projects/linux·blob v5.0-rc3 · refs

610 lines · 15.3 KiB

1/*
2 * linux/fs/pnode.c
3 *
4 * (C) Copyright IBM Corporation 2005.
5 * Released under GPL v2.
6 * Author : Ram Pai ([email protected])
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 <uapi/linux/mount.h>
14#include "internal.h"
15#include "pnode.h"
16
17/* return the next shared peer mount of @p */
18static inline struct mount *next_peer(struct mount *p)
19{
20 return list_entry(p->mnt_share.next, struct mount, mnt_share);
21}
22
23static inline struct mount *first_slave(struct mount *p)
24{
25 return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
26}
27
28static inline struct mount *last_slave(struct mount *p)
29{
30 return list_entry(p->mnt_slave_list.prev, struct mount, mnt_slave);
31}
32
33static inline struct mount *next_slave(struct mount *p)
34{
35 return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
36}
37
38static struct mount *get_peer_under_root(struct mount *mnt,
39 struct mnt_namespace *ns,
40 const struct path *root)
41{
42 struct mount *m = mnt;
43
44 do {
45 /* Check the namespace first for optimization */
46 if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
47 return m;
48
49 m = next_peer(m);
50 } while (m != mnt);
51
52 return NULL;
53}
54
55/*
56 * Get ID of closest dominating peer group having a representative
57 * under the given root.
58 *
59 * Caller must hold namespace_sem
60 */
61int get_dominating_id(struct mount *mnt, const struct path *root)
62{
63 struct mount *m;
64
65 for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
66 struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
67 if (d)
68 return d->mnt_group_id;
69 }
70
71 return 0;
72}
73
74static int do_make_slave(struct mount *mnt)
75{
76 struct mount *master, *slave_mnt;
77
78 if (list_empty(&mnt->mnt_share)) {
79 if (IS_MNT_SHARED(mnt)) {
80 mnt_release_group_id(mnt);
81 CLEAR_MNT_SHARED(mnt);
82 }
83 master = mnt->mnt_master;
84 if (!master) {
85 struct list_head *p = &mnt->mnt_slave_list;
86 while (!list_empty(p)) {
87 slave_mnt = list_first_entry(p,
88 struct mount, mnt_slave);
89 list_del_init(&slave_mnt->mnt_slave);
90 slave_mnt->mnt_master = NULL;
91 }
92 return 0;
93 }
94 } else {
95 struct mount *m;
96 /*
97 * slave 'mnt' to a peer mount that has the
98 * same root dentry. If none is available then
99 * slave it to anything that is available.
100 */
101 for (m = master = next_peer(mnt); m != mnt; m = next_peer(m)) {
102 if (m->mnt.mnt_root == mnt->mnt.mnt_root) {
103 master = m;
104 break;
105 }
106 }
107 list_del_init(&mnt->mnt_share);
108 mnt->mnt_group_id = 0;
109 CLEAR_MNT_SHARED(mnt);
110 }
111 list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
112 slave_mnt->mnt_master = master;
113 list_move(&mnt->mnt_slave, &master->mnt_slave_list);
114 list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
115 INIT_LIST_HEAD(&mnt->mnt_slave_list);
116 mnt->mnt_master = master;
117 return 0;
118}
119
120/*
121 * vfsmount lock must be held for write
122 */
123void change_mnt_propagation(struct mount *mnt, int type)
124{
125 if (type == MS_SHARED) {
126 set_mnt_shared(mnt);
127 return;
128 }
129 do_make_slave(mnt);
130 if (type != MS_SLAVE) {
131 list_del_init(&mnt->mnt_slave);
132 mnt->mnt_master = NULL;
133 if (type == MS_UNBINDABLE)
134 mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
135 else
136 mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
137 }
138}
139
140/*
141 * get the next mount in the propagation tree.
142 * @m: the mount seen last
143 * @origin: the original mount from where the tree walk initiated
144 *
145 * Note that peer groups form contiguous segments of slave lists.
146 * We rely on that in get_source() to be able to find out if
147 * vfsmount found while iterating with propagation_next() is
148 * a peer of one we'd found earlier.
149 */
150static struct mount *propagation_next(struct mount *m,
151 struct mount *origin)
152{
153 /* are there any slaves of this mount? */
154 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
155 return first_slave(m);
156
157 while (1) {
158 struct mount *master = m->mnt_master;
159
160 if (master == origin->mnt_master) {
161 struct mount *next = next_peer(m);
162 return (next == origin) ? NULL : next;
163 } else if (m->mnt_slave.next != &master->mnt_slave_list)
164 return next_slave(m);
165
166 /* back at master */
167 m = master;
168 }
169}
170
171static struct mount *skip_propagation_subtree(struct mount *m,
172 struct mount *origin)
173{
174 /*
175 * Advance m such that propagation_next will not return
176 * the slaves of m.
