media: dmxdev: remove dvb_ringbuffer_flush() on writer side

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@web.de>
Reviewed-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/media/dvb/dvb-core/dmxdev.c b/drivers/media/dvb/dvb-core/dmxdev.c
index e4b5c03..4f8c3f7 100644 (file)
--- 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(const u8 *buffer1, size_t buffer1_len,
                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 u8 *buffer1, size_t buffer1_len,
        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;