diff --git a/lib/libkvm/kvm_proc.c b/lib/libkvm/kvm_proc.c
--- a/lib/libkvm/kvm_proc.c
+++ b/lib/libkvm/kvm_proc.c
@@ -426,7 +426,7 @@
 					    TD_CAN_RUN(&mtd) ||
 					    TD_IS_RUNNING(&mtd)) {
 						kp->ki_stat = SRUN;
-					} else if (mtd.td_state ==
+					} else if (TD_GET_STATE(&mtd) ==
 					    TDS_INHIBITED) {
 						if (P_SHOULDSTOP(&proc)) {
 							kp->ki_stat = SSTOP;
diff --git a/sys/compat/linprocfs/linprocfs.c b/sys/compat/linprocfs/linprocfs.c
--- a/sys/compat/linprocfs/linprocfs.c
+++ b/sys/compat/linprocfs/linprocfs.c
@@ -1054,7 +1054,7 @@
 				state = "X (exiting)";
 				break;
 			}
-			switch(td2->td_state) {
+			switch(TD_GET_STATE(td2)) {
 			case TDS_INHIBITED:
 				state = "S (sleeping)";
 				break;
diff --git a/sys/ddb/db_command.c b/sys/ddb/db_command.c
--- a/sys/ddb/db_command.c
+++ b/sys/ddb/db_command.c
@@ -854,7 +854,7 @@
 	for (td = kdb_thr_first(); td != NULL; td = kdb_thr_next(td)) {
 		prev_jb = kdb_jmpbuf(jb);
 		if (setjmp(jb) == 0) {
-			if (td->td_state == TDS_RUNNING)
+			if (TD_IS_RUNNING(td))
 				db_printf("\nTracing command %s pid %d"
 				    " tid %ld td %p (CPU %d)\n",
 				    td->td_proc->p_comm, td->td_proc->p_pid,
diff --git a/sys/ddb/db_ps.c b/sys/ddb/db_ps.c
--- a/sys/ddb/db_ps.c
+++ b/sys/ddb/db_ps.c
@@ -173,9 +173,9 @@
 			 */
 			rflag = sflag = dflag = lflag = wflag = 0;
 			FOREACH_THREAD_IN_PROC(p, td) {
-				if (td->td_state == TDS_RUNNING ||
-				    td->td_state == TDS_RUNQ ||
-				    td->td_state == TDS_CAN_RUN)
+				if (TD_GET_STATE(td) == TDS_RUNNING ||
+				    TD_GET_STATE(td) == TDS_RUNQ ||
+				    TD_GET_STATE(td) == TDS_CAN_RUN)
 					rflag++;
 				if (TD_ON_LOCK(td))
 					lflag++;
@@ -267,7 +267,7 @@
 
 	if (all) {
 		db_printf("%6d                  ", td->td_tid);
-		switch (td->td_state) {
+		switch (TD_GET_STATE(td)) {
 		case TDS_RUNNING:
 			snprintf(state, sizeof(state), "Run");
 			break;
@@ -367,7 +367,7 @@
 	db_printf(" flags: %#x ", td->td_flags);
 	db_printf(" pflags: %#x\n", td->td_pflags);
 	db_printf(" state: ");
-	switch (td->td_state) {
+	switch (TD_GET_STATE(td)) {
 	case TDS_INACTIVE:
 		db_printf("INACTIVE\n");
 		break;
@@ -413,7 +413,7 @@
 		db_printf("}\n");
 		break;
 	default:
-		db_printf("??? (%#x)\n", td->td_state);
+		db_printf("??? (%#x)\n", TD_GET_STATE(td));
 		break;
 	}
 	if (TD_ON_LOCK(td))
diff --git a/sys/gdb/gdb_main.c b/sys/gdb/gdb_main.c
--- a/sys/gdb/gdb_main.c
+++ b/sys/gdb/gdb_main.c
@@ -510,11 +510,11 @@
 
 			sbuf_putc(&ctx.qXfer.sb, '>');
 
