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Commit c79041a4 authored by Du Xing's avatar Du Xing Committed by Greg Kroah-Hartman
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USB: usb-skeleton.c: fix blocked forever in skel_read 



In skel_read,the reader blocked in wait_for_completion before submit
bulk in urb.
Using processed_urb is for retaining the completion in the case that
previous interruptible wait in skel_read was interrupted and complete
before next skel_read.  Replacing completion with waitqueue can avoid
working around the counting nature of completions
and fix the bug.

Signed-off-by: default avatarDu Xing <duxing2007@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3edce1cf

drivers/usb/usb-skeleton.c

+8 −24
Original line number Diff line number Diff line
@@ -61,11 +61,10 @@ struct usb_skel { 
	__u8			bulk_out_endpointAddr;	/* the address of the bulk out endpoint */

	int			errors;			/* the last request tanked */

	bool			ongoing_read;		/* a read is going on */

	bool			processed_urb;		/* indicates we haven't processed the urb */

	spinlock_t		err_lock;		/* lock for errors */

	struct kref		kref;

	struct mutex		io_mutex;		/* synchronize I/O with disconnect */

	struct completion	bulk_in_completion;	/* to wait for an ongoing read */

	wait_queue_head_t	bulk_in_wait;		/* to wait for an ongoing read */

};

#define to_skel_dev(d) container_of(d, struct usb_skel, kref)
@@ -185,7 +184,7 @@ static void skel_read_bulk_callback(struct urb *urb) 
	dev->ongoing_read = 0;

	spin_unlock(&dev->err_lock);



	complete(&dev->bulk_in_completion);

	wake_up_interruptible(&dev->bulk_in_wait);

}



static int skel_do_read_io(struct usb_skel *dev, size_t count)
@@ -206,13 +205,16 @@ static int skel_do_read_io(struct usb_skel *dev, size_t count) 
	dev->ongoing_read = 1;

	spin_unlock_irq(&dev->err_lock);



	/* submit bulk in urb, which means no data to deliver */

	dev->bulk_in_filled = 0;

	dev->bulk_in_copied = 0;



	/* do it */

	rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL);

	if (rv < 0) {

		dev_err(&dev->interface->dev,

			"%s - failed submitting read urb, error %d\n",

			__func__, rv);

		dev->bulk_in_filled = 0;

		rv = (rv == -ENOMEM) ? rv : -EIO;

		spin_lock_irq(&dev->err_lock);

		dev->ongoing_read = 0;
@@ -261,25 +263,9 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count, 
		 * IO may take forever

		 * hence wait in an interruptible state

		 */

		rv = wait_for_completion_interruptible(&dev->bulk_in_completion);

		rv = wait_event_interruptible(dev->bulk_in_wait, (!dev->ongoing_read));

		if (rv < 0)

			goto exit;

		/*

		 * by waiting we also semiprocessed the urb

		 * we must finish now

		 */

		dev->bulk_in_copied = 0;

		dev->processed_urb = 1;

	}



	if (!dev->processed_urb) {

		/*

		 * the URB hasn't been processed

		 * do it now

		 */

		wait_for_completion(&dev->bulk_in_completion);

		dev->bulk_in_copied = 0;

		dev->processed_urb = 1;

	}



	/* errors must be reported */
@@ -289,8 +275,6 @@ static ssize_t skel_read(struct file *file, char *buffer, size_t count, 
		dev->errors = 0;

		/* to preserve notifications about reset */

		rv = (rv == -EPIPE) ? rv : -EIO;

		/* no data to deliver */

		dev->bulk_in_filled = 0;

		/* report it */

		goto exit;

	}
@@ -526,7 +510,7 @@ static int skel_probe(struct usb_interface *interface, 
	mutex_init(&dev->io_mutex);

	spin_lock_init(&dev->err_lock);

	init_usb_anchor(&dev->submitted);

	init_completion(&dev->bulk_in_completion);

	init_waitqueue_head(&dev->bulk_in_wait);



	dev->udev = usb_get_dev(interface_to_usbdev(interface));

	dev->interface = interface;