[PATCH] media: dmxdev: remove dvb_ringbuffer_flush() on writer side

[Soeren Moch <smoch@web.de>]

In dvb_ringbuffer lock-less synchronizationof reader and writer threads is done
with separateread and write pointers. Sincedvb_ringbuffer_flush() modifies the
read pointer, this function must not be called from the writer thread.

This patch removes the dvb_ringbuffer_flush() calls in the dmxdev ringbuffer
write functions, this fixes Oopses "Unable to handle kernel paging request"
I could observe for the call chaindvb_demux_read ->dvb_dmxdev_buffer_read ->
dvb_ringbuffer_read_user -> __copy_to_user (the reader side of the ringbuffer).

The flush calls at the write side are not necessary anyway since ringbuffer_flush
is also called in dvb_dmxdev_buffer_read() when an error condition is set in the
ringbuffer.

This patch should also be applied to stable kernels.

Signed-off-by: Soeren Moch <smoch@web.de>
CC: <stable@vger.kernel.org>


--- a/drivers/media/dvb-core/dmxdev.c	2013-04-05 21:21:15.000000000 +0200
+++ b/drivers/media/dvb-core/dmxdev.c	2013-04-14 09:01:58.000000000 +0200
@@ -377,10 +377,8 @@ static int dvb_dmxdev_section_callback(c
  		ret = dvb_dmxdev_buffer_write(&dmxdevfilter->buffer, buffer2,
  					      buffer2_len);
  	}
-	if (ret < 0) {
-		dvb_ringbuffer_flush(&dmxdevfilter->buffer);
+	if (ret < 0)
  		dmxdevfilter->buffer.error = ret;
-	}
  	if (dmxdevfilter->params.sec.flags & DMX_ONESHOT)
  		dmxdevfilter->state = DMXDEV_STATE_DONE;
  	spin_unlock(&dmxdevfilter->dev->lock);
@@ -416,10 +414,8 @@ static int dvb_dmxdev_ts_callback(const
  	ret = dvb_dmxdev_buffer_write(buffer, buffer1, buffer1_len);
  	if (ret == buffer1_len)
  		ret = dvb_dmxdev_buffer_write(buffer, buffer2, buffer2_len);
-	if (ret < 0) {
-		dvb_ringbuffer_flush(buffer);
+	if (ret < 0)
  		buffer->error = ret;
-	}
  	spin_unlock(&dmxdevfilter->dev->lock);
  	wake_up(&buffer->queue);
  	return 0;