[PATCH for-next v11 11/11] RDMA/rxe: Convert mca read locking to RCU

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Replace spinlock with rcu read locks for read side operations
on mca in rxe_recv.c and rxe_mcast.c. Use rcu list extensions on
write side operations and use spinlock to separate write threads.

Signed-off-by: Bob Pearson <rpearsonhpe@xxxxxxxxx>
---
 drivers/infiniband/sw/rxe/rxe_mcast.c | 73 +++++++++++++++------------
 drivers/infiniband/sw/rxe/rxe_recv.c  |  6 +--
 2 files changed, 45 insertions(+), 34 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_mcast.c b/drivers/infiniband/sw/rxe/rxe_mcast.c
index b66839276aa6..19cfa06c62ec 100644
--- a/drivers/infiniband/sw/rxe/rxe_mcast.c
+++ b/drivers/infiniband/sw/rxe/rxe_mcast.c
@@ -17,6 +17,12 @@
  * mca is created. It holds a pointer to the qp and is added to a list
  * of qp's that are attached to the mcg. The qp_list is used to replicate
  * mcast packets in the rxe receive path.
+ *
+ * The highest performance operations are mca list traversal when
+ * processing incoming multicast packets which need to be fanned out
+ * to the attached qp's. This list is protected by RCU locking for read
+ * operations and a spinlock in the rxe_dev struct for write operations.
+ * The red-black tree is protected by the same spinlock.
  */
 
 #include "rxe.h"
@@ -284,7 +290,7 @@ static void rxe_destroy_mcg(struct rxe_mcg *mcg)
 }
 
 /**
- * __rxe_init_mca - initialize a new mca holding lock
+ * __rxe_init_mca_rcu - initialize a new mca holding lock
  * @qp: qp object
  * @mcg: mcg object
  * @mca: empty space for new mca
@@ -294,8 +300,8 @@ static void rxe_destroy_mcg(struct rxe_mcg *mcg)
  *
  * Returns: 0 on success else an error
  */
-static int __rxe_init_mca(struct rxe_qp *qp, struct rxe_mcg *mcg,
-			  struct rxe_mca *mca)
+static int __rxe_init_mca_rcu(struct rxe_qp *qp, struct rxe_mcg *mcg,
+			      struct rxe_mca *mca)
 {
 	struct rxe_dev *rxe = to_rdev(qp->ibqp.device);
 	int n;
@@ -318,7 +324,7 @@ static int __rxe_init_mca(struct rxe_qp *qp, struct rxe_mcg *mcg,
 	rxe_add_ref(qp);
 	mca->qp = qp;
 
-	list_add_tail(&mca->qp_list, &mcg->qp_list);
+	list_add_tail_rcu(&mca->qp_list, &mcg->qp_list);
 
 	return 0;
 }
@@ -338,14 +344,14 @@ static int rxe_attach_mcg(struct rxe_mcg *mcg, struct rxe_qp *qp)
 	int err;
 
 	/* check to see if the qp is already a member of the group */
-	spin_lock_bh(&rxe->mcg_lock);
-	list_for_each_entry(mca, &mcg->qp_list, qp_list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(mca, &mcg->qp_list, qp_list) {
 		if (mca->qp == qp) {
-			spin_unlock_bh(&rxe->mcg_lock);
+			rcu_read_unlock();
 			return 0;
 		}
 	}
-	spin_unlock_bh(&rxe->mcg_lock);
+	rcu_read_unlock();
 
 	/* speculative alloc new mca without using GFP_ATOMIC */
 	mca = kzalloc(sizeof(*mca), GFP_KERNEL);
@@ -362,7 +368,7 @@ static int rxe_attach_mcg(struct rxe_mcg *mcg, struct rxe_qp *qp)
 		}
 	}
 
-	err = __rxe_init_mca(qp, mcg, mca);
+	err = __rxe_init_mca_rcu(qp, mcg, mca);
 	if (err)
 		kfree(mca);
 out:
@@ -371,22 +377,22 @@ static int rxe_attach_mcg(struct rxe_mcg *mcg, struct rxe_qp *qp)
 }
 
