linux-kernel - [patch] usb-skeleton leaking locks on open.

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Date:	Mon, 24 Sep 2007 09:18:22 -0700
From:	Mark Gross <mgross@...ux.intel.com>
To:	lkml <linux-kernel@...r.kernel.org>,
	usbdev <linux-usb-devel@...ts.sourceforge.net>
Subject: [patch] usb-skeleton leaking locks on open.

This weekend I was hacking around with a trivial USB driver for talking
to the boot load firmware of a USB Bit Whacker.  It's running the
MicroChip Pic18 boot loader firmware and I'm putting together a flash
program for writing new FW to the thing.

Anyway in my use of the usb-skeleton.c as my starting point I discovered
my test program was getting hung up after attempting to write a buffer.
The application and driver where hung in a way that required me to
reboot to get it to clean up so I could try again.

It turned out the code path through skel_open can grap the driver's
io_mutex lock and forget to release it.

The following patch fixes the problem for me.

--mgross

Signed-off-by: Mark Gross <mgross@...ux.intel.com>

diff -urN -X linux-2.6.23-rc7/Documentation/dontdiff linux-2.6.23-rc7/drivers/usb/usb-skeleton.c linux-2.6.23-rc7-bugfix/drivers/usb/usb-skeleton.c
--- linux-2.6.23-rc7/drivers/usb/usb-skeleton.c	2007-09-24 08:57:54.000000000 -0700
+++ linux-2.6.23-rc7-bugfix/drivers/usb/usb-skeleton.c	2007-09-24 09:01:43.000000000 -0700
@@ -125,6 +125,7 @@

 	/* save our object in the file's private structure */
 	file->private_data = dev;
+	mutex_unlock(&dev->io_mutex);

 exit:
 	return retval;
-
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