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1/*
2 * linux/fs/pnode.c
3 *
4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai (linuxram@us.ibm.com)
7 *
8 */
9#include <linux/mnt_namespace.h>
10#include <linux/mount.h>
11#include <linux/fs.h>
12#include <linux/nsproxy.h>
13#include "internal.h"
14#include "pnode.h"
15
16/* return the next shared peer mount of @p */
17static inline struct mount *next_peer(struct mount *p)
18{
19 return list_entry(p->mnt_share.next, struct mount, mnt_share);
20}
21
22static inline struct mount *first_slave(struct mount *p)
23{
24 return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
25}
26
27static inline struct mount *next_slave(struct mount *p)
28{
29 return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
30}
31
32static struct mount *get_peer_under_root(struct mount *mnt,
33 struct mnt_namespace *ns,
34 const struct path *root)
35{
36 struct mount *m = mnt;
37
38 do {
39 /* Check the namespace first for optimization */
40 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
41 return m;
42
43 m = next_peer(m);
44 } while (m != mnt);
45
46 return NULL;
47}
48
49/*
50 * Get ID of closest dominating peer group having a representative
51 * under the given root.
52 *
53 * Caller must hold namespace_sem
54 */
55int get_dominating_id(struct mount *mnt, const struct path *root)
56{
57 struct mount *m;
58
59 for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
60 struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
61 if (d)
62 return d->mnt_group_id;
63 }
64
65 return 0;
66}
67
68static int do_make_slave(struct mount *mnt)
69{
70 struct mount *master, *slave_mnt;
71
72 if (list_empty(&mnt->mnt_share)) {
73 if (IS_MNT_SHARED(mnt)) {
74 mnt_release_group_id(mnt);
75 CLEAR_MNT_SHARED(mnt);
76 }
77 master = mnt->mnt_master;
78 if (!master) {
79 struct list_head *p = &mnt->mnt_slave_list;
80 while (!list_empty(p)) {
81 slave_mnt = list_first_entry(p,
82 struct mount, mnt_slave);
83 list_del_init(&slave_mnt->mnt_slave);
84 slave_mnt->mnt_master = NULL;
85 }
86 return 0;
87 }
88 } else {
89 struct mount *m;
90 /*
91 * slave 'mnt' to a peer mount that has the
92 * same root dentry. If none is available then
93 * slave it to anything that is available.
94 */
95 for (m = master = next_peer(mnt); m != mnt; m = next_peer(m)) {
96 if (m->mnt.mnt_root == mnt->mnt.mnt_root) {
97 master = m;
98 break;
99 }
100 }
101 list_del_init(&mnt->mnt_share);
102 mnt->mnt_group_id = 0;
103 CLEAR_MNT_SHARED(mnt);
104 }
105 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
106 slave_mnt->mnt_master = master;
107 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
108 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
109 INIT_LIST_HEAD(&mnt->mnt_slave_list);
110 mnt->mnt_master = master;
111 return 0;
112}
113
114/*
115 * vfsmount lock must be held for write
116 */
117void change_mnt_propagation(struct mount *mnt, int type)
118{
119 if (type == MS_SHARED) {
120 set_mnt_shared(mnt);
121 return;
122 }
123 do_make_slave(mnt);
124 if (type != MS_SLAVE) {
125 list_del_init(&mnt->mnt_slave);
126 mnt->mnt_master = NULL;
127 if (type == MS_UNBINDABLE)
128 mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
129 else
130 mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
131 }
132}
133
134/*
135 * get the next mount in the propagation tree.
136 * @m: the mount seen last
137 * @origin: the original mount from where the tree walk initiated
138 *
139 * Note that peer groups form contiguous segments of slave lists.
140 * We rely on that in get_source() to be able to find out if
141 * vfsmount found while iterating with propagation_next() is
142 * a peer of one we'd found earlier.
143 */
144static struct mount *propagation_next(struct mount *m,
145 struct mount *origin)
146{
147 /* are there any slaves of this mount? */
148 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
149 return first_slave(m);
150
151 while (1) {
152 struct mount *master = m->mnt_master;
153
154 if (master == origin->mnt_master) {
155 struct mount *next = next_peer(m);
156 return (next == origin) ? NULL : next;
157 } else if (m->mnt_slave.next != &master->mnt_slave_list)
158 return next_slave(m);
159
160 /* back at master */
161 m = master;
162 }
163}
164
165static struct mount *next_group(struct mount *m, struct mount *origin)
166{
167 while (1) {
168 while (1) {
169 struct mount *next;
170 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
171 return first_slave(m);
172 next = next_peer(m);
173 if (m->mnt_group_id == origin->mnt_group_id) {
174 if (next == origin)
175 return NULL;
176 } else if (m->mnt_slave.next != &next->mnt_slave)
177 break;
178 m = next;
179 }
180 /* m is the last peer */
181 while (1) {
182 struct mount *master = m->mnt_master;
183 if (m->mnt_slave.next != &master->mnt_slave_list)
184 return next_slave(m);
185 m = next_peer(master);
186 if (master->mnt_group_id == origin->mnt_group_id)
187 break;
188 if (master->mnt_slave.next == &m->mnt_slave)
189 break;
190 m = master;
191 }
192 if (m == origin)
193 return NULL;
194 }
195}
196
197/* all accesses are serialized by namespace_sem */
198static struct user_namespace *user_ns;
199static struct mount *last_dest, *first_source, *last_source, *dest_master;
200static struct mountpoint *mp;
201static struct hlist_head *list;
202
203static inline bool peers(struct mount *m1, struct mount *m2)
204{
205 return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
206}
207
208static int propagate_one(struct mount *m)
209{
210 struct mount *child;
211 int type;
212 /* skip ones added by this propagate_mnt() */
213 if (IS_MNT_NEW(m))
214 return 0;
215 /* skip if mountpoint isn't covered by it */
216 if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
217 return 0;
218 if (peers(m, last_dest)) {
219 type = CL_MAKE_SHARED;
220 } else {
221 struct mount *n, *p;
222 bool done;
223 for (n = m; ; n = p) {
224 p = n->mnt_master;
225 if (p == dest_master || IS_MNT_MARKED(p))
226 break;
227 }
228 do {
229 struct mount *parent = last_source->mnt_parent;
230 if (last_source == first_source)
231 break;
232 done = parent->mnt_master == p;
233 if (done && peers(n, parent))
234 break;
235 last_source = last_source->mnt_master;
236 } while (!done);
237
238 type = CL_SLAVE;
239 /* beginning of peer group among the slaves? */
240 if (IS_MNT_SHARED(m))
241 type |= CL_MAKE_SHARED;
242 }
243
244 /* Notice when we are propagating across user namespaces */
245 if (m->mnt_ns->user_ns != user_ns)
246 type |= CL_UNPRIVILEGED;
247 child = copy_tree(last_source, last_source->mnt.mnt_root, type);
248 if (IS_ERR(child))
249 return PTR_ERR(child);
250 child->mnt.mnt_flags &= ~MNT_LOCKED;
251 mnt_set_mountpoint(m, mp, child);
252 last_dest = m;
253 last_source = child;
254 if (m->mnt_master != dest_master) {
255 read_seqlock_excl(&mount_lock);
256 SET_MNT_MARK(m->mnt_master);
257 read_sequnlock_excl(&mount_lock);
258 }
259 hlist_add_head(&child->mnt_hash, list);
260 return count_mounts(m->mnt_ns, child);
261}
262
263/*
264 * mount 'source_mnt' under the destination 'dest_mnt' at
265 * dentry 'dest_dentry'. And propagate that mount to
266 * all the peer and slave mounts of 'dest_mnt'.
267 * Link all the new mounts into a propagation tree headed at
268 * source_mnt. Also link all the new mounts using ->mnt_list
269 * headed at source_mnt's ->mnt_list
270 *
271 * @dest_mnt: destination mount.
272 * @dest_dentry: destination dentry.
273 * @source_mnt: source mount.
274 * @tree_list : list of heads of trees to be attached.
275 */
276int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
277 struct mount *source_mnt, struct hlist_head *tree_list)
278{
279 struct mount *m, *n;
280 int ret = 0;
281
282 /*
283 * we don't want to bother passing tons of arguments to
284 * propagate_one(); everything is serialized by namespace_sem,
285 * so globals will do just fine.
