[PATCH] dvb-core: Fix several locking related problems.

[Simon Arlott <simon@fire.lp0.eu>]

Fix several instances of dvb-core functions using mutex_lock_interruptible and 
returning -ERESTARTSYS where the calling function will either never retry or 
never check the return value.

These cause a race condition with dvb_dmxdev_filter_free and dvb_dvr_release, 
both of which are filesystem release functions whose return value is ignored 
and will never be retried. When this happens it becomes impossible to open dvr0 
again (-EBUSY) since it has not been released properly.

Signed-off-by: Simon Arlott <simon@fire.lp0.eu>
---
On 04/03/07 15:41, Andreas Oberritter wrote:
> please send an updated patch together with
> Signed-off-by line to Mauro <mchehab@infradead.org> and ask him to apply
> it for inclusion into the -mm tree for further testing.

Unless there are other -mm trees I've not heard about, presumably I should just 
do this myself. Doesn't linux-dvb have it's own development tree this would 
get better tested in?

The dvb_dvr_release change has been working for me for 6 months and the 
dvb_dmxdev_filter_free (dvb_dmxdev_filter_free) change looks equivalent.
See http://www.linuxtv.org/pipermail/linux-dvb/2007-February/016120.html for 
an example of the bug before and after fixing.

All the other changes run ok for me but should have lockdep enabled when 
testing (if there's a possible deadlock somewhere, using _interruptible will 
hide it).

 drivers/media/dvb/dvb-core/dmxdev.c    |   12 +++---------
 drivers/media/dvb/dvb-core/dvb_demux.c |   21 +++++++--------------
 drivers/media/dvb/dvb-core/dvbdev.c    |    9 +++------
 3 files changed, 13 insertions(+), 29 deletions(-)

diff --git a/drivers/media/dvb/dvb-core/dmxdev.c b/drivers/media/dvb/dvb-core/dmxdev.c
index fc77de4..a5c0e1a 100644
--- a/drivers/media/dvb/dvb-core/dmxdev.c
+++ b/drivers/media/dvb/dvb-core/dmxdev.c
@@ -180,8 +180,7 @@ static int dvb_dvr_release(struct inode *inode, struct file *file)
 	struct dvb_device *dvbdev = file->private_data;
 	struct dmxdev *dmxdev = dvbdev->priv;
 
-	if (mutex_lock_interruptible(&dmxdev->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&dmxdev->mutex);
 
 	if ((file->f_flags & O_ACCMODE) == O_WRONLY) {
 		dmxdev->demux->disconnect_frontend(dmxdev->demux);
@@ -673,13 +672,8 @@ static int dvb_demux_open(struct inode *inode, struct file *file)
 static int dvb_dmxdev_filter_free(struct dmxdev *dmxdev,
 				  struct dmxdev_filter *dmxdevfilter)
 {
-	if (mutex_lock_interruptible(&dmxdev->mutex))
-		return -ERESTARTSYS;
-
-	if (mutex_lock_interruptible(&dmxdevfilter->mutex)) {
-		mutex_unlock(&dmxdev->mutex);
-		return -ERESTARTSYS;
-	}
+	mutex_lock(&dmxdev->mutex);
+	mutex_lock(&dmxdevfilter->mutex);
 
 	dvb_dmxdev_filter_stop(dmxdevfilter);
 	dvb_dmxdev_filter_reset(dmxdevfilter);
diff --git a/drivers/media/dvb/dvb-core/dvb_demux.c b/drivers/media/dvb/dvb-core/dvb_demux.c
index fcff5ea..6d8d1c3 100644
--- a/drivers/media/dvb/dvb-core/dvb_demux.c
+++ b/drivers/media/dvb/dvb-core/dvb_demux.c
@@ -673,8 +673,7 @@ static int dmx_ts_feed_stop_filtering(struct dmx_ts_feed *ts_feed)
 	struct dvb_demux *demux = feed->demux;
 	int ret;
 
-	if (mutex_lock_interruptible(&demux->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&demux->mutex);
 
 	if (feed->state < DMX_STATE_GO) {
 		mutex_unlock(&demux->mutex);
@@ -748,8 +747,7 @@ static int dvbdmx_release_ts_feed(struct dmx_demux *dmx,
 	struct dvb_demux *demux = (struct dvb_demux *)dmx;
 	struct dvb_demux_feed *feed = (struct dvb_demux_feed *)ts_feed;
 
