1 | // SPDX-License-Identifier: GPL-2.0-or-later |
2 | /* |
3 | * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com> |
4 | */ |
5 | |
6 | /* |
7 | * fsnotify inode mark locking/lifetime/and refcnting |
8 | * |
9 | * REFCNT: |
10 | * The group->recnt and mark->refcnt tell how many "things" in the kernel |
11 | * currently are referencing the objects. Both kind of objects typically will |
12 | * live inside the kernel with a refcnt of 2, one for its creation and one for |
13 | * the reference a group and a mark hold to each other. |
14 | * If you are holding the appropriate locks, you can take a reference and the |
15 | * object itself is guaranteed to survive until the reference is dropped. |
16 | * |
17 | * LOCKING: |
18 | * There are 3 locks involved with fsnotify inode marks and they MUST be taken |
19 | * in order as follows: |
20 | * |
21 | * group->mark_mutex |
22 | * mark->lock |
23 | * mark->connector->lock |
24 | * |
25 | * group->mark_mutex protects the marks_list anchored inside a given group and |
26 | * each mark is hooked via the g_list. It also protects the groups private |
27 | * data (i.e group limits). |
28 | |
29 | * mark->lock protects the marks attributes like its masks and flags. |
30 | * Furthermore it protects the access to a reference of the group that the mark |
31 | * is assigned to as well as the access to a reference of the inode/vfsmount |
32 | * that is being watched by the mark. |
33 | * |
34 | * mark->connector->lock protects the list of marks anchored inside an |
35 | * inode / vfsmount and each mark is hooked via the i_list. |
36 | * |
37 | * A list of notification marks relating to inode / mnt is contained in |
38 | * fsnotify_mark_connector. That structure is alive as long as there are any |
39 | * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets |
40 | * detached from fsnotify_mark_connector when last reference to the mark is |
41 | * dropped. Thus having mark reference is enough to protect mark->connector |
42 | * pointer and to make sure fsnotify_mark_connector cannot disappear. Also |
43 | * because we remove mark from g_list before dropping mark reference associated |
44 | * with that, any mark found through g_list is guaranteed to have |
45 | * mark->connector set until we drop group->mark_mutex. |
46 | * |
47 | * LIFETIME: |
48 | * Inode marks survive between when they are added to an inode and when their |
49 | * refcnt==0. Marks are also protected by fsnotify_mark_srcu. |
50 | * |
51 | * The inode mark can be cleared for a number of different reasons including: |
52 | * - The inode is unlinked for the last time. (fsnotify_inode_remove) |
53 | * - The inode is being evicted from cache. (fsnotify_inode_delete) |
54 | * - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes) |
55 | * - Something explicitly requests that it be removed. (fsnotify_destroy_mark) |
56 | * - The fsnotify_group associated with the mark is going away and all such marks |
57 | * need to be cleaned up. (fsnotify_clear_marks_by_group) |
58 | * |
59 | * This has the very interesting property of being able to run concurrently with |
60 | * any (or all) other directions. |
61 | */ |
62 | |
63 | #include <linux/fs.h> |
64 | #include <linux/init.h> |
65 | #include <linux/kernel.h> |
66 | #include <linux/kthread.h> |
67 | #include <linux/module.h> |
68 | #include <linux/mutex.h> |
69 | #include <linux/slab.h> |
70 | #include <linux/spinlock.h> |
71 | #include <linux/srcu.h> |
72 | #include <linux/ratelimit.h> |
73 | |
74 | #include <linux/atomic.h> |
75 | |
