ml_iterator_apply

Switch from direct mountlist traversal to mountlist iterator.

diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/compat/common/vfs_syscalls_20.c
--- sys/compat/common/vfs_syscalls_20.c
+++ sys/compat/common/vfs_syscalls_20.c
@@ -203,7 +203,8 @@ compat_20_sys_getfsstat(struct lwp *l, c
 		syscallarg(int) flags;
 	} */
 	int root = 0;
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	struct statvfs *sbuf;
 	struct statfs12 *sfsp;
 	size_t count, maxcount;
@@ -212,16 +213,13 @@ compat_20_sys_getfsstat(struct lwp *l, c
 	sbuf = malloc(sizeof(*sbuf), M_TEMP, M_WAITOK);
 	maxcount = (size_t)SCARG(uap, bufsize) / sizeof(struct statfs12);
 	sfsp = SCARG(uap, buf);
-	mutex_enter(&mountlist_lock);
 	count = 0;
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		if (sfsp && count < maxcount) {
 			error = dostatvfs(mp, sbuf, l, SCARG(uap, flags), 0);
 			if (error) {
-				vfs_unbusy(mp, false, &nmp);
+				mountlist_iterator_done(iter);
 				continue;
 			}
 			error = vfs2fs(sfsp, sbuf);
@@ -233,9 +231,8 @@ compat_20_sys_getfsstat(struct lwp *l, c
 			root |= strcmp(sbuf->f_mntonname, "/") == 0;
 		}
 		count++;
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
 	if (root == 0 && l->l_proc->p_cwdi->cwdi_rdir) {
 		/*
 		 * fake a root entry
@@ -252,6 +249,7 @@ compat_20_sys_getfsstat(struct lwp *l, c
 	else
 		*retval = count;
 out:
+	mountlist_iterator_destroy(iter);
 	free(sbuf, M_TEMP);
 	return error;
 }
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/compat/ndis/subr_ndis.c
--- sys/compat/ndis/subr_ndis.c
+++ sys/compat/ndis/subr_ndis.c
@@ -3042,6 +3042,8 @@ NdisOpenFile(ndis_status *status, ndis_h
 	char			*path;
 	linker_file_t		head, lf;
 	void			*kldstart, *kldend;
+	mount_iterator_t	*iter;
+	struct mount		*mp;
 
 	ndis_unicode_to_ascii(filename->us_buf,
 	    filename->us_len, &afilename);
@@ -3094,7 +3096,11 @@ NdisOpenFile(ndis_status *status, ndis_h
 		return;
 	}
 
-	if (TAILQ_EMPTY(&mountlist)) {
+	mountlist_iterator_init(&iter);
+	if ((mp = mountlist_iterator_next(iter)) != NULL)
+		mountlist_iterator_done(iter);
+	mountlist_iterator_destroy(iter);
+	if (mp == NULL) {
 		ExFreePool(fh);
 		*status = NDIS_STATUS_FILE_NOT_FOUND;
 		printf("NDIS: could not find file %s in linker list\n",
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/compat/netbsd32/netbsd32_compat_20.c
--- sys/compat/netbsd32/netbsd32_compat_20.c
+++ sys/compat/netbsd32/netbsd32_compat_20.c
@@ -85,7 +85,8 @@ compat_20_netbsd32_getfsstat(struct lwp 
 	} */
 	int root = 0;
 	struct proc *p = l->l_proc;
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	struct statvfs *sb;
 	struct netbsd32_statfs sb32;
 	void *sfsp;
@@ -95,16 +96,13 @@ compat_20_netbsd32_getfsstat(struct lwp 
 	sb = STATVFSBUF_GET();
 	maxcount = SCARG(uap, bufsize) / sizeof(struct netbsd32_statfs);
 	sfsp = SCARG_P32(uap, buf);
-	mutex_enter(&mountlist_lock);
+	mountlist_iterator_init(&iter);
 	count = 0;
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		if (sfsp && count < maxcount) {
 			error = dostatvfs(mp, sb, l, SCARG(uap, flags), 0);
 			if (error) {
-				vfs_unbusy(mp, false, &nmp);
+				mountlist_iterator_done(iter);
 				error = 0;
 				continue;
 			}
@@ -118,9 +116,8 @@ compat_20_netbsd32_getfsstat(struct lwp 
 			root |= strcmp(sb->f_mntonname, "/") == 0;
 		}
 		count++;
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
 
