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Linux/fs/pnode.c

  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 */
 17 static inline struct mount *next_peer(struct mount *p)
 18 {
 19         return list_entry(p->mnt_share.next, struct mount, mnt_share);
 20 }
 21 
 22 static inline struct mount *first_slave(struct mount *p)
 23 {
 24         return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
 25 }
 26 
 27 static inline struct mount *next_slave(struct mount *p)
 28 {
 29         return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
 30 }
 31 
 32 static 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  */
 55 int 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 
 68 static 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  */
117 void 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  */
144 static 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 static 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 */
198 static struct user_namespace *user_ns;
199 static struct mount *last_dest, *first_source, *last_source, *dest_master;
200 static struct mountpoint *mp;
201 static struct hlist_head *list;
202 
203 static 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 
208 static 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  */
276 int 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         }
314 out:
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 
325 /*
326  * return true if the refcount is greater than count
327  */
328 static inline int do_refcount_check(struct mount *mnt, int count)
329 {
330         return mnt_get_count(mnt) > count;
331 }
332 
333 /*
334  * check if the mount 'mnt' can be unmounted successfully.
335  * @mnt: the mount to be checked for unmount
336  * NOTE: unmounting 'mnt' would naturally propagate to all
337  * other mounts its parent propagates to.
338  * Check if any of these mounts that **do not have submounts**
339  * have more references than 'refcnt'. If so return busy.
340  *
341  * vfsmount lock must be held for write
342  */
343 int propagate_mount_busy(struct mount *mnt, int refcnt)
344 {
345         struct mount *m, *child;
346         struct mount *parent = mnt->mnt_parent;
347         int ret = 0;
348 
349         if (mnt == parent)
350                 return do_refcount_check(mnt, refcnt);
351 
352         /*
353          * quickly check if the current mount can be unmounted.
354          * If not, we don't have to go checking for all other
355          * mounts
356          */
357         if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
358                 return 1;
359 
360         for (m = propagation_next(parent, parent); m;
361                         m = propagation_next(m, parent)) {
362                 child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
363                 if (child && list_empty(&child->mnt_mounts) &&
364                     (ret = do_refcount_check(child, 1)))
365                         break;
366         }
367         return ret;
368 }
369 
370 /*
371  * Clear MNT_LOCKED when it can be shown to be safe.
372  *
373  * mount_lock lock must be held for write
374  */
375 void propagate_mount_unlock(struct mount *mnt)
376 {
377         struct mount *parent = mnt->mnt_parent;
378         struct mount *m, *child;
379 
380         BUG_ON(parent == mnt);
381 
382         for (m = propagation_next(parent, parent); m;
383                         m = propagation_next(m, parent)) {
384                 child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
385                 if (child)
386                         child->mnt.mnt_flags &= ~MNT_LOCKED;
387         }
388 }
389 
390 /*
391  * Mark all mounts that the MNT_LOCKED logic will allow to be unmounted.
392  */
393 static void mark_umount_candidates(struct mount *mnt)
394 {
395         struct mount *parent = mnt->mnt_parent;
396         struct mount *m;
397 
398         BUG_ON(parent == mnt);
399 
400         for (m = propagation_next(parent, parent); m;
401                         m = propagation_next(m, parent)) {
402                 struct mount *child = __lookup_mnt_last(&m->mnt,
403                                                 mnt->mnt_mountpoint);
404                 if (child && (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m))) {
405                         SET_MNT_MARK(child);
406                 }
407         }
408 }
409 
410 /*
411  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
412  * parent propagates to.
413  */
414 static void __propagate_umount(struct mount *mnt)
415 {
416         struct mount *parent = mnt->mnt_parent;
417         struct mount *m;
418 
419         BUG_ON(parent == mnt);
420 
421         for (m = propagation_next(parent, parent); m;
422                         m = propagation_next(m, parent)) {
423 
424                 struct mount *child = __lookup_mnt_last(&m->mnt,
425                                                 mnt->mnt_mountpoint);
426                 /*
427                  * umount the child only if the child has no children
428                  * and the child is marked safe to unmount.
429                  */
430                 if (!child || !IS_MNT_MARKED(child))
431                         continue;
432                 CLEAR_MNT_MARK(child);
433                 if (list_empty(&child->mnt_mounts)) {
434                         list_del_init(&child->mnt_child);
435                         child->mnt.mnt_flags |= MNT_UMOUNT;
436                         list_move_tail(&child->mnt_list, &mnt->mnt_list);
437                 }
438         }
439 }
440 
441 /*
442  * collect all mounts that receive propagation from the mount in @list,
443  * and return these additional mounts in the same list.
444  * @list: the list of mounts to be unmounted.
445  *
446  * vfsmount lock must be held for write
447  */
448 int propagate_umount(struct list_head *list)
449 {
450         struct mount *mnt;
451 
452         list_for_each_entry_reverse(mnt, list, mnt_list)
453                 mark_umount_candidates(mnt);
454 
455         list_for_each_entry(mnt, list, mnt_list)
456                 __propagate_umount(mnt);
457         return 0;
458 }
459 

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