76 | #include <linux/fsnotify_backend.h> |
77 | #include "fsnotify.h" |
78 | |
79 | #define FSNOTIFY_REAPER_DELAY (1) /* 1 jiffy */ |
80 | |
81 | struct srcu_struct fsnotify_mark_srcu; |
82 | struct kmem_cache *fsnotify_mark_connector_cachep; |
83 | |
84 | static DEFINE_SPINLOCK(destroy_lock); |
85 | static LIST_HEAD(destroy_list); |
86 | static struct fsnotify_mark_connector *connector_destroy_list; |
87 | |
88 | static void fsnotify_mark_destroy_workfn(struct work_struct *work); |
89 | static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn); |
90 | |
91 | static void fsnotify_connector_destroy_workfn(struct work_struct *work); |
92 | static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn); |
93 | |
94 | void fsnotify_get_mark(struct fsnotify_mark *mark) |
95 | { |
96 | WARN_ON_ONCE(!refcount_read(&mark->refcnt)); |
97 | refcount_inc(r: &mark->refcnt); |
98 | } |
99 | |
100 | static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn) |
101 | { |
102 | if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) |
103 | return &fsnotify_conn_inode(conn)->i_fsnotify_mask; |
104 | else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) |
105 | return &fsnotify_conn_mount(conn)->mnt_fsnotify_mask; |
106 | else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) |
107 | return &fsnotify_conn_sb(conn)->s_fsnotify_mask; |
108 | return NULL; |
109 | } |
110 | |
111 | __u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn) |
112 | { |
113 | if (WARN_ON(!fsnotify_valid_obj_type(conn->type))) |
114 | return 0; |
115 | |
116 | return *fsnotify_conn_mask_p(conn); |
117 | } |
118 | |
119 | static void fsnotify_get_inode_ref(struct inode *inode) |
120 | { |
121 | ihold(inode); |
122 | atomic_long_inc(v: &inode->i_sb->s_fsnotify_connectors); |
123 | } |
124 | |
125 | /* |
126 | * Grab or drop inode reference for the connector if needed. |
127 | * |
128 | * When it's time to drop the reference, we only clear the HAS_IREF flag and |
129 | * return the inode object. fsnotify_drop_object() will be resonsible for doing |
130 | * iput() outside of spinlocks. This happens when last mark that wanted iref is |
131 | * detached. |
132 | */ |
133 | static struct inode *fsnotify_update_iref(struct fsnotify_mark_connector *conn, |
134 | bool want_iref) |
135 | { |
136 | bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF; |
137 | struct inode *inode = NULL; |
138 | |
139 | if (conn->type != FSNOTIFY_OBJ_TYPE_INODE || |
140 | want_iref == has_iref) |
141 | return NULL; |
142 | |
143 | if (want_iref) { |
144 | /* Pin inode if any mark wants inode refcount held */ |
145 | fsnotify_get_inode_ref(inode: fsnotify_conn_inode(conn)); |
146 | conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF; |
147 | } else { |
148 | /* Unpin inode after detach of last mark that wanted iref */ |
149 | inode = fsnotify_conn_inode(conn); |
150 | conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF; |
151 | } |
152 | |
153 | return inode; |
154 | } |
155 | |
156 | static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) |
157 | { |
158 | u32 new_mask = 0; |
159 | bool want_iref = false; |
160 | struct fsnotify_mark *mark; |
161 | |
162 | assert_spin_locked(&conn->lock); |
163 | /* We can get detached connector here when inode is getting unlinked. */ |
164 | if (!fsnotify_valid_obj_type(obj_type: conn->type)) |
165 | return NULL; |
166 | hlist_for_each_entry(mark, &conn->list, obj_list) { |
167 | if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) |
168 | continue; |
169 | new_mask |= fsnotify_calc_mask(mark); |
