linux-kernel - [127/197] Staging: comedi: usbdux.c: fix locking up of the driver when the comedi ringbuffer runs empty

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Message-Id: <20100422190918.708464409@kvm.kroah.org>
Date:	Thu, 22 Apr 2010 12:09:38 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Bernd Porr <berndporr@....com>,
	Leann Ogasawara <leann.ogasawara@...onical.com>
Subject: [127/197] Staging: comedi: usbdux.c: fix locking up of the driver when the comedi ringbuffer runs empty

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Bernd Porr <berndporr@....com>

commit d4c3a56587af3edbe5f618b20e800e9f9fde13cb upstream.

Jan-Matthias Braun spotted a bug which locks up the driver when the
comedi ring buffer runs empty and provided a patch. The driver would
still send the data to comedi but the reader won't wake up any more.
What's required is setting the flag COMEDI_CB_BLOCK after new data has
arrived which wakes up the reader and therefore the read() command.

Signed-off-by: Bernd Porr <berndporr@....com>
Signed-off-by: Leann Ogasawara <leann.ogasawara@...onical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/staging/comedi/drivers/usbdux.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/staging/comedi/drivers/usbdux.c
+++ b/drivers/staging/comedi/drivers/usbdux.c
@@ -1,4 +1,4 @@
-#define DRIVER_VERSION "v2.3"
+#define DRIVER_VERSION "v2.4"
 #define DRIVER_AUTHOR "Bernd Porr, BerndPorr@....com"
 #define DRIVER_DESC "Stirling/ITL USB-DUX -- Bernd.Porr@....com"
 /*
@@ -81,6 +81,8 @@ sampling rate. If you sample two channel
  * 2.1:  changed PWM API
  * 2.2:  added firmware kernel request to fix an udev problem
  * 2.3:  corrected a bug in bulk timeouts which were far too short
+ * 2.4:  fixed a bug which causes the driver to hang when it ran out of data.
+ *       Thanks to Jan-Matthias Braun and Ian to spot the bug and fix it.
  *
  */
 
@@ -532,6 +534,7 @@ static void usbduxsub_ai_IsocIrq(struct
 		}
 	}
 	/* tell comedi that data is there */
+	s->async->events |= COMEDI_CB_BLOCK | COMEDI_CB_EOS;
 	comedi_event(this_usbduxsub->comedidev, s);
 }
 


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