nvmet-fc: use RCU proctection for assoc_list

searching assoc_list protected by rcu_read_lock if list not changed inline.
and according to the rcu list rules.

queue array embedded into nvmet_fc_tgt_assoc protected by rcu_read_lock
according to rcu dereference/assign rules.

queue and assoc object freed after grace period by call_rcu.

tgtport lock taken for changing assoc_list.
Reviewed-by: Eldad Zinger <Eldad.Zinger@dell.com>
Reviewed-by: Elad Grupi <Elad.Grupi@dell.com>
Reviewed-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Leonid Ravich <Leonid.Ravich@emc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/fc.c

@@ -145,6 +145,7 @@ struct nvmet_fc_tgt_queue {
 	struct list_head		avail_defer_list;
 	struct workqueue_struct		*work_q;
 	struct kref			ref;
+	struct rcu_head			rcu;
 	struct nvmet_fc_fcp_iod		fod[];		/* array of fcp_iods */
 } __aligned(sizeof(unsigned long long));
 
@@ -167,6 +168,7 @@ struct nvmet_fc_tgt_assoc {
 	struct nvmet_fc_tgt_queue	*queues[NVMET_NR_QUEUES + 1];
 	struct kref			ref;
 	struct work_struct		del_work;
+	struct rcu_head			rcu;
 };
 
 
@@ -790,7 +792,6 @@ nvmet_fc_alloc_target_queue(struct nvmet_fc_tgt_assoc *assoc,
 			u16 qid, u16 sqsize)
 {
 	struct nvmet_fc_tgt_queue *queue;
-	unsigned long flags;
 	int ret;
 
 	if (qid > NVMET_NR_QUEUES)
@@ -829,9 +830,7 @@ nvmet_fc_alloc_target_queue(struct nvmet_fc_tgt_assoc *assoc,
 		goto out_fail_iodlist;
 
 	WARN_ON(assoc->queues[qid]);
-	spin_lock_irqsave(&assoc->tgtport->lock, flags);
-	assoc->queues[qid] = queue;
-	spin_unlock_irqrestore(&assoc->tgtport->lock, flags);
+	rcu_assign_pointer(assoc->queues[qid], queue);
 
 	return queue;
 
@@ -851,11 +850,8 @@ nvmet_fc_tgt_queue_free(struct kref *ref)
 {
 	struct nvmet_fc_tgt_queue *queue =
 		container_of(ref, struct nvmet_fc_tgt_queue, ref);
-	unsigned long flags;
 
-	spin_lock_irqsave(&queue->assoc->tgtport->lock, flags);
-	queue->assoc->queues[queue->qid] = NULL;
-	spin_unlock_irqrestore(&queue->assoc->tgtport->lock, flags);
+	rcu_assign_pointer(queue->assoc->queues[queue->qid], NULL);
 
 	nvmet_fc_destroy_fcp_iodlist(queue->assoc->tgtport, queue);
 
@@ -863,7 +859,7 @@ nvmet_fc_tgt_queue_free(struct kref *ref)
 
 	destroy_workqueue(queue->work_q);
 
-	kfree(queue);
+	kfree_rcu(queue, rcu);
 }
 
 static void
@@ -965,24 +961,23 @@ nvmet_fc_find_target_queue(struct nvmet_fc_tgtport *tgtport,
 	struct nvmet_fc_tgt_queue *queue;
 	u64 association_id = nvmet_fc_getassociationid(connection_id);
 	u16 qid = nvmet_fc_getqueueid(connection_id);
-	unsigned long flags;
 
 	if (qid > NVMET_NR_QUEUES)
 		return NULL;
 
-	spin_lock_irqsave(&tgtport->lock, flags);
-	list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
 		if (association_id == assoc->association_id) {
-			queue = assoc->queues[qid];
+			queue = rcu_dereference(assoc->queues[qid]);
 			if (queue &&
 			    (!atomic_read(&queue->connected) ||
 			     !nvmet_fc_tgt_q_get(queue)))
 				queue = NULL;
-			spin_unlock_irqrestore(&tgtport->lock, flags);
+			rcu_read_unlock();
 			return queue;
 		}
 	}
-	spin_unlock_irqrestore(&tgtport->lock, flags);
+	rcu_read_unlock();
 	return NULL;
 }
 
@@ -1137,7 +1132,7 @@ nvmet_fc_alloc_target_assoc(struct nvmet_fc_tgtport *tgtport, void *hosthandle)
 		}
 		if (!needrandom) {
 			assoc->association_id = ran;
-			list_add_tail(&assoc->a_list, &tgtport->assoc_list);
+			list_add_tail_rcu(&assoc->a_list, &tgtport->assoc_list);
 		}
 		spin_unlock_irqrestore(&tgtport->lock, flags);
 	}
@@ -1167,7 +1162,7 @@ nvmet_fc_target_assoc_free(struct kref *ref)
 
 	nvmet_fc_free_hostport(assoc->hostport);
 	spin_lock_irqsave(&tgtport->lock, flags);
-	list_del(&assoc->a_list);
+	list_del_rcu(&assoc->a_list);
 	oldls = assoc->rcv_disconn;
 	spin_unlock_irqrestore(&tgtport->lock, flags);
 	/* if pending Rcv Disconnect Association LS, send rsp now */
@@ -1177,7 +1172,7 @@ nvmet_fc_target_assoc_free(struct kref *ref)
 	dev_info(tgtport->dev,
 		"{%d:%d} Association freed\n",
 		tgtport->fc_target_port.port_num, assoc->a_id);
-	kfree(assoc);
+	kfree_rcu(assoc, rcu);
 	nvmet_fc_tgtport_put(tgtport);
 }
 