170 | if (conn->type == FSNOTIFY_OBJ_TYPE_INODE && |
171 | !(mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF)) |
172 | want_iref = true; |
173 | } |
174 | *fsnotify_conn_mask_p(conn) = new_mask; |
175 | |
176 | return fsnotify_update_iref(conn, want_iref); |
177 | } |
178 | |
179 | /* |
180 | * Calculate mask of events for a list of marks. The caller must make sure |
181 | * connector and connector->obj cannot disappear under us. Callers achieve |
182 | * this by holding a mark->lock or mark->group->mark_mutex for a mark on this |
183 | * list. |
184 | */ |
185 | void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) |
186 | { |
187 | if (!conn) |
188 | return; |
189 | |
190 | spin_lock(lock: &conn->lock); |
191 | __fsnotify_recalc_mask(conn); |
192 | spin_unlock(lock: &conn->lock); |
193 | if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) |
194 | __fsnotify_update_child_dentry_flags( |
195 | inode: fsnotify_conn_inode(conn)); |
196 | } |
197 | |
198 | /* Free all connectors queued for freeing once SRCU period ends */ |
199 | static void fsnotify_connector_destroy_workfn(struct work_struct *work) |
200 | { |
201 | struct fsnotify_mark_connector *conn, *free; |
202 | |
203 | spin_lock(lock: &destroy_lock); |
204 | conn = connector_destroy_list; |
205 | connector_destroy_list = NULL; |
206 | spin_unlock(lock: &destroy_lock); |
207 | |
208 | synchronize_srcu(ssp: &fsnotify_mark_srcu); |
209 | while (conn) { |
210 | free = conn; |
211 | conn = conn->destroy_next; |
212 | kmem_cache_free(s: fsnotify_mark_connector_cachep, objp: free); |
213 | } |
214 | } |
215 | |
216 | static void fsnotify_put_inode_ref(struct inode *inode) |
217 | { |
218 | struct super_block *sb = inode->i_sb; |
219 | |
220 | iput(inode); |
221 | if (atomic_long_dec_and_test(v: &sb->s_fsnotify_connectors)) |
222 | wake_up_var(var: &sb->s_fsnotify_connectors); |
223 | } |
224 | |
225 | static void fsnotify_get_sb_connectors(struct fsnotify_mark_connector *conn) |
226 | { |
227 | struct super_block *sb = fsnotify_connector_sb(conn); |
228 | |
229 | if (sb) |
230 | atomic_long_inc(v: &sb->s_fsnotify_connectors); |
231 | } |
232 | |
233 | static void fsnotify_put_sb_connectors(struct fsnotify_mark_connector *conn) |
234 | { |
235 | struct super_block *sb = fsnotify_connector_sb(conn); |
236 | |
237 | if (sb && atomic_long_dec_and_test(v: &sb->s_fsnotify_connectors)) |
238 | wake_up_var(var: &sb->s_fsnotify_connectors); |
239 | } |
240 | |
241 | static void *fsnotify_detach_connector_from_object( |
242 | struct fsnotify_mark_connector *conn, |
243 | unsigned int *type) |
244 | { |
245 | struct inode *inode = NULL; |
246 | |
247 | *type = conn->type; |
248 | if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) |
249 | return NULL; |
250 | |
251 | if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) { |
252 | inode = fsnotify_conn_inode(conn); |
253 | inode->i_fsnotify_mask = 0; |
254 | |
255 | /* Unpin inode when detaching from connector */ |
256 | if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF)) |
257 | inode = NULL; |
258 | } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) { |
259 | fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0; |
260 | } else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) { |
261 | fsnotify_conn_sb(conn)->s_fsnotify_mask = 0; |
262 | } |
263 | |
264 | fsnotify_put_sb_connectors(conn); |
265 | rcu_assign_pointer(*(conn->obj), NULL); |
266 | conn->obj = NULL; |
267 | conn->type = FSNOTIFY_OBJ_TYPE_DETACHED; |
268 | |
269 | return inode; |
270 | } |
271 | |
