Index: nfsclient/nfs_krpc.c
===================================================================
--- nfsclient/nfs_krpc.c	(revision 243732)
+++ nfsclient/nfs_krpc.c	(working copy)
@@ -647,7 +647,6 @@
 	SIGTERM,
 	SIGHUP,
 	SIGKILL,
-	SIGSTOP,
 	SIGQUIT
 };
 
@@ -698,6 +697,7 @@
 	}
 	mtx_unlock(&p->p_sigacts->ps_mtx);
 	PROC_UNLOCK(p);
+	sigdeferstop(td);
 	kern_sigprocmask(td, SIG_SETMASK, &newset, oldset, 0);
 }
 
@@ -707,6 +707,7 @@
 	if (td == NULL)
 		td = curthread; /* XXX */
 	kern_sigprocmask(td, SIG_SETMASK, set, NULL, 0);
+	sigallowstop(td);
 }
 
 /*
Index: kern/kern_sig.c
===================================================================
--- kern/kern_sig.c	(revision 243732)
+++ kern/kern_sig.c	(working copy)
@@ -2339,6 +2337,13 @@
 		}
 
 		/*
+		 * Don't awaken a sleeping thread for SIGSTOP if the
+		 * STOP signal is deferred.
+		 */
+		if ((prop & SA_STOP) && (td->td_flags & TDF_SBDRY))
+			goto out;
+
+		/*
 		 * Give low priority threads a better chance to run.
 		 */
 		if (td->td_priority > PUSER)
@@ -2379,12 +2384,13 @@
 		if ((TD_IS_SLEEPING(td2) || TD_IS_SWAPPED(td2)) &&
 		    (td2->td_flags & TDF_SINTR)) {
 			if (td2->td_flags & TDF_SBDRY) {
-				if (TD_IS_SUSPENDED(td2))
-					wakeup_swapper |=
-					    thread_unsuspend_one(td2);
-				if (TD_ON_SLEEPQ(td2))
-					wakeup_swapper |=
-					    sleepq_abort(td2, ERESTART);
+				/*
+				 * Once a thread is asleep with SBDRY set,
+				 * it should never become suspended due
+				 * to this check.
+				 */
+				KASSERT(!TD_IS_SUSPENDED(td2),
+				    ("thread with deferred stops suspended"));
 			} else if (!TD_IS_SUSPENDED(td2)) {
 				thread_suspend_one(td2);
 			}
@@ -2506,7 +2512,33 @@
 
 }
 
+/* Defer the delivery of SIGSTOP for the current thread. */
+void
+sigdeferstop(struct thread *td)
+{
+
+	KASSERT(!(td->td_flags & TDF_SBDRY),
+	    ("attempt to set TDF_SBDRY recursively"));
+	thread_lock(td);
+	td->td_flags |= TDF_SBDRY;
+	thread_unlock(td);
+}
+
 /*
+ * Permit the delivery of SIGSTOP for the current thread.  This does
+ * not immediately suspend if a stop was posted.  Instead, the thread
+ * will suspend either via ast() or a subsequent interruptible sleep.
+ */
+void
+sigallowstop(struct thread *td)
+{
+
+	thread_lock(td);
+	td->td_flags &= ~TDF_SBDRY;
+	thread_unlock(td);
+}
+
+/*
  * If the current process has received a signal (should be caught or cause
  * termination, should interrupt current syscall), return the signal number.
  * Stop signals with default action are processed immediately, then cleared;
@@ -2540,6 +2572,8 @@
 
 		if (p->p_flag & P_PPWAIT)
 			SIG_STOPSIGMASK(sigpending);
+		if (td->td_flags & TDF_SBDRY)
+			SIG_STOPSIGMASK(sigpending);
 		if (SIGISEMPTY(sigpending))	/* no signal to send */
 			return (0);
 		sig = sig_ffs(&sigpending);
@@ -2653,10 +2687,6 @@
 		    		    (p->p_pgrp->pg_jobc == 0 &&
 				     prop & SA_TTYSTOP))
 					break;	/* == ignore */
-
-				/* Ignore, but do not drop the stop signal. */
-				if (stop_allowed != SIG_STOP_ALLOWED)
-					return (sig);
 				mtx_unlock(&ps->ps_mtx);
 				WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
 				    &p->p_mtx.lock_object, "Catching SIGSTOP");
Index: kern/subr_sleepqueue.c
===================================================================
--- kern/subr_sleepqueue.c	(revision 243732)
+++ kern/subr_sleepqueue.c	(working copy)
@@ -350,8 +350,6 @@
 	if (flags & SLEEPQ_INTERRUPTIBLE) {
 		td->td_flags |= TDF_SINTR;
 		td->td_flags &= ~TDF_SLEEPABORT;
-		if (flags & SLEEPQ_STOP_ON_BDRY)
-			td->td_flags |= TDF_SBDRY;
 	}
 	thread_unlock(td);
 }
@@ -605,7 +601,7 @@
 
 	/* We are no longer in an interruptible sleep. */
 	if (td->td_flags & TDF_SINTR)
-		td->td_flags &= ~(TDF_SINTR | TDF_SBDRY);
+		td->td_flags &= ~TDF_SINTR;
 
 	if (td->td_flags & TDF_SLEEPABORT) {
 		td->td_flags &= ~TDF_SLEEPABORT;
@@ -750,7 +746,7 @@
 
 	td->td_wmesg = NULL;
 	td->td_wchan = NULL;
-	td->td_flags &= ~(TDF_SINTR | TDF_SBDRY);
+	td->td_flags &= ~TDF_SINTR;
 
 	CTR3(KTR_PROC, "sleepq_wakeup: thread %p (pid %ld, %s)",
 	    (void *)td, (long)td->td_proc->p_pid, td->td_name);
Index: fs/nfs/nfs_commonkrpc.c
===================================================================
--- fs/nfs/nfs_commonkrpc.c	(revision 243732)
+++ fs/nfs/nfs_commonkrpc.c	(working copy)
@@ -819,7 +819,6 @@
 	SIGTERM,
 	SIGHUP,
 	SIGKILL,
-	SIGSTOP,
 	SIGQUIT
 };
 
@@ -870,6 +869,7 @@
 	}
 	mtx_unlock(&p->p_sigacts->ps_mtx);
 	PROC_UNLOCK(p);
+	sigdeferstop(td);
 	kern_sigprocmask(td, SIG_SETMASK, &newset, oldset, 0);
 }
 
@@ -879,6 +879,7 @@
 	if (td == NULL)
 		td = curthread; /* XXX */
 	kern_sigprocmask(td, SIG_SETMASK, set, NULL, 0);
+	sigallowstop(td);
 }
 
 /*
Index: sys/signalvar.h
===================================================================
--- sys/signalvar.h	(revision 243732)
+++ sys/signalvar.h	(working copy)
@@ -326,7 +326,9 @@
 /*
  * Machine-independent functions:
  */
 int	cursig(struct thread *td, int stop_allowed);
+void	sigdeferstop(struct thread *td);
+void	sigallowstop(struct thread *td);
 void	execsigs(struct proc *p);
 void	gsignal(int pgid, int sig, ksiginfo_t *ksi);
 void	killproc(struct proc *p, char *why);