv_workqueue;
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static struct workqueue_struct *send_workqueue;
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static struct hlist_head connection_hash[CONN_HASH_SIZE];
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static DEFINE_MUTEX(connections_lock);
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static struct kmem_cache *con_cache;
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static DEFINE_SPINLOCK(connections_lock);
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DEFINE_STATIC_SRCU(connections_srcu);
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static void process_recv_sockets(struct work_struct *work);
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static void process_send_sockets(struct work_struct *work);
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@ -184,15 +185,20 @@ static inline int nodeid_hash(int nodeid)
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static struct connection *__find_con(int nodeid)
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{
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int r;
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int r, idx;
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struct connection *con;
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r = nodeid_hash(nodeid);
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hlist_for_each_entry(con, &connection_hash[r], list) {
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if (con->nodeid == nodeid)
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idx = srcu_read_lock(&connections_srcu);
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hlist_for_each_entry_rcu(con, &connection_hash[r], list) {
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if (con->nodeid == nodeid) {
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srcu_read_unlock(&connections_srcu, idx);
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return con;
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}
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}
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srcu_read_unlock(&connections_srcu, idx);
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return NULL;
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}
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@ -200,7 +206,7 @@ static struct connection *__find_con(int nodeid)
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* If 'allocation' is zero then we don't attempt to create a new
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* connection structure for this node.
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*/
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static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
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static struct connection *nodeid2con(int nodeid, gfp_t alloc)
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{
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struct connection *con = NULL;
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int r;
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@ -209,13 +215,10 @@ static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
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if (con || !alloc)
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return con;
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con = kmem_cache_zalloc(con_cache, alloc);
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con = kzalloc(sizeof(*con), alloc);
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if (!con)
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return NULL;
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r = nodeid_hash(nodeid);
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hlist_add_head(&con->list, &connection_hash[r]);
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con->nodeid = nodeid;
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mutex_init(&con->sock_mutex);
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INIT_LIST_HEAD(&con->writequeue);
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@ -233,31 +236,27 @@ static struct connection *__nodeid2con(int nodeid, gfp_t alloc)
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con->rx_action = zerocon->rx_action;
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}
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r = nodeid_hash(nodeid);
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spin_lock(&connections_lock);
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hlist_add_head_rcu(&con->list, &connection_hash[r]);
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spin_unlock(&connections_lock);
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return con;
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}
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/* Loop round all connections */
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static void foreach_conn(void (*conn_func)(struct connection *c))
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{
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int i;
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struct hlist_node *n;
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int i, idx;
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struct connection *con;
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idx = srcu_read_lock(&connections_srcu);
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for (i = 0; i < CONN_HASH_SIZE; i++) {
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hlist_for_each_entry_safe(con, n, &connection_hash[i], list)
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hlist_for_each_entry_rcu(con, &connection_hash[i], list)
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conn_func(con);
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}
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}
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static struct connection *nodeid2con(int nodeid, gfp_t allocation)
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{
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struct connection *con;
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mutex_lock(&connections_lock);
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con = __nodeid2con(nodeid, allocation);
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mutex_unlock(&connections_lock);
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return con;
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srcu_read_unlock(&connections_srcu, idx);
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}
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static struct dlm_node_addr *find_node_addr(int nodeid)
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@ -792,12 +791,9 @@ static int accept_from_sock(struct connection *con)
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struct connection *newcon;
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struct connection *addcon;
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mutex_lock(&connections_lock);
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if (!dlm_allow_conn) {
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mutex_unlock(&connections_lock);
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return -1;
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}
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mutex_unlock(&connections_lock);
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mutex_lock_nested(&con->sock_mutex, 0);
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@ -847,7 +843,7 @@ static int accept_from_sock(struct connection *con)
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struct connection *othercon = newcon->othercon;
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if (!othercon) {
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othercon = kmem_cache_zalloc(con_cache, GFP_NOFS);
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othercon = kzalloc(sizeof(*othercon), GFP_NOFS);
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if (!othercon) {
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log_print("failed to allocate incoming socket");
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mutex_unlock(&newcon->sock_mutex);
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@ -1612,16 +1608,17 @@ static void free_conn(struct connection *con)
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{
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close_connection(con, true, true, true);
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if (con->othercon)
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kmem_cache_free(con_cache, con->othercon);
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hlist_del(&con->list);
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kmem_cache_free(con_cache, con);
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kfree_rcu(con->othercon, rcu);
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spin_lock(&connections_lock);
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hlist_del_rcu(&con->list);
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spin_unlock(&connections_lock);
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kfree_rcu(con, rcu);
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}
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static void work_flush(void)
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{
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int ok;
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int ok, idx;
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int i;
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struct hlist_node *n;
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struct connection *con;
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do {
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@ -1631,9 +1628,10 @@ static void work_flush(void)
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flush_workqueue(recv_workqueue);
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if (send_workqueue)
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flush_workqueue(send_workqueue);
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idx = srcu_read_lock(&connections_srcu);
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for (i = 0; i < CONN_HASH_SIZE && ok; i++) {
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hlist_for_each_entry_safe(con, n,
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&connection_hash[i], list) {
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hlist_for_each_entry_rcu(con, &connection_hash[i],
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list) {
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ok &= test_bit(CF_READ_PENDING, &con->flags);
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ok &= test_bit(CF_WRITE_PENDING, &con->flags);
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if (con->othercon) {
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@ -1644,6 +1642,7 @@ static void work_flush(void)
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}
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}
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}
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srcu_read_unlock(&connections_srcu, idx);
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} while (!ok);
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}
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@ -1652,9 +1651,7 @@ void dlm_lowcomms_stop(void)
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/* Set all the flags to prevent any
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socket activity.
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*/
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mutex_lock(&connections_lock);
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dlm_allow_conn = 0;
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mutex_unlock(&connections_lock);
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if (recv_workqueue)
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flush_workqueue(recv_workqueue);
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@ -1666,8 +1663,6 @@ void dlm_lowcomms_stop(void)
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clean_writequeues();
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foreach_conn(free_conn);
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work_stop();
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kmem_cache_destroy(con_cache);
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}
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int dlm_lowcomms_start(void)
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@ -1686,16 +1681,9 @@ int dlm_lowcomms_start(void)
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goto fail;
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}
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error = -ENOMEM;
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con_cache = kmem_cache_create("dlm_conn", sizeof(struct connection),
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__alignof__(struct connection), 0,
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NULL);
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if (!con_cache)
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goto fail;
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error = work_start();
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if (error)
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goto fail_destroy;
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goto fail;
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dlm_allow_conn = 1;
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@ -1714,10 +1702,8 @@ fail_unlisten:
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con = nodeid2con(0,0);
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if (con) {
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close_connection(con, false, true, true);
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kmem_cache_free(con_cache, con);
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kfree_rcu(con, rcu);
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}
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fail_destroy:
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kmem_cache_destroy(con_cache);
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fail:
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return error;
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}
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