[media] media-device: Don't call notify callbacks holding a spinlock
diff mbox

Message ID 31ecc9d6d2f29b0bd76c03c516d12aa7d0be2f66.1457982982.git.mchehab@osg.samsung.com
State New
Headers show

Commit Message

Mauro Carvalho Chehab March 14, 2016, 7:16 p.m. UTC
The notify routines may sleep. So, they can't be called in spinlock
context. Also, they may want to call other media routines that might
be spinning the spinlock, like creating a link.

This fixes the following bug:

[ 1839.510587] BUG: sleeping function called from invalid context at mm/slub.c:1289
[ 1839.510881] in_atomic(): 1, irqs_disabled(): 0, pid: 3479, name: modprobe
[ 1839.511157] 4 locks held by modprobe/3479:
[ 1839.511415]  #0:  (&dev->mutex){......}, at: [<ffffffff81ce8933>] __driver_attach+0xa3/0x160
[ 1839.512381]  #1:  (&dev->mutex){......}, at: [<ffffffff81ce8941>] __driver_attach+0xb1/0x160
[ 1839.512388]  #2:  (register_mutex#5){+.+.+.}, at: [<ffffffffa10596c7>] usb_audio_probe+0x257/0x1c90 [snd_usb_audio]
[ 1839.512401]  #3:  (&(&mdev->lock)->rlock){+.+.+.}, at: [<ffffffffa0e6051b>] media_device_register_entity+0x1cb/0x700 [media]
[ 1839.512412] CPU: 2 PID: 3479 Comm: modprobe Not tainted 4.5.0-rc3+ #49
[ 1839.512415] Hardware name:                  /NUC5i7RYB, BIOS RYBDWi35.86A.0350.2015.0812.1722 08/12/2015
[ 1839.512417]  0000000000000000 ffff8803b3f6f288 ffffffff81933901 ffff8803c4bae000
[ 1839.512422]  ffff8803c4bae5c8 ffff8803b3f6f2b0 ffffffff811c6af5 ffff8803c4bae000
[ 1839.512427]  ffffffff8285d7f6 0000000000000509 ffff8803b3f6f2f0 ffffffff811c6ce5
[ 1839.512432] Call Trace:
[ 1839.512436]  [<ffffffff81933901>] dump_stack+0x85/0xc4
[ 1839.512440]  [<ffffffff811c6af5>] ___might_sleep+0x245/0x3a0
[ 1839.512443]  [<ffffffff811c6ce5>] __might_sleep+0x95/0x1a0
[ 1839.512446]  [<ffffffff8155aade>] kmem_cache_alloc_trace+0x20e/0x300
[ 1839.512451]  [<ffffffffa0e66e3d>] ? media_add_link+0x4d/0x140 [media]
[ 1839.512455]  [<ffffffffa0e66e3d>] media_add_link+0x4d/0x140 [media]
[ 1839.512459]  [<ffffffffa0e69931>] media_create_pad_link+0xa1/0x600 [media]
[ 1839.512463]  [<ffffffffa0fe11b3>] au0828_media_graph_notify+0x173/0x360 [au0828]
[ 1839.512467]  [<ffffffffa0e68a6a>] ? media_gobj_create+0x1ba/0x480 [media]
[ 1839.512471]  [<ffffffffa0e606fb>] media_device_register_entity+0x3ab/0x700 [media]

Tested with an HVR-950Q, under the following testcases:

1) load au0828 driver first, and then snd-usb-audio;
2) load snd-usb-audio driver first, and then au0828;
3) loading both drivers, and then connecting the device.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
---
 drivers/media/i2c/tvp5150.c           | 39 ++++++++++++++++++++++-------------
 drivers/media/media-device.c          |  5 +++--
 drivers/media/v4l2-core/v4l2-common.c |  8 +++++++
 include/media/v4l2-subdev.h           |  4 ++++
 4 files changed, 40 insertions(+), 16 deletions(-)

