Re: [v4.9-rc4] dvb-usb/cinergyT2 NULL pointer dereference

From: Mauro Carvalho Chehab
Date: Fri Nov 11 2016 - 08:55:58 EST

Em Thu, 10 Nov 2016 12:15:39 +0100
JÃrg Otte <jrg.otte@xxxxxxxxx> escreveu:

> 2016-11-10 9:40 GMT+01:00 Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>:
> > Em Wed, 9 Nov 2016 11:07:35 -0800
> > Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> escreveu:
> >
> >> On Wed, Nov 9, 2016 at 3:09 AM, JÃrg Otte <jrg.otte@xxxxxxxxx> wrote:
> >> >
> >> > Tried patch with no success. Again a NULL ptr dereferece.
> >>
> >> I suspect a much simpler approach is to just miove the "data_mutex"
> >> away from the priv area and into "struct dvb_usb_device" and
> >> "dvb_usb_adapter". Sure, that grows those structures a tiny bit, and
> >> not every driver may need that mutex, but it simplifies things
> >> enormously. Mauro?
> >>
> >> Linus

> The patch works for me.

Thanks for testing! That's the (hopefully) final version of it,
with the fix applied to the other dvb-usb drivers that use
data_mutex (except for the frontend ones, with uses a different
private structure, and where the mutex is initialized at attach).

Benjamin,

Could you please test it?

Thanks!
Mauro

-

[PATCH] dvb-usb: move data_mutex to struct dvb_usb_device

The data_mutex is initialized too late, as it is needed for
each device driver's power control, causing an OOPS:

dvb-usb: found a 'TerraTec/qanu USB2.0 Highspeed DVB-T Receiver' in warm state.
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [<ffffffff846617af>] __mutex_lock_slowpath+0x6f/0x100 PGD 0
Oops: 0002 [#1] SMP
Modules linked in: dvb_usb_cinergyT2(+) dvb_usb
CPU: 0 PID: 2029 Comm: modprobe Not tainted 4.9.0-rc4-dvbmod #24
Hardware name: FUJITSU LIFEBOOK A544/FJNBB35 , BIOS Version 1.17 05/09/2014
task: ffff88020e943840 task.stack: ffff8801f36ec000
RIP: 0010:[<ffffffff846617af>] [<ffffffff846617af>] __mutex_lock_slowpath+0x6f/0x100
RSP: 0018:ffff8801f36efb10 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff88021509bdc8 RCX: 00000000c0000100
RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff88021509bdcc
RBP: ffff8801f36efb58 R08: ffff88021f216320 R09: 0000000000100000
R10: ffff88021f216320 R11: 00000023fee6c5a1 R12: ffff88020e943840
R13: ffff88021509bdcc R14: 00000000ffffffff R15: ffff88021509bdd0
FS: 00007f21adb86740(0000) GS:ffff88021f200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000215bce000 CR4: 00000000001406f0
Stack:
ffff88021509bdd0 0000000000000000 0000000000000000 ffffffffc0137c80
ffff88021509bdc8 ffff8801f5944000 0000000000000001 ffffffffc0136b00
ffff880213e52000 ffff88021509bdc8 ffffffff84661856 ffff88021509bd80
Call Trace:
[<ffffffff84661856>] ? mutex_lock+0x16/0x25
[<ffffffffc013616f>] ? cinergyt2_power_ctrl+0x1f/0x60 [dvb_usb_cinergyT2]
[<ffffffffc012e67e>] ? dvb_usb_device_init+0x21e/0x5d0 [dvb_usb]
[<ffffffffc0136021>] ? cinergyt2_usb_probe+0x21/0x50 [dvb_usb_cinergyT2]
[<ffffffff844326f3>] ? usb_probe_interface+0xf3/0x2a0
[<ffffffff8438e348>] ? driver_probe_device+0x208/0x2b0
[<ffffffff8438e477>] ? __driver_attach+0x87/0x90
[<ffffffff8438e3f0>] ? driver_probe_device+0x2b0/0x2b0
[<ffffffff8438c612>] ? bus_for_each_dev+0x52/0x80
[<ffffffff8438d983>] ? bus_add_driver+0x1a3/0x220
[<ffffffff8438ec06>] ? driver_register+0x56/0xd0
[<ffffffff84431527>] ? usb_register_driver+0x77/0x130
[<ffffffffc013a000>] ? 0xffffffffc013a000
[<ffffffff84000426>] ? do_one_initcall+0x46/0x180
[<ffffffff840eb2c8>] ? free_vmap_area_noflush+0x38/0x70
[<ffffffff840f3844>] ? kmem_cache_alloc+0x84/0xc0
[<ffffffff840b802c>] ? do_init_module+0x50/0x1be
[<ffffffff84095adb>] ? load_module+0x1d8b/0x2100
[<ffffffff84093020>] ? find_symbol_in_section+0xa0/0xa0
[<ffffffff84095fe9>] ? SyS_finit_module+0x89/0x90
[<ffffffff846637a0>] ? entry_SYSCALL_64_fastpath+0x13/0x94
Code: e8 a7 1d 00 00 8b 03 83 f8 01 0f 84 97 00 00 00 48 8b 43 10 4c 8d 7b 08 48 89 63 10 4c 89 3c 24 41 be ff ff ff ff 48 89 44 24 08 <48> 89 20 4c 89 64 24 10 eb 1a 49 c7 44 24 08 02 00 00 00 c6 43 RIP [<ffffffff846617af>] __mutex_lock_slowpath+0x6f/0x100 RSP <ffff8801f36efb10>
CR2: 0000000000000000