 	if (root == 0 && p->p_cwdi->cwdi_rdir) {
 		/*
@@ -144,6 +141,7 @@ compat_20_netbsd32_getfsstat(struct lwp 
 	else
 		*retval = count;
 out:
+	mountlist_iterator_destroy(iter);
 	STATVFSBUF_PUT(sb);
 	return error;
 }
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/compat/osf1/osf1_mount.c
--- sys/compat/osf1/osf1_mount.c
+++ sys/compat/osf1/osf1_mount.c
@@ -132,7 +132,8 @@ osf1_sys_fstatfs(struct lwp *l, const st
 int
 osf1_sys_getfsstat(struct lwp *l, const struct osf1_sys_getfsstat_args *uap, register_t *retval)
 {
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	struct statvfs *sp;
 	struct osf1_statfs osfs;
 	char *osf_sfsp;
@@ -143,13 +144,9 @@ osf1_sys_getfsstat(struct lwp *l, const 
 
 	maxcount = SCARG(uap, bufsize) / sizeof(struct osf1_statfs);
 	osf_sfsp = (void *)SCARG(uap, buf);
-	mutex_enter(&mountlist_lock);
-	for (count = 0, mp = TAILQ_FIRST(&mountlist);
-	    mp != NULL;
-	    mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	mountlist_iterator_init(&iter);
+	count = 0;
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		if (osf_sfsp && count < maxcount) {
 			sp = &mp->mnt_stat;
 			/*
@@ -171,9 +168,9 @@ osf1_sys_getfsstat(struct lwp *l, const 
 			}
 		}
 		count++;
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 	if (osf_sfsp && count > maxcount)
 		*retval = maxcount;
 	else
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/compat/ultrix/ultrix_fs.c
--- sys/compat/ultrix/ultrix_fs.c
+++ sys/compat/ultrix/ultrix_fs.c
@@ -206,9 +206,10 @@ make_ultrix_mntent(struct statvfs *sp, s
 int
 ultrix_sys_getmnt(struct lwp *l, const struct ultrix_sys_getmnt_args *uap, register_t *retval)
 {
-	struct mount *mp, *nmp;
+	struct mount *mp;
 	struct statvfs *sp;
 	struct ultrix_fs_data *sfsp;
+	mount_iterator_t *iter;
 	char *path;
 	int mntflags;
 	int skip;
@@ -216,7 +217,6 @@ ultrix_sys_getmnt(struct lwp *l, const s
 	long count, maxcount;
 	int error;
 
-	nmp = NULL;	/* XXX keep gcc quiet */
 	path = NULL;
 	error = 0;
 	maxcount = SCARG(uap, bufsize) / sizeof(struct ultrix_fs_data);
@@ -247,20 +247,19 @@ ultrix_sys_getmnt(struct lwp *l, const s
 		if ((error = copyin((void *)SCARG(uap, start), &start,
 				    sizeof(*SCARG(uap, start))))  != 0)
 			goto bad;
-		mutex_enter(&mountlist_lock);
-		for (skip = start, mp = TAILQ_FIRST(&mountlist);
+		mountlist_iterator_init(&iter);
+		for (skip = start, mp = mountlist_iterator_next(iter);
 		    mp != NULL && skip-- > 0;
-		    mp = TAILQ_NEXT(mp, mnt_list))
-			continue;
-		mutex_exit(&mountlist_lock);
+		    mp = mountlist_iterator_next(iter)) {
+			mountlist_iterator_done(iter);
+		}
+		mountlist_iterator_destroy(iter);
 	}
 
