On Fri, Mar 17, 2017 at 08:20:27PM +0000, Chris Wilson wrote:
> Order the update to vblank->enabled after the timestamp is primed so
> that a concurrent unlocked reader will only see the vblank->enabled with
> the current timestamp.
>
> v2: vblank->enable is guarded by dev->vbl_lock not
> dev->vblank_time_lock, update the READ_ONCE accordingly.
The locking is indeed very confusing, and I don't know if it even makes
sense anymore. But this looks at least as sane as anything else here :)
For the series:
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> Do not add a READ_ONCE(vblank->enabled) inside the interrupt handler to
> avoid missing an interrupt whilst racing with enable_vblank()
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
> drivers/gpu/drm/drm_irq.c | 23 ++++++++++++++---------
> 1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
> index 53a526c7b24d..c47e07c89136 100644
> --- a/drivers/gpu/drm/drm_irq.c
> +++ b/drivers/gpu/drm/drm_irq.c
> @@ -325,6 +325,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe)
> struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> unsigned long irqflags;
>
> + assert_spin_locked(&dev->vbl_lock);
> +
> /* Prevent vblank irq processing while disabling vblank irqs,
> * so no updates of timestamps or count can happen after we've
> * disabled. Needed to prevent races in case of delayed irq's.
> @@ -336,10 +338,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe)
> * calling the ->disable_vblank() operation in atomic context with the
> * hardware potentially runtime suspended.
> */
> - if (vblank->enabled) {
> + if (cmpxchg_relaxed(&vblank->enabled, true, false))
> __disable_vblank(dev, pipe);
> - vblank->enabled = false;
> - }
>
> /*
> * Always update the count and timestamp to maintain the
> @@ -384,7 +384,7 @@ void drm_vblank_cleanup(struct drm_device *dev)
> for (pipe = 0; pipe < dev->num_crtcs; pipe++) {
> struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
>
> - WARN_ON(vblank->enabled &&
> + WARN_ON(READ_ONCE(vblank->enabled) &&
> drm_core_check_feature(dev, DRIVER_MODESET));
>
> del_timer_sync(&vblank->disable_timer);
> @@ -1105,11 +1105,16 @@ static int drm_vblank_enable(struct drm_device *dev, unsigned int pipe)
> */
> ret = __enable_vblank(dev, pipe);
> DRM_DEBUG("enabling vblank on crtc %u, ret: %d\n", pipe, ret);
> - if (ret)
> + if (ret) {
> atomic_dec(&vblank->refcount);
> - else {
> - vblank->enabled = true;
> + } else {
> drm_update_vblank_count(dev, pipe, 0);
> + /* drm_update_vblank_count() includes a wmb so we just
> + * need to ensure that the compiler emits the write
> + * to mark the vblank as enabled after the call
> + * to drm_update_vblank_count().
> + */
> + WRITE_ONCE(vblank->enabled, true);
> }
> }
>
> @@ -1517,7 +1522,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
> * vblank disable, so no need for further locking. The reference from
> * drm_vblank_get() protects against vblank disable from another source.
> */
> - if (!vblank->enabled) {
> + if (!READ_ONCE(vblank->enabled)) {
> ret = -EINVAL;
> goto err_unlock;
> }
> @@ -1644,7 +1649,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
> DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,
> (((drm_vblank_count(dev, pipe) -
> vblwait->request.sequence) <= (1 << 23)) ||
> - !vblank->enabled ||
> + !READ_ONCE(vblank->enabled) ||
> !dev->irq_enabled));
> }
>
> --
> 2.11.0
--
Ville Syrjälä
Intel OTC
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/intel-gfx
