wakeup the target thread in kthread_park()

fixes hang in amdgpu GPU reset sequence, mirrors the linux semantics.


diff --git a/sys/external/bsd/drm2/linux/linux_kthread.c b/sys/external/bsd/drm2/linux/linux_kthread.c
index bb5c7d576afe..211704bc0374 100644
--- a/sys/external/bsd/drm2/linux/linux_kthread.c
+++ b/sys/external/bsd/drm2/linux/linux_kthread.c
@@ -40,6 +40,7 @@ __KERNEL_RCSID(0, "$NetBSD$");
 #include <sys/lwp.h>
 #include <sys/mutex.h>
 #include <sys/specificdata.h>
+#include <sys/sleepq.h>
 
 #include <linux/kthread.h>
 
@@ -188,6 +189,8 @@ kthread_park(struct task_struct *T)
 	mutex_enter(&T->kt_lock);
 	KASSERT(!T->kt_shouldstop);
 	T->kt_shouldpark = true;
+	if (T->kt_lwp != curlwp)
+		sleepq_timeout(T->kt_lwp);
 	while (!T->kt_parked)
 		cv_wait(&T->kt_cv, &T->kt_lock);
 	mutex_exit(&T->kt_lock);