Comments

kbuild test robot March 14, 2016, 7:31 p.m. UTC | #1
Hi Mauro,

[auto build test WARNING on sailus-media/master]
[also build test WARNING on next-20160314]
[cannot apply to v4.5]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/Mauro-Carvalho-Chehab/media-device-Don-t-call-notify-callbacks-holding-a-spinlock/20160315-031954
base:   git://linuxtv.org/media_tree.git master
config: i386-randconfig-x001-201611 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   drivers/media/i2c/tvp5150.c: In function 'tvp5150_pad_init':
>> drivers/media/i2c/tvp5150.c:1214:6: warning: unused variable 'res' [-Wunused-variable]
     int res;
         ^
>> drivers/media/i2c/tvp5150.c:1213:18: warning: unused variable 'core' [-Wunused-variable]
     struct tvp5150 *core = to_tvp5150(sd);
                     ^

vim +/res +1214 drivers/media/i2c/tvp5150.c

  1207	
  1208		return 0;
  1209	}
  1210	
  1211	static int __maybe_unused tvp5150_pad_init(struct v4l2_subdev *sd)
  1212	{
> 1213		struct tvp5150 *core = to_tvp5150(sd);
> 1214		int res;
  1215	
  1216	#if defined(CONFIG_MEDIA_CONTROLLER)
  1217		core->pads[DEMOD_PAD_IF_INPUT].flags = MEDIA_PAD_FL_SINK;

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
Laurent Pinchart March 17, 2016, 11:38 a.m. UTC | #2
Hi Mauro,