-	mutex_enter(&mountlist_lock);
-	for (count = 0, mp = TAILQ_FIRST(&mountlist);
-	    mp != NULL && count < maxcount; mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	mountlist_iterator_init(&iter);
+	count = 0;
+	while (count < maxcount &&
+	    (mp = mountlist_iterator_next(iter)) != NULL) {
 		if (sfsp != NULL) {
 			struct ultrix_fs_data tem;
 			sp = &mp->mnt_stat;
@@ -288,9 +287,9 @@ ultrix_sys_getmnt(struct lwp *l, const s
 				count++;
 			}
 		}
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 
 	if (sfsp != NULL && count > maxcount)
 		*retval = maxcount;
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/gdbscripts/vchain
--- sys/gdbscripts/vchain
+++ sys/gdbscripts/vchain
@@ -53,14 +53,18 @@ print vnode chains for all mount points
 end
 
 define mountdump
-	set $mp=mountlist.tqh_first
-	while ($mp)
-		printf "%s on %s type %s, (mp 0x%x, privdata 0x%x)\n", \
-		    $mp->mnt_stat->f_mntfromname, $mp->mnt_stat->f_mntonname, \
-		    $mp->mnt_op->vfs_name, $mp, $mp->mnt_data
-		set $mp=$mp->mnt_list.tqe_next
-		if ((const void *)$mp == (const void *)&mountlist)
-			set $mp = 0
+	set $me=mount_list.tqh_first
+	while ($me)
+		if ($me->me_type == ME_MOUNT)
+			set $mp = $me->me_mount
+			printf "%s on %s type %s, (mp 0x%x, privdata 0x%x)\n", \
+			    $mp->mnt_stat->f_mntfromname, \
+			    $mp->mnt_stat->f_mntonname, \
+			    $mp->mnt_op->vfs_name, $mp, $mp->mnt_data
+		end
+		set $me=$me->me_list.tqe_next
+		if ((const void *)$me == (const void *)&mount_list)
+			set $me = 0
 		end
 	end
 end
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/kern/kern_veriexec.c
--- sys/kern/kern_veriexec.c
+++ sys/kern/kern_veriexec.c
@@ -1363,20 +1363,17 @@ veriexec_file_dump(struct veriexec_file_
 int
 veriexec_dump(struct lwp *l, prop_array_t rarray)
 {
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 
-	mutex_enter(&mountlist_lock);
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-		/* If it fails, the file-system is [being] unmounted. */
-		if (vfs_busy(mp, &nmp) != 0)
-			continue;
-
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		fileassoc_table_run(mp, veriexec_hook,
 		    (fileassoc_cb_t)veriexec_file_dump, rarray);
 
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 
 	return (0);
 }
@@ -1384,24 +1381,21 @@ veriexec_dump(struct lwp *l, prop_array_
 int
 veriexec_flush(struct lwp *l)
 {
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	int error = 0;
 
-	mutex_enter(&mountlist_lock);
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		int lerror;
 
-		/* If it fails, the file-system is [being] unmounted. */
-		if (vfs_busy(mp, &nmp) != 0)
-			continue;
-
 		lerror = veriexec_table_delete(l, mp);
 		if (lerror && lerror != ENOENT)
 			error = lerror;
 
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 
 	return (error);
 }
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/kern/vfs_mount.c
--- sys/kern/vfs_mount.c
+++ sys/kern/vfs_mount.c
@@ -235,11 +235,9 @@ vfs_getnewfsid(struct mount *mp)
 		++xxxfs_mntid;
 	tfsid.__fsid_val[0] = makedev(mtype & 0xff, xxxfs_mntid);
 	tfsid.__fsid_val[1] = mtype;
-	if (!TAILQ_EMPTY(&mountlist)) {
-		while (vfs_getvfs(&tfsid)) {
-			tfsid.__fsid_val[0]++;
-			xxxfs_mntid++;
-		}
+	while (vfs_getvfs(&tfsid)) {
+		tfsid.__fsid_val[0]++;
+		xxxfs_mntid++;
 	}
 	mp->mnt_stat.f_fsidx.__fsid_val[0] = tfsid.__fsid_val[0];
 	mp->mnt_stat.f_fsid = mp->mnt_stat.f_fsidx.__fsid_val[0];
@@ -254,17 +252,20 @@ vfs_getnewfsid(struct mount *mp)
 struct mount *
 vfs_getvfs(fsid_t *fsid)
 {
+	mount_iterator_t *iter;
 	struct mount *mp;
 
-	mutex_enter(&mountlist_lock);
-	TAILQ_FOREACH(mp, &mountlist, mnt_list) {
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		if (mp->mnt_stat.f_fsidx.__fsid_val[0] == fsid->__fsid_val[0] &&
 		    mp->mnt_stat.f_fsidx.__fsid_val[1] == fsid->__fsid_val[1]) {
-			mutex_exit(&mountlist_lock);
-			return (mp);
+			mountlist_iterator_done(iter);
+			mountlist_iterator_destroy(iter);
+			return mp;
 		}
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 	return NULL;
 }
 
@@ -833,6 +834,7 @@ err_unmounted:
 int
 dounmount(struct mount *mp, int flags, struct lwp *l)
 {
+	mount_iterator_t *iter;
 	struct mount *cmp;
 	vnode_t *coveredvp;
 	int error, async, used_syncer, used_extattr;
@@ -846,14 +848,16 @@ dounmount(struct mount *mp, int flags, s
 	/*
 	 * No unmount below layered mounts.
 	 */
-	mutex_enter(&mountlist_lock);
-	TAILQ_FOREACH(cmp, &mountlist, mnt_list) {
+	mountlist_iterator_init(&iter);
+	while ((cmp = mountlist_iterator_next(iter)) != NULL) {
 		if (cmp->mnt_lower == mp) {
-			mutex_exit(&mountlist_lock);
+			mountlist_iterator_done(iter);
+			mountlist_iterator_destroy(iter);
 			return EBUSY;
 		}
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 
 	/*
 	 * XXX Freeze syncer.  Must do this before locking the
@@ -987,16 +991,23 @@ vfs_unmount_print(struct mount *mp, cons
 bool
 vfs_unmount_forceone(struct lwp *l)
 {
+	mount_iterator_t *iter;
 	struct mount *mp, *nmp;
 	int error;
 
 	nmp = NULL;
 
-	TAILQ_FOREACH_REVERSE(mp, &mountlist, mntlist, mnt_list) {
+	mountlist_iterator_init_reverse(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		if (nmp == NULL || mp->mnt_gen > nmp->mnt_gen) {
+			if (nmp)
+				vfs_destroy(nmp);
 			nmp = mp;
+			atomic_inc_uint(&nmp->mnt_refcnt);
 		}
+		mountlist_iterator_done(iter);
 	}
+	mountlist_iterator_destroy(iter);
 	if (nmp == NULL) {
 		return false;
 	}
@@ -1005,7 +1016,6 @@ vfs_unmount_forceone(struct lwp *l)
 	printf("forcefully unmounting %s (%s)...\n",
 	    nmp->mnt_stat.f_mntonname, nmp->mnt_stat.f_mntfromname);
 #endif
-	atomic_inc_uint(&nmp->mnt_refcnt);
 	if ((error = dounmount(nmp, MNT_FORCE, l)) == 0) {
 		vfs_unmount_print(nmp, "forcefully ");
 		return true;
@@ -1024,17 +1034,20 @@ vfs_unmount_forceone(struct lwp *l)
 bool
 vfs_unmountall1(struct lwp *l, bool force, bool verbose)
 {
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	bool any_error = false, progress = false;
 	int error;
 
