Index: sys/kern/sched_4bsd.c
===================================================================
--- sys/kern/sched_4bsd.c	(revision 202541)
+++ sys/kern/sched_4bsd.c	(working copy)
@@ -920,6 +920,7 @@
 void
 sched_switch(struct thread *td, struct thread *newtd, int flags)
 {
+	struct mtx *tmtx;
 	struct td_sched *ts;
 	struct proc *p;
 
@@ -931,10 +932,14 @@
 	/* 
 	 * Switch to the sched lock to fix things up and pick
 	 * a new thread.
+	 * Switch the interlock to be sched_lock again in order to avoid
+	 * breaking of the critical path for threads willing to lock
+	 * on td_lock.
 	 */
-	if (td->td_lock != &sched_lock) {
+	tmtx = td->td_lock;
+	if (tmtx != &sched_lock) {
 		mtx_lock_spin(&sched_lock);
-		thread_unlock(td);
+		thread_lock_set(td, &sched_lock);
 	}
 
 	if ((td->td_flags & TDF_NOLOAD) == 0)
@@ -1004,7 +1009,7 @@
 			(*dtrace_vtime_switch_func)(newtd);
 #endif
 
-		cpu_switch(td, newtd, td->td_lock);
+		cpu_switch(td, newtd, tmtx);
 		lock_profile_obtain_lock_success(&sched_lock.lock_object,
 		    0, 0, __FILE__, __LINE__);
 		/*