286 */
287 user_ns = current->nsproxy->mnt_ns->user_ns;
288 last_dest = dest_mnt;
289 first_source = source_mnt;
290 last_source = source_mnt;
291 mp = dest_mp;
292 list = tree_list;
293 dest_master = dest_mnt->mnt_master;
294
295 /* all peers of dest_mnt, except dest_mnt itself */
296 for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
297 ret = propagate_one(n);
298 if (ret)
299 goto out;
300 }
301
302 /* all slave groups */
303 for (m = next_group(dest_mnt, dest_mnt); m;
304 m = next_group(m, dest_mnt)) {
305 /* everything in that slave group */
306 n = m;
307 do {
308 ret = propagate_one(n);
309 if (ret)
310 goto out;
311 n = next_peer(n);
312 } while (n != m);
313 }
314out:
315 read_seqlock_excl(&mount_lock);
316 hlist_for_each_entry(n, tree_list, mnt_hash) {
317 m = n->mnt_parent;
318 if (m->mnt_master != dest_mnt->mnt_master)
319 CLEAR_MNT_MARK(m->mnt_master);
320 }
321 read_sequnlock_excl(&mount_lock);
322 return ret;
323}
324
325static struct mount *find_topper(struct mount *mnt)
326{
327 /* If there is exactly one mount covering mnt completely return it. */
328 struct mount *child;
329
330 if (!list_is_singular(&mnt->mnt_mounts))
331 return NULL;
332
333 child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
334 if (child->mnt_mountpoint != mnt->mnt.mnt_root)
335 return NULL;
336
337 return child;
338}
339
340/*
341 * return true if the refcount is greater than count
342 */
343static inline int do_refcount_check(struct mount *mnt, int count)
344{
345 return mnt_get_count(mnt) > count;
346}
347
348/*
349 * check if the mount 'mnt' can be unmounted successfully.
350 * @mnt: the mount to be checked for unmount
351 * NOTE: unmounting 'mnt' would naturally propagate to all
352 * other mounts its parent propagates to.
353 * Check if any of these mounts that **do not have submounts**
354 * have more references than 'refcnt'. If so return busy.
355 *
356 * vfsmount lock must be held for write
357 */
358int propagate_mount_busy(struct mount *mnt, int refcnt)
359{
360 struct mount *m, *child, *topper;
361 struct mount *parent = mnt->mnt_parent;
362
363 if (mnt == parent)
364 return do_refcount_check(mnt, refcnt);
365
366 /*
367 * quickly check if the current mount can be unmounted.
368 * If not, we don't have to go checking for all other
369 * mounts
370 */
371 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
372 return 1;
373
374 for (m = propagation_next(parent, parent); m;
375 m = propagation_next(m, parent)) {
376 int count = 1;
377 child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
378 if (!child)
379 continue;
380
381 /* Is there exactly one mount on the child that covers
382 * it completely whose reference should be ignored?
383 */
384 topper = find_topper(child);
385 if (topper)
386 count += 1;
387 else if (!list_empty(&child->mnt_mounts))
388 continue;
389
390 if (do_refcount_check(child, count))
391 return 1;
392 }
393 return 0;
394}
395
396/*
397 * Clear MNT_LOCKED when it can be shown to be safe.
398 *
399 * mount_lock lock must be held for write
400 */
401void propagate_mount_unlock(struct mount *mnt)
402{
403 struct mount *parent = mnt->mnt_parent;
404 struct mount *m, *child;
405
406 BUG_ON(parent == mnt);
407
408 for (m = propagation_next(parent, parent); m;
409 m = propagation_next(m, parent)) {
410 child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
411 if (child)
412 child->mnt.mnt_flags &= ~MNT_LOCKED;
413 }
414}
415
416/*
417 * Mark all mounts that the MNT_LOCKED logic will allow to be unmounted.
418 */
419static void mark_umount_candidates(struct mount *mnt)
420{
421 struct mount *parent = mnt->mnt_parent;
422 struct mount *m;
423
424 BUG_ON(parent == mnt);
425
426 for (m = propagation_next(parent, parent); m;
427 m = propagation_next(m, parent)) {
428 struct mount *child = __lookup_mnt(&m->mnt,
429 mnt->mnt_mountpoint);
430 if (!child || (child->mnt.mnt_flags & MNT_UMOUNT))
431 continue;
432 if (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m)) {
433 SET_MNT_MARK(child);
434 }
435 }
436}
437
438/*
439 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
440 * parent propagates to.
441 */
442static void __propagate_umount(struct mount *mnt)
443{
444 struct mount *parent = mnt->mnt_parent;
445 struct mount *m;
446
447 BUG_ON(parent == mnt);
448
449 for (m = propagation_next(parent, parent); m;
450 m = propagation_next(m, parent)) {
451 struct mount *topper;
452 struct mount *child = __lookup_mnt(&m->mnt,
453 mnt->mnt_mountpoint);
454 /*
455 * umount the child only if the child has no children
456 * and the child is marked safe to unmount.
457 */
458 if (!child || !IS_MNT_MARKED(child))
459 continue;
460 CLEAR_MNT_MARK(child);
461
462 /* If there is exactly one mount covering all of child
463 * replace child with that mount.
464 */
465 topper = find_topper(child);
466 if (topper)
467 mnt_change_mountpoint(child->mnt_parent, child->mnt_mp,
468 topper);
469
470 if (list_empty(&child->mnt_mounts)) {
471 list_del_init(&child->mnt_child);
472 child->mnt.mnt_flags |= MNT_UMOUNT;
473 list_move_tail(&child->mnt_list, &mnt->mnt_list);
474 }
475 }
476}
477
478/*
479 * collect all mounts that receive propagation from the mount in @list,
480 * and return these additional mounts in the same list.
481 * @list: the list of mounts to be unmounted.
482 *
483 * vfsmount lock must be held for write
484 */
485int propagate_umount(struct list_head *list)
486{
487 struct mount *mnt;
488
489 list_for_each_entry_reverse(mnt, list, mnt_list)
490 mark_umount_candidates(mnt);
491
492 list_for_each_entry(mnt, list, mnt_list)
493 __propagate_umount(mnt);
494 return 0;
495}
1/*
2 * linux/fs/pnode.c
3 *
4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai (linuxram@us.ibm.com)
7 *
8 */
9#include <linux/mnt_namespace.h>
10#include <linux/mount.h>
11#include <linux/fs.h>
12#include "internal.h"
13#include "pnode.h"
14
15/* return the next shared peer mount of @p */
16static inline struct mount *next_peer(struct mount *p)
17{
18 return list_entry(p->mnt_share.next, struct mount, mnt_share);
19}
20
21static inline struct mount *first_slave(struct mount *p)
22{
23 return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
24}
25
26static inline struct mount *next_slave(struct mount *p)
27{
28 return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
29}
30
31static struct mount *get_peer_under_root(struct mount *mnt,
32 struct mnt_namespace *ns,
33 const struct path *root)
34{
35 struct mount *m = mnt;
36
37 do {
38 /* Check the namespace first for optimization */
39 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
40 return m;
41
42 m = next_peer(m);
43 } while (m != mnt);
44
45 return NULL;
46}
47
48/*
49 * Get ID of closest dominating peer group having a representative
50 * under the given root.
51 *
52 * Caller must hold namespace_sem
53 */
54int get_dominating_id(struct mount *mnt, const struct path *root)
55{
56 struct mount *m;
57
58 for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
59 struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
60 if (d)
61 return d->mnt_group_id;
62 }
63
64 return 0;
65}
66
67static int do_make_slave(struct mount *mnt)
68{
69 struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
70 struct mount *slave_mnt;
71
72 /*
73 * slave 'mnt' to a peer mount that has the
74 * same root dentry. If none is available then
75 * slave it to anything that is available.
76 */
77 while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
78 peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;
79
80 if (peer_mnt == mnt) {
81 peer_mnt = next_peer(mnt);
82 if (peer_mnt == mnt)
83 peer_mnt = NULL;
84 }
85 if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
86 mnt_release_group_id(mnt);
87
88 list_del_init(&mnt->mnt_share);
89 mnt->mnt_group_id = 0;
90
91 if (peer_mnt)
92 master = peer_mnt;
93
94 if (master) {
95 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
96 slave_mnt->mnt_master = master;
97 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
98 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
99 INIT_LIST_HEAD(&mnt->mnt_slave_list);
100 } else {
101 struct list_head *p = &mnt->mnt_slave_list;
102 while (!list_empty(p)) {
103 slave_mnt = list_first_entry(p,
104 struct mount, mnt_slave);
105 list_del_init(&slave_mnt->mnt_slave);
106 slave_mnt->mnt_master = NULL;
107 }
108 }
109 mnt->mnt_master = master;
110 CLEAR_MNT_SHARED(mnt);
111 return 0;
112}
113
114/*
115 * vfsmount lock must be held for write
116 */
117void change_mnt_propagation(struct mount *mnt, int type)
118{
119 if (type == MS_SHARED) {
120 set_mnt_shared(mnt);
121 return;
122 }
123 do_make_slave(mnt);
124 if (type != MS_SLAVE) {
125 list_del_init(&mnt->mnt_slave);
126 mnt->mnt_master = NULL;
127 if (type == MS_UNBINDABLE)
128 mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
129 else
130 mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
131 }
132}
133
134/*
135 * get the next mount in the propagation tree.
136 * @m: the mount seen last
137 * @origin: the original mount from where the tree walk initiated
138 *
139 * Note that peer groups form contiguous segments of slave lists.
140 * We rely on that in get_source() to be able to find out if
141 * vfsmount found while iterating with propagation_next() is
142 * a peer of one we'd found earlier.
143 */
144static struct mount *propagation_next(struct mount *m,
145 struct mount *origin)
146{
147 /* are there any slaves of this mount? */
148 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
149 return first_slave(m);
150
151 while (1) {
152 struct mount *master = m->mnt_master;
153
154 if (master == origin->mnt_master) {
155 struct mount *next = next_peer(m);
156 return (next == origin) ? NULL : next;
157 } else if (m->mnt_slave.next != &master->mnt_slave_list)
158 return next_slave(m);
159
160 /* back at master */
161 m = master;
162 }
163}
164
165/*
166 * return the source mount to be used for cloning
167 *
168 * @dest the current destination mount
169 * @last_dest the last seen destination mount
170 * @last_src the last seen source mount
171 * @type return CL_SLAVE if the new mount has to be
172 * cloned as a slave.
173 */
174static struct mount *get_source(struct mount *dest,
175 struct mount *last_dest,
176 struct mount *last_src,
177 int *type)
178{
179 struct mount *p_last_src = NULL;
180 struct mount *p_last_dest = NULL;
181
182 while (last_dest != dest->mnt_master) {
183 p_last_dest = last_dest;
184 p_last_src = last_src;
185 last_dest = last_dest->mnt_master;
186 last_src = last_src->mnt_master;
187 }
188
189 if (p_last_dest) {
190 do {
191 p_last_dest = next_peer(p_last_dest);
192 } while (IS_MNT_NEW(p_last_dest));
193 /* is that a peer of the earlier? */
194 if (dest == p_last_dest) {
195 *type = CL_MAKE_SHARED;
196 return p_last_src;
197 }
198 }
199 /* slave of the earlier, then */
200 *type = CL_SLAVE;
201 /* beginning of peer group among the slaves? */
202 if (IS_MNT_SHARED(dest))
203 *type |= CL_MAKE_SHARED;
204 return last_src;
205}
206
207/*
208 * mount 'source_mnt' under the destination 'dest_mnt' at
209 * dentry 'dest_dentry'. And propagate that mount to
210 * all the peer and slave mounts of 'dest_mnt'.
211 * Link all the new mounts into a propagation tree headed at
212 * source_mnt. Also link all the new mounts using ->mnt_list
213 * headed at source_mnt's ->mnt_list
214 *
215 * @dest_mnt: destination mount.
216 * @dest_dentry: destination dentry.
217 * @source_mnt: source mount.
218 * @tree_list : list of heads of trees to be attached.
219 */
220int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry,
221 struct mount *source_mnt, struct list_head *tree_list)
222{
223 struct mount *m, *child;
224 int ret = 0;
225 struct mount *prev_dest_mnt = dest_mnt;
226 struct mount *prev_src_mnt = source_mnt;
227 LIST_HEAD(tmp_list);
228 LIST_HEAD(umount_list);
229
230 for (m = propagation_next(dest_mnt, dest_mnt); m;
231 m = propagation_next(m, dest_mnt)) {
232 int type;
233 struct mount *source;
234
235 if (IS_MNT_NEW(m))
236 continue;
237
238 source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
239
240 if (!(child = copy_tree(source, source->mnt.mnt_root, type))) {
241 ret = -ENOMEM;
242 list_splice(tree_list, tmp_list.prev);
243 goto out;
244 }
245
246 if (is_subdir(dest_dentry, m->mnt.mnt_root)) {
247 mnt_set_mountpoint(m, dest_dentry, child);
248 list_add_tail(&child->mnt_hash, tree_list);
249 } else {
250 /*
251 * This can happen if the parent mount was bind mounted
252 * on some subdirectory of a shared/slave mount.
253 */
254 list_add_tail(&child->mnt_hash, &tmp_list);
255 }
256 prev_dest_mnt = m;
257 prev_src_mnt = child;
258 }
259out:
260 br_write_lock(&vfsmount_lock);
261 while (!list_empty(&tmp_list)) {
262 child = list_first_entry(&tmp_list, struct mount, mnt_hash);
263 umount_tree(child, 0, &umount_list);
264 }
265 br_write_unlock(&vfsmount_lock);
266 release_mounts(&umount_list);
267 return ret;
268}
269
270/*
271 * return true if the refcount is greater than count
272 */
273static inline int do_refcount_check(struct mount *mnt, int count)
274{
275 int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts;
276 return (mycount > count);
277}
278
279/*
280 * check if the mount 'mnt' can be unmounted successfully.
281 * @mnt: the mount to be checked for unmount
282 * NOTE: unmounting 'mnt' would naturally propagate to all
283 * other mounts its parent propagates to.
284 * Check if any of these mounts that **do not have submounts**
285 * have more references than 'refcnt'. If so return busy.
286 *
287 * vfsmount lock must be held for write
288 */
289int propagate_mount_busy(struct mount *mnt, int refcnt)
290{
291 struct mount *m, *child;
292 struct mount *parent = mnt->mnt_parent;
293 int ret = 0;
294
295 if (mnt == parent)
296 return do_refcount_check(mnt, refcnt);
297
298 /*
299 * quickly check if the current mount can be unmounted.
300 * If not, we don't have to go checking for all other
301 * mounts
302 */
303 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
304 return 1;
305
306 for (m = propagation_next(parent, parent); m;
307 m = propagation_next(m, parent)) {
308 child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint, 0);
309 if (child && list_empty(&child->mnt_mounts) &&
310 (ret = do_refcount_check(child, 1)))
311 break;
312 }
313 return ret;
314}
315
316/*
317 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
318 * parent propagates to.
319 */
320static void __propagate_umount(struct mount *mnt)
321{
322 struct mount *parent = mnt->mnt_parent;
323 struct mount *m;
324
325 BUG_ON(parent == mnt);
326
327 for (m = propagation_next(parent, parent); m;
328 m = propagation_next(m, parent)) {
329
330 struct mount *child = __lookup_mnt(&m->mnt,
331 mnt->mnt_mountpoint, 0);
332 /*
333 * umount the child only if the child has no
334 * other children
335 */
336 if (child && list_empty(&child->mnt_mounts))
337 list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
338 }
339}
340
341/*
342 * collect all mounts that receive propagation from the mount in @list,
343 * and return these additional mounts in the same list.
344 * @list: the list of mounts to be unmounted.
345 *
346 * vfsmount lock must be held for write
347 */
348int propagate_umount(struct list_head *list)
349{
350 struct mount *mnt;
351
352 list_for_each_entry(mnt, list, mnt_hash)
353 __propagate_umount(mnt);
354 return 0;
355}