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1 : : /*
2 : : * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
3 : : *
4 : : * This program is free software; you can redistribute it and/or modify
5 : : * it under the terms of the GNU General Public License as published by
6 : : * the Free Software Foundation; either version 2, or (at your option)
7 : : * any later version.
8 : : *
9 : : * This program is distributed in the hope that it will be useful,
10 : : * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 : : * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 : : * GNU General Public License for more details.
13 : : *
14 : : * You should have received a copy of the GNU General Public License
15 : : * along with this program; see the file COPYING. If not, write to
16 : : * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
17 : : */
18 : :
19 : : /*
20 : : * fsnotify inode mark locking/lifetime/and refcnting
21 : : *
22 : : * REFCNT:
23 : : * The group->recnt and mark->refcnt tell how many "things" in the kernel
24 : : * currently are referencing the objects. Both kind of objects typically will
25 : : * live inside the kernel with a refcnt of 2, one for its creation and one for
26 : : * the reference a group and a mark hold to each other.
27 : : * If you are holding the appropriate locks, you can take a reference and the
28 : : * object itself is guaranteed to survive until the reference is dropped.
29 : : *
30 : : * LOCKING:
31 : : * There are 3 locks involved with fsnotify inode marks and they MUST be taken
32 : : * in order as follows:
33 : : *
34 : : * group->mark_mutex
35 : : * mark->lock
36 : : * inode->i_lock
37 : : *
38 : : * group->mark_mutex protects the marks_list anchored inside a given group and
39 : : * each mark is hooked via the g_list. It also protects the groups private
40 : : * data (i.e group limits).
41 : :
42 : : * mark->lock protects the marks attributes like its masks and flags.
43 : : * Furthermore it protects the access to a reference of the group that the mark
44 : : * is assigned to as well as the access to a reference of the inode/vfsmount
45 : : * that is being watched by the mark.
46 : : *
47 : : * inode->i_lock protects the i_fsnotify_marks list anchored inside a
48 : : * given inode and each mark is hooked via the i_list. (and sorta the
49 : : * free_i_list)
50 : : *
51 : : *
52 : : * LIFETIME:
53 : : * Inode marks survive between when they are added to an inode and when their
54 : : * refcnt==0.
55 : : *
56 : : * The inode mark can be cleared for a number of different reasons including:
57 : : * - The inode is unlinked for the last time. (fsnotify_inode_remove)
58 : : * - The inode is being evicted from cache. (fsnotify_inode_delete)
59 : : * - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
60 : : * - Something explicitly requests that it be removed. (fsnotify_destroy_mark)
61 : : * - The fsnotify_group associated with the mark is going away and all such marks
62 : : * need to be cleaned up. (fsnotify_clear_marks_by_group)
63 : : *
64 : : * Worst case we are given an inode and need to clean up all the marks on that
65 : : * inode. We take i_lock and walk the i_fsnotify_marks safely. For each
66 : : * mark on the list we take a reference (so the mark can't disappear under us).
67 : : * We remove that mark form the inode's list of marks and we add this mark to a
68 : : * private list anchored on the stack using i_free_list; we walk i_free_list
69 : : * and before we destroy the mark we make sure that we dont race with a
70 : : * concurrent destroy_group by getting a ref to the marks group and taking the
71 : : * groups mutex.
72 : :
73 : : * Very similarly for freeing by group, except we use free_g_list.
74 : : *
75 : : * This has the very interesting property of being able to run concurrently with
76 : : * any (or all) other directions.
77 : : */
78 : :
79 : : #include <linux/fs.h>
80 : : #include <linux/init.h>
81 : : #include <linux/kernel.h>
82 : : #include <linux/kthread.h>
83 : : #include <linux/module.h>
84 : : #include <linux/mutex.h>
85 : : #include <linux/slab.h>
86 : : #include <linux/spinlock.h>
87 : : #include <linux/srcu.h>
88 : :
89 : : #include <linux/atomic.h>
90 : :
91 : : #include <linux/fsnotify_backend.h>
92 : : #include "fsnotify.h"
93 : :
94 : : struct srcu_struct fsnotify_mark_srcu;
95 : : static DEFINE_SPINLOCK(destroy_lock);
96 : : static LIST_HEAD(destroy_list);
97 : : static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
98 : :
99 : 0 : void fsnotify_get_mark(struct fsnotify_mark *mark)
100 : : {
101 : 16 : atomic_inc(&mark->refcnt);
102 : 12 : }
103 : :
104 : 0 : void fsnotify_put_mark(struct fsnotify_mark *mark)
105 : : {
106 [ + + ]: 20 : if (atomic_dec_and_test(&mark->refcnt)) {
107 [ + - ]: 4 : if (mark->group)
108 : 4 : fsnotify_put_group(mark->group);
109 : 4 : mark->free_mark(mark);
110 : : }
111 : 20 : }
112 : :
113 : : /*
114 : : * Any time a mark is getting freed we end up here.
