On 10/16/2012 06:43 PM, Greg KH wrote:

On Tue, Oct 16, 2012 at 02:53:45PM +0200, Roland Stigge wrote:

quoted

On 10/16/2012 01:57 AM, Greg KH wrote:

quoted

On Tue, Oct 16, 2012 at 01:31:18AM +0200, Roland Stigge wrote:

quoted

+int gpio_block_export(struct gpio_block *block)
+{
+	int		status;
+	struct device	*dev;
+
+	/* can't export until sysfs is available ... */
+	if (!gpio_class.p) {
+		pr_debug("%s: called too early!\n", __func__);
+		return -ENOENT;
+	}
+
+	mutex_lock(&sysfs_lock);
+	dev = device_create(&gpio_class, NULL, MKDEV(0, 0), block,
+			    block->name);
+	if (!IS_ERR(dev))
+		status = sysfs_create_group(&dev->kobj, &gpio_block_attr_group);
+	else
+		status = PTR_ERR(dev);
+	mutex_unlock(&sysfs_lock);

You just raced with userspace telling it that the device was present,
yet the attributes are not there.  Don't do that, use the default class
attributes for the class and then the driver core will create them
automagically without needing to this "by hand" at all.

I guess you mean class attributes like gpio_class_attrs[] of gpio_class?

Yes.

quoted

Aren't class attributes specific to a class only (i.e. only one
attribute at the root for all devices)? What I needed above are
attributes for the block itself (of which there can be several). So we
need device attributes for each block, not class attributes here.

Yes, that is what the dev_attrs field in 'struct class' is for.

That's what I was missing. Will update.

Thanks,

Roland