linux-kernel - [27/85] [media] media: dmxdev: remove dvb_ringbuffer

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Date:	Wed, 24 Jul 2013 15:02:45 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Soeren Moch" <smoch@....de>,
	"Sakari Ailus" <sakari.ailus@....fi>,
	"Mauro Carvalho Chehab" <mchehab@...hat.com>
Subject: [27/85] [media] media: dmxdev: remove dvb_ringbuffer_flush() on
 writer side

3.2.49-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Soeren Moch <smoch@....de>

commit 414abbd2cd4c2618895f02ed3a76ec6647281436 upstream.

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@....de>
Reviewed-by: Sakari Ailus <sakari.ailus@....fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...hat.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/media/dvb/dvb-core/dmxdev.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

--- a/drivers/media/dvb/dvb-core/dmxdev.c
+++ b/drivers/media/dvb/dvb-core/dmxdev.c
@@ -380,10 +380,8 @@ 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);
@@ -419,10 +417,8 @@ 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;

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