177 */
178 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
179 m = last_slave(m);
180
181 return m;
182}
183
184static struct mount *next_group(struct mount *m, struct mount *origin)
185{
186 while (1) {
187 while (1) {
188 struct mount *next;
189 if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
190 return first_slave(m);
191 next = next_peer(m);
192 if (m->mnt_group_id == origin->mnt_group_id) {
193 if (next == origin)
194 return NULL;
195 } else if (m->mnt_slave.next != &next->mnt_slave)
196 break;
197 m = next;
198 }
199 /* m is the last peer */
200 while (1) {
201 struct mount *master = m->mnt_master;
202 if (m->mnt_slave.next != &master->mnt_slave_list)
203 return next_slave(m);
204 m = next_peer(master);
205 if (master->mnt_group_id == origin->mnt_group_id)
206 break;
207 if (master->mnt_slave.next == &m->mnt_slave)
208 break;
209 m = master;
210 }
211 if (m == origin)
212 return NULL;
213 }
214}
215
216/* all accesses are serialized by namespace_sem */
217static struct user_namespace *user_ns;
218static struct mount *last_dest, *first_source, *last_source, *dest_master;
219static struct mountpoint *mp;
220static struct hlist_head *list;
221
222static inline bool peers(struct mount *m1, struct mount *m2)
223{
224 return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
225}
226
227static int propagate_one(struct mount *m)
228{
229 struct mount *child;
230 int type;
231 /* skip ones added by this propagate_mnt() */
232 if (IS_MNT_NEW(m))
233 return 0;
234 /* skip if mountpoint isn't covered by it */
235 if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
236 return 0;
237 if (peers(m, last_dest)) {
238 type = CL_MAKE_SHARED;
239 } else {
240 struct mount *n, *p;
241 bool done;
242 for (n = m; ; n = p) {
243 p = n->mnt_master;
244 if (p == dest_master || IS_MNT_MARKED(p))
245 break;
246 }
247 do {
248 struct mount *parent = last_source->mnt_parent;
249 if (last_source == first_source)
250 break;
251 done = parent->mnt_master == p;
252 if (done && peers(n, parent))
253 break;
254 last_source = last_source->mnt_master;
255 } while (!done);
256
257 type = CL_SLAVE;
258 /* beginning of peer group among the slaves? */
259 if (IS_MNT_SHARED(m))
260 type |= CL_MAKE_SHARED;
261 }
262
263 /* Notice when we are propagating across user namespaces */
264 if (m->mnt_ns->user_ns != user_ns)
265 type |= CL_UNPRIVILEGED;
266 child = copy_tree(last_source, last_source->mnt.mnt_root, type);
267 if (IS_ERR(child))
268 return PTR_ERR(child);
269 child->mnt.mnt_flags &= ~MNT_LOCKED;
270 mnt_set_mountpoint(m, mp, child);
271 last_dest = m;
272 last_source = child;
273 if (m->mnt_master != dest_master) {
274 read_seqlock_excl(&mount_lock);
275 SET_MNT_MARK(m->mnt_master);
276 read_sequnlock_excl(&mount_lock);
277 }
278 hlist_add_head(&child->mnt_hash, list);
279 return count_mounts(m->mnt_ns, child);
280}
281
282/*
283 * mount 'source_mnt' under the destination 'dest_mnt' at
284 * dentry 'dest_dentry'. And propagate that mount to
285 * all the peer and slave mounts of 'dest_mnt'.
286 * Link all the new mounts into a propagation tree headed at
287 * source_mnt. Also link all the new mounts using ->mnt_list
288 * headed at source_mnt's ->mnt_list
289 *
290 * @dest_mnt: destination mount.
291 * @dest_dentry: destination dentry.
292 * @source_mnt: source mount.
293 * @tree_list : list of heads of trees to be attached.
294 */
295int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
296 struct mount *source_mnt, struct hlist_head *tree_list)
297{
298 struct mount *m, *n;
299 int ret = 0;
300
301 /*
302 * we don't want to bother passing tons of arguments to
303 * propagate_one(); everything is serialized by namespace_sem,
304 * so globals will do just fine.
