[PATCH, RESEND] drm/vmwgfx: Don't double-free the mode stored in par->set_mode

[Thomas Hellstrom]

Hi, Deepak,

On Mon, 2019-03-18 at 09:59 -0700, Deepak Singh Rawat wrote:
> Hi Thomas,
> 
> Thanks for doing this and somehow I missed the last patch, sorry
> about
> that. Have some questions below otherwise the patch looks good to me.
> 
> Reviewed-by: Deepak Rawat <drawat at vmware.com>
> 
> I will include your changes in vmwgfx-next and run tests.

I think we need to run this through vmwgfx-fixes and CC stable. I'll
pick up the patch for that.


> 
> On Mon, 2019-03-18 at 15:47 +0100, Thomas Zimmermann wrote:
> > When calling vmw_fb_set_par(), the mode stored in par->set_mode
> > gets
> > free'd
> > twice. The first free is in vmw_fb_kms_detach(), the second is near
> > the
> > end of vmw_fb_set_par() under the name of 'old_mode'. The mode-
> > setting code
> > only works correctly if the mode doesn't actually change.
> 
> You mean to say that without your patch vmwgfx fb driver fail to
> change
> the mode?
> 
> >  Removing 'old_mode'
> > in favor of using par->set_mode directly fixes the problem.
> > 
> > Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> > ---
> >  drivers/gpu/drm/vmwgfx/vmwgfx_fb.c | 12 +++---------
> >  1 file changed, 3 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c
> > b/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c
> > index b913a56f3426..2a9112515f46 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_fb.c
> > @@ -564,11 +564,9 @@ static int vmw_fb_set_par(struct fb_info
> > *info)
> >  		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
> >  		DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_PVSYNC)
> >  	};
> > -	struct drm_display_mode *old_mode;
> >  	struct drm_display_mode *mode;
> >  	int ret;
> > 
> > -	old_mode = par->set_mode;
> >  	mode = drm_mode_duplicate(vmw_priv->dev, &new_mode);
> >  	if (!mode) {
> >  		DRM_ERROR("Could not create new fb mode.\n");
> > @@ -579,11 +577,7 @@ static int vmw_fb_set_par(struct fb_info
> > *info)
> >  	mode->vdisplay = var->yres;
> >  	vmw_guess_mode_timing(mode);
> > 
> > -	if (old_mode && drm_mode_equal(old_mode, mode)) {
> > -		drm_mode_destroy(vmw_priv->dev, mode);
> > -		mode = old_mode;
> > -		old_mode = NULL;
> 
> I am having hard time understanding original intention for this piece
> of code. Was there a restriction to send pointer to old mode if mode
> were same and that restriction don't hold anymore. Sorry I am not
> familiar with this code area.

It looks like that code is there to reuse the old mode if possible. In
that case things work, but if a new mode is indeed created, the old
mode will be double-freed :(

/Thomas



> 
> > -	} else if (!vmw_kms_validate_mode_vram(vmw_priv,
> > +	if (!vmw_kms_validate_mode_vram(vmw_priv,
> >  					mode->hdisplay *
> >  					DIV_ROUND_UP(var-
> > > bits_per_pixel, 8),
> >  					mode->vdisplay)) {
> > @@ -620,8 +614,8 @@ static int vmw_fb_set_par(struct fb_info *info)
> >  	schedule_delayed_work(&par->local_work, 0);
> > 
> >  out_unlock:
> > -	if (old_mode)
> > -		drm_mode_destroy(vmw_priv->dev, old_mode);
> > +	if (par->set_mode)
> > +		drm_mode_destroy(vmw_priv->dev, par->set_mode);
> >  	par->set_mode = mode;
> > 
> >  	mutex_unlock(&par->bo_mutex);
> > --
> > 2.20.1
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel at lists.freedesktop.org
> > 
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