On Monday 14 March 2016 16:16:29 Mauro Carvalho Chehab wrote:
> The notify routines may sleep. So, they can't be called in spinlock
> context. Also, they may want to call other media routines that might
> be spinning the spinlock, like creating a link.
> 
> This fixes the following bug:
> 
> [ 1839.510587] BUG: sleeping function called from invalid context at
> mm/slub.c:1289 [ 1839.510881] in_atomic(): 1, irqs_disabled(): 0, pid:
> 3479, name: modprobe [ 1839.511157] 4 locks held by modprobe/3479:
> [ 1839.511415]  #0:  (&dev->mutex){......}, at: [<ffffffff81ce8933>]
> __driver_attach+0xa3/0x160 [ 1839.512381]  #1:  (&dev->mutex){......}, at:
> [<ffffffff81ce8941>] __driver_attach+0xb1/0x160 [ 1839.512388]  #2: 
> (register_mutex#5){+.+.+.}, at: [<ffffffffa10596c7>]
> usb_audio_probe+0x257/0x1c90 [snd_usb_audio] [ 1839.512401]  #3: 
> (&(&mdev->lock)->rlock){+.+.+.}, at: [<ffffffffa0e6051b>]
> media_device_register_entity+0x1cb/0x700 [media] [ 1839.512412] CPU: 2 PID:
> 3479 Comm: modprobe Not tainted 4.5.0-rc3+ #49 [ 1839.512415] Hardware
> name:                  /NUC5i7RYB, BIOS RYBDWi35.86A.0350.2015.0812.1722
> 08/12/2015 [ 1839.512417]  0000000000000000 ffff8803b3f6f288
> ffffffff81933901 ffff8803c4bae000 [ 1839.512422]  ffff8803c4bae5c8
> ffff8803b3f6f2b0 ffffffff811c6af5 ffff8803c4bae000 [ 1839.512427] 
> ffffffff8285d7f6 0000000000000509 ffff8803b3f6f2f0 ffffffff811c6ce5 [
> 1839.512432] Call Trace:
> [ 1839.512436]  [<ffffffff81933901>] dump_stack+0x85/0xc4
> [ 1839.512440]  [<ffffffff811c6af5>] ___might_sleep+0x245/0x3a0
> [ 1839.512443]  [<ffffffff811c6ce5>] __might_sleep+0x95/0x1a0
> [ 1839.512446]  [<ffffffff8155aade>] kmem_cache_alloc_trace+0x20e/0x300
> [ 1839.512451]  [<ffffffffa0e66e3d>] ? media_add_link+0x4d/0x140 [media]
> [ 1839.512455]  [<ffffffffa0e66e3d>] media_add_link+0x4d/0x140 [media]
> [ 1839.512459]  [<ffffffffa0e69931>] media_create_pad_link+0xa1/0x600
> [media] [ 1839.512463]  [<ffffffffa0fe11b3>]
> au0828_media_graph_notify+0x173/0x360 [au0828] [ 1839.512467] 
> [<ffffffffa0e68a6a>] ? media_gobj_create+0x1ba/0x480 [media] [ 1839.512471]
>  [<ffffffffa0e606fb>] media_device_register_entity+0x3ab/0x700 [media]
> 
> Tested with an HVR-950Q, under the following testcases:
> 
> 1) load au0828 driver first, and then snd-usb-audio;
> 2) load snd-usb-audio driver first, and then au0828;
> 3) loading both drivers, and then connecting the device.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> ---
>  drivers/media/i2c/tvp5150.c           | 39 ++++++++++++++++++++------------
>  drivers/media/media-device.c          |  5 +++--
>  drivers/media/v4l2-core/v4l2-common.c |  8 +++++++
>  include/media/v4l2-subdev.h           |  4 ++++
>  4 files changed, 40 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/media/i2c/tvp5150.c b/drivers/media/i2c/tvp5150.c
> index ff18444e19e4..14004fd7d0fb 100644
> --- a/drivers/media/i2c/tvp5150.c
> +++ b/drivers/media/i2c/tvp5150.c
> @@ -1208,6 +1208,28 @@ static int tvp5150_registered_async(struct
> v4l2_subdev *sd) return 0;
>  }
> 
> +static int __maybe_unused tvp5150_pad_init(struct v4l2_subdev *sd)
> +{
> +	struct tvp5150 *core = to_tvp5150(sd);
> +	int res;
> +
> +#if defined(CONFIG_MEDIA_CONTROLLER)
> +	core->pads[DEMOD_PAD_IF_INPUT].flags = MEDIA_PAD_FL_SINK;
> +	core->pads[DEMOD_PAD_VID_OUT].flags = MEDIA_PAD_FL_SOURCE;
> +	core->pads[DEMOD_PAD_VBI_OUT].flags = MEDIA_PAD_FL_SOURCE;
> +
> +	sd->entity.function = MEDIA_ENT_F_ATV_DECODER;
> +
> +	res = media_entity_pads_init(&sd->entity, DEMOD_NUM_PADS, core->pads);
> +	if (res < 0)
> +		return res;
> +
> +	sd->entity.ops = &tvp5150_sd_media_ops;
> +#endif
> +	return 0;
> +}
> +
> +
>  /* -----------------------------------------------------------------------
> */
> 
>  static const struct v4l2_ctrl_ops tvp5150_ctrl_ops = {
> @@ -1246,6 +1268,9 @@ static const struct v4l2_subdev_vbi_ops
> tvp5150_vbi_ops = { };
> 
>  static const struct v4l2_subdev_pad_ops tvp5150_pad_ops = {
> +#ifdef CONFIG_MEDIA_CONTROLLER
> +	.pad_init = tvp5150_pad_init,
> +#endif
>  	.enum_mbus_code = tvp5150_enum_mbus_code,
>  	.enum_frame_size = tvp5150_enum_frame_size,
>  	.set_fmt = tvp5150_fill_fmt,
> @@ -1475,20 +1500,6 @@ static int tvp5150_probe(struct i2c_client *c,
>  	v4l2_i2c_subdev_init(sd, c, &tvp5150_ops);
>  	sd->flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
> 
> -#if defined(CONFIG_MEDIA_CONTROLLER)
> -	core->pads[DEMOD_PAD_IF_INPUT].flags = MEDIA_PAD_FL_SINK;
> -	core->pads[DEMOD_PAD_VID_OUT].flags = MEDIA_PAD_FL_SOURCE;
> -	core->pads[DEMOD_PAD_VBI_OUT].flags = MEDIA_PAD_FL_SOURCE;
> -
> -	sd->entity.function = MEDIA_ENT_F_ATV_DECODER;
> -
> -	res = media_entity_pads_init(&sd->entity, DEMOD_NUM_PADS, core->pads);
> -	if (res < 0)
> -		return res;
> -
> -	sd->entity.ops = &tvp5150_sd_media_ops;
> -#endif
> -
>  	res = tvp5150_detect_version(core);
>  	if (res < 0)
>  		return res;
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index 6ba6e8f982fc..fc3c199e5500 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -587,14 +587,15 @@ int __must_check media_device_register_entity(struct
> media_device *mdev, media_gobj_create(mdev, MEDIA_GRAPH_PAD,
>  			       &entity->pads[i].graph_obj);
> 
> +	spin_unlock(&mdev->lock);
> +
>  	/* invoke entity_notify callbacks */
>  	list_for_each_entry_safe(notify, next, &mdev->entity_notify, list) {
>  		(notify)->notify(entity, notify->notify_data);
>  	}

I don't think this is the right approach. There's no lock protecting the 
entity_notify list, and nothing that prevents the notifiers from touching the 
entity_notify list. The list_for_each_entry_safe() function doesn't help you 
there, it only protects against deletion of the current list entry.

Locking needs to be audited and fixed, let's not push a bug fix that 
introduces another bug.

Furthermore, I wonder if we really need notifiers. They add complexity and are 
difficult to get right, isn't there another possible approach ?

> -	spin_unlock(&mdev->lock);
> -
>  	mutex_lock(&mdev->graph_mutex);
> +
>  	if (mdev->entity_internal_idx_max
> 
>  	    >= mdev->pm_count_walk.ent_enum.idx_max) {
> 
>  		struct media_entity_graph new = { .top = 0 };
> diff --git a/drivers/media/v4l2-core/v4l2-common.c
> b/drivers/media/v4l2-core/v4l2-common.c index 5b808500e7e7..6bcdf557e027
> 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -112,6 +112,14 @@ EXPORT_SYMBOL(v4l2_ctrl_query_fill);
>  void v4l2_i2c_subdev_init(struct v4l2_subdev *sd, struct i2c_client
> *client, const struct v4l2_subdev_ops *ops)
>  {
> +	/*
> +	 * Initialize the MC pads - for now, this will be called
> +	 * unconditionally, since the current implementation will defer
> +	 * the pads initialization until the media_dev is created.
> +	 */
> +	if (v4l2_subdev_has_op(sd, pad, pad_init))
> +		sd->ops->pad->pad_init(sd);
> +
>  	v4l2_subdev_init(sd, ops);
>  	sd->flags |= V4L2_SUBDEV_FL_IS_I2C;
>  	/* the owner is the same as the i2c_client's driver owner */
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index 11e2dfec0198..c9bb221029e4 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -572,6 +572,9 @@ struct v4l2_subdev_pad_config {
>  /**
>   * struct v4l2_subdev_pad_ops - v4l2-subdev pad level operations
>   *
> + * @pad_init: callback that initializes the media-controller specific part
> + *	      of the subdev driver, creating its pads
> + *
>   * @enum_mbus_code: callback for VIDIOC_SUBDEV_ENUM_MBUS_CODE ioctl handler
> *		    code.
>   * @enum_frame_size: callback for VIDIOC_SUBDEV_ENUM_FRAME_SIZE ioctl
> handler @@ -607,6 +610,7 @@ struct v4l2_subdev_pad_config {
>   *                  may be adjusted by the subdev driver to device
> capabilities. */
>  struct v4l2_subdev_pad_ops {
> +	int (*pad_init)(struct v4l2_subdev *sd);
>  	int (*enum_mbus_code)(struct v4l2_subdev *sd,
>  			      struct v4l2_subdev_pad_config *cfg,
>  			      struct v4l2_subdev_mbus_code_enum *code);
Mauro Carvalho Chehab March 17, 2016, 5:43 p.m. UTC | #3
Em Thu, 17 Mar 2016 13:38:56 +0200
Laurent Pinchart <laurent.pinchart@ideasonboard.com> escreveu:

> Hi Mauro,
> 
> On Monday 14 March 2016 16:16:29 Mauro Carvalho Chehab wrote:
> > The notify routines may sleep. So, they can't be called in spinlock
> > context. Also, they may want to call other media routines that might
> > be spinning the spinlock, like creating a link.
> > 
> > This fixes the following bug:
> > 
> > [ 1839.510587] BUG: sleeping function called from invalid context at
> > mm/slub.c:1289 [ 1839.510881] in_atomic(): 1, irqs_disabled(): 0, pid:
> > 3479, name: modprobe [ 1839.511157] 4 locks held by modprobe/3479:
> > [ 1839.511415]  #0:  (&dev->mutex){......}, at: [<ffffffff81ce8933>]
> > __driver_attach+0xa3/0x160 [ 1839.512381]  #1:  (&dev->mutex){......}, at:
> > [<ffffffff81ce8941>] __driver_attach+0xb1/0x160 [ 1839.512388]  #2: 
> > (register_mutex#5){+.+.+.}, at: [<ffffffffa10596c7>]
> > usb_audio_probe+0x257/0x1c90 [snd_usb_audio] [ 1839.512401]  #3: 
> > (&(&mdev->lock)->rlock){+.+.+.}, at: [<ffffffffa0e6051b>]
> > media_device_register_entity+0x1cb/0x700 [media] [ 1839.512412] CPU: 2 PID:
> > 3479 Comm: modprobe Not tainted 4.5.0-rc3+ #49 [ 1839.512415] Hardware
> > name:                  /NUC5i7RYB, BIOS RYBDWi35.86A.0350.2015.0812.1722
> > 08/12/2015 [ 1839.512417]  0000000000000000 ffff8803b3f6f288
> > ffffffff81933901 ffff8803c4bae000 [ 1839.512422]  ffff8803c4bae5c8
> > ffff8803b3f6f2b0 ffffffff811c6af5 ffff8803c4bae000 [ 1839.512427] 
> > ffffffff8285d7f6 0000000000000509 ffff8803b3f6f2f0 ffffffff811c6ce5 [
> > 1839.512432] Call Trace:
> > [ 1839.512436]  [<ffffffff81933901>] dump_stack+0x85/0xc4
> > [ 1839.512440]  [<ffffffff811c6af5>] ___might_sleep+0x245/0x3a0
> > [ 1839.512443]  [<ffffffff811c6ce5>] __might_sleep+0x95/0x1a0
> > [ 1839.512446]  [<ffffffff8155aade>] kmem_cache_alloc_trace+0x20e/0x300
> > [ 1839.512451]  [<ffffffffa0e66e3d>] ? media_add_link+0x4d/0x140 [media]
> > [ 1839.512455]  [<ffffffffa0e66e3d>] media_add_link+0x4d/0x140 [media]
> > [ 1839.512459]  [<ffffffffa0e69931>] media_create_pad_link+0xa1/0x600
> > [media] [ 1839.512463]  [<ffffffffa0fe11b3>]
> > au0828_media_graph_notify+0x173/0x360 [au0828] [ 1839.512467] 
> > [<ffffffffa0e68a6a>] ? media_gobj_create+0x1ba/0x480 [media] [ 1839.512471]
> >  [<ffffffffa0e606fb>] media_device_register_entity+0x3ab/0x700 [media]
> > 
> > Tested with an HVR-950Q, under the following testcases:
> > 
> > 1) load au0828 driver first, and then snd-usb-audio;
> > 2) load snd-usb-audio driver first, and then au0828;
> > 3) loading both drivers, and then connecting the device.
> > 
> > Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> > ---
> >  drivers/media/i2c/tvp5150.c           | 39 ++++++++++++++++++++------------
> >  drivers/media/media-device.c          |  5 +++--
> >  drivers/media/v4l2-core/v4l2-common.c |  8 +++++++
> >  include/media/v4l2-subdev.h           |  4 ++++
> >  4 files changed, 40 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/media/i2c/tvp5150.c b/drivers/media/i2c/tvp5150.c
> > index ff18444e19e4..14004fd7d0fb 100644
> > --- a/drivers/media/i2c/tvp5150.c
> > +++ b/drivers/media/i2c/tvp5150.c