272 | static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark) |
273 | { |
274 | struct fsnotify_group *group = mark->group; |
275 | |
276 | if (WARN_ON_ONCE(!group)) |
277 | return; |
278 | group->ops->free_mark(mark); |
279 | fsnotify_put_group(group); |
280 | } |
281 | |
282 | /* Drop object reference originally held by a connector */ |
283 | static void fsnotify_drop_object(unsigned int type, void *objp) |
284 | { |
285 | if (!objp) |
286 | return; |
287 | /* Currently only inode references are passed to be dropped */ |
288 | if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE)) |
289 | return; |
290 | fsnotify_put_inode_ref(inode: objp); |
291 | } |
292 | |
293 | void fsnotify_put_mark(struct fsnotify_mark *mark) |
294 | { |
295 | struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector); |
296 | void *objp = NULL; |
297 | unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED; |
298 | bool free_conn = false; |
299 | |
300 | /* Catch marks that were actually never attached to object */ |
301 | if (!conn) { |
302 | if (refcount_dec_and_test(r: &mark->refcnt)) |
303 | fsnotify_final_mark_destroy(mark); |
304 | return; |
305 | } |
306 | |
307 | /* |
308 | * We have to be careful so that traversals of obj_list under lock can |
309 | * safely grab mark reference. |
310 | */ |
311 | if (!refcount_dec_and_lock(r: &mark->refcnt, lock: &conn->lock)) |
312 | return; |
313 | |
314 | hlist_del_init_rcu(n: &mark->obj_list); |
315 | if (hlist_empty(h: &conn->list)) { |
316 | objp = fsnotify_detach_connector_from_object(conn, type: &type); |
317 | free_conn = true; |
318 | } else { |
319 | objp = __fsnotify_recalc_mask(conn); |
320 | type = conn->type; |
321 | } |
322 | WRITE_ONCE(mark->connector, NULL); |
323 | spin_unlock(lock: &conn->lock); |
324 | |
325 | fsnotify_drop_object(type, objp); |
326 | |
327 | if (free_conn) { |
328 | spin_lock(lock: &destroy_lock); |
329 | conn->destroy_next = connector_destroy_list; |
330 | connector_destroy_list = conn; |
331 | spin_unlock(lock: &destroy_lock); |
332 | queue_work(wq: system_unbound_wq, work: &connector_reaper_work); |
333 | } |
334 | /* |
335 | * Note that we didn't update flags telling whether inode cares about |
336 | * what's happening with children. We update these flags from |
337 | * __fsnotify_parent() lazily when next event happens on one of our |
338 | * children. |
339 | */ |
340 | spin_lock(lock: &destroy_lock); |
341 | list_add(new: &mark->g_list, head: &destroy_list); |
342 | spin_unlock(lock: &destroy_lock); |
343 | queue_delayed_work(wq: system_unbound_wq, dwork: &reaper_work, |
344 | FSNOTIFY_REAPER_DELAY); |
345 | } |
346 | EXPORT_SYMBOL_GPL(fsnotify_put_mark); |
347 | |
348 | /* |
349 | * Get mark reference when we found the mark via lockless traversal of object |
350 | * list. Mark can be already removed from the list by now and on its way to be |
351 | * destroyed once SRCU period ends. |
352 | * |
353 | * Also pin the group so it doesn't disappear under us. |
354 | */ |
355 | static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark) |
356 | { |
357 | if (!mark) |
358 | return true; |
359 | |
360 | if (refcount_inc_not_zero(r: &mark->refcnt)) { |
361 | spin_lock(lock: &mark->lock); |
362 | if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) { |
363 | /* mark is attached, group is still alive then */ |
364 | atomic_inc(v: &mark->group->user_waits); |
365 | spin_unlock(lock: &mark->lock); |
366 | return true; |
367 | } |
368 | spin_unlock(lock: &mark->lock); |
369 | fsnotify_put_mark(mark); |
370 | } |
371 | return false; |
