[PATCH v2] drm/fb-helper: Don't call dirty callback for untouched clips

[Daniel Vetter]

On Tue, Oct 25, 2016 at 08:46:28AM +0200, Takashi Iwai wrote:
> On Fri, 21 Oct 2016 14:52:07 +0200,
> Ville Syrjälä wrote:
> > 
> > On Thu, Oct 20, 2016 at 05:05:30PM +0200, Takashi Iwai wrote:
> > > Since 4.7 kernel, we've seen the error messages like
> > > 
> > >  kernel: [TTM] Buffer eviction failed
> > >  kernel: qxl 0000:00:02.0: object_init failed for (4026540032, 0x00000001)
> > >  kernel: [drm:qxl_alloc_bo_reserved [qxl]] *ERROR* failed to allocate VRAM BO
> > > 
> > > on QXL when switching and accessing on VT.  The culprit was the
> > > generic deferred_io code (qxl driver switched to it since 4.7).
> > > There is a race between the dirty clip update and the call of
> > > callback.
> > > 
> > > In drm_fb_helper_dirty(), the dirty clip is updated in the spinlock,
> > > while it kicks off the update worker outside the spinlock.  Meanwhile
> > > the update worker clears the dirty clip in the spinlock, too.  Thus,
> > > when drm_fb_helper_dirty() is called concurrently, schedule_work() is
> > > called after the clip is cleared in the first worker call.
> > > 
> > > This patch addresses it by validating the clip before calling the
> > > dirty fb callback.
> > > 
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98322
> > > Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1003298
> > > Fixes: eaa434defaca ('drm/fb-helper: Add fb_deferred_io support')
> > > Cc: <stable at vger.kernel.org>
> > > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> > 
> > Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Daniel, could you pick this if it's OK as a quick fix?  Currently
> qxl driver is utterly broken, and we should recover it ASAP.  On top
> of this, we can put a more comprehensive fix covering both this and
> dirtyfb ioctl code paths.

I thought I've pinged Dave already to pick up, I'll poke him again.
-Daniel

> 
> 
> thanks,
> 
> Takashi
> 
> > 
> > > ---
> > > v1->v2: simplified the code as suggested by Ville
> > > 
> > >  drivers/gpu/drm/drm_fb_helper.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > > index 03414bde1f15..aae7df01864d 100644
> > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > @@ -644,7 +644,9 @@ static void drm_fb_helper_dirty_work(struct work_struct *work)
> > >  	clip->x2 = clip->y2 = 0;
> > >  	spin_unlock_irqrestore(&helper->dirty_lock, flags);
> > >  
> > > -	helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
> > > +	/* call dirty callback only when it has been really touched */
> > > +	if (clip_copy.x1 < clip_copy.x2 && clip_copy.y1 < clip_copy.y2)
> > > +		helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
> > >  }
> > >  
> > >  /**
> > > -- 
> > > 2.10.1
> > 
> > -- 
> > Ville Syrjälä
> > Intel OTC
> > 

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