305 */
306 user_ns = current->nsproxy->mnt_ns->user_ns;
307 last_dest = dest_mnt;
308 first_source = source_mnt;
309 last_source = source_mnt;
310 mp = dest_mp;
311 list = tree_list;
312 dest_master = dest_mnt->mnt_master;
313
314 /* all peers of dest_mnt, except dest_mnt itself */
315 for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
316 ret = propagate_one(n);
317 if (ret)
318 goto out;
319 }
320
321 /* all slave groups */
322 for (m = next_group(dest_mnt, dest_mnt); m;
323 m = next_group(m, dest_mnt)) {
324 /* everything in that slave group */
325 n = m;
326 do {
327 ret = propagate_one(n);
328 if (ret)
329 goto out;
330 n = next_peer(n);
331 } while (n != m);
332 }
333out:
334 read_seqlock_excl(&mount_lock);
335 hlist_for_each_entry(n, tree_list, mnt_hash) {
336 m = n->mnt_parent;
337 if (m->mnt_master != dest_mnt->mnt_master)
338 CLEAR_MNT_MARK(m->mnt_master);
339 }
340 read_sequnlock_excl(&mount_lock);
341 return ret;
342}
343
344static struct mount *find_topper(struct mount *mnt)
345{
346 /* If there is exactly one mount covering mnt completely return it. */
347 struct mount *child;
348
349 if (!list_is_singular(&mnt->mnt_mounts))
350 return NULL;
351
352 child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
353 if (child->mnt_mountpoint != mnt->mnt.mnt_root)
354 return NULL;
355
356 return child;
357}
358
359/*
360 * return true if the refcount is greater than count
361 */
362static inline int do_refcount_check(struct mount *mnt, int count)
363{
364 return mnt_get_count(mnt) > count;
365}
366
367/*
368 * check if the mount 'mnt' can be unmounted successfully.
369 * @mnt: the mount to be checked for unmount
370 * NOTE: unmounting 'mnt' would naturally propagate to all
371 * other mounts its parent propagates to.
372 * Check if any of these mounts that **do not have submounts**
373 * have more references than 'refcnt'. If so return busy.
374 *
375 * vfsmount lock must be held for write
376 */
377int propagate_mount_busy(struct mount *mnt, int refcnt)
378{
379 struct mount *m, *child, *topper;
380 struct mount *parent = mnt->mnt_parent;
381
382 if (mnt == parent)
383 return do_refcount_check(mnt, refcnt);
384
385 /*
386 * quickly check if the current mount can be unmounted.
387 * If not, we don't have to go checking for all other
388 * mounts
389 */
390 if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
391 return 1;
392
393 for (m = propagation_next(parent, parent); m;
394 m = propagation_next(m, parent)) {
395 int count = 1;
396 child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
397 if (!child)
398 continue;
399
400 /* Is there exactly one mount on the child that covers
401 * it completely whose reference should be ignored?
402 */
403 topper = find_topper(child);
404 if (topper)
405 count += 1;
406 else if (!list_empty(&child->mnt_mounts))
407 continue;
408
409 if (do_refcount_check(child, count))
410 return 1;
411 }
412 return 0;
413}
414
415/*
416 * Clear MNT_LOCKED when it can be shown to be safe.
417 *
418 * mount_lock lock must be held for write
419 */
420void propagate_mount_unlock(struct mount *mnt)
421{
422 struct mount *parent = mnt->mnt_parent;
423 struct mount *m, *child;
424
425 BUG_ON(parent == mnt);
426
427 for (m = propagation_next(parent, parent); m;
428 m = propagation_next(m, parent)) {
429 child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
430 if (child)
431 child->mnt.mnt_flags &= ~MNT_LOCKED;
432 }
433}
434
435static void umount_one(struct mount *mnt, struct list_head *to_umount)
436{
437 CLEAR_MNT_MARK(mnt);
438 mnt->mnt.mnt_flags |= MNT_UMOUNT;
439 list_del_init(&mnt->mnt_child);
440 list_del_init(&mnt->mnt_umounting);
441 list_move_tail(&mnt->mnt_list, to_umount);
442}
443
444/*
445 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
446 * parent propagates to.
447 */
448static bool __propagate_umount(struct mount *mnt,
449 struct list_head *to_umount,
450 struct list_head *to_restore)
451{
452 bool progress = false;
453 struct mount *child;
454
455 /*
456 * The state of the parent won't change if this mount is
457 * already unmounted or marked as without children.
458 */
459 if (mnt->mnt.mnt_flags & (MNT_UMOUNT | MNT_MARKED))
460 goto out;
461
462 /* Verify topper is the only grandchild that has not been
463 * speculatively unmounted.