372 | } |
373 | |
374 | /* |
375 | * Puts marks and wakes up group destruction if necessary. |
376 | * |
377 | * Pairs with fsnotify_get_mark_safe() |
378 | */ |
379 | static void fsnotify_put_mark_wake(struct fsnotify_mark *mark) |
380 | { |
381 | if (mark) { |
382 | struct fsnotify_group *group = mark->group; |
383 | |
384 | fsnotify_put_mark(mark); |
385 | /* |
386 | * We abuse notification_waitq on group shutdown for waiting for |
387 | * all marks pinned when waiting for userspace. |
388 | */ |
389 | if (atomic_dec_and_test(v: &group->user_waits) && group->shutdown) |
390 | wake_up(&group->notification_waitq); |
391 | } |
392 | } |
393 | |
394 | bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info) |
395 | __releases(&fsnotify_mark_srcu) |
396 | { |
397 | int type; |
398 | |
399 | fsnotify_foreach_iter_type(type) { |
400 | /* This can fail if mark is being removed */ |
401 | if (!fsnotify_get_mark_safe(mark: iter_info->marks[type])) { |
402 | __release(&fsnotify_mark_srcu); |
403 | goto fail; |
404 | } |
405 | } |
406 | |
407 | /* |
408 | * Now that both marks are pinned by refcount in the inode / vfsmount |
409 | * lists, we can drop SRCU lock, and safely resume the list iteration |
410 | * once userspace returns. |
411 | */ |
412 | srcu_read_unlock(ssp: &fsnotify_mark_srcu, idx: iter_info->srcu_idx); |
413 | |
414 | return true; |
415 | |
416 | fail: |
417 | for (type--; type >= 0; type--) |
418 | fsnotify_put_mark_wake(mark: iter_info->marks[type]); |
419 | return false; |
420 | } |
421 | |
422 | void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info) |
423 | __acquires(&fsnotify_mark_srcu) |
424 | { |
425 | int type; |
426 | |
427 | iter_info->srcu_idx = srcu_read_lock(ssp: &fsnotify_mark_srcu); |
428 | fsnotify_foreach_iter_type(type) |
429 | fsnotify_put_mark_wake(mark: iter_info->marks[type]); |
430 | } |
431 | |
432 | /* |
433 | * Mark mark as detached, remove it from group list. Mark still stays in object |
434 | * list until its last reference is dropped. Note that we rely on mark being |
435 | * removed from group list before corresponding reference to it is dropped. In |
436 | * particular we rely on mark->connector being valid while we hold |
437 | * group->mark_mutex if we found the mark through g_list. |
438 | * |
439 | * Must be called with group->mark_mutex held. The caller must either hold |
440 | * reference to the mark or be protected by fsnotify_mark_srcu. |
441 | */ |
442 | void fsnotify_detach_mark(struct fsnotify_mark *mark) |
443 | { |
444 | fsnotify_group_assert_locked(group: mark->group); |
445 | WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) && |
446 | refcount_read(&mark->refcnt) < 1 + |
447 | !!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)); |
448 | |
449 | spin_lock(lock: &mark->lock); |
450 | /* something else already called this function on this mark */ |
451 | if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) { |
452 | spin_unlock(lock: &mark->lock); |
453 | return; |
454 | } |
455 | mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED; |
456 | list_del_init(entry: &mark->g_list); |
457 | spin_unlock(lock: &mark->lock); |
458 | |
459 | /* Drop mark reference acquired in fsnotify_add_mark_locked() */ |
460 | fsnotify_put_mark(mark); |
461 | } |
462 | |
463 | /* |
464 | * Free fsnotify mark. The mark is actually only marked as being freed. The |
465 | * freeing is actually happening only once last reference to the mark is |
466 | * dropped from a workqueue which first waits for srcu period end. |
467 | * |
