On Fri, Jul 22, 2022 at 05:52:34PM -0400, Yunxiang Li wrote:
> Acquire vbl_lock before accessing vblank refcount in drm_vblank_put,
> just like everywhere else that access the refcount.
>
> Signed-off-by: Yunxiang Li <Yunxiang.Li@xxxxxxx>
The entire point of using atomic for the refcount is that we can check it
lockless, so I'm not sure what you're trying to fix here?
For the first patch I think it's clear that the bug needs to be fixed in
amdgpu dc code already.
-Daniel
> ---
> drivers/gpu/drm/drm_vblank.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 159d13b5d97b..77b8c40fc7ba 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -1203,15 +1203,22 @@ EXPORT_SYMBOL(drm_crtc_vblank_get);
> void drm_vblank_put(struct drm_device *dev, unsigned int pipe)
> {
> struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> + unsigned long irqflags;
> + int ret;
>
> if (drm_WARN_ON(dev, pipe >= dev->num_crtcs))
> return;
>
> - if (drm_WARN_ON(dev, atomic_read(&vblank->refcount) == 0))
> + spin_lock_irqsave(&dev->vbl_lock, irqflags);
> + if (drm_WARN_ON(dev, atomic_read(&vblank->refcount) == 0)) {
> + spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
> return;
> + }
>
> /* Last user schedules interrupt disable */
> - if (atomic_dec_and_test(&vblank->refcount)) {
> + ret = atomic_dec_and_test(&vblank->refcount);
> + spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
> + if (ret) {
> if (drm_vblank_offdelay == 0)
> return;
> else if (drm_vblank_offdelay < 0)
> --
> 2.37.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
