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

[Takashi Iwai <tiwai@suse.de>]

On Fri, 21 Oct 2016 14:30:32 +0200,
Daniel Vetter wrote:
> 
> On Thu, Oct 20, 2016 at 05:00:35PM +0200, Takashi Iwai wrote:
> > On Thu, 20 Oct 2016 16:56:04 +0200,
> > Ville Syrjälä wrote:
> > > 
> > > On Thu, Oct 20, 2016 at 04:39:52PM +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>
> > > > ---
> > > >  drivers/gpu/drm/drm_fb_helper.c | 13 +++++++++----
> > > >  1 file changed, 9 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> > > > index 03414bde1f15..d790d205129e 100644
> > > > --- a/drivers/gpu/drm/drm_fb_helper.c
> > > > +++ b/drivers/gpu/drm/drm_fb_helper.c
> > > > @@ -636,15 +636,20 @@ static void drm_fb_helper_dirty_work(struct work_struct *work)
> > > >  						    dirty_work);
> > > >  	struct drm_clip_rect *clip = &helper->dirty_clip;
> > > >  	struct drm_clip_rect clip_copy;
> > > > +	bool dirty;
> > > >  	unsigned long flags;
> > > >  
> > > >  	spin_lock_irqsave(&helper->dirty_lock, flags);
> > > > -	clip_copy = *clip;
> > > > -	clip->x1 = clip->y1 = ~0;
> > > > -	clip->x2 = clip->y2 = 0;
> > > > +	dirty = (clip->x1 < clip->x2 && clip->y1 < clip->y2);
> > > > +	if (dirty) {
> > > > +		clip_copy = *clip;
> > > > +		clip->x1 = clip->y1 = ~0;
> > > > +		clip->x2 = clip->y2 = 0;
> > > > +	}
> > > >  	spin_unlock_irqrestore(&helper->dirty_lock, flags);
> > > >  
> > > > -	helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
> > > > +	if (dirty)
> > > 
> > > Could do it the other way too, ie. just make the copy, and then check the
> > > copy (can be done after dropping the lock even). Would avoid having to
> > > add the 'dirty' variable.
> > 
> > Sounds good.  Let me try...
> 
> Another thing: How do we prevent userspace from doing the same, i.e.
> submitting an empty rectangle? Do we need to patch up
> drm_mode_dirtyfb_ioctl too? Not much point if we fix this bug in the fb
> helpers and leave the barn door wide open for userspace to oops drivers
> ;-)

OK, then how about adding a helper to call the dirty callback with a
sanity check like below?


Takashi

---
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 03414bde1f15..7bef4d642511 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -644,7 +644,7 @@ 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);
+	drm_framebuffer_update_dirty(helper->fb, NULL, 0, 0, &clip_copy, 1);
 }
 
 /**
diff --git a/drivers/gpu/drm/drm_framebuffer.c b/drivers/gpu/drm/drm_framebuffer.c
index 398efd67cb93..0817a0b607c5 100644
--- a/drivers/gpu/drm/drm_framebuffer.c
+++ b/drivers/gpu/drm/drm_framebuffer.c
@@ -529,6 +529,25 @@ int drm_mode_getfb(struct drm_device *dev,
 }
 
 /**
+ * blah blah
+ */
+int drm_framebuffer_update_dirty(struct drm_framebuffer *fb,
+				 struct drm_file *file_priv,
+				 unsigned flags, unsigned color,
+				 struct drm_clip_rect *clips,
+				 unsigned num_clips)
+{
+	if (!fb->funcs->dirty)
+		return -ENOSYS;
+	if (!num_clips)
+		return 0;
+	if (clips->x1 >= clips->x2 || clips->y1 >= clips->y2)
+		return 0;
+	return fb->funcs->dirty(fb, file_priv, flags, color, clips, num_clips);
+}
+EXPORT_SYMBOL(drm_framebuffer_update_dirty);
+
+/**
  * drm_mode_dirtyfb_ioctl - flush frontbuffer rendering on an FB
  * @dev: drm device for the ioctl
  * @data: data pointer for the ioctl
@@ -600,12 +619,8 @@ int drm_mode_dirtyfb_ioctl(struct drm_device *dev,
 		}
 	}
 
-	if (fb->funcs->dirty) {
-		ret = fb->funcs->dirty(fb, file_priv, flags, r->color,
-				       clips, num_clips);
-	} else {
-		ret = -ENOSYS;
-	}
+	ret = drm_framebuffer_update_dirty(fb, file_priv, flags, r->color,
+					   clips, num_clips);
 
 out_err2:
 	kfree(clips);
diff --git a/include/drm/drm_framebuffer.h b/include/drm/drm_framebuffer.h
index f5ae1f436a4b..feabd9139fdb 100644
--- a/include/drm/drm_framebuffer.h
+++ b/include/drm/drm_framebuffer.h
@@ -217,6 +217,12 @@ void drm_framebuffer_remove(struct drm_framebuffer *fb);
 void drm_framebuffer_cleanup(struct drm_framebuffer *fb);
 void drm_framebuffer_unregister_private(struct drm_framebuffer *fb);
 
+int drm_framebuffer_update_dirty(struct drm_framebuffer *fb,
+				 struct drm_file *file_priv,
+				 unsigned flags, unsigned color,
+				 struct drm_clip_rect *clips,
+				 unsigned num_clips);
+
 /**
  * drm_framebuffer_reference - incr the fb refcnt
  * @fb: framebuffer