468 | * Caller must have a reference to the mark or be protected by |
469 | * fsnotify_mark_srcu. |
470 | */ |
471 | void fsnotify_free_mark(struct fsnotify_mark *mark) |
472 | { |
473 | struct fsnotify_group *group = mark->group; |
474 | |
475 | spin_lock(lock: &mark->lock); |
476 | /* something else already called this function on this mark */ |
477 | if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) { |
478 | spin_unlock(lock: &mark->lock); |
479 | return; |
480 | } |
481 | mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE; |
482 | spin_unlock(lock: &mark->lock); |
483 | |
484 | /* |
485 | * Some groups like to know that marks are being freed. This is a |
486 | * callback to the group function to let it know that this mark |
487 | * is being freed. |
488 | */ |
489 | if (group->ops->freeing_mark) |
490 | group->ops->freeing_mark(mark, group); |
491 | } |
492 | |
493 | void fsnotify_destroy_mark(struct fsnotify_mark *mark, |
494 | struct fsnotify_group *group) |
495 | { |
496 | fsnotify_group_lock(group); |
497 | fsnotify_detach_mark(mark); |
498 | fsnotify_group_unlock(group); |
499 | fsnotify_free_mark(mark); |
500 | } |
501 | EXPORT_SYMBOL_GPL(fsnotify_destroy_mark); |
502 | |
503 | /* |
504 | * Sorting function for lists of fsnotify marks. |
505 | * |
506 | * Fanotify supports different notification classes (reflected as priority of |
507 | * notification group). Events shall be passed to notification groups in |
508 | * decreasing priority order. To achieve this marks in notification lists for |
509 | * inodes and vfsmounts are sorted so that priorities of corresponding groups |
510 | * are descending. |
511 | * |
512 | * Furthermore correct handling of the ignore mask requires processing inode |
513 | * and vfsmount marks of each group together. Using the group address as |
514 | * further sort criterion provides a unique sorting order and thus we can |
515 | * merge inode and vfsmount lists of marks in linear time and find groups |
516 | * present in both lists. |
517 | * |
518 | * A return value of 1 signifies that b has priority over a. |
519 | * A return value of 0 signifies that the two marks have to be handled together. |
520 | * A return value of -1 signifies that a has priority over b. |
521 | */ |
522 | int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b) |
523 | { |
524 | if (a == b) |
525 | return 0; |
526 | if (!a) |
527 | return 1; |
528 | if (!b) |
529 | return -1; |
530 | if (a->priority < b->priority) |
531 | return 1; |
532 | if (a->priority > b->priority) |
533 | return -1; |
534 | if (a < b) |
535 | return 1; |
536 | return -1; |
537 | } |
538 | |
539 | static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp, |
540 | unsigned int obj_type, |
541 | __kernel_fsid_t *fsid) |
542 | { |
543 | struct fsnotify_mark_connector *conn; |
544 | |
545 | conn = kmem_cache_alloc(cachep: fsnotify_mark_connector_cachep, GFP_KERNEL); |
546 | if (!conn) |
547 | return -ENOMEM; |
548 | spin_lock_init(&conn->lock); |
549 | INIT_HLIST_HEAD(&conn->list); |
550 | conn->flags = 0; |
551 | conn->type = obj_type; |
552 | conn->obj = connp; |
553 | /* Cache fsid of filesystem containing the object */ |
554 | if (fsid) { |
555 | conn->fsid = *fsid; |
556 | conn->flags = FSNOTIFY_CONN_FLAG_HAS_FSID; |
557 | } else { |
558 | conn->fsid.val[0] = conn->fsid.val[1] = 0; |
559 | conn->flags = 0; |
560 | } |
561 | fsnotify_get_sb_connectors(conn); |
562 | |
563 | /* |
564 | * cmpxchg() provides the barrier so that readers of *connp can see |
565 | * only initialized structure |
566 | */ |