-	TAILQ_FOREACH_REVERSE_SAFE(mp, &mountlist, mntlist, mnt_list, nmp) {
+	mountlist_iterator_init_reverse(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 #ifdef DEBUG
 		printf("unmounting %p %s (%s)...\n",
 		    (void *)mp, mp->mnt_stat.f_mntonname,
 		    mp->mnt_stat.f_mntfromname);
 #endif
 		atomic_inc_uint(&mp->mnt_refcnt);
+		mountlist_iterator_done(iter);
 		if ((error = dounmount(mp, force ? MNT_FORCE : 0, l)) == 0) {
 			vfs_unmount_print(mp, "");
 			progress = true;
@@ -1047,6 +1060,7 @@ vfs_unmountall1(struct lwp *l, bool forc
 			any_error = true;
 		}
 	}
+	mountlist_iterator_destroy(iter);
 	if (verbose) {
 		printf("unmounting done\n");
 	}
@@ -1230,10 +1244,16 @@ done:
 		vrele(rootvp);
 	}
 	if (error == 0) {
+		mount_iterator_t *iter;
 		struct mount *mp;
 		extern struct cwdinfo cwdi0;
 
-		mp = TAILQ_FIRST(&mountlist);
+		mountlist_iterator_init(&iter);
+		mp = mountlist_iterator_next(iter);
+		KASSERT(mp != NULL);
+		mountlist_iterator_done(iter);
+		mountlist_iterator_destroy(iter);
+
 		mp->mnt_flag |= MNT_ROOTFS;
 		mp->mnt_op->vfs_refcount++;
 		error = fstrans_mount(mp);
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/kern/vfs_subr.c
--- sys/kern/vfs_subr.c
+++ sys/kern/vfs_subr.c
@@ -759,9 +759,10 @@ lazy_sync_vnode(struct vnode *vp)
 void
 sched_sync(void *arg)
 {
+	mount_iterator_t *iter;
 	synclist_t *slp;
 	struct vnode *vp;
-	struct mount *mp, *nmp;
+	struct mount *mp;
 	time_t starttime;
 	bool synced;
 
@@ -773,23 +774,21 @@ sched_sync(void *arg)
 		/*
 		 * Sync mounts whose dirty time has expired.
 		 */
-		mutex_enter(&mountlist_lock);
-		for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
+		mountlist_iterator_init(&iter);
+		while ((mp = mountlist_iterator_next(iter)) != NULL) {
 			if ((mp->mnt_iflag & IMNT_ONWORKLIST) == 0 ||
 			    mp->mnt_synclist_slot != syncer_delayno) {
-				nmp = TAILQ_NEXT(mp, mnt_list);
+				mountlist_iterator_done(iter);
 				continue;
 			}
 			mp->mnt_synclist_slot = sync_delay_slot(sync_delay(mp));
-			if (vfs_busy(mp, &nmp))
-				continue;
 			if (fstrans_start_nowait(mp, FSTRANS_SHARED) == 0) {
 				VFS_SYNC(mp, MNT_LAZY, curlwp->l_cred);
 				fstrans_done(mp);
 			}
-			vfs_unbusy(mp, false, &nmp);
+			mountlist_iterator_done(iter);
 		}
-		mutex_exit(&mountlist_lock);
+		mountlist_iterator_destroy(iter);
 
 		mutex_enter(&syncer_data_lock);
 
@@ -967,8 +966,9 @@ sysctl_kern_vnode(SYSCTLFN_ARGS)
 {
 	char *where = oldp;
 	size_t *sizep = oldlenp;
-	struct mount *mp, *nmp;
+	struct mount *mp;
 	vnode_t *vp, vbuf;
+	mount_iterator_t *iter;
 	struct vnode_iterator *marker;
 	char *bp = where;
 	char *ewhere;
@@ -988,17 +988,15 @@ sysctl_kern_vnode(SYSCTLFN_ARGS)
 	ewhere = where + *sizep;
 
