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From: Alan Stern <stern@rowland.harvard.edu>
To: Jiri Kosina <jikos@kernel.org>, Oliver Neukum <oneukum@suse.com>
Cc: USB list <linux-usb@vger.kernel.org>
Subject: Duplicated code in hiddev_open()
Date: Fri, 16 Aug 2019 13:10:00 -0400 (EDT)
Message-ID: <Pine.LNX.4.44L0.1908161228310.1525-100000@iolanthe.rowland.org> (raw)

Oliver and Jiri:

Why is there duplicated code in
drivers/hid/usbhid/hiddev.c:hiddev_open()?

Line 267:
	/*
	 * no need for locking because the USB major number
	 * is shared which usbcore guards against disconnect
	 */
	if (list->hiddev->exist) {
		if (!list->hiddev->open++) {
			res = hid_hw_open(hiddev->hid);
			if (res < 0)
				goto bail;
		}
	} else {
		res = -ENODEV;
		goto bail;
	}

Line 286:
	mutex_lock(&hiddev->existancelock);
	if (!list->hiddev->open++)
		if (list->hiddev->exist) {
			struct hid_device *hid = hiddev->hid;
			res = hid_hw_power(hid, PM_HINT_FULLON);
			if (res < 0)
				goto bail_unlock;
			res = hid_hw_open(hid);
			if (res < 0)
				goto bail_normal_power;
		}
	mutex_unlock(&hiddev->existancelock);

The second part can never execute, because the first part ensures that 
list->hiddev->open > 0 by the time the second part runs.

Even more disturbing, why is one of these code sections protected by a 
mutex and the other not?

Note: The second section was added in commit 0361a28d3f9a ("HID: 
autosuspend support for USB HID") over ten years ago!

Alan Stern


             reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-16 17:10 Alan Stern [this message]
2019-08-19 10:41 ` Oliver Neukum
2019-08-19 14:17   ` Alan Stern
2019-08-20 14:34     ` Oliver Neukum

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