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

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Date:   Tue, 25 Oct 2016 08:46:28 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel@...ll.ch>,
        Noralf Trønnes <noralf@...nnes.org>,
        David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH v2] drm/fb-helper: Don't call dirty callback for untouched clips

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@...r.kernel.org>
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> 
> Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.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.


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
>