-			if (ctx.iter->td_state == TDS_RUNNING)
+			if (TD_GET_STATE(ctx.iter) == TDS_RUNNING)
 				sbuf_cat(&ctx.qXfer.sb, "Running");
-			else if (ctx.iter->td_state == TDS_RUNQ)
+			else if (TD_GET_STATE(ctx.iter) == TDS_RUNQ)
 				sbuf_cat(&ctx.qXfer.sb, "RunQ");
-			else if (ctx.iter->td_state == TDS_CAN_RUN)
+			else if (TD_GET_STATE(ctx.iter) == TDS_CAN_RUN)
 				sbuf_cat(&ctx.qXfer.sb, "CanRun");
 			else if (TD_ON_LOCK(ctx.iter))
 				sbuf_cat(&ctx.qXfer.sb, "Blocked");
diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -499,7 +499,7 @@
 	p->p_nice = NZERO;
 	td->td_tid = THREAD0_TID;
 	tidhash_add(td);
-	td->td_state = TDS_RUNNING;
+	TD_SET_STATE(td, TDS_RUNNING);
 	td->td_pri_class = PRI_TIMESHARE;
 	td->td_user_pri = PUSER;
 	td->td_base_user_pri = PUSER;
diff --git a/sys/kern/kern_intr.c b/sys/kern/kern_intr.c
--- a/sys/kern/kern_intr.c
+++ b/sys/kern/kern_intr.c
@@ -992,7 +992,7 @@
 		sched_add(td, SRQ_INTR);
 	} else {
 		CTR5(KTR_INTR, "%s: pid %d (%s): it_need %d, state %d",
-		    __func__, td->td_proc->p_pid, td->td_name, it->it_need, td->td_state);
+		    __func__, td->td_proc->p_pid, td->td_name, it->it_need, TD_GET_STATE(td));
 		thread_unlock(td);
 	}
 
diff --git a/sys/kern/kern_prot.c b/sys/kern/kern_prot.c
--- a/sys/kern/kern_prot.c
+++ b/sys/kern/kern_prot.c
@@ -1955,7 +1955,7 @@
 
 	MPASS(td->td_realucred != NULL);
 	MPASS(td->td_realucred == td->td_ucred);
-	MPASS(td->td_state == TDS_INACTIVE);
+	MPASS(TD_GET_STATE(td) == TDS_INACTIVE);
 	cr = td->td_realucred;
 	KASSERT(cr->cr_users > 0, ("%s: users %d not > 0 on cred %p",
 	    __func__, cr->cr_users, cr));
diff --git a/sys/kern/kern_racct.c b/sys/kern/kern_racct.c
--- a/sys/kern/kern_racct.c
+++ b/sys/kern/kern_racct.c
@@ -1147,7 +1147,7 @@
 		thread_lock(td);
 		td->td_flags |= TDF_ASTPENDING;
 
-		switch (td->td_state) {
+		switch (TD_GET_STATE(td)) {
 		case TDS_RUNQ:
 			/*
 			 * If the thread is on the scheduler run-queue, we can
diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -570,7 +570,7 @@
 	    ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
 
 	swapin = 0;
-	switch (td->td_state) {
+	switch (TD_GET_STATE(td)) {
 	case TDS_RUNNING:
 	case TDS_RUNQ:
 		break;
@@ -593,7 +593,7 @@
 		}
 		break;
 	default:
-		panic("setrunnable: state 0x%x", td->td_state);
+		panic("setrunnable: state 0x%x", TD_GET_STATE(td));
 	}
 	if ((srqflags & (SRQ_HOLD | SRQ_HOLDTD)) == 0)
 		thread_unlock(td);
diff --git a/sys/kern/kern_thread.c b/sys/kern/kern_thread.c
--- a/sys/kern/kern_thread.c
+++ b/sys/kern/kern_thread.c
@@ -346,7 +346,7 @@
 	struct thread	*td;
 
 	td = (struct thread *)mem;
-	td->td_state = TDS_INACTIVE;
+	TD_SET_STATE(td, TDS_INACTIVE);
 	td->td_lastcpu = td->td_oncpu = NOCPU;
 
