diff --git a/sys/kern/sysv_shm.c b/sys/kern/sysv_shm.c
index 64ba74d..24709b0 100644
--- a/sys/kern/sysv_shm.c
+++ b/sys/kern/sysv_shm.c
@@ -181,10 +181,15 @@ SYSCTL_INT(_kern_ipc, OID_AUTO, shm_use_phys, CTLFLAG_RWTUN,
 SYSCTL_INT(_kern_ipc, OID_AUTO, shm_allow_removed, CTLFLAG_RWTUN,
     &shm_allow_removed, 0,
     "Enable/Disable attachment to attached segments marked for removal");
-SYSCTL_PROC(_kern_ipc, OID_AUTO, shmsegs, CTLTYPE_OPAQUE | CTLFLAG_RD,
-    NULL, 0, sysctl_shmsegs, "",
+SYSCTL_PROC(_kern_ipc, OID_AUTO, shmsegs, CTLTYPE_OPAQUE | CTLFLAG_RD |
+    CTLFLAG_MPSAFE, NULL, 0, sysctl_shmsegs, "",
     "Current number of shared memory segments allocated");
 
+static struct sx sysvshmsx;
+#define	SYSVSHM_LOCK()		sx_xlock(&sysvshmsx)
+#define	SYSVSHM_UNLOCK()	sx_xunlock(&sysvshmsx)
+#define	SYSVSHM_ASSERT_LOCKED()	sx_assert(&sysvshmsx, SA_LOCKED)
+
 static int
 shm_find_segment_by_key(key)
 	key_t key;
@@ -237,7 +242,7 @@ shm_deallocate_segment(shmseg)
 {
 	vm_size_t size;
 
-	GIANT_REQUIRED;
+	SYSVSHM_ASSERT_LOCKED();
 
 	vm_object_deallocate(shmseg->object);
 	shmseg->object = NULL;
@@ -261,7 +266,7 @@ shm_delete_mapping(struct vmspace *vm, struct shmmap_state *shmmap_s)
 	int segnum, result;
 	vm_size_t size;
 
-	GIANT_REQUIRED;
+	SYSVSHM_ASSERT_LOCKED();
 
 	segnum = IPCID_TO_IX(shmmap_s->shmid);
 	shmseg = &shmsegs[segnum];
@@ -299,7 +304,7 @@ sys_shmdt(td, uap)
 
 	if (!prison_allow(td->td_ucred, PR_ALLOW_SYSVIPC))
 		return (ENOSYS);
-	mtx_lock(&Giant);
+	SYSVSHM_LOCK();
 	shmmap_s = p->p_vmspace->vm_shm;
  	if (shmmap_s == NULL) {
 		error = EINVAL;
@@ -323,7 +328,7 @@ sys_shmdt(td, uap)
 #endif
 	error = shm_delete_mapping(p->p_vmspace, shmmap_s);
 done2:
-	mtx_unlock(&Giant);
+	SYSVSHM_UNLOCK();
 	return (error);
 }
 
@@ -353,27 +358,15 @@ kern_shmat(td, shmid, shmaddr, shmflg)
 
 	if (!prison_allow(td->td_ucred, PR_ALLOW_SYSVIPC))
 		return (ENOSYS);
-	mtx_lock(&Giant);
+	SYSVSHM_LOCK();
 	shmmap_s = p->p_vmspace->vm_shm;
 	if (shmmap_s == NULL) {
 		shmmap_s = malloc(shminfo.shmseg * sizeof(struct shmmap_state),
 		    M_SHM, M_WAITOK);
-
-		/*
-		 * If malloc() above sleeps, the Giant lock is
-		 * temporarily dropped, which allows another thread to
-		 * allocate shmmap_state and set vm_shm.  Recheck
-		 * vm_shm and free the new shmmap_state if another one
-		 * is already allocated.
-		 */
-		if (p->p_vmspace->vm_shm != NULL) {
-			free(shmmap_s, M_SHM);
-			shmmap_s = p->p_vmspace->vm_shm;
-		} else {
-			for (i = 0; i < shminfo.shmseg; i++)
-				shmmap_s[i].shmid = -1;
-			p->p_vmspace->vm_shm = shmmap_s;
-		}
+		for (i = 0; i < shminfo.shmseg; i++)
+			shmmap_s[i].shmid = -1;
+		KASSERT(p->p_vmspace->vm_shm == NULL, ("raced"));
+		p->p_vmspace->vm_shm = shmmap_s;
 	}
 	shmseg = shm_find_segment_by_shmid(shmid);
 	if (shmseg == NULL) {
@@ -439,7 +432,7 @@ kern_shmat(td, shmid, shmaddr, shmflg)
 	shmseg->u.shm_nattch++;
 	td->td_retval[0] = attach_va;
 done2:
-	mtx_unlock(&Giant);
+	SYSVSHM_UNLOCK();
 	return (error);
 }
 
@@ -465,7 +458,7 @@ kern_shmctl(td, shmid, cmd, buf, bufsz)
 	if (!prison_allow(td->td_ucred, PR_ALLOW_SYSVIPC))
 		return (ENOSYS);
 
-	mtx_lock(&Giant);
+	SYSVSHM_LOCK();
 	switch (cmd) {
 	/*
 	 * It is possible that kern_shmctl is being called from the Linux ABI
@@ -557,7 +550,7 @@ kern_shmctl(td, shmid, cmd, buf, bufsz)
 		break;
 	}
 done2:
-	mtx_unlock(&Giant);
+	SYSVSHM_UNLOCK();
 	return (error);
 }
 
@@ -622,6 +615,7 @@ shmget_existing(td, uap, mode, segnum)
 	struct shmid_kernel *shmseg;
 	int error;
 