> > @@ -1208,6 +1208,28 @@ static int tvp5150_registered_async(struct
> > v4l2_subdev *sd) return 0;
> >  }
> > 
> > +static int __maybe_unused tvp5150_pad_init(struct v4l2_subdev *sd)
> > +{
> > +	struct tvp5150 *core = to_tvp5150(sd);
> > +	int res;
> > +
> > +#if defined(CONFIG_MEDIA_CONTROLLER)
> > +	core->pads[DEMOD_PAD_IF_INPUT].flags = MEDIA_PAD_FL_SINK;
> > +	core->pads[DEMOD_PAD_VID_OUT].flags = MEDIA_PAD_FL_SOURCE;
> > +	core->pads[DEMOD_PAD_VBI_OUT].flags = MEDIA_PAD_FL_SOURCE;
> > +
> > +	sd->entity.function = MEDIA_ENT_F_ATV_DECODER;
> > +
> > +	res = media_entity_pads_init(&sd->entity, DEMOD_NUM_PADS, core->pads);
> > +	if (res < 0)
> > +		return res;
> > +
> > +	sd->entity.ops = &tvp5150_sd_media_ops;
> > +#endif
> > +	return 0;
> > +}
> > +
> > +
> >  /* -----------------------------------------------------------------------
> > */
> > 
> >  static const struct v4l2_ctrl_ops tvp5150_ctrl_ops = {
> > @@ -1246,6 +1268,9 @@ static const struct v4l2_subdev_vbi_ops
> > tvp5150_vbi_ops = { };
> > 
> >  static const struct v4l2_subdev_pad_ops tvp5150_pad_ops = {
> > +#ifdef CONFIG_MEDIA_CONTROLLER
> > +	.pad_init = tvp5150_pad_init,
> > +#endif
> >  	.enum_mbus_code = tvp5150_enum_mbus_code,
> >  	.enum_frame_size = tvp5150_enum_frame_size,
> >  	.set_fmt = tvp5150_fill_fmt,
> > @@ -1475,20 +1500,6 @@ static int tvp5150_probe(struct i2c_client *c,
> >  	v4l2_i2c_subdev_init(sd, c, &tvp5150_ops);
> >  	sd->flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
> > 
> > -#if defined(CONFIG_MEDIA_CONTROLLER)
> > -	core->pads[DEMOD_PAD_IF_INPUT].flags = MEDIA_PAD_FL_SINK;
> > -	core->pads[DEMOD_PAD_VID_OUT].flags = MEDIA_PAD_FL_SOURCE;
> > -	core->pads[DEMOD_PAD_VBI_OUT].flags = MEDIA_PAD_FL_SOURCE;
> > -
> > -	sd->entity.function = MEDIA_ENT_F_ATV_DECODER;
> > -
> > -	res = media_entity_pads_init(&sd->entity, DEMOD_NUM_PADS, core->pads);
> > -	if (res < 0)
> > -		return res;
> > -
> > -	sd->entity.ops = &tvp5150_sd_media_ops;
> > -#endif
> > -
> >  	res = tvp5150_detect_version(core);
> >  	if (res < 0)
> >  		return res;
> > diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> > index 6ba6e8f982fc..fc3c199e5500 100644
> > --- a/drivers/media/media-device.c
> > +++ b/drivers/media/media-device.c
> > @@ -587,14 +587,15 @@ int __must_check media_device_register_entity(struct
> > media_device *mdev, media_gobj_create(mdev, MEDIA_GRAPH_PAD,
> >  			       &entity->pads[i].graph_obj);
> > 
> > +	spin_unlock(&mdev->lock);
> > +
> >  	/* invoke entity_notify callbacks */
> >  	list_for_each_entry_safe(notify, next, &mdev->entity_notify, list) {
> >  		(notify)->notify(entity, notify->notify_data);
> >  	}  
> 
> I don't think this is the right approach. There's no lock protecting the 
> entity_notify list, and nothing that prevents the notifiers from touching the 
> entity_notify list. The list_for_each_entry_safe() function doesn't help you 
> there, it only protects against deletion of the current list entry.
> 
> Locking needs to be audited and fixed, let's not push a bug fix that 
> introduces another bug.