115 : : * The caller had better be holding a reference to this mark so we don't actually
116 : : * do the final put under the mark->lock
117 : : */
118 : 0 : void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
119 : : struct fsnotify_group *group)
120 : : {
121 : : struct inode *inode = NULL;
122 : :
123 [ - + ]: 4 : BUG_ON(!mutex_is_locked(&group->mark_mutex));
124 : :
125 : : spin_lock(&mark->lock);
126 : :
127 : : /* something else already called this function on this mark */
128 [ - + ]: 8 : if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
129 : : spin_unlock(&mark->lock);
130 : 4 : return;
131 : : }
132 : :
133 : 4 : mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
134 : :
135 [ + - ]: 4 : if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
136 : 4 : inode = mark->i.inode;
137 : 4 : fsnotify_destroy_inode_mark(mark);
138 [ # # ]: 0 : } else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
139 : 0 : fsnotify_destroy_vfsmount_mark(mark);
140 : : else
141 : 0 : BUG();
142 : :
143 : 4 : list_del_init(&mark->g_list);
144 : :
145 : : spin_unlock(&mark->lock);
146 : :
147 [ + - ][ + - ]: 4 : if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
148 : 4 : iput(inode);
149 : : /* release lock temporarily */
150 : 4 : mutex_unlock(&group->mark_mutex);
151 : :
152 : : spin_lock(&destroy_lock);
153 : 4 : list_add(&mark->destroy_list, &destroy_list);
154 : : spin_unlock(&destroy_lock);
155 : 4 : wake_up(&destroy_waitq);
156 : : /*
157 : : * We don't necessarily have a ref on mark from caller so the above destroy
158 : : * may have actually freed it, unless this group provides a 'freeing_mark'
159 : : * function which must be holding a reference.
160 : : */
161 : :
162 : : /*
163 : : * Some groups like to know that marks are being freed. This is a
164 : : * callback to the group function to let it know that this mark
165 : : * is being freed.
166 : : */
167 [ + - ]: 4 : if (group->ops->freeing_mark)
168 : 4 : group->ops->freeing_mark(mark, group);
169 : :
170 : : /*
171 : : * __fsnotify_update_child_dentry_flags(inode);
172 : : *
173 : : * I really want to call that, but we can't, we have no idea if the inode
174 : : * still exists the second we drop the mark->lock.
175 : : *
176 : : * The next time an event arrive to this inode from one of it's children
177 : : * __fsnotify_parent will see that the inode doesn't care about it's
178 : : * children and will update all of these flags then. So really this
179 : : * is just a lazy update (and could be a perf win...)
180 : : */
181 : :
182 : 4 : atomic_dec(&group->num_marks);
183 : :
184 : 4 : mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
185 : : }
186 : :
187 : 0 : void fsnotify_destroy_mark(struct fsnotify_mark *mark,
188 : : struct fsnotify_group *group)
189 : : {
190 : 4 : mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
191 : 4 : fsnotify_destroy_mark_locked(mark, group);
192 : 4 : mutex_unlock(&group->mark_mutex);
193 : 4 : }
194 : :
195 : 0 : void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
196 : : {
197 [ - + ]: 4 : assert_spin_locked(&mark->lock);
198 : :
199 : 4 : mark->mask = mask;
200 : :
201 [ + - ]: 4 : if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
202 : 4 : fsnotify_set_inode_mark_mask_locked(mark, mask);
203 : 0 : }
204 : :
205 : 0 : void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
206 : : {
207 [ # # ]: 0 : assert_spin_locked(&mark->lock);
208 : :
209 : 0 : mark->ignored_mask = mask;
210 : 0 : }
211 : :
212 : : /*
213 : : * Attach an initialized mark to a given group and fs object.
214 : : * These marks may be used for the fsnotify backend to determine which
215 : : * event types should be delivered to which group.
216 : : */
217 : 0 : int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
218 : : struct fsnotify_group *group, struct inode *inode,
219 : : struct vfsmount *mnt, int allow_dups)
220 : : {
221 : : int ret = 0;
222 : :
223 [ - + ]: 4 : BUG_ON(inode && mnt);
224 [ - + ]: 4 : BUG_ON(!inode && !mnt);
225 [ - + ]: 4 : BUG_ON(!mutex_is_locked(&group->mark_mutex));
226 : :
227 : : /*
228 : : * LOCKING ORDER!!!!