 	sysctl_unlock();
-	mutex_enter(&mountlist_lock);
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		vfs_vnode_iterator_init(mp, &marker);
 		while ((vp = vfs_vnode_iterator_next(marker, NULL, NULL))) {
 			if (bp + VPTRSZ + VNODESZ > ewhere) {
 				vrele(vp);
 				vfs_vnode_iterator_destroy(marker);
 				vfs_unbusy(mp, false, NULL);
+				mountlist_iterator_destroy(iter);
 				sysctl_relock();
 				*sizep = bp - where;
 				return (ENOMEM);
@@ -1009,6 +1007,7 @@ sysctl_kern_vnode(SYSCTLFN_ARGS)
 				vrele(vp);
 				vfs_vnode_iterator_destroy(marker);
 				vfs_unbusy(mp, false, NULL);
+				mountlist_iterator_destroy(iter);
 				sysctl_relock();
 				return (error);
 			}
@@ -1016,9 +1015,9 @@ sysctl_kern_vnode(SYSCTLFN_ARGS)
 			bp += VPTRSZ + VNODESZ;
 		}
 		vfs_vnode_iterator_destroy(marker);
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 	sysctl_relock();
 
 	*sizep = bp - where;
@@ -1549,7 +1548,7 @@ vfs_vnode_lock_print(void *vlock, int fu
 	struct mount *mp;
 	vnode_impl_t *vip;
 
-	TAILQ_FOREACH(mp, &mountlist, mnt_list) {
+	for (mp = _mountlist_next(NULL); mp; mp = _mountlist_next(mp)) {
 		TAILQ_FOREACH(vip, &mp->mnt_vnodelist, vi_mntvnodes) {
 			if (&vip->vi_lock != vlock)
 				continue;
@@ -1656,25 +1655,18 @@ void printlockedvnodes(void);
 void
 printlockedvnodes(void)
 {
-	struct mount *mp, *nmp;
+	struct mount *mp;
 	vnode_t *vp;
 	vnode_impl_t *vip;
 
 	printf("Locked vnodes\n");
-	mutex_enter(&mountlist_lock);
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	for (mp = _mountlist_next(NULL); mp; mp = _mountlist_next(mp)) {
 		TAILQ_FOREACH(vip, &mp->mnt_vnodelist, vi_mntvnodes) {
 			vp = VIMPL_TO_VNODE(vip);
 			if (VOP_ISLOCKED(vp))
 				vprint(NULL, vp);
 		}
-		mutex_enter(&mountlist_lock);
-		vfs_unbusy(mp, false, &nmp);
 	}
-	mutex_exit(&mountlist_lock);
 }
 
 #endif /* DDB || DEBUGPRINT */
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/kern/vfs_syscalls.c
--- sys/kern/vfs_syscalls.c
+++ sys/kern/vfs_syscalls.c
@@ -641,14 +641,12 @@ struct ctldebug debug0 = { "syncprt", &s
 void
 do_sys_sync(struct lwp *l)
 {
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	int asyncflag;
 
-	mutex_enter(&mountlist_lock);
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		fstrans_start(mp, FSTRANS_SHARED);
 		mutex_enter(&mp->mnt_updating);
 		if ((mp->mnt_flag & MNT_RDONLY) == 0) {
@@ -660,9 +658,9 @@ do_sys_sync(struct lwp *l)
 		}
 		mutex_exit(&mp->mnt_updating);
 		fstrans_done(mp);
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 #ifdef DEBUG
 	if (syncprt)
 		vfs_bufstats();
@@ -1251,24 +1249,22 @@ do_sys_getvfsstat(struct lwp *l, void *s
     register_t *retval)
 {
 	int root = 0;
+	mount_iterator_t *iter;
 	struct proc *p = l->l_proc;
-	struct mount *mp, *nmp;
+	struct mount *mp;
 	struct statvfs *sb;
 	size_t count, maxcount;
 	int error = 0;
 
