RDMA/cm: Use RCU synchronization mechanism to protect cm_id_private xa_load()

The RCU mechanism is optimized for read-mostly scenarios and therefore
more suitable to protect the cm_id_private to decrease "cm.lock"
congestion.

This patch replaces the existing spinlock locking mechanism and kfree with
RCU mechanism in places where spinlock(cm.lock) protected xa_load
returning the cm_id_priv

In addition, delete the cm_get_id() function as there is no longer a
distinction if the caller already holds the cm_lock.

Remove an open coded version of cm_get_id().

Link: https://lore.kernel.org/r/20191219134750.413429-1-leon@kernel.org
Signed-off-by: Danit Goldberg <danitg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index 455b365..2945031 100644 (file)
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -241,6 +241,7 @@ struct cm_id_private {
        /* Number of clients sharing this ib_cm_id. Only valid for listeners.
         * Protected by the cm.lock spinlock. */
        int listen_sharecount;
+       struct rcu_head rcu;
 
        struct ib_mad_send_buf *msg;
        struct cm_timewait_info *timewait_info;
@@ -593,28 +594,16 @@ static void cm_free_id(__be32 local_id)
        xa_erase_irq(&cm.local_id_table, cm_local_id(local_id));
 }
 
-static struct cm_id_private * cm_get_id(__be32 local_id, __be32 remote_id)
+static struct cm_id_private *cm_acquire_id(__be32 local_id, __be32 remote_id)
 {
        struct cm_id_private *cm_id_priv;
 
+       rcu_read_lock();
        cm_id_priv = xa_load(&cm.local_id_table, cm_local_id(local_id));
-       if (cm_id_priv) {
-               if (cm_id_priv->id.remote_id == remote_id)
-                       refcount_inc(&cm_id_priv->refcount);
-               else
-                       cm_id_priv = NULL;
-       }
-
-       return cm_id_priv;
-}
-
-static struct cm_id_private * cm_acquire_id(__be32 local_id, __be32 remote_id)
-{
-       struct cm_id_private *cm_id_priv;
-
-       spin_lock_irq(&cm.lock);
-       cm_id_priv = cm_get_id(local_id, remote_id);
-       spin_unlock_irq(&cm.lock);
+       if (!cm_id_priv || cm_id_priv->id.remote_id != remote_id ||
+           !refcount_inc_not_zero(&cm_id_priv->refcount))
+               cm_id_priv = NULL;
+       rcu_read_unlock();
 
        return cm_id_priv;
 }
@@ -1089,7 +1078,7 @@ retest:
        rdma_destroy_ah_attr(&cm_id_priv->av.ah_attr);
        rdma_destroy_ah_attr(&cm_id_priv->alt_av.ah_attr);
        kfree(cm_id_priv->private_data);
-       kfree(cm_id_priv);
+       kfree_rcu(cm_id_priv, rcu);
 }
 
 void ib_destroy_cm_id(struct ib_cm_id *cm_id)
@@ -1821,7 +1810,7 @@ static struct cm_id_private * cm_match_req(struct cm_work *work,
        spin_lock_irq(&cm.lock);
        timewait_info = cm_insert_remote_id(cm_id_priv->timewait_info);
        if (timewait_info) {
-               cur_cm_id_priv = cm_get_id(timewait_info->work.local_id,
+               cur_cm_id_priv = cm_acquire_id(timewait_info->work.local_id,
                                           timewait_info->work.remote_id);
                spin_unlock_irq(&cm.lock);
                if (cur_cm_id_priv) {
@@ -1835,7 +1824,7 @@ static struct cm_id_private * cm_match_req(struct cm_work *work,
        timewait_info = cm_insert_remote_qpn(cm_id_priv->timewait_info);
        if (timewait_info) {
                cm_cleanup_timewait(cm_id_priv->timewait_info);
-               cur_cm_id_priv = cm_get_id(timewait_info->work.local_id,
+               cur_cm_id_priv = cm_acquire_id(timewait_info->work.local_id,
                                           timewait_info->work.remote_id);
 
                spin_unlock_irq(&cm.lock);
@@ -2293,7 +2282,7 @@ static int cm_rep_handler(struct cm_work *work)
                rb_erase(&cm_id_priv->timewait_info->remote_id_node,
                         &cm.remote_id_table);
                cm_id_priv->timewait_info->inserted_remote_id = 0;
-               cur_cm_id_priv = cm_get_id(timewait_info->work.local_id,
+               cur_cm_id_priv = cm_acquire_id(timewait_info->work.local_id,
                                           timewait_info->work.remote_id);
 
                spin_unlock(&cm.lock);
@@ -2788,14 +2777,8 @@ static struct cm_id_private * cm_acquire_rejected_id(struct cm_rej_msg *rej_msg)
                        spin_unlock_irq(&cm.lock);
                        return NULL;
                }
-               cm_id_priv = xa_load(&cm.local_id_table,
-                               cm_local_id(timewait_info->work.local_id));
-               if (cm_id_priv) {
-                       if (cm_id_priv->id.remote_id == remote_id)
-                               refcount_inc(&cm_id_priv->refcount);
-                       else
-                               cm_id_priv = NULL;
-               }
+               cm_id_priv =
+                       cm_acquire_id(timewait_info->work.local_id, remote_id);
                spin_unlock_irq(&cm.lock);
        } else if (cm_rej_get_msg_rejected(rej_msg) == CM_MSG_RESPONSE_REQ)
                cm_id_priv = cm_acquire_id(rej_msg->remote_comm_id, 0);