drm/vkms: Bugfix racing hrtimer vblank handle

shayenne · rodrigosiqueira · commit ba420afab565 · 2019-02-03T19:28:21.000-02:00
When the vblank irq happens, kernel time subsystem executes `vkms_vblank_simulate`. In parallel or not, it prepares all stuff necessary to the next vblank with arm, and it must flush these stuff before the next vblank irq. However, vblank counter is ahead when arm is executed in parallel with handle vblank. CPU 0: CPU 1: | | atomic_commit_tail is ongoing | | | | hrtimer: vkms_vblank_simulate() | | | drm_crtc_handle_vblank() | | drm_crtc_arm_vblank() | | | ->get_vblank_timestamp() | | | | hrtimer_forward_now() Then, we should guarantee that the vblank interval time is correct (not changed) before finish the vblank handle. Fix the bug including the call to `hrtimer_forward_now()` in the same lock of `drm_crtc_handle_vblank()` to ensure that the timestamp update is correct when finish the vblank handle. Signed-off-by: Shayenne Moura <shayenneluzmoura@gmail.com> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com> Link: https://patchwork.freedesktop.org/patch/msgid/e2e4b8f3a5cab7b2dba75bf1930f86b0a4ee08c9.1548856186.git.shayenneluzmoura@gmail.com
diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -10,13 +10,17 @@
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_probe_helper.h>
 
-static void _vblank_handle(struct vkms_output *output)
+static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
 {
+	struct vkms_output *output = container_of(timer, struct vkms_output,
+						  vblank_hrtimer);
 	struct drm_crtc *crtc = &output->crtc;
 	struct vkms_crtc_state *state = to_vkms_crtc_state(crtc->state);
+	int ret_overrun;
 	bool ret;
 
 	spin_lock(&output->lock);
+
 	ret = drm_crtc_handle_vblank(crtc);
 	if (!ret)
 		DRM_ERROR("vkms failure on handling vblank");
@@ -37,19 +41,9 @@ static void _vblank_handle(struct vkms_output *output)
 			DRM_WARN("failed to queue vkms_crc_work_handle");
 	}
 
-	spin_unlock(&output->lock);
-}
-
-static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
-{
-	struct vkms_output *output = container_of(timer, struct vkms_output,
-						  vblank_hrtimer);
-	int ret_overrun;
-
-	_vblank_handle(output);
-
 	ret_overrun = hrtimer_forward_now(&output->vblank_hrtimer,
 					  output->period_ns);
+	spin_unlock(&output->lock);
 
 	return HRTIMER_RESTART;
 }
