diff --git a/sys/alpha/include/mutex.h b/sys/alpha/include/mutex.h
index 9b04128e964a..a6e295d612d0 100644
--- a/sys/alpha/include/mutex.h
+++ b/sys/alpha/include/mutex.h
@@ -36,8 +36,6 @@
 
 #ifdef _KERNEL
 
-#define	mtx_legal2block()						\
-	((alpha_pal_rdps() & ALPHA_PSL_IPL_MASK) == ALPHA_PSL_IPL_0)
 #define	mtx_intr_enable(mutex)	(mutex)->mtx_saveintr = ALPHA_PSL_IPL_0
 
 /*
diff --git a/sys/amd64/include/mutex.h b/sys/amd64/include/mutex.h
index a5f88dea236c..4184cde390f9 100644
--- a/sys/amd64/include/mutex.h
+++ b/sys/amd64/include/mutex.h
@@ -40,7 +40,6 @@
 /* Global locks */
 extern struct mtx	clock_lock;
 
-#define	mtx_legal2block()	(read_eflags() & PSL_I)
 #define	mtx_intr_enable(mutex)	(mutex)->mtx_saveintr |= PSL_I
 
 /*
diff --git a/sys/i386/include/mutex.h b/sys/i386/include/mutex.h
index a5f88dea236c..4184cde390f9 100644
--- a/sys/i386/include/mutex.h
+++ b/sys/i386/include/mutex.h
@@ -40,7 +40,6 @@
 /* Global locks */
 extern struct mtx	clock_lock;
 
-#define	mtx_legal2block()	(read_eflags() & PSL_I)
 #define	mtx_intr_enable(mutex)	(mutex)->mtx_saveintr |= PSL_I
 
 /*
diff --git a/sys/ia64/include/mutex.h b/sys/ia64/include/mutex.h
index 809a56eb7377..f325f2b307f8 100644
--- a/sys/ia64/include/mutex.h
+++ b/sys/ia64/include/mutex.h
@@ -38,7 +38,6 @@
 
 #ifdef _KERNEL
 
-#define	mtx_legal2block()	(ia64_get_psr() & IA64_PSR_I)
 #define	mtx_intr_enable(mutex)	(mutex)->mtx_saveintr |= IA64_PSR_I
 
 #endif	/* _KERNEL */
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index c6776de0a23b..2f9b3aa79802 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -406,6 +406,10 @@ fork1(p1, flags, procp)
 	if (p1->p_sflag & PS_PROFIL)
 		startprofclock(p2);
 	mtx_unlock_spin(&sched_lock);
+	/*
+	 * We start off holding one spinlock after fork: sched_lock.
+	 */
+	p2->p_spinlocks = 1;
 	PROC_UNLOCK(p2);
 	MALLOC(p2->p_cred, struct pcred *, sizeof(struct pcred),
 	    M_SUBPROC, M_WAITOK);
diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
index 1ca5cca6eaab..6540b561b66e 100644
--- a/sys/kern/kern_mutex.c
+++ b/sys/kern/kern_mutex.c
@@ -1094,6 +1094,8 @@ witness_enter(struct mtx *m, int flags, const char *file, int line)
 		}
 		PCPU_SET(witness_spin_check, i | w->w_level);
 		mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
+		p->p_spinlocks++;
+		MPASS(p->p_spinlocks > 0);
 		w->w_file = file;
 		w->w_line = line;
 		m->mtx_line = line;
@@ -1116,7 +1118,7 @@ witness_enter(struct mtx *m, int flags, const char *file, int line)
 	if (cold)
 		goto out;
 
-	if (!mtx_legal2block())
+	if (p->p_spinlocks != 0)
 		panic("blockable mtx_lock() of %s when not legal @ %s:%d",
 			    m->mtx_description, file, line);
 	/*
@@ -1263,10 +1265,12 @@ void
 witness_exit(struct mtx *m, int flags, const char *file, int line)
 {
 	struct witness *w;
+	struct proc *p;
 
 	if (witness_cold || m->mtx_witness == NULL || panicstr)
 		return;
 	w = m->mtx_witness;
+	p = curproc;
 
 	if (flags & MTX_SPIN) {
 		if ((m->mtx_flags & MTX_SPIN) == 0)
@@ -1283,6 +1287,8 @@ witness_exit(struct mtx *m, int flags, const char *file, int line)
 		PCPU_SET(witness_spin_check,
 		    PCPU_GET(witness_spin_check) & ~w->w_level);
 		mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
+		MPASS(p->p_spinlocks > 0);
+		p->p_spinlocks--;
 		return;
 	}
 	if ((m->mtx_flags & MTX_SPIN) != 0)
@@ -1297,7 +1303,7 @@ witness_exit(struct mtx *m, int flags, const char *file, int line)
 		return;
 	}
 
-	if ((flags & MTX_NOSWITCH) == 0 && !mtx_legal2block() && !cold)
+	if ((flags & MTX_NOSWITCH) == 0 && p->p_spinlocks != 0 && !cold)
 		panic("switchable mtx_unlock() of %s when not legal @ %s:%d",
 			    m->mtx_description, file, line);
 	LIST_REMOVE(m, mtx_held);
diff --git a/sys/kern/subr_turnstile.c b/sys/kern/subr_turnstile.c
index 1ca5cca6eaab..6540b561b66e 100644
--- a/sys/kern/subr_turnstile.c
+++ b/sys/kern/subr_turnstile.c
@@ -1094,6 +1094,8 @@ witness_enter(struct mtx *m, int flags, const char *file, int line)
 		}
 		PCPU_SET(witness_spin_check, i | w->w_level);
 		mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
+		p->p_spinlocks++;
+		MPASS(p->p_spinlocks > 0);
 		w->w_file = file;
 		w->w_line = line;
 		m->mtx_line = line;
@@ -1116,7 +1118,7 @@ witness_enter(struct mtx *m, int flags, const char *file, int line)
 	if (cold)
 		goto out;
 