-	if (mutex_lock_interruptible(&demux->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&demux->mutex);
 
 	if (feed->state == DMX_STATE_FREE) {
 		mutex_unlock(&demux->mutex);
@@ -916,8 +914,7 @@ static int dmx_section_feed_stop_filtering(struct dmx_section_feed *feed)
 	struct dvb_demux *dvbdmx = dvbdmxfeed->demux;
 	int ret;
 
-	if (mutex_lock_interruptible(&dvbdmx->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdmx->mutex);
 
 	if (!dvbdmx->stop_feed) {
 		mutex_unlock(&dvbdmx->mutex);
@@ -942,8 +939,7 @@ static int dmx_section_feed_release_filter(struct dmx_section_feed *feed,
 	struct dvb_demux_feed *dvbdmxfeed = (struct dvb_demux_feed *)feed;
 	struct dvb_demux *dvbdmx = dvbdmxfeed->demux;
 
-	if (mutex_lock_interruptible(&dvbdmx->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdmx->mutex);
 
 	if (dvbdmxfilter->feed != dvbdmxfeed) {
 		mutex_unlock(&dvbdmx->mutex);
@@ -1016,8 +1012,7 @@ static int dvbdmx_release_section_feed(struct dmx_demux *demux,
 	struct dvb_demux_feed *dvbdmxfeed = (struct dvb_demux_feed *)feed;
 	struct dvb_demux *dvbdmx = (struct dvb_demux *)demux;
 
-	if (mutex_lock_interruptible(&dvbdmx->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdmx->mutex);
 
 	if (dvbdmxfeed->state == DMX_STATE_FREE) {
 		mutex_unlock(&dvbdmx->mutex);
@@ -1126,8 +1121,7 @@ static int dvbdmx_connect_frontend(struct dmx_demux *demux,
 	if (demux->frontend)
 		return -EINVAL;
 
-	if (mutex_lock_interruptible(&dvbdemux->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdemux->mutex);
 
 	demux->frontend = frontend;
 	mutex_unlock(&dvbdemux->mutex);
@@ -1138,8 +1132,7 @@ static int dvbdmx_disconnect_frontend(struct dmx_demux *demux)
 {
 	struct dvb_demux *dvbdemux = (struct dvb_demux *)demux;
 
-	if (mutex_lock_interruptible(&dvbdemux->mutex))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdemux->mutex);
 
 	demux->frontend = NULL;
 	mutex_unlock(&dvbdemux->mutex);
diff --git a/drivers/media/dvb/dvb-core/dvbdev.c b/drivers/media/dvb/dvb-core/dvbdev.c
index b4553ae..1e0f01a 100644
--- a/drivers/media/dvb/dvb-core/dvbdev.c
+++ b/drivers/media/dvb/dvb-core/dvbdev.c
@@ -203,8 +203,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 
 	int id;
 
-	if (mutex_lock_interruptible(&dvbdev_register_lock))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdev_register_lock);
 
 	if ((id = dvbdev_get_free_id (adap, type)) < 0){
 		mutex_unlock(&dvbdev_register_lock);
@@ -294,8 +293,7 @@ int dvb_register_adapter(struct dvb_adapter *adap, const char *name, struct modu
 {
 	int num;
 
-	if (mutex_lock_interruptible(&dvbdev_register_lock))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdev_register_lock);
 
 	if ((num = dvbdev_get_free_adapter_num ()) < 0) {
 		mutex_unlock(&dvbdev_register_lock);
@@ -323,8 +321,7 @@ EXPORT_SYMBOL(dvb_register_adapter);
 
 int dvb_unregister_adapter(struct dvb_adapter *adap)
 {
-	if (mutex_lock_interruptible(&dvbdev_register_lock))
-		return -ERESTARTSYS;
+	mutex_lock(&dvbdev_register_lock);
 	list_del (&adap->list_head);
 	mutex_unlock(&dvbdev_register_lock);
 	return 0;
-- 
1.5.0.1

-- 
Simon Arlott