Sakari proposed a different approach. I ran a loop 1000 times doing 
unbinding/rebinding au0828, keeping snd-usb-audio bind, and running 3
other processes calling G_TOPOLOGY. It worked 100%. Not a single
trouble.

Such patch is at:
	https://patchwork.linuxtv.org/patch/33490/

> Furthermore, I wonder if we really need notifiers. They add complexity and are 
> difficult to get right, isn't there another possible approach ?

Sorry, but I can't see any other approach to create links between the 
entities created by different and independent drivers that would be
better than notifiers.

In this specific case, the USB Audio Class driver (snd-usb-audio)
doesn't know anything about the V4L2 driver. Only the V4L2 driver
knows what links should be created to connect the audio I2S inputs.

The probing order is also random, meaning that either the V4L2
driver or the ALSA driver will be probed first.

Thanks,
Mauro
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Patch
diff mbox

diff --git a/drivers/media/i2c/tvp5150.c b/drivers/media/i2c/tvp5150.c
index ff18444e19e4..14004fd7d0fb 100644
--- a/drivers/media/i2c/tvp5150.c
+++ b/drivers/media/i2c/tvp5150.c
@@ -1208,6 +1208,28 @@  static int tvp5150_registered_async(struct v4l2_subdev *sd)
 	return 0;
 }
 
+static int __maybe_unused tvp5150_pad_init(struct v4l2_subdev *sd)
+{
+	struct tvp5150 *core = to_tvp5150(sd);
+	int res;
+
+#if defined(CONFIG_MEDIA_CONTROLLER)
+	core->pads[DEMOD_PAD_IF_INPUT].flags = MEDIA_PAD_FL_SINK;
+	core->pads[DEMOD_PAD_VID_OUT].flags = MEDIA_PAD_FL_SOURCE;
+	core->pads[DEMOD_PAD_VBI_OUT].flags = MEDIA_PAD_FL_SOURCE;
+
+	sd->entity.function = MEDIA_ENT_F_ATV_DECODER;
+
+	res = media_entity_pads_init(&sd->entity, DEMOD_NUM_PADS, core->pads);
+	if (res < 0)
+		return res;
+
+	sd->entity.ops = &tvp5150_sd_media_ops;
+#endif
+	return 0;
+}
+
+
 /* ----------------------------------------------------------------------- */
 
 static const struct v4l2_ctrl_ops tvp5150_ctrl_ops = {
@@ -1246,6 +1268,9 @@  static const struct v4l2_subdev_vbi_ops tvp5150_vbi_ops = {
 };
 
 static const struct v4l2_subdev_pad_ops tvp5150_pad_ops = {
+#ifdef CONFIG_MEDIA_CONTROLLER
+	.pad_init = tvp5150_pad_init,
+#endif
 	.enum_mbus_code = tvp5150_enum_mbus_code,
 	.enum_frame_size = tvp5150_enum_frame_size,
 	.set_fmt = tvp5150_fill_fmt,
@@ -1475,20 +1500,6 @@  static int tvp5150_probe(struct i2c_client *c,
 	v4l2_i2c_subdev_init(sd, c, &tvp5150_ops);
 	sd->flags |= V4L2_SUBDEV_FL_HAS_DEVNODE;
 