So, move it to the struct dvb_usb_device and initialize it
before calling the driver's callbacks.

Reported-by: JÃrg Otte <jrg.otte@xxxxxxxxx>
Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx>

diff --git a/drivers/media/usb/dvb-usb/af9005.c b/drivers/media/usb/dvb-usb/af9005.c
index b257780fb380..7853261906b1 100644
--- a/drivers/media/usb/dvb-usb/af9005.c
+++ b/drivers/media/usb/dvb-usb/af9005.c
@@ -53,7 +53,6 @@ struct af9005_device_state {
u8 sequence;
int led_state;
unsigned char data[256];
- struct mutex data_mutex;
};

static int af9005_generic_read_write(struct dvb_usb_device *d, u16 reg,
@@ -72,7 +71,7 @@ static int af9005_generic_read_write(struct dvb_usb_device *d, u16 reg,
return -EINVAL;
}

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = 14; /* rest of buffer length low */
st->data[1] = 0; /* rest of buffer length high */

@@ -140,7 +139,7 @@ static int af9005_generic_read_write(struct dvb_usb_device *d, u16 reg,
values[i] = st->data[8 + i];

ret:
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);
return ret;

}
@@ -481,7 +480,7 @@ int af9005_send_command(struct dvb_usb_device *d, u8 command, u8 * wbuf,
}
packet_len = wlen + 5;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);

st->data[0] = (u8) (packet_len & 0xff);
st->data[1] = (u8) ((packet_len & 0xff00) >> 8);
@@ -512,7 +511,7 @@ int af9005_send_command(struct dvb_usb_device *d, u8 command, u8 * wbuf,
rbuf[i] = st->data[i + 7];
}

- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);
return ret;
}

@@ -523,7 +522,7 @@ int af9005_read_eeprom(struct dvb_usb_device *d, u8 address, u8 * values,
u8 seq;
int ret, i;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);

memset(st->data, 0, sizeof(st->data));

@@ -559,7 +558,7 @@ int af9005_read_eeprom(struct dvb_usb_device *d, u8 address, u8 * values,
for (i = 0; i < len; i++)
values[i] = st->data[6 + i];
}
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);

return ret;
}
@@ -847,7 +846,7 @@ static int af9005_rc_query(struct dvb_usb_device *d, u32 * event, int *state)
return 0;
}

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);