 	/*
@@ -379,7 +379,7 @@
 
 #ifdef INVARIANTS
 	/* Verify that this thread is in a safe state to free. */
-	switch (td->td_state) {
+	switch (TD_GET_STATE(td)) {
 	case TDS_INHIBITED:
 	case TDS_RUNNING:
 	case TDS_CAN_RUN:
@@ -944,7 +944,7 @@
 	rucollect(&p->p_ru, &td->td_ru);
 	PROC_STATUNLOCK(p);
 
-	td->td_state = TDS_INACTIVE;
+	TD_SET_STATE(td, TDS_INACTIVE);
 #ifdef WITNESS
 	witness_thread_exit(td);
 #endif
@@ -993,7 +993,7 @@
 	 * its lock has been created.
 	 * PROC_LOCK_ASSERT(p, MA_OWNED);
 	 */
-	td->td_state    = TDS_INACTIVE;
+	TD_SET_STATE(td, TDS_INACTIVE);
 	td->td_proc     = p;
 	td->td_flags    = TDF_INMEM;
 
diff --git a/sys/kern/sched_4bsd.c b/sys/kern/sched_4bsd.c
--- a/sys/kern/sched_4bsd.c
+++ b/sys/kern/sched_4bsd.c
@@ -1764,7 +1764,7 @@
 	if (td->td_pinned != 0 || td->td_flags & TDF_BOUND)
 		return;
 
-	switch (td->td_state) {
+	switch (TD_GET_STATE(td)) {
 	case TDS_RUNQ:
 		/*
 		 * If we are on a per-CPU runqueue that is in the set,
diff --git a/sys/kern/subr_turnstile.c b/sys/kern/subr_turnstile.c
--- a/sys/kern/subr_turnstile.c
+++ b/sys/kern/subr_turnstile.c
@@ -288,7 +288,7 @@
 		 */
 		KASSERT(TD_ON_LOCK(td), (
 		    "thread %d(%s):%d holds %s but isn't blocked on a lock\n",
-		    td->td_tid, td->td_name, td->td_state,
+		    td->td_tid, td->td_name, TD_GET_STATE(td),
 		    ts->ts_lockobj->lo_name));
 
 		/*
@@ -1185,7 +1185,7 @@
 		}
 		db_printf("%sthread %d (pid %d, %s) is ", prefix, td->td_tid,
 		    td->td_proc->p_pid, td->td_name);
-		switch (td->td_state) {
+		switch (TD_GET_STATE(td)) {
 		case TDS_INACTIVE:
 			db_printf("inactive\n");
 			return;
@@ -1224,7 +1224,7 @@
 			db_printf("inhibited: %s\n", KTDSTATE(td));
 			return;
 		default:
-			db_printf("??? (%#x)\n", td->td_state);
+			db_printf("??? (%#x)\n", TD_GET_STATE(td));
 			return;
 		}
 	}
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -347,6 +347,7 @@
 		TDS_RUNQ,
 		TDS_RUNNING
 	} td_state;			/* (t) thread state */
+	/* Note: td_state must be accessed using TD_{GET,SET}_STATE(). */
 	union {
 		register_t	tdu_retval[2];
 		off_t		tdu_off;
@@ -540,10 +541,15 @@
 #define	TD_IS_SWAPPED(td)	((td)->td_inhibitors & TDI_SWAPPED)
 #define	TD_ON_LOCK(td)		((td)->td_inhibitors & TDI_LOCK)
 #define	TD_AWAITING_INTR(td)	((td)->td_inhibitors & TDI_IWAIT)
-#define	TD_IS_RUNNING(td)	((td)->td_state == TDS_RUNNING)
-#define	TD_ON_RUNQ(td)		((td)->td_state == TDS_RUNQ)
-#define	TD_CAN_RUN(td)		((td)->td_state == TDS_CAN_RUN)
-#define	TD_IS_INHIBITED(td)	((td)->td_state == TDS_INHIBITED)
+#ifdef _KERNEL
+#define	TD_GET_STATE(td)	atomic_load_int(&(td)->td_state)
+#else
+#define	TD_GET_STATE(td)	((td)->td_state)
+#endif
+#define	TD_IS_RUNNING(td)	(TD_GET_STATE(td) == TDS_RUNNING)
+#define	TD_ON_RUNQ(td)		(TD_GET_STATE(td) == TDS_RUNQ)
+#define	TD_CAN_RUN(td)		(TD_GET_STATE(td) == TDS_CAN_RUN)
+#define	TD_IS_INHIBITED(td)	(TD_GET_STATE(td) == TDS_INHIBITED)
 #define	TD_ON_UPILOCK(td)	((td)->td_flags & TDF_UPIBLOCKED)
 #define TD_IS_IDLETHREAD(td)	((td)->td_flags & TDF_IDLETD)
 
