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