/* deb_info("rc_query\n"); */
st->data[0] = 3; /* rest of packet length low */
@@ -890,7 +889,7 @@ static int af9005_rc_query(struct dvb_usb_device *d, u32 * event, int *state)
}

ret:
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);
return ret;
}

@@ -1004,20 +1003,8 @@ static struct dvb_usb_device_properties af9005_properties;
static int af9005_usb_probe(struct usb_interface *intf,
const struct usb_device_id *id)
{
- struct dvb_usb_device *d;
- struct af9005_device_state *st;
- int ret;
-
- ret = dvb_usb_device_init(intf, &af9005_properties,
- THIS_MODULE, &d, adapter_nr);
-
- if (ret < 0)
- return ret;
-
- st = d->priv;
- mutex_init(&st->data_mutex);
-
- return 0;
+ return dvb_usb_device_init(intf, &af9005_properties,
+ THIS_MODULE, NULL, adapter_nr);
}

enum af9005_usb_table_entry {
diff --git a/drivers/media/usb/dvb-usb/cinergyT2-core.c b/drivers/media/usb/dvb-usb/cinergyT2-core.c
index 8ac825413d5a..290275bc7fde 100644
--- a/drivers/media/usb/dvb-usb/cinergyT2-core.c
+++ b/drivers/media/usb/dvb-usb/cinergyT2-core.c
@@ -42,7 +42,6 @@ DVB_DEFINE_MOD_OPT_ADAPTER_NR(adapter_nr);
struct cinergyt2_state {
u8 rc_counter;
unsigned char data[64];
- struct mutex data_mutex;
};

/* We are missing a release hook with usb_device data */
@@ -56,12 +55,12 @@ static int cinergyt2_streaming_ctrl(struct dvb_usb_adapter *adap, int enable)
struct cinergyt2_state *st = d->priv;
int ret;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = CINERGYT2_EP1_CONTROL_STREAM_TRANSFER;
st->data[1] = enable ? 1 : 0;

ret = dvb_usb_generic_rw(d, st->data, 2, st->data, 64, 0);
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);

return ret;
}
@@ -71,12 +70,12 @@ static int cinergyt2_power_ctrl(struct dvb_usb_device *d, int enable)
struct cinergyt2_state *st = d->priv;
int ret;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = CINERGYT2_EP1_SLEEP_MODE;
st->data[1] = enable ? 0 : 1;

ret = dvb_usb_generic_rw(d, st->data, 2, st->data, 3, 0);
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);

return ret;
}
@@ -89,7 +88,7 @@ static int cinergyt2_frontend_attach(struct dvb_usb_adapter *adap)

adap->fe_adap[0].fe = cinergyt2_fe_attach(adap->dev);

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = CINERGYT2_EP1_GET_FIRMWARE_VERSION;

ret = dvb_usb_generic_rw(d, st->data, 1, st->data, 3, 0);
@@ -97,7 +96,7 @@ static int cinergyt2_frontend_attach(struct dvb_usb_adapter *adap)
deb_rc("cinergyt2_power_ctrl() Failed to retrieve sleep "
"state info\n");
}
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);

/* Copy this pointer as we are gonna need it in the release phase */
cinergyt2_usb_device = adap->dev;
@@ -166,7 +165,7 @@ static int cinergyt2_rc_query(struct dvb_usb_device *d, u32 *event, int *state)

*state = REMOTE_NO_KEY_PRESSED;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = CINERGYT2_EP1_GET_RC_EVENTS;

ret = dvb_usb_generic_rw(d, st->data, 1, st->data, 5, 0);
@@ -202,29 +201,17 @@ static int cinergyt2_rc_query(struct dvb_usb_device *d, u32 *event, int *state)
}

ret:
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);
return ret;
}

static int cinergyt2_usb_probe(struct usb_interface *intf,
const struct usb_device_id *id)
{
- struct dvb_usb_device *d;
- struct cinergyt2_state *st;
- int ret;
-
- ret = dvb_usb_device_init(intf, &cinergyt2_properties,
- THIS_MODULE, &d, adapter_nr);
- if (ret < 0)
- return ret;
-
- st = d->priv;
- mutex_init(&st->data_mutex);
-
- return 0;
+ return dvb_usb_device_init(intf, &cinergyt2_properties,
+ THIS_MODULE, NULL, adapter_nr);
}

