linux-kernel - Re: [PATCH v5 1/3] [media] media-device: check before unregister if mdev was registered

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Message-ID: <20151215084153.1f54d561@recife.lan>
Date:	Tue, 15 Dec 2015 08:41:53 -0200
From:	Mauro Carvalho Chehab <mchehab@....samsung.com>
To:	Shuah Khan <shuahkh@....samsung.com>
Cc:	Javier Martinez Canillas <javier@....samsung.com>,
	linux-kernel@...r.kernel.org,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH v5 1/3] [media] media-device: check before unregister if
 mdev was registered

Em Fri, 11 Dec 2015 16:36:27 -0700
Shuah Khan <shuahkh@....samsung.com> escreveu:

> On 12/11/2015 03:57 PM, Javier Martinez Canillas wrote:
> > Most media functions that unregister, check if the corresponding register
> > function succeed before. So these functions can safely be called even if a
> > registration was never made or the component as already been unregistered.
> > 
> > Add the same check to media_device_unregister() function for consistency.
> > 
> > This will also allow to split the media_device_register() function in an
> > initialization and registration functions without the need to change the
> > generic cleanup functions and error code paths for all the media drivers.
> > 
> > Suggested-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > Signed-off-by: Javier Martinez Canillas <javier@....samsung.com>
> > Acked-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> > 
> > ---
> > 
> > Changes in v5: None
> > Changes in v4: None
> > Changes in v3: None
> > Changes in v2:
> > - Reword the documentation for media_device_unregister(). Suggested by Sakari.
> > - Added Sakari's Acked-by tag for patch #1.
> > 
> >  drivers/media/media-device.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> > index c12481c753a0..11c1c7383361 100644
> > --- a/drivers/media/media-device.c
> > +++ b/drivers/media/media-device.c
> > @@ -577,6 +577,8 @@ EXPORT_SYMBOL_GPL(__media_device_register);
> >   * media_device_unregister - unregister a media device
> >   * @mdev:	The media device
> >   *
> > + * It is safe to call this function on an unregistered
> > + * (but initialised) media device.
> >   */
> >  void media_device_unregister(struct media_device *mdev)
> >  {
> > @@ -584,6 +586,10 @@ void media_device_unregister(struct media_device *mdev)
> >  	struct media_entity *next;
> >  	struct media_interface *intf, *tmp_intf;
> >  
> > +	/* Check if mdev was ever registered at all */
> > +	if (!media_devnode_is_registered(&mdev->devnode))
> > +		return;
> 
> This is a good check, however, this check will not prevent
> media_device_unregister() from getting run twice by two
> different drivers. i.e media_devnode gets unregistered
> towards the end of at the end of media_device_unregister().
> 
> In an example case, if bridge driver and snd-usb-aduio both
> call media_device_unregister(), this check won't help prevent
> media_device_unregister() being done only once. I think we
> need a different state variable in struct media_device
> to ensure unregister is done only once.

True. We need move the spin_lock() code to be called before
calling media_device_is_registered().

I'm sending such patches.

Thanks for reporting it.

Regards,
Mauro

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