2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
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)
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.
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.
20 * fsnotify inode mark locking/lifetime/and refcnting
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.
30 * There are 3 spinlocks involved with fsnotify inode marks and they MUST
31 * be taken in order as follows:
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
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.
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
52 * Inode marks survive between when they are added to an inode and when their
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)
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.
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.
79 * Very similarly for freeing by group, except we use free_g_list.
81 * This has the very interesting property of being able to run concurrently with
82 * any (or all) other directions.
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>
95 #include <linux/atomic.h>
97 #include <linux/fsnotify_backend.h>
100 struct srcu_struct fsnotify_mark_srcu;
101 static DEFINE_SPINLOCK(destroy_lock);
102 static LIST_HEAD(destroy_list);
103 static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
105 void fsnotify_get_mark(struct fsnotify_mark *mark)
107 atomic_inc(&mark->refcnt);
110 void fsnotify_put_mark(struct fsnotify_mark *mark)
112 if (atomic_dec_and_test(&mark->refcnt)) {
114 fsnotify_put_group(mark->group);
115 mark->free_mark(mark);
120 * Any time a mark is getting freed we end up here.
121 * The caller had better be holding a reference to this mark so we don't actually
122 * do the final put under the mark->lock
124 void fsnotify_destroy_mark(struct fsnotify_mark *mark)
126 struct fsnotify_group *group;
127 struct inode *inode = NULL;
129 spin_lock(&mark->lock);
130 /* dont get the group from a mark that is not alive yet */
131 if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
132 spin_unlock(&mark->lock);
135 fsnotify_get_group(mark->group);
137 spin_unlock(&mark->lock);
139 mutex_lock(&group->mark_mutex);
140 spin_lock(&mark->lock);
142 /* something else already called this function on this mark */
143 if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
144 spin_unlock(&mark->lock);
145 mutex_unlock(&group->mark_mutex);
149 mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
151 if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
152 inode = mark->i.inode;
153 fsnotify_destroy_inode_mark(mark);
154 } else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
155 fsnotify_destroy_vfsmount_mark(mark);
159 list_del_init(&mark->g_list);
161 spin_unlock(&mark->lock);
162 mutex_unlock(&group->mark_mutex);
164 spin_lock(&destroy_lock);
165 list_add(&mark->destroy_list, &destroy_list);
166 spin_unlock(&destroy_lock);
167 wake_up(&destroy_waitq);
170 * Some groups like to know that marks are being freed. This is a
171 * callback to the group function to let it know that this mark
174 if (group->ops->freeing_mark)
175 group->ops->freeing_mark(mark, group);
178 * __fsnotify_update_child_dentry_flags(inode);
180 * I really want to call that, but we can't, we have no idea if the inode
181 * still exists the second we drop the mark->lock.
183 * The next time an event arrive to this inode from one of it's children
184 * __fsnotify_parent will see that the inode doesn't care about it's
185 * children and will update all of these flags then. So really this
186 * is just a lazy update (and could be a perf win...)
189 if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
192 * We don't necessarily have a ref on mark from caller so the above iput
193 * may have already destroyed it. Don't touch from now on.
196 atomic_dec(&group->num_marks);
199 fsnotify_put_group(group);
202 void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
204 assert_spin_locked(&mark->lock);
208 if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
209 fsnotify_set_inode_mark_mask_locked(mark, mask);
212 void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
214 assert_spin_locked(&mark->lock);
216 mark->ignored_mask = mask;
220 * Attach an initialized mark to a given group and fs object.
221 * These marks may be used for the fsnotify backend to determine which
222 * event types should be delivered to which group.
224 int fsnotify_add_mark(struct fsnotify_mark *mark,
225 struct fsnotify_group *group, struct inode *inode,
226 struct vfsmount *mnt, int allow_dups)
230 BUG_ON(inode && mnt);
231 BUG_ON(!inode && !mnt);
239 mutex_lock(&group->mark_mutex);
241 spin_lock(&mark->lock);
242 mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
244 fsnotify_get_group(group);
246 list_add(&mark->g_list, &group->marks_list);
247 atomic_inc(&group->num_marks);
248 fsnotify_get_mark(mark); /* for i_list and g_list */
251 ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
255 ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
262 /* this will pin the object if appropriate */
263 fsnotify_set_mark_mask_locked(mark, mark->mask);
264 spin_unlock(&mark->lock);
266 mutex_unlock(&group->mark_mutex);
269 __fsnotify_update_child_dentry_flags(inode);
273 mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
274 list_del_init(&mark->g_list);
275 fsnotify_put_group(group);
277 atomic_dec(&group->num_marks);
279 spin_unlock(&mark->lock);
280 mutex_unlock(&group->mark_mutex);
282 spin_lock(&destroy_lock);
283 list_add(&mark->destroy_list, &destroy_list);
284 spin_unlock(&destroy_lock);
285 wake_up(&destroy_waitq);
291 * clear any marks in a group in which mark->flags & flags is true
293 void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
296 struct fsnotify_mark *lmark, *mark;
297 LIST_HEAD(free_list);
299 mutex_lock(&group->mark_mutex);
300 list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
301 if (mark->flags & flags) {
302 list_add(&mark->free_g_list, &free_list);
303 list_del_init(&mark->g_list);
304 fsnotify_get_mark(mark);
307 mutex_unlock(&group->mark_mutex);
309 list_for_each_entry_safe(mark, lmark, &free_list, free_g_list) {
310 fsnotify_destroy_mark(mark);
311 fsnotify_put_mark(mark);
316 * Given a group, destroy all of the marks associated with that group.
318 void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
320 fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
323 void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
325 assert_spin_locked(&old->lock);
326 new->i.inode = old->i.inode;
327 new->m.mnt = old->m.mnt;
329 fsnotify_get_group(old->group);
330 new->group = old->group;
331 new->mask = old->mask;
332 new->free_mark = old->free_mark;
336 * Nothing fancy, just initialize lists and locks and counters.
338 void fsnotify_init_mark(struct fsnotify_mark *mark,
339 void (*free_mark)(struct fsnotify_mark *mark))
341 memset(mark, 0, sizeof(*mark));
342 spin_lock_init(&mark->lock);
343 atomic_set(&mark->refcnt, 1);
344 mark->free_mark = free_mark;
347 static int fsnotify_mark_destroy(void *ignored)
349 struct fsnotify_mark *mark, *next;
350 LIST_HEAD(private_destroy_list);
353 spin_lock(&destroy_lock);
354 /* exchange the list head */
355 list_replace_init(&destroy_list, &private_destroy_list);
356 spin_unlock(&destroy_lock);
358 synchronize_srcu(&fsnotify_mark_srcu);
360 list_for_each_entry_safe(mark, next, &private_destroy_list, destroy_list) {
361 list_del_init(&mark->destroy_list);
362 fsnotify_put_mark(mark);
365 wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
371 static int __init fsnotify_mark_init(void)
373 struct task_struct *thread;
375 thread = kthread_run(fsnotify_mark_destroy, NULL,
378 panic("unable to start fsnotify mark destruction thread.");
382 device_initcall(fsnotify_mark_init);