net/mlx5: Delay events till ib registration ends

When mlx5_ib registers itself to mlx5_core as an interface, it will
call mlx5_add_device which will call mlx5_ib interface add callback,
in case the latter successfully returns, only then mlx5_core will add
it to the interface list and async events will be forwarded to mlx5_ib.
Between mlx5_ib interface add callback and mlx5_core adding the mlx5_ib
interface to its devices list, arriving mlx5_core events can be missed
by the new mlx5_ib registering interface.

In other words:
thread 1: mlx5_ib: mlx5_register_interface(dev)
thread 1: mlx5_core: mlx5_add_device(dev)
thread 1: mlx5_core: ctx = dev->add => (mlx5_ib)->mlx5_ib_add
thread 2: mlx5_core_event: **new event arrives, forward to dev_list
thread 1: mlx5_core: add_ctx_to_dev_list(ctx)
/* previous event was missed by the new interface.*/
It is ok to miss events before dev->add (mlx5_ib)->mlx5_ib_add_device
but not after.

We fix this race by accumulating the events that come between the
ib_register_device (inside mlx5_add_device->(dev->add)) till the adding
to the list completes and fire them to the new registering interface
after that.

Fixes: f1ee87fe ("net/mlx5: Organize device list API in one place")
Signed-off-by: Erez Shitrit <erezsh@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/net/ethernet/mellanox/mlx5/core/dev.c

@@ -45,11 +45,70 @@ struct mlx5_device_context {
 	unsigned long		state;
 };
 
+struct mlx5_delayed_event {
+	struct list_head	list;
+	struct mlx5_core_dev	*dev;
+	enum mlx5_dev_event	event;
+	unsigned long		param;
+};
+
 enum {
 	MLX5_INTERFACE_ADDED,
 	MLX5_INTERFACE_ATTACHED,
 };
 
+static void add_delayed_event(struct mlx5_priv *priv,
+			      struct mlx5_core_dev *dev,
+			      enum mlx5_dev_event event,
+			      unsigned long param)
+{
+	struct mlx5_delayed_event *delayed_event;
+
+	delayed_event = kzalloc(sizeof(*delayed_event), GFP_ATOMIC);
+	if (!delayed_event) {
+		mlx5_core_err(dev, "event %d is missed\n", event);
+		return;
+	}
+
+	mlx5_core_dbg(dev, "Accumulating event %d\n", event);
+	delayed_event->dev = dev;
+	delayed_event->event = event;
+	delayed_event->param = param;
+	list_add_tail(&delayed_event->list, &priv->waiting_events_list);
+}
+
+static void fire_delayed_event_locked(struct mlx5_device_context *dev_ctx,
+				      struct mlx5_core_dev *dev,
+				      struct mlx5_priv *priv)
+{
+	struct mlx5_delayed_event *de;
+	struct mlx5_delayed_event *n;
+
+	/* stop delaying events */
+	priv->is_accum_events = false;
+
+	/* fire all accumulated events before new event comes */
+	list_for_each_entry_safe(de, n, &priv->waiting_events_list, list) {
+		dev_ctx->intf->event(dev, dev_ctx->context, de->event, de->param);
+		list_del(&de->list);
+		kfree(de);
+	}
+}
+
+static void cleanup_delayed_evets(struct mlx5_priv *priv)
+{
+	struct mlx5_delayed_event *de;
+	struct mlx5_delayed_event *n;
+
+	spin_lock_irq(&priv->ctx_lock);
+	priv->is_accum_events = false;
+	list_for_each_entry_safe(de, n, &priv->waiting_events_list, list) {
+		list_del(&de->list);
+		kfree(de);
+	}
+	spin_unlock_irq(&priv->ctx_lock);
+}
+
 void mlx5_add_device(struct mlx5_interface *intf, struct mlx5_priv *priv)
 {
 	struct mlx5_device_context *dev_ctx;
@@ -63,6 +122,12 @@ void mlx5_add_device(struct mlx5_interface *intf, struct mlx5_priv *priv)
 		return;
 
 	dev_ctx->intf = intf;
+	/* accumulating events that can come after mlx5_ib calls to
+	 * ib_register_device, till adding that interface to the events list.
+	 */
+
+	priv->is_accum_events = true;
+
 	dev_ctx->context = intf->add(dev);
 	set_bit(MLX5_INTERFACE_ADDED, &dev_ctx->state);
 	if (intf->attach)
@@ -71,6 +136,9 @@ void mlx5_add_device(struct mlx5_interface *intf, struct mlx5_priv *priv)
 	if (dev_ctx->context) {
 		spin_lock_irq(&priv->ctx_lock);
 		list_add_tail(&dev_ctx->list, &priv->ctx_list);
+
+		fire_delayed_event_locked(dev_ctx, dev, priv);
+
 #ifdef CONFIG_INFINIBAND_ON_DEMAND_PAGING
 		if (dev_ctx->intf->pfault) {
 			if (priv->pfault) {
@@ -84,6 +152,8 @@ void mlx5_add_device(struct mlx5_interface *intf, struct mlx5_priv *priv)
 		spin_unlock_irq(&priv->ctx_lock);
 	} else {
 		kfree(dev_ctx);
+		 /* delete all accumulated events */
+		cleanup_delayed_evets(priv);
 	}
 }
 
@@ -341,6 +411,9 @@ void mlx5_core_event(struct mlx5_core_dev *dev, enum mlx5_dev_event event,
 
 	spin_lock_irqsave(&priv->ctx_lock, flags);
 
+	if (priv->is_accum_events)
+		add_delayed_event(priv, dev, event, param);
+
 	list_for_each_entry(dev_ctx, &priv->ctx_list, list)
 		if (dev_ctx->intf->event)
 			dev_ctx->intf->event(dev, dev_ctx->context, event, param);

drivers/net/ethernet/mellanox/mlx5/core/main.c

@@ -1343,6 +1343,9 @@ static int init_one(struct pci_dev *pdev,
 	mutex_init(&dev->pci_status_mutex);
 	mutex_init(&dev->intf_state_mutex);
 
+	INIT_LIST_HEAD(&priv->waiting_events_list);
+	priv->is_accum_events = false;
+
 #ifdef CONFIG_INFINIBAND_ON_DEMAND_PAGING
 	err = init_srcu_struct(&priv->pfault_srcu);
 	if (err) {

include/linux/mlx5/driver.h

@@ -647,6 +647,9 @@ struct mlx5_priv {
 	struct list_head        ctx_list;
 	spinlock_t              ctx_lock;
 
+	struct list_head	waiting_events_list;
+	bool			is_accum_events;
+
 	struct mlx5_flow_steering *steering;
 	struct mlx5_mpfs        *mpfs;
 	struct mlx5_eswitch     *eswitch;