464 */
465 list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
466 if (child->mnt_mountpoint == mnt->mnt.mnt_root)
467 continue;
468 if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
469 continue;
470 /* Found a mounted child */
471 goto children;
472 }
473
474 /* Mark mounts that can be unmounted if not locked */
475 SET_MNT_MARK(mnt);
476 progress = true;
477
478 /* If a mount is without children and not locked umount it. */
479 if (!IS_MNT_LOCKED(mnt)) {
480 umount_one(mnt, to_umount);
481 } else {
482children:
483 list_move_tail(&mnt->mnt_umounting, to_restore);
484 }
485out:
486 return progress;
487}
488
489static void umount_list(struct list_head *to_umount,
490 struct list_head *to_restore)
491{
492 struct mount *mnt, *child, *tmp;
493 list_for_each_entry(mnt, to_umount, mnt_list) {
494 list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
495 /* topper? */
496 if (child->mnt_mountpoint == mnt->mnt.mnt_root)
497 list_move_tail(&child->mnt_umounting, to_restore);
498 else
499 umount_one(child, to_umount);
500 }
501 }
502}
503
504static void restore_mounts(struct list_head *to_restore)
505{
506 /* Restore mounts to a clean working state */
507 while (!list_empty(to_restore)) {
508 struct mount *mnt, *parent;
509 struct mountpoint *mp;
510
511 mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
512 CLEAR_MNT_MARK(mnt);
513 list_del_init(&mnt->mnt_umounting);
514
515 /* Should this mount be reparented? */
516 mp = mnt->mnt_mp;
517 parent = mnt->mnt_parent;
518 while (parent->mnt.mnt_flags & MNT_UMOUNT) {
519 mp = parent->mnt_mp;
520 parent = parent->mnt_parent;
521 }
522 if (parent != mnt->mnt_parent)
523 mnt_change_mountpoint(parent, mp, mnt);
524 }
525}
526
527static void cleanup_umount_visitations(struct list_head *visited)
528{
529 while (!list_empty(visited)) {
530 struct mount *mnt =
531 list_first_entry(visited, struct mount, mnt_umounting);
532 list_del_init(&mnt->mnt_umounting);
533 }
534}
535
536/*
537 * collect all mounts that receive propagation from the mount in @list,
538 * and return these additional mounts in the same list.
539 * @list: the list of mounts to be unmounted.
540 *
541 * vfsmount lock must be held for write
542 */
543int propagate_umount(struct list_head *list)
544{
545 struct mount *mnt;
546 LIST_HEAD(to_restore);
547 LIST_HEAD(to_umount);
548 LIST_HEAD(visited);
549
550 /* Find candidates for unmounting */
551 list_for_each_entry_reverse(mnt, list, mnt_list) {
552 struct mount *parent = mnt->mnt_parent;
553 struct mount *m;
554
555 /*
556 * If this mount has already been visited it is known that it's
557 * entire peer group and all of their slaves in the propagation
558 * tree for the mountpoint has already been visited and there is
559 * no need to visit them again.
560 */
561 if (!list_empty(&mnt->mnt_umounting))
562 continue;
563
564 list_add_tail(&mnt->mnt_umounting, &visited);
565 for (m = propagation_next(parent, parent); m;
566 m = propagation_next(m, parent)) {
567 struct mount *child = __lookup_mnt(&m->mnt,
568 mnt->mnt_mountpoint);
569 if (!child)
570 continue;
571
572 if (!list_empty(&child->mnt_umounting)) {
573 /*
574 * If the child has already been visited it is
575 * know that it's entire peer group and all of
576 * their slaves in the propgation tree for the
577 * mountpoint has already been visited and there
578 * is no need to visit this subtree again.
579 */
580 m = skip_propagation_subtree(m, parent);
581 continue;
582 } else if (child->mnt.mnt_flags & MNT_UMOUNT) {
583 /*
584 * We have come accross an partially unmounted
585 * mount in list that has not been visited yet.
586 * Remember it has been visited and continue
587 * about our merry way.
588 */
589 list_add_tail(&child->mnt_umounting, &visited);
590 continue;
591 }
592
593 /* Check the child and parents while progress is made */
594 while (__propagate_umount(child,
595 &to_umount, &to_restore)) {
596 /* Is the parent a umount candidate? */
597 child = child->mnt_parent;
598 if (list_empty(&child->mnt_umounting))
599 break;
600 }
601 }
602 }
603
604 umount_list(&to_umount, &to_restore);
605 restore_mounts(&to_restore);
606 cleanup_umount_visitations(&visited);
607 list_splice_tail(&to_umount, list);
608
609 return 0;
610}