@@ -557,15 +563,15 @@
 	((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" :		\
 	((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding")
 
-#define	TD_SET_INHIB(td, inhib) do {			\
-	(td)->td_state = TDS_INHIBITED;			\
-	(td)->td_inhibitors |= (inhib);			\
+#define	TD_SET_INHIB(td, inhib) do {		\
+	TD_SET_STATE(td, TDS_INHIBITED);	\
+	(td)->td_inhibitors |= (inhib);		\
 } while (0)
 
 #define	TD_CLR_INHIB(td, inhib) do {			\
 	if (((td)->td_inhibitors & (inhib)) &&		\
 	    (((td)->td_inhibitors &= ~(inhib)) == 0))	\
-		(td)->td_state = TDS_CAN_RUN;		\
+		TD_SET_STATE(td, TDS_CAN_RUN);		\
 } while (0)
 
 #define	TD_SET_SLEEPING(td)	TD_SET_INHIB((td), TDI_SLEEPING)
@@ -581,9 +587,15 @@
 #define	TD_CLR_SUSPENDED(td)	TD_CLR_INHIB((td), TDI_SUSPENDED)
 #define	TD_CLR_IWAIT(td)	TD_CLR_INHIB((td), TDI_IWAIT)
 
-#define	TD_SET_RUNNING(td)	(td)->td_state = TDS_RUNNING
-#define	TD_SET_RUNQ(td)		(td)->td_state = TDS_RUNQ
-#define	TD_SET_CAN_RUN(td)	(td)->td_state = TDS_CAN_RUN
+#ifdef _KERNEL
+#define	TD_SET_STATE(td, state)	atomic_store_int(&(td)->td_state, state)
+#else
+#define	TD_SET_STATE(td, state)	(td)->td_state = state
+#endif
+#define	TD_SET_RUNNING(td)	TD_SET_STATE(td, TDS_RUNNING)
+#define	TD_SET_RUNQ(td)		TD_SET_STATE(td, TDS_RUNQ)
+#define	TD_SET_CAN_RUN(td)	TD_SET_STATE(td, TDS_CAN_RUN)
+
 
 #define	TD_SBDRY_INTR(td) \
     (((td)->td_flags & (TDF_SEINTR | TDF_SERESTART)) != 0)
diff --git a/sys/vm/vm_meter.c b/sys/vm/vm_meter.c
--- a/sys/vm/vm_meter.c
+++ b/sys/vm/vm_meter.c
@@ -207,7 +207,7 @@
 		if (p->p_state != PRS_NEW) {
 			FOREACH_THREAD_IN_PROC(p, td) {
 				thread_lock(td);
-				switch (td->td_state) {
+				switch (TD_GET_STATE(td)) {
 				case TDS_INHIBITED:
 					if (TD_IS_SWAPPED(td))
 						total.t_sw++;