Index: sys/kern/kern_clock.c
===================================================================
--- sys/kern/kern_clock.c	(revision 222069)
+++ sys/kern/kern_clock.c	(working copy)
@@ -440,10 +440,12 @@
 			flags |= TDF_PROFPEND | TDF_ASTPENDING;
 		PROC_SUNLOCK(p);
 	}
-	thread_lock(td);
 	sched_tick(1);
-	td->td_flags |= flags;
-	thread_unlock(td);
+	if (flags != 0) {
+		thread_lock(td);
+		td->td_flags |= flags;
+		thread_unlock(td);
+	}
 
 #ifdef	HWPMC_HOOKS
 	if (PMC_CPU_HAS_SAMPLES(PCPU_GET(cpuid)))
@@ -528,10 +530,12 @@
 			flags |= TDF_PROFPEND | TDF_ASTPENDING;
 		PROC_SUNLOCK(p);
 	}
-	thread_lock(td);
 	sched_tick(cnt);
-	td->td_flags |= flags;
-	thread_unlock(td);
+	if (flags != 0) {
+		thread_lock(td);
+		td->td_flags |= flags;
+		thread_unlock(td);
+	}
 
 #ifdef	HWPMC_HOOKS
 	if (PMC_CPU_HAS_SAMPLES(PCPU_GET(cpuid)))