229 : : * group->mark_mutex
230 : : * mark->lock
231 : : * inode->i_lock
232 : : */
233 : : spin_lock(&mark->lock);
234 : 4 : mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
235 : :
236 : 4 : fsnotify_get_group(group);
237 : 4 : mark->group = group;
238 : 4 : list_add(&mark->g_list, &group->marks_list);
239 : 4 : atomic_inc(&group->num_marks);
240 : : fsnotify_get_mark(mark); /* for i_list and g_list */
241 : :
242 [ + - ]: 4 : if (inode) {
243 : 4 : ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
244 [ + - ]: 4 : if (ret)
245 : : goto err;
246 [ # # ]: 0 : } else if (mnt) {
247 : 0 : ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
248 [ # # ]: 0 : if (ret)
249 : : goto err;
250 : : } else {
251 : 0 : BUG();
252 : : }
253 : :
254 : : /* this will pin the object if appropriate */
255 : 4 : fsnotify_set_mark_mask_locked(mark, mark->mask);
256 : : spin_unlock(&mark->lock);
257 : :
258 [ + - ]: 4 : if (inode)
259 : 4 : __fsnotify_update_child_dentry_flags(inode);
260 : :
261 : 4 : return ret;
262 : : err:
263 : 0 : mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
264 : : list_del_init(&mark->g_list);
265 : 0 : fsnotify_put_group(group);
266 : 0 : mark->group = NULL;
267 : : atomic_dec(&group->num_marks);
268 : :
269 : : spin_unlock(&mark->lock);
270 : :
271 : : spin_lock(&destroy_lock);
272 : 0 : list_add(&mark->destroy_list, &destroy_list);
273 : : spin_unlock(&destroy_lock);
274 : 0 : wake_up(&destroy_waitq);
275 : :
276 : 0 : return ret;
277 : : }
278 : :
279 : 0 : int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
280 : : struct inode *inode, struct vfsmount *mnt, int allow_dups)
281 : : {
282 : : int ret;
283 : 0 : mutex_lock(&group->mark_mutex);
284 : 0 : ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups);
285 : 0 : mutex_unlock(&group->mark_mutex);
286 : 0 : return ret;
287 : : }
288 : :
289 : : /*
290 : : * clear any marks in a group in which mark->flags & flags is true
291 : : */
292 : 0 : void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
293 : : unsigned int flags)
294 : : {
295 : : struct fsnotify_mark *lmark, *mark;
296 : :
297 : 7 : mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
298 [ - + ]: 14 : list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
299 [ # # ]: 0 : if (mark->flags & flags) {
300 : : fsnotify_get_mark(mark);
301 : 0 : fsnotify_destroy_mark_locked(mark, group);
302 : 0 : fsnotify_put_mark(mark);
303 : : }
304 : : }
305 : 7 : mutex_unlock(&group->mark_mutex);
306 : 7 : }
307 : :
308 : : /*
309 : : * Given a group, destroy all of the marks associated with that group.
310 : : */
311 : 0 : void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
312 : : {
313 : 7 : fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
314 : 7 : }
315 : :
316 : 0 : void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
317 : : {
318 [ # # ]: 0 : assert_spin_locked(&old->lock);
319 : 0 : new->i.inode = old->i.inode;
320 : 0 : new->m.mnt = old->m.mnt;
321 [ # # ]: 0 : if (old->group)
322 : 0 : fsnotify_get_group(old->group);
323 : 0 : new->group = old->group;
324 : 0 : new->mask = old->mask;
325 : 0 : new->free_mark = old->free_mark;
326 : 0 : }
327 : :
328 : : /*
329 : : * Nothing fancy, just initialize lists and locks and counters.
330 : : */
331 : 0 : void fsnotify_init_mark(struct fsnotify_mark *mark,
332 : : void (*free_mark)(struct fsnotify_mark *mark))
333 : : {
334 : 4 : memset(mark, 0, sizeof(*mark));
335 : 4 : spin_lock_init(&mark->lock);
336 : 4 : atomic_set(&mark->refcnt, 1);
337 : 4 : mark->free_mark = free_mark;
338 : 4 : }
339 : :
340 : 0 : static int fsnotify_mark_destroy(void *ignored)
341 : : {
342 : : struct fsnotify_mark *mark, *next;
343 : 4 : LIST_HEAD(private_destroy_list);
344 : :
345 : : for (;;) {
346 : : spin_lock(&destroy_lock);
347 : : /* exchange the list head */
348 : : list_replace_init(&destroy_list, &private_destroy_list);
349 : : spin_unlock(&destroy_lock);
350 : :
351 : 4 : synchronize_srcu(&fsnotify_mark_srcu);
352 : :
353 [ + + ]: 8 : list_for_each_entry_safe(mark, next, &private_destroy_list, destroy_list) {
354 : : list_del_init(&mark->destroy_list);
355 : 4 : fsnotify_put_mark(mark);
356 : : }
357 : :
358 [ - + ][ + + ]: 8 : wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
[ + - ]
359 : : }
360 : :
361 : : return 0;
362 : : }
363 : :
364 : 0 : static int __init fsnotify_mark_init(void)
365 : : {
366 : : struct task_struct *thread;
367 : :
368 [ # # ]: 0 : thread = kthread_run(fsnotify_mark_destroy, NULL,
369 : : "fsnotify_mark");
370 [ # # ]: 0 : if (IS_ERR(thread))
371 : 0 : panic("unable to start fsnotify mark destruction thread.");
372 : :
373 : 0 : return 0;
374 : : }
375 : : device_initcall(fsnotify_mark_init);
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