-	if (!mtx_legal2block())
+	if (p->p_spinlocks != 0)
 		panic("blockable mtx_lock() of %s when not legal @ %s:%d",
 			    m->mtx_description, file, line);
 	/*
@@ -1263,10 +1265,12 @@ void
 witness_exit(struct mtx *m, int flags, const char *file, int line)
 {
 	struct witness *w;
+	struct proc *p;
 
 	if (witness_cold || m->mtx_witness == NULL || panicstr)
 		return;
 	w = m->mtx_witness;
+	p = curproc;
 
 	if (flags & MTX_SPIN) {
 		if ((m->mtx_flags & MTX_SPIN) == 0)
@@ -1283,6 +1287,8 @@ witness_exit(struct mtx *m, int flags, const char *file, int line)
 		PCPU_SET(witness_spin_check,
 		    PCPU_GET(witness_spin_check) & ~w->w_level);
 		mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
+		MPASS(p->p_spinlocks > 0);
+		p->p_spinlocks--;
 		return;
 	}
 	if ((m->mtx_flags & MTX_SPIN) != 0)
@@ -1297,7 +1303,7 @@ witness_exit(struct mtx *m, int flags, const char *file, int line)
 		return;
 	}
 
-	if ((flags & MTX_NOSWITCH) == 0 && !mtx_legal2block() && !cold)
+	if ((flags & MTX_NOSWITCH) == 0 && p->p_spinlocks != 0 && !cold)
 		panic("switchable mtx_unlock() of %s when not legal @ %s:%d",
 			    m->mtx_description, file, line);
 	LIST_REMOVE(m, mtx_held);
diff --git a/sys/kern/subr_witness.c b/sys/kern/subr_witness.c
index 1ca5cca6eaab..6540b561b66e 100644
--- a/sys/kern/subr_witness.c
+++ b/sys/kern/subr_witness.c
@@ -1094,6 +1094,8 @@ witness_enter(struct mtx *m, int flags, const char *file, int line)
 		}
 		PCPU_SET(witness_spin_check, i | w->w_level);
 		mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
+		p->p_spinlocks++;
+		MPASS(p->p_spinlocks > 0);
 		w->w_file = file;
 		w->w_line = line;
 		m->mtx_line = line;
@@ -1116,7 +1118,7 @@ witness_enter(struct mtx *m, int flags, const char *file, int line)
 	if (cold)
 		goto out;
 
-	if (!mtx_legal2block())
+	if (p->p_spinlocks != 0)
 		panic("blockable mtx_lock() of %s when not legal @ %s:%d",
 			    m->mtx_description, file, line);
 	/*
@@ -1263,10 +1265,12 @@ void
 witness_exit(struct mtx *m, int flags, const char *file, int line)
 {
 	struct witness *w;
+	struct proc *p;
 
 	if (witness_cold || m->mtx_witness == NULL || panicstr)
 		return;
 	w = m->mtx_witness;
+	p = curproc;
 
 	if (flags & MTX_SPIN) {
 		if ((m->mtx_flags & MTX_SPIN) == 0)
@@ -1283,6 +1287,8 @@ witness_exit(struct mtx *m, int flags, const char *file, int line)
 		PCPU_SET(witness_spin_check,
 		    PCPU_GET(witness_spin_check) & ~w->w_level);
 		mtx_unlock_spin_flags(&w_mtx, MTX_QUIET);
+		MPASS(p->p_spinlocks > 0);
+		p->p_spinlocks--;
 		return;
 	}
 	if ((m->mtx_flags & MTX_SPIN) != 0)
@@ -1297,7 +1303,7 @@ witness_exit(struct mtx *m, int flags, const char *file, int line)
 		return;
 	}
 
-	if ((flags & MTX_NOSWITCH) == 0 && !mtx_legal2block() && !cold)
+	if ((flags & MTX_NOSWITCH) == 0 && p->p_spinlocks != 0 && !cold)
 		panic("switchable mtx_unlock() of %s when not legal @ %s:%d",
 			    m->mtx_description, file, line);
 	LIST_REMOVE(m, mtx_held);
diff --git a/sys/powerpc/include/mutex.h b/sys/powerpc/include/mutex.h
index 9b04128e964a..a6e295d612d0 100644
--- a/sys/powerpc/include/mutex.h
+++ b/sys/powerpc/include/mutex.h
@@ -36,8 +36,6 @@
 
 #ifdef _KERNEL
 
-#define	mtx_legal2block()						\
-	((alpha_pal_rdps() & ALPHA_PSL_IPL_MASK) == ALPHA_PSL_IPL_0)
 #define	mtx_intr_enable(mutex)	(mutex)->mtx_saveintr = ALPHA_PSL_IPL_0
 
 /*
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index e96dffa0b7f3..b77d49ec2077 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -213,6 +213,7 @@ struct	proc {
 	struct	vnode *p_textvp;	/* (b) Vnode of executable. */
 
 	struct	mtx p_mtx;		/* (k) Lock for this struct. */
+	u_int	p_spinlocks;		/* (k) Count of held spin locks. */
 	char	p_lock;		/* (c) Process lock (prevent swap) count. */
 	u_char	p_oncpu;		/* (j) Which cpu we are on. */
 	u_char	p_lastcpu;		/* (j) Last cpu we were on. */