-
static struct usb_device_id cinergyt2_usb_table[] = {
{ USB_DEVICE(USB_VID_TERRATEC, 0x0038) },
{ 0 }
diff --git a/drivers/media/usb/dvb-usb/cxusb.c b/drivers/media/usb/dvb-usb/cxusb.c
index 39772812269d..243403081fa5 100644
--- a/drivers/media/usb/dvb-usb/cxusb.c
+++ b/drivers/media/usb/dvb-usb/cxusb.c
@@ -68,7 +68,7 @@ static int cxusb_ctrl_msg(struct dvb_usb_device *d,

wo = (rbuf == NULL || rlen == 0); /* write-only */

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = cmd;
memcpy(&st->data[1], wbuf, wlen);
if (wo)
@@ -77,7 +77,7 @@ static int cxusb_ctrl_msg(struct dvb_usb_device *d,
ret = dvb_usb_generic_rw(d, st->data, 1 + wlen,
rbuf, rlen, 0);

- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);
return ret;
}

@@ -1461,43 +1461,36 @@ static struct dvb_usb_device_properties cxusb_mygica_t230_properties;
static int cxusb_probe(struct usb_interface *intf,
const struct usb_device_id *id)
{
- struct dvb_usb_device *d;
- struct cxusb_state *st;
-
if (0 == dvb_usb_device_init(intf, &cxusb_medion_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_bluebird_lgh064f_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_bluebird_dee1601_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_bluebird_lgz201_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_bluebird_dtt7579_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_bluebird_dualdig4_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_bluebird_nano2_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf,
&cxusb_bluebird_nano2_needsfirmware_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_aver_a868r_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf,
&cxusb_bluebird_dualdig4_rev2_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_d680_dmb_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_mygica_d689_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &cxusb_mygica_t230_properties,
- THIS_MODULE, &d, adapter_nr) ||
- 0) {
- st = d->priv;
- mutex_init(&st->data_mutex);
-
+ THIS_MODULE, NULL, adapter_nr) ||
+ 0)
return 0;
- }

return -EINVAL;
}
diff --git a/drivers/media/usb/dvb-usb/cxusb.h b/drivers/media/usb/dvb-usb/cxusb.h
index 9f3ee0e47d5c..18acda19527a 100644
--- a/drivers/media/usb/dvb-usb/cxusb.h
+++ b/drivers/media/usb/dvb-usb/cxusb.h
@@ -37,7 +37,6 @@ struct cxusb_state {
struct i2c_client *i2c_client_tuner;

unsigned char data[MAX_XFER_SIZE];
- struct mutex data_mutex;
};

#endif
diff --git a/drivers/media/usb/dvb-usb/dtt200u.c b/drivers/media/usb/dvb-usb/dtt200u.c
index f88572c7ae7c..fcbff7fb0c4e 100644
--- a/drivers/media/usb/dvb-usb/dtt200u.c
+++ b/drivers/media/usb/dvb-usb/dtt200u.c
@@ -22,7 +22,6 @@ DVB_DEFINE_MOD_OPT_ADAPTER_NR(adapter_nr);

struct dtt200u_state {
unsigned char data[80];
- struct mutex data_mutex;
};

static int dtt200u_power_ctrl(struct dvb_usb_device *d, int onoff)
@@ -30,23 +29,24 @@ static int dtt200u_power_ctrl(struct dvb_usb_device *d, int onoff)
struct dtt200u_state *st = d->priv;
int ret = 0;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);

st->data[0] = SET_INIT;

if (onoff)
ret = dvb_usb_generic_write(d, st->data, 2);

- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);
return ret;
}

static int dtt200u_streaming_ctrl(struct dvb_usb_adapter *adap, int onoff)
{
- struct dtt200u_state *st = adap->dev->priv;
+ struct dvb_usb_device *d = adap->dev;
+ struct dtt200u_state *st = d->priv;
int ret;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = SET_STREAMING;
st->data[1] = onoff;

