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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 guarenteed 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 | * entry->lock | |
34 | * group->mark_lock | |
35 | * inode->i_lock | |
36 | * | |
37 | * entry->lock protects 2 things, entry->group and entry->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 mark_entries list anchored inside a given group | |
42 | * and each entry 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_mark_entries list anchored inside a | |
47 | * given inode and each entry 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_by_entry) | |
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_mark_entries 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/module.h> | |
89 | #include <linux/mutex.h> | |
90 | #include <linux/slab.h> | |
91 | #include <linux/spinlock.h> | |
164bc619 | 92 | #include <linux/writeback.h> /* for inode_lock */ |
3be25f49 EP |
93 | |
94 | #include <asm/atomic.h> | |
95 | ||
96 | #include <linux/fsnotify_backend.h> | |
97 | #include "fsnotify.h" | |
98 | ||
99 | void fsnotify_get_mark(struct fsnotify_mark_entry *entry) | |
100 | { | |
101 | atomic_inc(&entry->refcnt); | |
102 | } | |
103 | ||
104 | void fsnotify_put_mark(struct fsnotify_mark_entry *entry) | |
105 | { | |
106 | if (atomic_dec_and_test(&entry->refcnt)) | |
107 | entry->free_mark(entry); | |
108 | } | |
109 | ||
110 | /* | |
111 | * Recalculate the mask of events relevant to a given inode locked. | |
112 | */ | |
113 | static void fsnotify_recalc_inode_mask_locked(struct inode *inode) | |
114 | { | |
115 | struct fsnotify_mark_entry *entry; | |
116 | struct hlist_node *pos; | |
117 | __u32 new_mask = 0; | |
118 | ||
119 | assert_spin_locked(&inode->i_lock); | |
120 | ||
121 | hlist_for_each_entry(entry, pos, &inode->i_fsnotify_mark_entries, i_list) | |
122 | new_mask |= entry->mask; | |
123 | inode->i_fsnotify_mask = new_mask; | |
124 | } | |
125 | ||
126 | /* | |
127 | * Recalculate the inode->i_fsnotify_mask, or the mask of all FS_* event types | |
128 | * any notifier is interested in hearing for this inode. | |
129 | */ | |
130 | void fsnotify_recalc_inode_mask(struct inode *inode) | |
131 | { | |
132 | spin_lock(&inode->i_lock); | |
133 | fsnotify_recalc_inode_mask_locked(inode); | |
134 | spin_unlock(&inode->i_lock); | |
c28f7e56 EP |
135 | |
136 | __fsnotify_update_child_dentry_flags(inode); | |
3be25f49 EP |
137 | } |
138 | ||
139 | /* | |
140 | * Any time a mark is getting freed we end up here. | |
141 | * The caller had better be holding a reference to this mark so we don't actually | |
142 | * do the final put under the entry->lock | |
143 | */ | |
144 | void fsnotify_destroy_mark_by_entry(struct fsnotify_mark_entry *entry) | |
145 | { | |
146 | struct fsnotify_group *group; | |
147 | struct inode *inode; | |
148 | ||
149 | spin_lock(&entry->lock); | |
150 | ||
151 | group = entry->group; | |
152 | inode = entry->inode; | |
153 | ||
154 | BUG_ON(group && !inode); | |
155 | BUG_ON(!group && inode); | |
156 | ||
157 | /* if !group something else already marked this to die */ | |
158 | if (!group) { | |
159 | spin_unlock(&entry->lock); | |
160 | return; | |
161 | } | |
162 | ||
163 | /* 1 from caller and 1 for being on i_list/g_list */ | |
164 | BUG_ON(atomic_read(&entry->refcnt) < 2); | |
165 | ||
166 | spin_lock(&group->mark_lock); | |
167 | spin_lock(&inode->i_lock); | |
168 | ||
169 | hlist_del_init(&entry->i_list); | |
170 | entry->inode = NULL; | |
171 | ||
172 | list_del_init(&entry->g_list); | |
173 | entry->group = NULL; | |
174 | ||
175 | fsnotify_put_mark(entry); /* for i_list and g_list */ | |
176 | ||
177 | /* | |
178 | * this mark is now off the inode->i_fsnotify_mark_entries list and we | |
179 | * hold the inode->i_lock, so this is the perfect time to update the | |
180 | * inode->i_fsnotify_mask | |
181 | */ | |
182 | fsnotify_recalc_inode_mask_locked(inode); | |
183 | ||
184 | spin_unlock(&inode->i_lock); | |
185 | spin_unlock(&group->mark_lock); | |
186 | spin_unlock(&entry->lock); | |
187 | ||
188 | /* | |
189 | * Some groups like to know that marks are being freed. This is a | |
190 | * callback to the group function to let it know that this entry | |
