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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 6 deletions

diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxdev.c
index a1a3a5159d71..0b4616b87195 100644
--- a/drivers/media/dvb-core/dmxdev.c
+++ b/drivers/media/dvb-core/dmxdev.c
@@ -377,10 +377,8 @@ 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);
@@ -416,10 +414,8 @@ 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;