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	core->pads[DEMOD_PAD_IF_INPUT].flags = MEDIA_PAD_FL_SINK;
-	core->pads[DEMOD_PAD_VID_OUT].flags = MEDIA_PAD_FL_SOURCE;
-	core->pads[DEMOD_PAD_VBI_OUT].flags = MEDIA_PAD_FL_SOURCE;
-
-	sd->entity.function = MEDIA_ENT_F_ATV_DECODER;
-
-	res = media_entity_pads_init(&sd->entity, DEMOD_NUM_PADS, core->pads);
-	if (res < 0)
-		return res;
-
-	sd->entity.ops = &tvp5150_sd_media_ops;
-#endif
-
 	res = tvp5150_detect_version(core);
 	if (res < 0)
 		return res;
diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
index 6ba6e8f982fc..fc3c199e5500 100644
--- a/drivers/media/media-device.c
+++ b/drivers/media/media-device.c
@@ -587,14 +587,15 @@  int __must_check media_device_register_entity(struct media_device *mdev,
 		media_gobj_create(mdev, MEDIA_GRAPH_PAD,
 			       &entity->pads[i].graph_obj);
 
+	spin_unlock(&mdev->lock);
+
 	/* invoke entity_notify callbacks */
 	list_for_each_entry_safe(notify, next, &mdev->entity_notify, list) {
 		(notify)->notify(entity, notify->notify_data);
 	}
 
-	spin_unlock(&mdev->lock);
-
 	mutex_lock(&mdev->graph_mutex);
+
 	if (mdev->entity_internal_idx_max
 	    >= mdev->pm_count_walk.ent_enum.idx_max) {
 		struct media_entity_graph new = { .top = 0 };
diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
index 5b808500e7e7..6bcdf557e027 100644
--- a/drivers/media/v4l2-core/v4l2-common.c
+++ b/drivers/media/v4l2-core/v4l2-common.c
@@ -112,6 +112,14 @@  EXPORT_SYMBOL(v4l2_ctrl_query_fill);
 void v4l2_i2c_subdev_init(struct v4l2_subdev *sd, struct i2c_client *client,
 		const struct v4l2_subdev_ops *ops)
 {
+	/*
+	 * Initialize the MC pads - for now, this will be called
+	 * unconditionally, since the current implementation will defer
+	 * the pads initialization until the media_dev is created.
+	 */
+	if (v4l2_subdev_has_op(sd, pad, pad_init))
+		sd->ops->pad->pad_init(sd);
+
 	v4l2_subdev_init(sd, ops);
 	sd->flags |= V4L2_SUBDEV_FL_IS_I2C;
 	/* the owner is the same as the i2c_client's driver owner */
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index 11e2dfec0198..c9bb221029e4 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -572,6 +572,9 @@  struct v4l2_subdev_pad_config {
 /**
  * struct v4l2_subdev_pad_ops - v4l2-subdev pad level operations
  *
+ * @pad_init: callback that initializes the media-controller specific part
+ *	      of the subdev driver, creating its pads
+ *
  * @enum_mbus_code: callback for VIDIOC_SUBDEV_ENUM_MBUS_CODE ioctl handler
  *		    code.
  * @enum_frame_size: callback for VIDIOC_SUBDEV_ENUM_FRAME_SIZE ioctl handler
@@ -607,6 +610,7 @@  struct v4l2_subdev_pad_config {
  *                  may be adjusted by the subdev driver to device capabilities.
  */
 struct v4l2_subdev_pad_ops {
+	int (*pad_init)(struct v4l2_subdev *sd);
 	int (*enum_mbus_code)(struct v4l2_subdev *sd,
 			      struct v4l2_subdev_pad_config *cfg,
 			      struct v4l2_subdev_mbus_code_enum *code);