191 | * is being freed. | |
192 | */ | |
193 | group->ops->freeing_mark(entry, group); | |
194 | ||
c28f7e56 EP |
195 | /* |
196 | * __fsnotify_update_child_dentry_flags(inode); | |
197 | * | |
198 | * I really want to call that, but we can't, we have no idea if the inode | |
199 | * still exists the second we drop the entry->lock. | |
200 | * | |
201 | * The next time an event arrive to this inode from one of it's children | |
202 | * __fsnotify_parent will see that the inode doesn't care about it's | |
203 | * children and will update all of these flags then. So really this | |
204 | * is just a lazy update (and could be a perf win...) | |
205 | */ | |
206 | ||
207 | ||
1ef5f13c EP |
208 | iput(inode); |
209 | ||
3be25f49 EP |
210 | /* |
211 | * it's possible that this group tried to destroy itself, but this | |
212 | * this mark was simultaneously being freed by inode. If that's the | |
213 | * case, we finish freeing the group here. | |
214 | */ | |
215 | if (unlikely(atomic_dec_and_test(&group->num_marks))) | |
216 | fsnotify_final_destroy_group(group); | |
217 | } | |
218 | ||
219 | /* | |
220 | * Given a group, destroy all of the marks associated with that group. | |
221 | */ | |
222 | void fsnotify_clear_marks_by_group(struct fsnotify_group *group) | |
223 | { | |
224 | struct fsnotify_mark_entry *lentry, *entry; | |
225 | LIST_HEAD(free_list); | |
226 | ||
227 | spin_lock(&group->mark_lock); | |
228 | list_for_each_entry_safe(entry, lentry, &group->mark_entries, g_list) { | |
229 | list_add(&entry->free_g_list, &free_list); | |
230 | list_del_init(&entry->g_list); | |
231 | fsnotify_get_mark(entry); | |
232 | } | |
233 | spin_unlock(&group->mark_lock); | |
234 | ||
235 | list_for_each_entry_safe(entry, lentry, &free_list, free_g_list) { | |
236 | fsnotify_destroy_mark_by_entry(entry); | |
237 | fsnotify_put_mark(entry); | |
238 | } | |
239 | } | |
240 | ||
241 | /* | |
242 | * Given an inode, destroy all of the marks associated with that inode. | |
243 | */ | |
244 | void fsnotify_clear_marks_by_inode(struct inode *inode) | |
245 | { | |
246 | struct fsnotify_mark_entry *entry, *lentry; | |
247 | struct hlist_node *pos, *n; | |
248 | LIST_HEAD(free_list); | |
249 | ||
250 | spin_lock(&inode->i_lock); | |
251 | hlist_for_each_entry_safe(entry, pos, n, &inode->i_fsnotify_mark_entries, i_list) { | |
252 | list_add(&entry->free_i_list, &free_list); | |
253 | hlist_del_init(&entry->i_list); | |
254 | fsnotify_get_mark(entry); | |
255 | } | |
256 | spin_unlock(&inode->i_lock); | |
257 | ||
258 | list_for_each_entry_safe(entry, lentry, &free_list, free_i_list) { | |
259 | fsnotify_destroy_mark_by_entry(entry); | |
260 | fsnotify_put_mark(entry); | |
261 | } | |
262 | } | |
263 | ||
264 | /* | |
265 | * given a group and inode, find the mark associated with that combination. | |
266 | * if found take a reference to that mark and return it, else return NULL | |
267 | */ | |
268 | struct fsnotify_mark_entry *fsnotify_find_mark_entry(struct fsnotify_group *group, | |
269 | struct inode *inode) | |
270 | { | |
271 | struct fsnotify_mark_entry *entry; | |
272 | struct hlist_node *pos; | |
273 | ||
274 | assert_spin_locked(&inode->i_lock); | |
275 | ||
276 | hlist_for_each_entry(entry, pos, &inode->i_fsnotify_mark_entries, i_list) { | |
277 | if (entry->group == group) { | |
278 | fsnotify_get_mark(entry); | |
279 | return entry; | |
280 | } | |
281 | } | |
282 | return NULL; | |
283 | } | |
284 | ||
285 | /* | |
286 | * Nothing fancy, just initialize lists and locks and counters. | |
287 | */ | |
288 | void fsnotify_init_mark(struct fsnotify_mark_entry *entry, | |
289 | void (*free_mark)(struct fsnotify_mark_entry *entry)) | |
290 | ||
291 | { | |
292 | spin_lock_init(&entry->lock); | |
293 | atomic_set(&entry->refcnt, 1); | |
294 | INIT_HLIST_NODE(&entry->i_list); | |
295 | entry->group = NULL; | |
296 | entry->mask = 0; | |
297 | entry->inode = NULL; | |
298 | entry->free_mark = free_mark; | |
299 | } | |
300 | ||
301 | /* | |
302 | * Attach an initialized mark entry to a given group and inode. | |
303 | * These marks may be used for the fsnotify backend to determine which | |
