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

[Takashi Iwai <tiwai@suse.de>]

On Tue, 25 Oct 2016 10:09:30 +0200,
Daniel Vetter wrote:
> 
> 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@vger.kernel.org>
> > > > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > > 
> > > Reviewed-by: Ville Syrjälä <ville.syrjala@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.

Thanks!


Takashi
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