@@ -61,26 +61,27 @@ static int dtt200u_streaming_ctrl(struct dvb_usb_adapter *adap, int onoff)
ret = dvb_usb_generic_write(adap->dev, st->data, 1);

ret:
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);

return ret;
}

static int dtt200u_pid_filter(struct dvb_usb_adapter *adap, int index, u16 pid, int onoff)
{
- struct dtt200u_state *st = adap->dev->priv;
+ struct dvb_usb_device *d = adap->dev;
+ struct dtt200u_state *st = d->priv;
int ret;

pid = onoff ? pid : 0;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = SET_PID_FILTER;
st->data[1] = index;
st->data[2] = pid & 0xff;
st->data[3] = (pid >> 8) & 0x1f;

ret = dvb_usb_generic_write(adap->dev, st->data, 4);
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);

return ret;
}
@@ -91,7 +92,7 @@ static int dtt200u_rc_query(struct dvb_usb_device *d)
u32 scancode;
int ret;

- mutex_lock(&st->data_mutex);
+ mutex_lock(&d->data_mutex);
st->data[0] = GET_RC_CODE;

ret = dvb_usb_generic_rw(d, st->data, 1, st->data, 5, 0);
@@ -126,7 +127,7 @@ static int dtt200u_rc_query(struct dvb_usb_device *d)
deb_info("st->data: %*ph\n", 5, st->data);

ret:
- mutex_unlock(&st->data_mutex);
+ mutex_unlock(&d->data_mutex);
return ret;
}

@@ -145,24 +146,17 @@ static struct dvb_usb_device_properties wt220u_miglia_properties;
static int dtt200u_usb_probe(struct usb_interface *intf,
const struct usb_device_id *id)
{
- struct dvb_usb_device *d;
- struct dtt200u_state *st;
-
if (0 == dvb_usb_device_init(intf, &dtt200u_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &wt220u_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &wt220u_fc_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &wt220u_zl0353_properties,
- THIS_MODULE, &d, adapter_nr) ||
+ THIS_MODULE, NULL, adapter_nr) ||
0 == dvb_usb_device_init(intf, &wt220u_miglia_properties,
- THIS_MODULE, &d, adapter_nr)) {
- st = d->priv;
- mutex_init(&st->data_mutex);
-
+ THIS_MODULE, NULL, adapter_nr))
return 0;
- }

return -ENODEV;
}
diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
index 3896ba9a4179..84308569e7dc 100644
--- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
+++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
@@ -142,6 +142,7 @@ static int dvb_usb_init(struct dvb_usb_device *d, short *adapter_nums)
{
int ret = 0;

+ mutex_init(&d->data_mutex);
mutex_init(&d->usb_mutex);
mutex_init(&d->i2c_mutex);

diff --git a/drivers/media/usb/dvb-usb/dvb-usb.h b/drivers/media/usb/dvb-usb/dvb-usb.h
index 1448c3d27ea2..67f898b6f6d0 100644
--- a/drivers/media/usb/dvb-usb/dvb-usb.h
+++ b/drivers/media/usb/dvb-usb/dvb-usb.h
@@ -404,8 +404,12 @@ struct dvb_usb_adapter {
* Powered is in/decremented for each call to modify the state.
* @udev: pointer to the device's struct usb_device.
*
- * @usb_mutex: semaphore of USB control messages (reading needs two messages)
- * @i2c_mutex: semaphore for i2c-transfers
+ * @data_mutex: mutex to protect the data structure used to store URB data
+ * @usb_mutex: mutex of USB control messages (reading needs two messages).
+ * Please notice that this mutex is used internally at the generic
+ * URB control functions. So, drivers using dvb_usb_generic_rw() and
+ * derivated functions should not lock it internally.
+ * @i2c_mutex: mutex for i2c-transfers
*
* @i2c_adap: device's i2c_adapter if it uses I2CoverUSB
*
@@ -433,6 +437,7 @@ struct dvb_usb_device {
int powered;

/* locking */
+ struct mutex data_mutex;
struct mutex usb_mutex;

/* i2c */