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

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Date:   Wed, 9 Jun 2021 17:28:10 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     jic23@...nel.org, linux-stm32@...md-mailman.stormreply.com,
        kernel@...gutronix.de, a.fatoum@...gutronix.de,
        kamel.bouhara@...tlin.com, gwendal@...omium.org,
        alexandre.belloni@...tlin.com, david@...hnology.com,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, syednwaris@...il.com,
        patrick.havelange@...ensium.com, fabrice.gasnier@...com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        o.rempel@...gutronix.de, jarkko.nikula@...ux.intel.com
Subject: 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:
> > +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.

> > +	/* 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

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