[media] dvb_demux: fix deadlock in dmx_section_feed_release_filter()

dmx_section_feed_release_filter() locks dvbdmx->mutex and
if the feed is still filtering, it calls feed->stop_filtering(feed).
stop_filtering() is implemented by dmx_section_feed_stop_filtering()
that first of all try to lock the same mutex: dvbdmx->mutex.
That leads to a deadlock.
It does not happen often in practice because all callers of
release_filter() stop filtering by themselves.
So the problem can happen in case of race condition only.
The patch releases dvbdmx->mutex before call to feed->stop_filtering(feed)
and reacquires the mutex after that.
Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

diff --git a/drivers/media/dvb-core/dvb_demux.c b/drivers/media/dvb-core/dvb_demux.c
index 58de441..25f3c64 100644 (file)
--- a/drivers/media/dvb-core/dvb_demux.c
+++ b/drivers/media/dvb-core/dvb_demux.c
@@ -1032,8 +1032,13 @@ static int dmx_section_feed_release_filter(struct dmx_section_feed *feed,
                return -EINVAL;
        }
 
-       if (feed->is_filtering)
+       if (feed->is_filtering) {
+               /* release dvbdmx->mutex as far as 
+                  it is acquired by stop_filtering() itself */
+               mutex_unlock(&dvbdmx->mutex);
                feed->stop_filtering(feed);
+               mutex_lock(&dvbdmx->mutex);
+       }
 
        spin_lock_irq(&dvbdmx->lock);
        f = dvbdmxfeed->filter;