Re: [Intel-gfx] [PATCH 01/13] video: fb_defio: preserve user fb_ops

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Nov 27, 2019 at 07:17:41PM +0100, Daniel Vetter wrote:
> On Wed, Nov 27, 2019 at 06:31:57PM +0200, Jani Nikula wrote:
> > Modifying fb_ops directly to override fb_mmap with fb_deferred_io_mmap
> > and then resetting it to NULL afterwards causes problems all over the
> > place. First, it prevents making the fbops member of struct fb_info a
> > const pointer, which means we can't make struct fb_ops const
> > anywhere. Second, a few places have to go out of their way to restore
> > the original fb_mmap pointer that gets reset to NULL.
> > 
> > Preserve the passed in fb_ops by making a copy of it and modifying that
> > instead. Add a deferred_io_private member to struct fb_info to store the
> > pointer to the old fb_ops, and restore that at cleanup.
> > 
> > Cc: Jaya Kumar <jayalk@intworks.biz>
> > Cc: linux-fbdev@vger.kernel.org
> > Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> > 
> > ---
> > 
> > Note: If the approach is acceptable, we'll also need to handle the error
> > returns on memory allocation failures at fb_deferred_io_init() call
> > sites. There are 13.
> 
> it's fbdev defio, I think we can do worse with less effort. Just embed a
> copy of fb_ops into fb_info, and use that, and tada! no memory allocation
> needed :-)
> 
> I'd totally r-b that patch.
> 
> Or do what Ville suggested, add an fb_info->fbdefio.enabled, set that in
> the _init function and in fb_mmap call fb_deferred_io_mmap for that case
> instead of the driver's fb_ops->fb_mmap. There's only one caller of that
> in the entire tree, in fbmem.c. Also, we could/should nuke the
> EXPORT_SYMBOL(fb_deferred_io_mmap) I think.

I just realized that fb_info->fbdefio is a pointer, so this would be
really simple to pull off I think.
-Daniel

> 
> That version would also get my r-b stamp. So up to you what you prefer.
> -Daniel
> 
> > ---
> >  drivers/video/fbdev/core/fb_defio.c | 25 ++++++++++++++++++++++---
> >  include/linux/fb.h                  |  3 ++-
> >  2 files changed, 24 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
> > index 82c20c6047b0..36697844c1e0 100644
> > --- a/drivers/video/fbdev/core/fb_defio.c
> > +++ b/drivers/video/fbdev/core/fb_defio.c
> > @@ -200,13 +200,23 @@ static void fb_deferred_io_work(struct work_struct *work)
> >  	mutex_unlock(&fbdefio->lock);
> >  }
> >  
> > -void fb_deferred_io_init(struct fb_info *info)
> > +int fb_deferred_io_init(struct fb_info *info)
> >  {
> >  	struct fb_deferred_io *fbdefio = info->fbdefio;
> > +	struct fb_ops *fbops;
> >  
> >  	BUG_ON(!fbdefio);
> > +
> > +	fbops = kmemdup(info->fbops, sizeof(*fbops), GFP_KERNEL);
> > +	if (!fbops)
> > +		return -ENOMEM;
> > +
> > +	fbops->fb_mmap = fb_deferred_io_mmap;
> > +	info->deferred_io_private = info->fbops;
> > +	info->fbops = fbops;
> > +
> >  	mutex_init(&fbdefio->lock);
> > -	info->fbops->fb_mmap = fb_deferred_io_mmap;
> > +
> >  	INIT_DELAYED_WORK(&info->deferred_work, fb_deferred_io_work);
> >  	INIT_LIST_HEAD(&fbdefio->pagelist);
> >  	if (fbdefio->delay = 0) /* set a default of 1 s */
> > @@ -229,6 +239,12 @@ void fb_deferred_io_cleanup(struct fb_info *info)
> >  	int i;
> >  
> >  	BUG_ON(!fbdefio);
> > +
> > +	/* sanity check against misuse */
> > +	if (WARN_ON(!info->deferred_io_private ||
> > +		    info->fbops->fb_mmap != fb_deferred_io_mmap))
> > +		return;
> > +
> >  	cancel_delayed_work_sync(&info->deferred_work);
> >  
> >  	/* clear out the mapping that we setup */
> > @@ -237,7 +253,10 @@ void fb_deferred_io_cleanup(struct fb_info *info)
> >  		page->mapping = NULL;
> >  	}
> >  
> > -	info->fbops->fb_mmap = NULL;
> > +	kfree(info->fbops);
> > +	info->fbops = info->deferred_io_private;
> > +	info->deferred_io_private = NULL;
> > +
> >  	mutex_destroy(&fbdefio->lock);
> >  }
> >  EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
> > diff --git a/include/linux/fb.h b/include/linux/fb.h
> > index a6ad528990de..65f2abd47745 100644
> > --- a/include/linux/fb.h
> > +++ b/include/linux/fb.h
> > @@ -470,6 +470,7 @@ struct fb_info {
> >  #ifdef CONFIG_FB_DEFERRED_IO
> >  	struct delayed_work deferred_work;
> >  	struct fb_deferred_io *fbdefio;
> > +	void *deferred_io_private;
> >  #endif
> >  
> >  	struct fb_ops *fbops;
> > @@ -658,7 +659,7 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,
> >  
> >  /* drivers/video/fb_defio.c */
> >  int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma);
> > -extern void fb_deferred_io_init(struct fb_info *info);
> > +extern int fb_deferred_io_init(struct fb_info *info);
> >  extern void fb_deferred_io_open(struct fb_info *info,
> >  				struct inode *inode,
> >  				struct file *file);
> > -- 
> > 2.20.1
> > 
> > _______________________________________________
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> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch