Loading...
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 vfsmount *next_peer(struct vfsmount *p)
17{
18 return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
19}
20
21static inline struct vfsmount *first_slave(struct vfsmount *p)
22{
23 return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
24}
25
26static inline struct vfsmount *next_slave(struct vfsmount *p)
27{
28 return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
29}
30
31/*
32 * Return true if path is reachable from root
33 *
34 * namespace_sem is held, and mnt is attached
35 */
36static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
37 const struct path *root)
38{
39 while (mnt != root->mnt && mnt->mnt_parent != mnt) {
40 dentry = mnt->mnt_mountpoint;
41 mnt = mnt->mnt_parent;
42 }
43 return mnt == root->mnt && is_subdir(dentry, root->dentry);
44}
45
46static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
47 struct mnt_namespace *ns,
48 const struct path *root)
49{
50 struct vfsmount *m = mnt;
51
52 do {
53 /* Check the namespace first for optimization */
54 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
55 return m;
56
57 m = next_peer(m);
58 } while (m != mnt);
59
60 return NULL;
61}
62
63/*
64 * Get ID of closest dominating peer group having a representative
65 * under the given root.
66 *
67 * Caller must hold namespace_sem
68 */
69int get_dominating_id(struct vfsmount *mnt, const struct path *root)
70{
71 struct vfsmount *m;
72
73 for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
74 struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root);
75 if (d)
76 return d->mnt_group_id;
77 }
78
79 return 0;
80}
81
82static int do_make_slave(struct vfsmount *mnt)
83{
84 struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
85 struct vfsmount *slave_mnt;
86
87 /*
88 * slave 'mnt' to a peer mount that has the
89 * same root dentry. If none is available then
90 * slave it to anything that is available.
91 */
92 while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
93 peer_mnt->mnt_root != mnt->mnt_root) ;
94
95 if (peer_mnt == mnt) {
96 peer_mnt = next_peer(mnt);
97 if (peer_mnt == mnt)
98 peer_mnt = NULL;
99 }
100 if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
101 mnt_release_group_id(mnt);
102
103 list_del_init(&mnt->mnt_share);
104 mnt->mnt_group_id = 0;
105
106 if (peer_mnt)
107 master = peer_mnt;
108
109 if (master) {
110 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
111 slave_mnt->mnt_master = master;
112 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
113 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
114 INIT_LIST_HEAD(&mnt->mnt_slave_list);
115 } else {
116 struct list_head *p = &mnt->mnt_slave_list;
117 while (!list_empty(p)) {
118 slave_mnt = list_first_entry(p,
119 struct vfsmount, mnt_slave);
120 list_del_init(&slave_mnt->mnt_slave);
121 slave_mnt->mnt_master = NULL;
122 }
123 }
124 mnt->mnt_master = master;
125 CLEAR_MNT_SHARED(mnt);
126 return 0;
127}
128
129/*
130 * vfsmount lock must be held for write
131 */
132void change_mnt_propagation(struct vfsmount *mnt, int type)
133{
134 if (type == MS_SHARED) {
135 set_mnt_shared(mnt);
136 return;
137 }
138 do_make_slave(mnt);
139 if (type != MS_SLAVE) {
140 list_del_init(&mnt->mnt_slave);
141 mnt->mnt_master = NULL;
142 if (type == MS_UNBINDABLE)
143 mnt->mnt_flags |= MNT_UNBINDABLE;
144 else
145 mnt->mnt_flags &= ~MNT_UNBINDABLE;
146 }
147}
148
149/*
150 * get the next mount in the propagation tree.
151 * @m: the mount seen last
152 * @origin: the original mount from where the tree walk initiated
153 *
154 * Note that peer groups form contiguous segments of slave lists.
155 * We rely on that in get_source() to be able to find out if
156 * vfsmount found while iterating with propagation_next() is
157 * a peer of one we'd found earlier.
158 */
159static struct vfsmount *propagation_next(struct vfsmount *m,
160 struct vfsmount *origin)
161{
162 /* are there any slaves of this mount? */
163 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
164 return first_slave(m);
165
166 while (1) {
167 struct vfsmount *next;
168 struct vfsmount *master = m->mnt_master;
169
170 if (master == origin->mnt_master) {
171 next = next_peer(m);
172 return ((next == origin) ? NULL : next);
173 } else if (m->mnt_slave.next != &master->mnt_slave_list)
174 return next_slave(m);
175
176 /* back at master */
177 m = master;
178 }
179}
180
181/*
182 * return the source mount to be used for cloning
183 *
184 * @dest the current destination mount
185 * @last_dest the last seen destination mount
186 * @last_src the last seen source mount
187 * @type return CL_SLAVE if the new mount has to be
188 * cloned as a slave.
189 */
190static struct vfsmount *get_source(struct vfsmount *dest,
191 struct vfsmount *last_dest,
192 struct vfsmount *last_src,
193 int *type)
194{
195 struct vfsmount *p_last_src = NULL;
196 struct vfsmount *p_last_dest = NULL;
197
198 while (last_dest != dest->mnt_master) {
199 p_last_dest = last_dest;
200 p_last_src = last_src;
201 last_dest = last_dest->mnt_master;
202 last_src = last_src->mnt_master;
203 }
204
205 if (p_last_dest) {
206 do {
207 p_last_dest = next_peer(p_last_dest);
208 } while (IS_MNT_NEW(p_last_dest));
209 /* is that a peer of the earlier? */
210 if (dest == p_last_dest) {
211 *type = CL_MAKE_SHARED;
212 return p_last_src;
213 }
214 }
215 /* slave of the earlier, then */
216 *type = CL_SLAVE;
217 /* beginning of peer group among the slaves? */
218 if (IS_MNT_SHARED(dest))
219 *type |= CL_MAKE_SHARED;
220 return last_src;
221}
222
223/*
224 * mount 'source_mnt' under the destination 'dest_mnt' at
225 * dentry 'dest_dentry'. And propagate that mount to
226 * all the peer and slave mounts of 'dest_mnt'.
227 * Link all the new mounts into a propagation tree headed at
228 * source_mnt. Also link all the new mounts using ->mnt_list
229 * headed at source_mnt's ->mnt_list
230 *
231 * @dest_mnt: destination mount.
232 * @dest_dentry: destination dentry.
233 * @source_mnt: source mount.
234 * @tree_list : list of heads of trees to be attached.
235 */
236int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
237 struct vfsmount *source_mnt, struct list_head *tree_list)
238{
239 struct vfsmount *m, *child;
240 int ret = 0;
241 struct vfsmount *prev_dest_mnt = dest_mnt;
242 struct vfsmount *prev_src_mnt = source_mnt;
243 LIST_HEAD(tmp_list);
244 LIST_HEAD(umount_list);
245
246 for (m = propagation_next(dest_mnt, dest_mnt); m;
247 m = propagation_next(m, dest_mnt)) {
248 int type;
249 struct vfsmount *source;
250
251 if (IS_MNT_NEW(m))
252 continue;
253
254 source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
255
256 if (!(child = copy_tree(source, source->mnt_root, type))) {
257 ret = -ENOMEM;
258 list_splice(tree_list, tmp_list.prev);
259 goto out;
260 }
261
262 if (is_subdir(dest_dentry, m->mnt_root)) {
263 mnt_set_mountpoint(m, dest_dentry, child);
264 list_add_tail(&child->mnt_hash, tree_list);
265 } else {
266 /*
267 * This can happen if the parent mount was bind mounted
268 * on some subdirectory of a shared/slave mount.
269 */
270 list_add_tail(&child->mnt_hash, &tmp_list);
271 }
272 prev_dest_mnt = m;
273 prev_src_mnt = child;
274 }
275out:
276 br_write_lock(vfsmount_lock);
277 while (!list_empty(&tmp_list)) {
278 child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
279 umount_tree(child, 0, &umount_list);
280 }
281 br_write_unlock(vfsmount_lock);
282 release_mounts(&umount_list);
283 return ret;
284}
285
286/*
287 * return true if the refcount is greater than count
288 */
289static inline int do_refcount_check(struct vfsmount *mnt, int count)
290{
291 int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts;
292 return (mycount > count);
293}
294
295/*
296 * check if the mount 'mnt' can be unmounted successfully.
297 * @mnt: the mount to be checked for unmount
298 * NOTE: unmounting 'mnt' would naturally propagate to all
299 * other mounts its parent propagates to.
300 * Check if any of these mounts that **do not have submounts**
301 * have more references than 'refcnt'. If so return busy.
302 *
303 * vfsmount lock must be held for write
304 */
305int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
306{
307 struct vfsmount *m, *child;
308 struct vfsmount *parent = mnt->mnt_parent;
309 int ret = 0;
310
311 if (mnt == parent)
312 return do_refcount_check(mnt, refcnt);
313
314 /*
315 * quickly check if the current mount can be unmounted.
316 * If not, we don't have to go checking for all other
317 * mounts
318 */
319 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
320 return 1;
321
322 for (m = propagation_next(parent, parent); m;
323 m = propagation_next(m, parent)) {
324 child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
325 if (child && list_empty(&child->mnt_mounts) &&
326 (ret = do_refcount_check(child, 1)))
327 break;
328 }
329 return ret;
330}
331
332/*
333 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
334 * parent propagates to.
335 */
336static void __propagate_umount(struct vfsmount *mnt)
337{
338 struct vfsmount *parent = mnt->mnt_parent;
339 struct vfsmount *m;
340
341 BUG_ON(parent == mnt);
342
343 for (m = propagation_next(parent, parent); m;
344 m = propagation_next(m, parent)) {
345
346 struct vfsmount *child = __lookup_mnt(m,
347 mnt->mnt_mountpoint, 0);
348 /*
349 * umount the child only if the child has no
350 * other children
351 */
352 if (child && list_empty(&child->mnt_mounts))
353 list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
354 }
355}
356
357/*
358 * collect all mounts that receive propagation from the mount in @list,
359 * and return these additional mounts in the same list.
360 * @list: the list of mounts to be unmounted.
361 *
362 * vfsmount lock must be held for write
363 */
364int propagate_umount(struct list_head *list)
365{
366 struct vfsmount *mnt;
367
368 list_for_each_entry(mnt, list, mnt_hash)
369 __propagate_umount(mnt);
370 return 0;
371}