 	sb = STATVFSBUF_GET();
 	maxcount = bufsize / entry_sz;
-	mutex_enter(&mountlist_lock);
 	count = 0;
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-		if (vfs_busy(mp, &nmp)) {
-			continue;
-		}
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		if (sfsp && count < maxcount) {
 			error = dostatvfs(mp, sb, l, flags, 0);
 			if (error) {
-				vfs_unbusy(mp, false, &nmp);
+				mountlist_iterator_done(iter);
 				error = 0;
 				continue;
 			}
@@ -1281,9 +1277,8 @@ do_sys_getvfsstat(struct lwp *l, void *s
 			root |= strcmp(sb->f_mntonname, "/") == 0;
 		}
 		count++;
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
 
 	if (root == 0 && p->p_cwdi->cwdi_rdir) {
 		/*
@@ -1305,6 +1300,7 @@ do_sys_getvfsstat(struct lwp *l, void *s
 	else
 		*retval = count;
 out:
+	mountlist_iterator_destroy(iter);
 	STATVFSBUF_PUT(sb);
 	return error;
 }
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/kern/vfs_trans.c
--- sys/kern/vfs_trans.c
+++ sys/kern/vfs_trans.c
@@ -871,7 +871,7 @@ fstrans_dump(int full)
 				fstrans_print_lwp(p, l, full == 1);
 
 	printf("Fstrans state by mount:\n");
-	TAILQ_FOREACH(mp, &mountlist, mnt_list)
+	for (mp = _mountlist_next(NULL); mp; mp = _mountlist_next(mp))
 		fstrans_print_mount(mp, full == 1);
 }
 #endif /* defined(DDB) */
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/miscfs/procfs/procfs_linux.c
--- sys/miscfs/procfs/procfs_linux.c
+++ sys/miscfs/procfs/procfs_linux.c
@@ -603,26 +603,24 @@ procfs_domounts(struct lwp *curl, struct
 {
 	char *bf, *mtab = NULL;
 	size_t mtabsz = 0;
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	int error = 0, root = 0;
 	struct cwdinfo *cwdi = curl->l_proc->p_cwdi;
 
 	bf = malloc(LBFSZ, M_TEMP, M_WAITOK);
 
-	mutex_enter(&mountlist_lock);
-	for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
+	mountlist_iterator_init(&iter);
+	while ((mp = mountlist_iterator_next(iter)) != NULL) {
 		struct statvfs sfs;
 
-		if (vfs_busy(mp, &nmp))
-			continue;
-
 		if ((error = dostatvfs(mp, &sfs, curl, MNT_WAIT, 0)) == 0)
 			root |= procfs_format_sfs(&mtab, &mtabsz, bf, LBFSZ,
 			    &sfs, curl, 0);
 
-		vfs_unbusy(mp, false, &nmp);
+		mountlist_iterator_done(iter);
 	}
-	mutex_exit(&mountlist_lock);
+	mountlist_iterator_destroy(iter);
 
 	/*
 	 * If we are inside a chroot that is not itself a mount point,
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/ufs/lfs/lfs_bio.c
--- sys/ufs/lfs/lfs_bio.c
+++ sys/ufs/lfs/lfs_bio.c
@@ -514,7 +514,8 @@ void
 lfs_flush(struct lfs *fs, int flags, int only_onefs)
 {
 	extern u_int64_t locked_fakequeue_count;
-	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+	struct mount *mp;
 	struct lfs *tfs;
 
