Index: sys/kern/kern_tc.c
===================================================================
--- sys/kern/kern_tc.c	(revision 277285)
+++ sys/kern/kern_tc.c	(working copy)
@@ -1424,7 +1424,15 @@
 		(void)newtc->tc_get_timecount(newtc);
 
 		timecounter = newtc;
-		timekeep_push_vdso();
+
+		/*
+		 * The vdso timehands update is deferred until the next
+		 * 'tc_windup()'.
+		 *
+		 * This is prudent given that 'timekeep_push_vdso()' does not
+		 * use any locking and that it can be called in hard interrupt
+		 * context via 'tc_windup()'.
+		 */
 		return (0);
 	}
 	return (EINVAL);
@@ -1982,7 +1990,6 @@
 	if (error != 0)
 		return (error);
 	vdso_th_enable = old_vdso_th_enable;
-	timekeep_push_vdso();
 	return (0);
 }
 SYSCTL_PROC(_kern_timecounter, OID_AUTO, fast_gettime,
@@ -2002,7 +2009,7 @@
 	vdso_th->th_counter_mask = th->th_counter->tc_counter_mask;
 	vdso_th->th_offset = th->th_offset;
 	vdso_th->th_boottime = boottimebin;
-	enabled = cpu_fill_vdso_timehands(vdso_th);
+	enabled = cpu_fill_vdso_timehands(vdso_th, th->th_counter);
 	if (!vdso_th_enable)
 		enabled = 0;
 	return (enabled);
@@ -2024,7 +2031,7 @@
 	*(uint64_t *)&vdso_th32->th_offset.frac[0] = th->th_offset.frac;
 	vdso_th32->th_boottime.sec = boottimebin.sec;
 	*(uint64_t *)&vdso_th32->th_boottime.frac[0] = boottimebin.frac;
-	enabled = cpu_fill_vdso_timehands32(vdso_th32);
+	enabled = cpu_fill_vdso_timehands32(vdso_th32, th->th_counter);
 	if (!vdso_th_enable)
 		enabled = 0;
 	return (enabled);
Index: sys/kern/subr_dummy_vdso_tc.c
===================================================================
--- sys/kern/subr_dummy_vdso_tc.c	(revision 277285)
+++ sys/kern/subr_dummy_vdso_tc.c	(working copy)
@@ -33,7 +33,7 @@
 #include <sys/vdso.h>
 
 uint32_t
-cpu_fill_vdso_timehands(struct vdso_timehands *vdso_th)
+cpu_fill_vdso_timehands(struct vdso_timehands *vdso_th, struct timecounter *tc)
 {
 
 	return (0);
@@ -41,7 +41,8 @@
 
 #ifdef COMPAT_FREEBSD32
 uint32_t
-cpu_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32)
+cpu_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32,
+    struct timecounter *tc)
 {
 
 	return (0);
Index: sys/sys/vdso.h
===================================================================
--- sys/sys/vdso.h	(revision 277285)
+++ sys/sys/vdso.h	(working copy)
@@ -69,6 +69,8 @@
 
 #ifdef _KERNEL
 
+struct timecounter;
+
 void timekeep_push_vdso(void);
 
 uint32_t tc_fill_vdso_timehands(struct vdso_timehands *vdso_th);
@@ -81,7 +83,8 @@
  * global sysctl enable override is handled by machine-independed code
  * after cpu_fill_vdso_timehands() call is made.
  */
-uint32_t cpu_fill_vdso_timehands(struct vdso_timehands *vdso_th);
+uint32_t cpu_fill_vdso_timehands(struct vdso_timehands *vdso_th,
+    struct timecounter *tc);
 
 #define	VDSO_TH_NUM	4
 
@@ -110,7 +113,8 @@
 };
 
 uint32_t tc_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32);
-uint32_t cpu_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32);
+uint32_t cpu_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32,
+    struct timecounter *tc);
 
 #endif
 #endif
Index: sys/x86/x86/tsc.c
===================================================================
--- sys/x86/x86/tsc.c	(revision 277285)
+++ sys/x86/x86/tsc.c	(working copy)
@@ -720,21 +720,22 @@
 }
 
 uint32_t
-cpu_fill_vdso_timehands(struct vdso_timehands *vdso_th)
+cpu_fill_vdso_timehands(struct vdso_timehands *vdso_th, struct timecounter *tc)
 {
 
-	vdso_th->th_x86_shift = (int)(intptr_t)timecounter->tc_priv;
+	vdso_th->th_x86_shift = (int)(intptr_t)tc->tc_priv;
 	bzero(vdso_th->th_res, sizeof(vdso_th->th_res));
-	return (timecounter == &tsc_timecounter);
+	return (tc == &tsc_timecounter);
 }
 
 #ifdef COMPAT_FREEBSD32
 uint32_t
-cpu_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32)
+cpu_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32,
+    struct timecounter *tc)
 {
 
-	vdso_th32->th_x86_shift = (int)(intptr_t)timecounter->tc_priv;
+	vdso_th32->th_x86_shift = (int)(intptr_t)tc->tc_priv;
 	bzero(vdso_th32->th_res, sizeof(vdso_th32->th_res));
-	return (timecounter == &tsc_timecounter);
+	return (tc == &tsc_timecounter);
 }
 #endif