Re: [PATCH] drm/fb-helper: Fix race between deferred_io worker and dirty updater

Takashi Iwai
2016-10-20T13:23:19Z

On Thu, 20 Oct 2016 15:20:55 +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.
>
> The fix is simply moving schedule_work() inside the spinlock.
>
> 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')
> Signed-off-by: Takashi Iwai <tiwai@suse.de>

I forgot to put Cc to stable. Feel free to add it once if it's
accepted.

thanks,

Takashi

> ---
> drivers/gpu/drm/drm_fb_helper.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 03414bde1f15..bae392dea2cc 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -861,9 +861,8 @@ static void drm_fb_helper_dirty(struct fb_info *info, u32 x, u32 y,
> clip->y1 = min_t(u32, clip->y1, y);
> clip->x2 = max_t(u32, clip->x2, x + width);
> clip->y2 = max_t(u32, clip->y2, y + height);
> - spin_unlock_irqrestore(&helper->dirty_lock, flags);
> -
> schedule_work(&helper->dirty_work);
> + spin_unlock_irqrestore(&helper->dirty_lock, flags);
> }
>
> /**
> --
> 2.10.1
>