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

[Ville Syrjälä]

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>

> ---
> 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