[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, 8 insertions, 0 deletions

diff --git a/drivers/media/pci/ttpci/av7110_av.c b/drivers/media/pci/ttpci/av7110_av.c
index 952b33dbac4f..301029ca4535 100644
--- a/drivers/media/pci/ttpci/av7110_av.c
+++ b/drivers/media/pci/ttpci/av7110_av.c
@@ -1109,6 +1109,9 @@ static int dvb_video_ioctl(struct file *file,
 		}
 	}
 
+	if (mutex_lock_interruptible(&av7110->ioctl_mutex))
+		return -ERESTARTSYS;
+
 	switch (cmd) {
 	case VIDEO_STOP:
 		av7110->videostate.play_state = VIDEO_STOPPED;
@@ -1297,6 +1300,7 @@ static int dvb_video_ioctl(struct file *file,
 		break;
 	}
 
+	mutex_unlock(&av7110->ioctl_mutex);
 	return ret;
 }
 
@@ -1314,6 +1318,9 @@ static int dvb_audio_ioctl(struct file *file,
 	    (cmd != AUDIO_GET_STATUS))
 		return -EPERM;
 
+	if (mutex_lock_interruptible(&av7110->ioctl_mutex))
+		return -ERESTARTSYS;
+
 	switch (cmd) {
 	case AUDIO_STOP:
 		if (av7110->audiostate.stream_source == AUDIO_SOURCE_MEMORY)
@@ -1442,6 +1449,7 @@ static int dvb_audio_ioctl(struct file *file,
 		ret = -ENOIOCTLCMD;
 	}
 
+	mutex_unlock(&av7110->ioctl_mutex);
 	return ret;
 }