Re: [PATCH v4 for-next 06/12] RDMA/core: Use refcount_t instead of atomic_t on refcount of mcast_group

[Jason Gunthorpe <jgg@xxxxxxxxxx>]

On Fri, May 28, 2021 at 05:37:37PM +0800, Weihang Li wrote:
> @@ -565,8 +565,11 @@ static struct mcast_group *acquire_group(struct mcast_port *port,
>  	if (!is_mgid0) {
>  		spin_lock_irqsave(&port->lock, flags);
>  		group = mcast_find(port, mgid);
> -		if (group)
> +		if (group) {
> +			refcount_inc(&group->refcount);
>  			goto found;
> +		}
> +
>  		spin_unlock_irqrestore(&port->lock, flags);
>  	}
>  
> @@ -590,8 +593,10 @@ static struct mcast_group *acquire_group(struct mcast_port *port,
>  		group = cur_group;
>  	} else
>  		refcount_inc(&port->refcount);
> +
> +	refcount_set(&group->refcount, 1);
> +

This isn't right, when mcast_insert() returns an existing group we
need to incr not set the refcount. Change it like this:

diff --git a/drivers/infiniband/core/multicast.c b/drivers/infiniband/core/multicast.c
index 17abc212b87d05..cf99e17b81ce79 100644
--- a/drivers/infiniband/core/multicast.c
+++ b/drivers/infiniband/core/multicast.c
@@ -585,17 +585,17 @@ static struct mcast_group *acquire_group(struct mcast_port *port,
 	INIT_LIST_HEAD(&group->active_list);
 	INIT_WORK(&group->work, mcast_work_handler);
 	spin_lock_init(&group->lock);
+	refcount_set(&group->refcount, 1);
 
 	spin_lock_irqsave(&port->lock, flags);
 	cur_group = mcast_insert(port, group, is_mgid0);
 	if (cur_group) {
 		kfree(group);
 		group = cur_group;
+		refcount_inc(&group->refcount);
 	} else
 		refcount_inc(&port->refcount);
 
-	refcount_set(&group->refcount, 1);
-
 found:
 	spin_unlock_irqrestore(&port->lock, flags);
 	return group;