 /**
- * __rxe_cleanup_mca - cleanup mca object holding lock
+ * __rxe_cleanup_mca_rcu - cleanup mca object holding lock
  * @mca: mca object
  * @mcg: mcg object
  *
  * Context: caller must hold a reference to mcg and rxe->mcg_lock
  */
-static void __rxe_cleanup_mca(struct rxe_mca *mca, struct rxe_mcg *mcg)
+static void __rxe_cleanup_mca_rcu(struct rxe_mca *mca, struct rxe_mcg *mcg)
 {
-	list_del(&mca->qp_list);
+	list_del_rcu(&mca->qp_list);
 
 	atomic_dec(&mcg->qp_num);
 	atomic_dec(&mcg->rxe->mcg_attach);
 	atomic_dec(&mca->qp->mcg_num);
 	rxe_drop_ref(mca->qp);
 
-	kfree(mca);
+	kfree_rcu(mca);
 }
 
 /**
@@ -399,30 +405,35 @@ static void __rxe_cleanup_mca(struct rxe_mca *mca, struct rxe_mcg *mcg)
 static int rxe_detach_mcg(struct rxe_mcg *mcg, struct rxe_qp *qp)
 {
 	struct rxe_dev *rxe = mcg->rxe;
-	struct rxe_mca *mca, *tmp;
+	struct rxe_mca *mca;
+	int ret;
 
 	spin_lock_bh(&rxe->mcg_lock);
-	list_for_each_entry_safe(mca, tmp, &mcg->qp_list, qp_list) {
-		if (mca->qp == qp) {
-			__rxe_cleanup_mca(mca, mcg);
-
-			/* if the number of qp's attached to the
-			 * mcast group falls to zero go ahead and
-			 * tear it down. This will not free the
-			 * object since we are still holding a ref
-			 * from the caller
-			 */
-			if (atomic_read(&mcg->qp_num) <= 0)
-				__rxe_destroy_mcg(mcg);
-
-			spin_unlock_bh(&rxe->mcg_lock);
-			return 0;
-		}
+	list_for_each_entry_rcu(mca, &mcg->qp_list, qp_list) {
+		if (mca->qp == qp)
+			goto found;
 	}
 
 	/* we didn't find the qp on the list */
+	ret = -EINVAL;
+	goto done;
+
+found:
+	__rxe_cleanup_mca_rcu(mca, mcg);
+
+	/* if the number of qp's attached to the
+	 * mcast group falls to zero go ahead and
+	 * tear it down. This will not free the
+	 * object since we are still holding a ref
+	 * from the caller
+	 */
+	if (atomic_read(&mcg->qp_num) <= 0)
+		__rxe_destroy_mcg(mcg);
+
+	ret = 0;
+done:
 	spin_unlock_bh(&rxe->mcg_lock);
-	return -EINVAL;
+	return ret;
 }
 
 /**
diff --git a/drivers/infiniband/sw/rxe/rxe_recv.c b/drivers/infiniband/sw/rxe/rxe_recv.c
index 9b21cbb22602..c2cab85c6576 100644
--- a/drivers/infiniband/sw/rxe/rxe_recv.c
+++ b/drivers/infiniband/sw/rxe/rxe_recv.c
@@ -265,15 +265,15 @@ static void rxe_rcv_mcast_pkt(struct rxe_dev *rxe, struct sk_buff *skb)
 	qp_array = kmalloc_array(nmax, sizeof(qp), GFP_KERNEL);
 	n = 0;
 
-	spin_lock_bh(&rxe->mcg_lock);
-	list_for_each_entry(mca, &mcg->qp_list, qp_list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(mca, &mcg->qp_list, qp_list) {
 		/* protect the qp pointers in the list */
 		rxe_add_ref(mca->qp);
 		qp_array[n++] = mca->qp;
 		if (n == nmax)
 			break;
 	}
-	spin_unlock_bh(&rxe->mcg_lock);
+	rcu_read_unlock();
 	nmax = n;
 	kref_put(&mcg->ref_cnt, rxe_cleanup_mcg);
 
-- 
2.32.0




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