Re: [PATCH v2 10/29] media: mc: Delete character device early

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Laurent,

On Wed, Feb 07, 2024 at 12:08:10PM +0200, Laurent Pinchart wrote:
> Hi Sakari,
> 
> Thank you for the patch.
> 
> On Wed, Dec 20, 2023 at 12:36:54PM +0200, Sakari Ailus wrote:
> > The parent of the character device related to the media devnode is the
> > media devnode. Thus the character device needs to be released before the
> > media devnode's release function. Move it to unregistering of the media
> > devnode, which mirrors adding the character device in conjunction with
> > registering the media devnode.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> > ---
> >  drivers/media/mc/mc-devnode.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/drivers/media/mc/mc-devnode.c b/drivers/media/mc/mc-devnode.c
> > index 7e22938dfd81..8bc7450ac144 100644
> > --- a/drivers/media/mc/mc-devnode.c
> > +++ b/drivers/media/mc/mc-devnode.c
> > @@ -51,9 +51,6 @@ static void media_devnode_release(struct device *cd)
> >  
> >  	mutex_lock(&media_devnode_lock);
> >  
> > -	/* Delete the cdev on this minor as well */
> > -	cdev_del(&devnode->cdev);
> > -
> >  	/* Mark device node number as free */
> >  	clear_bit(devnode->minor, media_devnode_nums);
> 
> Should this be moved to media_devnode_unregister() too ? It can be done
> in a separate patch.

Good question. Yes, I think that seems reasonable. The minor isn't needed
after unregistering the device.

> 
> >  
> > @@ -270,6 +267,7 @@ void media_devnode_unregister(struct media_devnode *devnode)
> >  	clear_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
> >  	mutex_unlock(&media_devnode_lock);
> >  
> > +	cdev_del(&devnode->cdev);
> 
> I initially wondered if this could raise with the cdev access in
> media_open(), as the media_devnode_lock is released just before calling
> cdev_dev(), but my understanding is that the dev/open race is properly
> handled in the cdev layer.
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Thanks!

> 
> I wonder if a similar change in v4l2-dev.c would be beneficial.

Quite possibly. Let's see...

-- 
Kind regards,

Sakari Ailus