+	SYSVSHM_ASSERT_LOCKED();
 	shmseg = &shmsegs[segnum];
 	if (shmseg->u.shm_perm.mode & SHMSEG_REMOVED) {
 		/*
@@ -630,7 +624,8 @@ shmget_existing(td, uap, mode, segnum)
 		 * allocation failed or it was freed).
 		 */
 		shmseg->u.shm_perm.mode |= SHMSEG_WANTED;
-		error = tsleep(shmseg, PLOCK | PCATCH, "shmget", 0);
+		error = sx_sleep(shmseg, &sysvshmsx, PLOCK | PCATCH,
+		    "shmget", 0);
 		if (error)
 			return (error);
 		return (EAGAIN);
@@ -660,7 +655,7 @@ shmget_allocate_segment(td, uap, mode)
 	struct shmid_kernel *shmseg;
 	vm_object_t shm_object;
 
-	GIANT_REQUIRED;
+	SYSVSHM_ASSERT_LOCKED();
 
 	if (uap->size < shminfo.shmmin || uap->size > shminfo.shmmax)
 		return (EINVAL);
@@ -770,7 +765,7 @@ sys_shmget(td, uap)
 
 	if (!prison_allow(td->td_ucred, PR_ALLOW_SYSVIPC))
 		return (ENOSYS);
-	mtx_lock(&Giant);
+	SYSVSHM_LOCK();
 	mode = uap->shmflg & ACCESSPERMS;
 	if (uap->key != IPC_PRIVATE) {
 	again:
@@ -788,7 +783,7 @@ sys_shmget(td, uap)
 	}
 	error = shmget_allocate_segment(td, uap, mode);
 done2:
-	mtx_unlock(&Giant);
+	SYSVSHM_UNLOCK();
 	return (error);
 }
 
@@ -800,15 +795,16 @@ shmfork_myhook(p1, p2)
 	size_t size;
 	int i;
 
-	mtx_lock(&Giant);
+	SYSVSHM_LOCK();
 	size = shminfo.shmseg * sizeof(struct shmmap_state);
 	shmmap_s = malloc(size, M_SHM, M_WAITOK);
 	bcopy(p1->p_vmspace->vm_shm, shmmap_s, size);
 	p2->p_vmspace->vm_shm = shmmap_s;
-	for (i = 0; i < shminfo.shmseg; i++, shmmap_s++)
+	for (i = 0; i < shminfo.shmseg; i++, shmmap_s++) {
 		if (shmmap_s->shmid != -1)
 			shmsegs[IPCID_TO_IX(shmmap_s->shmid)].u.shm_nattch++;
-	mtx_unlock(&Giant);
+	}
+	SYSVSHM_UNLOCK();
 }
 
 static void
@@ -817,16 +813,16 @@ shmexit_myhook(struct vmspace *vm)
 	struct shmmap_state *base, *shm;
 	int i;
 
+	SYSVSHM_LOCK();
 	if ((base = vm->vm_shm) != NULL) {
 		vm->vm_shm = NULL;
-		mtx_lock(&Giant);
 		for (i = 0, shm = base; i < shminfo.shmseg; i++, shm++) {
 			if (shm->shmid != -1)
 				shm_delete_mapping(vm, shm);
 		}
-		mtx_unlock(&Giant);
 		free(base, M_SHM);
 	}
+	SYSVSHM_UNLOCK();
 }
 
 static void
@@ -919,6 +915,7 @@ shminit()
 	shm_last_free = 0;
 	shm_nused = 0;
 	shm_committed = 0;
+	sx_init(&sysvshmsx, "sysvshmsx");
 	shmexit_hook = &shmexit_myhook;
 	shmfork_hook = &shmfork_myhook;
 
@@ -961,14 +958,19 @@ shmunload()
 	free(shmsegs, M_SHM);
 	shmexit_hook = NULL;
 	shmfork_hook = NULL;
+	sx_destroy(&sysvshmsx);
 	return (0);
 }
 
 static int
 sysctl_shmsegs(SYSCTL_HANDLER_ARGS)
 {
+	int error;
 
-	return (SYSCTL_OUT(req, shmsegs, shmalloced * sizeof(shmsegs[0])));
+	SYSVSHM_LOCK();
+	error = SYSCTL_OUT(req, shmsegs, shmalloced * sizeof(shmsegs[0]));
+	SYSVSHM_UNLOCK();
+	return (error);
 }
 
 #if defined(__i386__) && (defined(COMPAT_FREEBSD4) || defined(COMPAT_43))
@@ -1000,7 +1002,7 @@ oshmctl(struct thread *td, struct oshmctl_args *uap)
 
 	if (!prison_allow(td->td_ucred, PR_ALLOW_SYSVIPC))
 		return (ENOSYS);
-	mtx_lock(&Giant);
+	SYSVSHM_LOCK();
 	shmseg = shm_find_segment_by_shmid(uap->shmid);
 	if (shmseg == NULL) {
 		error = EINVAL;
@@ -1034,7 +1036,7 @@ oshmctl(struct thread *td, struct oshmctl_args *uap)
 		break;
 	}
 done2:
-	mtx_unlock(&Giant);
+	SYSVSHM_UNLOCK();
 	return (error);
 #else
 	return (EINVAL);
@@ -1066,9 +1068,9 @@ sys_shmsys(td, uap)
 	if (uap->which < 0 ||
 	    uap->which >= sizeof(shmcalls)/sizeof(shmcalls[0]))
 		return (EINVAL);
-	mtx_lock(&Giant);
+	SYSVSHM_LOCK();
 	error = (*shmcalls[uap->which])(td, &uap->a2);
-	mtx_unlock(&Giant);
+	SYSVSHM_UNLOCK();
 	return (error);
 }