[media] dvb: push down ioctl lock in dvb_usercopy

Since most dvb ioctls wrap their real work with dvb_usercopy, the static mutex
used in dvb_usercopy effectively is a global lock for dvb ioctls.
Unfortunately, frontend ioctls can be blocked by the frontend thread for
several seconds; this leads to unacceptable lock contention.  Mitigate that by
pushing the mutex from dvb_usercopy down to the individual, device specific
ioctls.
There are 10 such ioctl functions using dvb_usercopy, either calling it
directly, or via the trivial wrapper dvb_generic_ioctl. The following already
employ their own locking and look safe:
    • dvb_demux_ioctl           (as per dvb_demux_do_ioctl)
    • dvb_dvr_ioctl             (as per dvb_dvr_do_ioctl)
    • dvb_osd_ioctl             (as per single non-trivial callee)
    • fdtv_ca_ioctl             (as per callees)
    • dvb_frontend_ioctl
The following functions do not, and are thus changed to use a device specific
mutex:
    • dvb_net_ioctl             (as per dvb_net_do_ioctl)
    • dvb_ca_en50221_io_ioctl   (as per dvb_ca_en50221_io_do_ioctl)
    • dvb_video_ioctl
    • dvb_audio_ioctl
    • dvb_ca_ioctl

Signed-off-by: Nikolaus Schulz <schulz@macnetix.de>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/media/dvb-core/dvb_ca_en50221.c b/drivers/media/dvb-core/dvb_ca_en50221.c
index 9be65a3b931f..190e5e0f48c7 100644
--- a/drivers/media/dvb-core/dvb_ca_en50221.c
+++ b/drivers/media/dvb-core/dvb_ca_en50221.c
@@ -156,6 +156,9 @@ struct dvb_ca_private {
 
 	/* Slot to start looking for data to read from in the next user-space read operation */
 	int next_read_slot;
+
+	/* mutex serializing ioctls */
+	struct mutex ioctl_mutex;
 };
 
 static void dvb_ca_en50221_thread_wakeup(struct dvb_ca_private *ca);
@@ -1191,6 +1194,9 @@ static int dvb_ca_en50221_io_do_ioctl(struct file *file,
 
 	dprintk("%s\n", __func__);
 
+	if (mutex_lock_interruptible(&ca->ioctl_mutex))
+		return -ERESTARTSYS;
+
 	switch (cmd) {
 	case CA_RESET:
 		for (slot = 0; slot < ca->slot_count; slot++) {
@@ -1241,6 +1247,7 @@ static int dvb_ca_en50221_io_do_ioctl(struct file *file,
 		break;
 	}
 
+	mutex_unlock(&ca->ioctl_mutex);
 	return err;
 }
 
@@ -1695,6 +1702,8 @@ int dvb_ca_en50221_init(struct dvb_adapter *dvb_adapter,
 		mutex_init(&ca->slot_info[i].slot_lock);
 	}
 
+	mutex_init(&ca->ioctl_mutex);
+
 	if (signal_pending(current)) {
 		ret = -EINTR;
 		goto error;