@@ -1198,7 +1193,6 @@ nvmet_fc_delete_target_assoc(struct nvmet_fc_tgt_assoc *assoc)
 {
 	struct nvmet_fc_tgtport *tgtport = assoc->tgtport;
 	struct nvmet_fc_tgt_queue *queue;
-	unsigned long flags;
 	int i, terminating;
 
 	terminating = atomic_xchg(&assoc->terminating, 1);
@@ -1207,19 +1201,23 @@ nvmet_fc_delete_target_assoc(struct nvmet_fc_tgt_assoc *assoc)
 	if (terminating)
 		return;
 
-	spin_lock_irqsave(&tgtport->lock, flags);
+
 	for (i = NVMET_NR_QUEUES; i >= 0; i--) {
-		queue = assoc->queues[i];
-		if (queue) {
-			if (!nvmet_fc_tgt_q_get(queue))
+		rcu_read_lock();
+		queue = rcu_dereference(assoc->queues[i]);
+		if (!queue) {
+			rcu_read_unlock();
 			continue;
-			spin_unlock_irqrestore(&tgtport->lock, flags);
+		}
+
+		if (!nvmet_fc_tgt_q_get(queue)) {
+			rcu_read_unlock();
+			continue;
+		}
+		rcu_read_unlock();
 		nvmet_fc_delete_target_queue(queue);
 		nvmet_fc_tgt_q_put(queue);
-			spin_lock_irqsave(&tgtport->lock, flags);
-		}
 	}
-	spin_unlock_irqrestore(&tgtport->lock, flags);
 
 	dev_info(tgtport->dev,
 		"{%d:%d} Association deleted\n",
@@ -1234,10 +1232,9 @@ nvmet_fc_find_target_assoc(struct nvmet_fc_tgtport *tgtport,
 {
 	struct nvmet_fc_tgt_assoc *assoc;
 	struct nvmet_fc_tgt_assoc *ret = NULL;
-	unsigned long flags;
 
-	spin_lock_irqsave(&tgtport->lock, flags);
-	list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
 		if (association_id == assoc->association_id) {
 			ret = assoc;
 			if (!nvmet_fc_tgt_a_get(assoc))
@@ -1245,7 +1242,7 @@ nvmet_fc_find_target_assoc(struct nvmet_fc_tgtport *tgtport,
 			break;
 		}
 	}
-	spin_unlock_irqrestore(&tgtport->lock, flags);
+	rcu_read_unlock();
 
 	return ret;
 }
@@ -1473,19 +1470,17 @@ nvmet_fc_tgtport_get(struct nvmet_fc_tgtport *tgtport)
 static void
 __nvmet_fc_free_assocs(struct nvmet_fc_tgtport *tgtport)
 {
-	struct nvmet_fc_tgt_assoc *assoc, *next;
-	unsigned long flags;
+	struct nvmet_fc_tgt_assoc *assoc;
 
-	spin_lock_irqsave(&tgtport->lock, flags);
-	list_for_each_entry_safe(assoc, next,
-				&tgtport->assoc_list, a_list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
 		if (!nvmet_fc_tgt_a_get(assoc))
 			continue;
 		if (!schedule_work(&assoc->del_work))
 			/* already deleting - release local reference */
 			nvmet_fc_tgt_a_put(assoc);
 	}
-	spin_unlock_irqrestore(&tgtport->lock, flags);
+	rcu_read_unlock();
 }
 
 /**
@@ -1568,16 +1563,16 @@ nvmet_fc_delete_ctrl(struct nvmet_ctrl *ctrl)
 			continue;
 		spin_unlock_irqrestore(&nvmet_fc_tgtlock, flags);
 
-		spin_lock_irqsave(&tgtport->lock, flags);
-		list_for_each_entry(assoc, &tgtport->assoc_list, a_list) {
-			queue = assoc->queues[0];
+		rcu_read_lock();
+		list_for_each_entry_rcu(assoc, &tgtport->assoc_list, a_list) {
+			queue = rcu_dereference(assoc->queues[0]);
 			if (queue && queue->nvme_sq.ctrl == ctrl) {
 				if (nvmet_fc_tgt_a_get(assoc))
 					found_ctrl = true;
 				break;
 			}
 		}
-		spin_unlock_irqrestore(&tgtport->lock, flags);
+		rcu_read_unlock();
 
 		nvmet_fc_tgtport_put(tgtport);