Re: [PATCH v11 26/33] counter: Add character device interface

On Wed, Jun 09, 2021 at 11:07:08AM +0300, Dan Carpenter wrote:

On Wed, Jun 09, 2021 at 10:31:29AM +0900, William Breathitt Gray wrote:

quoted

+static int counter_set_event_node(struct counter_device *const counter,
+				  struct counter_watch *const watch,
+				  const struct counter_comp_node *const cfg)
+{
+	struct counter_event_node *event_node;
+	struct counter_comp_node *comp_node;
+

The caller should be holding the counter->events_list_lock lock but it's
not.

Hi Dan,

The counter_set_event_node() function doesn't access or modify
counter->events_list (it works on counter->next_events_list) so holding
the counter->events_list_lock here isn't necessary.

quoted

+	/* Search for event in the list */
+	list_for_each_entry(event_node, &counter->next_events_list, l)
+		if (event_node->event == watch->event &&
+		    event_node->channel == watch->channel)
+			break;
+
+	/* If event is not already in the list */
+	if (&event_node->l == &counter->next_events_list) {
+		/* Allocate new event node */
+		event_node = kmalloc(sizeof(*event_node), GFP_ATOMIC);
+		if (!event_node)
+			return -ENOMEM;
+
+		/* Configure event node and add to the list */
+		event_node->event = watch->event;
+		event_node->channel = watch->channel;
+		INIT_LIST_HEAD(&event_node->comp_list);
+		list_add(&event_node->l, &counter->next_events_list);
+	}
+
+	/* Check if component watch has already been set before */
+	list_for_each_entry(comp_node, &event_node->comp_list, l)
+		if (comp_node->parent == cfg->parent &&
+		    comp_node->comp.count_u8_read == cfg->comp.count_u8_read)
+			return -EINVAL;
+
+	/* Allocate component node */
+	comp_node = kmalloc(sizeof(*comp_node), GFP_ATOMIC);
+	if (!comp_node) {
+		/* Free event node if no one else is watching */
+		if (list_empty(&event_node->comp_list)) {
+			list_del(&event_node->l);
+			kfree(event_node);
+		}
+		return -ENOMEM;
+	}
+	*comp_node = *cfg;
+
+	/* Add component node to event node */
+	list_add_tail(&comp_node->l, &event_node->comp_list);
+
+	return 0;
+}
+
+static int counter_disable_events(struct counter_device *const counter)
+{
+	unsigned long flags;
+	int err = 0;
+
+	spin_lock_irqsave(&counter->events_list_lock, flags);
+
+	counter_events_list_free(&counter->events_list);
+
+	if (counter->ops->events_configure)
+		err = counter->ops->events_configure(counter);
+
+	spin_unlock_irqrestore(&counter->events_list_lock, flags);
+
+	counter_events_list_free(&counter->next_events_list);
+
+	return err;
+}
+
+static int counter_add_watch(struct counter_device *const counter,
+			     const unsigned long arg)
+{
+	void __user *const uwatch = (void __user *)arg;
+	struct counter_watch watch;
+	struct counter_comp_node comp_node = {0};

Always use = {};.  It's the new hotness, and it avoids a Sparse warning
for using 0 instead of NULL.  #IDidNotTest #CouldBeWrongAboutSparse

Thanks for the heads-up! I think this is the only patch where I have
this, so I'll hold off submitting a v12 for just this change unless
something else comes up with this patchset (I can fix this spare warning
in a subsequent patch).

William Breathitt Gray