304 | * event types should be delivered to which group and for which inodes. | |
305 | */ | |
306 | int fsnotify_add_mark(struct fsnotify_mark_entry *entry, | |
307 | struct fsnotify_group *group, struct inode *inode) | |
308 | { | |
309 | struct fsnotify_mark_entry *lentry; | |
310 | int ret = 0; | |
311 | ||
1ef5f13c EP |
312 | inode = igrab(inode); |
313 | if (unlikely(!inode)) | |
314 | return -EINVAL; | |
315 | ||
3be25f49 EP |
316 | /* |
317 | * LOCKING ORDER!!!! | |
318 | * entry->lock | |
319 | * group->mark_lock | |
320 | * inode->i_lock | |
321 | */ | |
322 | spin_lock(&entry->lock); | |
323 | spin_lock(&group->mark_lock); | |
324 | spin_lock(&inode->i_lock); | |
325 | ||
326 | entry->group = group; | |
327 | entry->inode = inode; | |
328 | ||
329 | lentry = fsnotify_find_mark_entry(group, inode); | |
330 | if (!lentry) { | |
331 | hlist_add_head(&entry->i_list, &inode->i_fsnotify_mark_entries); | |
332 | list_add(&entry->g_list, &group->mark_entries); | |
333 | ||
334 | fsnotify_get_mark(entry); /* for i_list and g_list */ | |
335 | ||
336 | atomic_inc(&group->num_marks); | |
337 | ||
338 | fsnotify_recalc_inode_mask_locked(inode); | |
339 | } | |
340 | ||
341 | spin_unlock(&inode->i_lock); | |
342 | spin_unlock(&group->mark_lock); | |
343 | spin_unlock(&entry->lock); | |
344 | ||
345 | if (lentry) { | |
346 | ret = -EEXIST; | |
1ef5f13c | 347 | iput(inode); |
3be25f49 | 348 | fsnotify_put_mark(lentry); |
c28f7e56 EP |
349 | } else { |
350 | __fsnotify_update_child_dentry_flags(inode); | |
3be25f49 EP |
351 | } |
352 | ||
353 | return ret; | |
354 | } | |
164bc619 EP |
355 | |
356 | /** | |
357 | * fsnotify_unmount_inodes - an sb is unmounting. handle any watched inodes. | |
358 | * @list: list of inodes being unmounted (sb->s_inodes) | |
359 | * | |
360 | * Called with inode_lock held, protecting the unmounting super block's list | |
361 | * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay. | |
362 | * We temporarily drop inode_lock, however, and CAN block. | |
363 | */ | |
364 | void fsnotify_unmount_inodes(struct list_head *list) | |
365 | { | |
366 | struct inode *inode, *next_i, *need_iput = NULL; | |
367 | ||
368 | list_for_each_entry_safe(inode, next_i, list, i_sb_list) { | |
369 | struct inode *need_iput_tmp; | |
370 | ||
371 | /* | |
372 | * We cannot __iget() an inode in state I_CLEAR, I_FREEING, | |
373 | * I_WILL_FREE, or I_NEW which is fine because by that point | |
374 | * the inode cannot have any associated watches. | |
375 | */ | |
376 | if (inode->i_state & (I_CLEAR|I_FREEING|I_WILL_FREE|I_NEW)) | |
377 | continue; | |
378 | ||
379 | /* | |
380 | * If i_count is zero, the inode cannot have any watches and | |
381 | * doing an __iget/iput with MS_ACTIVE clear would actually | |
382 | * evict all inodes with zero i_count from icache which is | |
383 | * unnecessarily violent and may in fact be illegal to do. | |
384 | */ | |
385 | if (!atomic_read(&inode->i_count)) | |
386 | continue; | |
387 | ||
388 | need_iput_tmp = need_iput; | |
389 | need_iput = NULL; | |
390 | ||
391 | /* In case fsnotify_inode_delete() drops a reference. */ | |
392 | if (inode != need_iput_tmp) | |
393 | __iget(inode); | |
394 | else | |
395 | need_iput_tmp = NULL; | |
396 | ||
397 | /* In case the dropping of a reference would nuke next_i. */ | |
398 | if ((&next_i->i_sb_list != list) && | |
399 | atomic_read(&next_i->i_count) && | |
400 | !(next_i->i_state & (I_CLEAR | I_FREEING | I_WILL_FREE))) { | |
401 | __iget(next_i); | |
402 | need_iput = next_i; | |
403 | } | |
404 | ||
405 | /* | |
406 | * We can safely drop inode_lock here because we hold | |
407 | * references on both inode and next_i. Also no new inodes | |
408 | * will be added since the umount has begun. Finally, | |
409 | * iprune_mutex keeps shrink_icache_memory() away. | |
410 | */ | |
411 | spin_unlock(&inode_lock); | |
412 | ||
413 | if (need_iput_tmp) | |
414 | iput(need_iput_tmp); | |
415 | ||
416 | /* for each watch, send FS_UNMOUNT and then remove it */ | |
417 | fsnotify(inode, FS_UNMOUNT, inode, FSNOTIFY_EVENT_INODE, NULL, 0); | |
418 | ||
419 | fsnotify_inode_delete(inode); | |
420 | ||
421 | iput(inode); | |
422 | ||
423 | spin_lock(&inode_lock); | |
424 | } | |
425 | } |