 	KASSERT(mutex_owned(&lfs_lock));
@@ -543,12 +544,8 @@ lfs_flush(struct lfs *fs, int flags, int
 		vfs_unbusy(fs->lfs_ivnode->v_mount, false, NULL);
 	} else {
 		locked_fakequeue_count = 0;
-		mutex_enter(&mountlist_lock);
-		for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
-			if (vfs_busy(mp, &nmp)) {
-				DLOG((DLOG_FLUSH, "lfs_flush: fs vfs_busy\n"));
-				continue;
-			}
+		mountlist_iterator_init(&iter);
+		while ((mp = mountlist_iterator_next(iter)) != NULL) {
 			if (strncmp(&mp->mnt_stat.f_fstypename[0], MOUNT_LFS,
 			    sizeof(mp->mnt_stat.f_fstypename)) == 0) {
 				tfs = VFSTOULFS(mp)->um_lfs;
@@ -556,9 +553,9 @@ lfs_flush(struct lfs *fs, int flags, int
 				lfs_flush_fs(tfs, flags);
 				mutex_exit(&lfs_lock);
 			}
-			vfs_unbusy(mp, false, &nmp);
+			mountlist_iterator_done(iter);
 		}
-		mutex_exit(&mountlist_lock);
+		mountlist_iterator_destroy(iter);
 	}
 	LFS_DEBUG_COUNTLOCKED("flush");
 	wakeup(&lfs_subsys_pages);
diff -r 61eb299077d8 -r 2d7dfb96a6d8 sys/ufs/lfs/lfs_vfsops.c
--- sys/ufs/lfs/lfs_vfsops.c
+++ sys/ufs/lfs/lfs_vfsops.c
@@ -387,11 +387,11 @@ struct pool lfs_lbnentry_pool;
 static void
 lfs_writerd(void *arg)
 {
- 	struct mount *mp, *nmp;
+	mount_iterator_t *iter;
+ 	struct mount *mp;
  	struct lfs *fs;
 	struct vfsops *vfs = NULL;
  	int fsflags;
-	int skipc;
 	int lfsc;
 	int wrote_something = 0;
  
@@ -446,14 +446,9 @@ lfs_writerd(void *arg)
  		 * Look through the list of LFSs to see if any of them
  		 * have requested pageouts.
  		 */
- 		mutex_enter(&mountlist_lock);
+ 		mountlist_iterator_init(&iter);
 		lfsc = 0;
-		skipc = 0;
- 		for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
- 			if (vfs_busy(mp, &nmp)) {
-				++skipc;
- 				continue;
- 			}
+		while ((mp = mountlist_iterator_next(iter)) != NULL) {
 			KASSERT(!mutex_owned(&lfs_lock));
  			if (strncmp(mp->mnt_stat.f_fstypename, MOUNT_LFS,
  			    sizeof(mp->mnt_stat.f_fstypename)) == 0) {
@@ -468,7 +463,7 @@ lfs_writerd(void *arg)
 				if (lfs_sb_getnextseg(fs) < lfs_sb_getcurseg(fs) && fs->lfs_nowrap) {
 					/* Don't try to write if we're suspended */
 					mutex_exit(&lfs_lock);
-					vfs_unbusy(mp, false, &nmp);
+					mountlist_iterator_done(iter);
 					continue;
 				}
 				if (LFS_STARVED_FOR_SEGS(fs)) {
@@ -476,7 +471,7 @@ lfs_writerd(void *arg)
 
 					DLOG((DLOG_FLUSH, "lfs_writerd: need cleaning before writing possible\n"));
 					lfs_wakeup_cleaner(fs);
-					vfs_unbusy(mp, false, &nmp);
+					mountlist_iterator_done(iter);
 					continue;
 				}
 
@@ -503,21 +498,20 @@ lfs_writerd(void *arg)
 				mutex_exit(&lfs_lock);
  			}
 			KASSERT(!mutex_owned(&lfs_lock));
- 			vfs_unbusy(mp, false, &nmp);
+ 			mountlist_iterator_done(iter);
  		}
-		if (lfsc + skipc == 0) {
+		if (lfsc == 0) {
 			mutex_enter(&lfs_lock);
 			lfs_writer_daemon = NULL;
 			mutex_exit(&lfs_lock);
-			mutex_exit(&mountlist_lock);
+			mountlist_iterator_destroy(iter);
 			break;
 		}
- 		mutex_exit(&mountlist_lock);
+ 		mountlist_iterator_destroy(iter);
  
  		mutex_enter(&lfs_lock);
  	}
 	KASSERT(!mutex_owned(&lfs_lock));
-	KASSERT(!mutex_owned(&mountlist_lock));
 
 	/* Give up our extra reference so the module can be unloaded. */
 	mutex_enter(&vfs_list_lock);