567 | if (cmpxchg(connp, NULL, conn)) { |
568 | /* Someone else created list structure for us */ |
569 | fsnotify_put_sb_connectors(conn); |
570 | kmem_cache_free(s: fsnotify_mark_connector_cachep, objp: conn); |
571 | } |
572 | |
573 | return 0; |
574 | } |
575 | |
576 | /* |
577 | * Get mark connector, make sure it is alive and return with its lock held. |
578 | * This is for users that get connector pointer from inode or mount. Users that |
579 | * hold reference to a mark on the list may directly lock connector->lock as |
580 | * they are sure list cannot go away under them. |
581 | */ |
582 | static struct fsnotify_mark_connector *fsnotify_grab_connector( |
583 | fsnotify_connp_t *connp) |
584 | { |
585 | struct fsnotify_mark_connector *conn; |
586 | int idx; |
587 | |
588 | idx = srcu_read_lock(ssp: &fsnotify_mark_srcu); |
589 | conn = srcu_dereference(*connp, &fsnotify_mark_srcu); |
590 | if (!conn) |
591 | goto out; |
592 | spin_lock(lock: &conn->lock); |
593 | if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) { |
594 | spin_unlock(lock: &conn->lock); |
595 | srcu_read_unlock(ssp: &fsnotify_mark_srcu, idx); |
596 | return NULL; |
597 | } |
598 | out: |
599 | srcu_read_unlock(ssp: &fsnotify_mark_srcu, idx); |
600 | return conn; |
601 | } |
602 | |
603 | /* |
604 | * Add mark into proper place in given list of marks. These marks may be used |
605 | * for the fsnotify backend to determine which event types should be delivered |
606 | * to which group and for which inodes. These marks are ordered according to |
607 | * priority, highest number first, and then by the group's location in memory. |
608 | */ |
609 | static int fsnotify_add_mark_list(struct fsnotify_mark *mark, |
610 | fsnotify_connp_t *connp, |
611 | unsigned int obj_type, |
612 | int add_flags, __kernel_fsid_t *fsid) |
613 | { |
614 | struct fsnotify_mark *lmark, *last = NULL; |
615 | struct fsnotify_mark_connector *conn; |
616 | int cmp; |
617 | int err = 0; |
618 | |
619 | if (WARN_ON(!fsnotify_valid_obj_type(obj_type))) |
620 | return -EINVAL; |
621 | |
622 | /* Backend is expected to check for zero fsid (e.g. tmpfs) */ |
623 | if (fsid && WARN_ON_ONCE(!fsid->val[0] && !fsid->val[1])) |
624 | return -ENODEV; |
625 | |
626 | restart: |
627 | spin_lock(lock: &mark->lock); |
628 | conn = fsnotify_grab_connector(connp); |
629 | if (!conn) { |
630 | spin_unlock(lock: &mark->lock); |
631 | err = fsnotify_attach_connector_to_object(connp, obj_type, |
632 | fsid); |
633 | if (err) |
634 | return err; |
635 | goto restart; |
636 | } else if (fsid && !(conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID)) { |
637 | conn->fsid = *fsid; |
638 | /* Pairs with smp_rmb() in fanotify_get_fsid() */ |
639 | smp_wmb(); |
640 | conn->flags |= FSNOTIFY_CONN_FLAG_HAS_FSID; |
641 | } else if (fsid && (conn->flags & FSNOTIFY_CONN_FLAG_HAS_FSID) && |
642 | (fsid->val[0] != conn->fsid.val[0] || |
643 | fsid->val[1] != conn->fsid.val[1])) { |
644 | /* |
645 | * Backend is expected to check for non uniform fsid |
646 | * (e.g. btrfs), but maybe we missed something? |
647 | * Only allow setting conn->fsid once to non zero fsid. |
648 | * inotify and non-fid fanotify groups do not set nor test |
649 | * conn->fsid. |
650 | */ |
651 | pr_warn_ratelimited("%s: fsid mismatch on object of type %u: " |
652 | "%x.%x != %x.%x\n" , __func__, conn->type, |
653 | fsid->val[0], fsid->val[1], |
654 | conn->fsid.val[0], conn->fsid.val[1]); |
655 | err = -EXDEV; |
656 | goto out_err; |
657 | } |
658 | |
659 | /* is mark the first mark? */ |
660 | if (hlist_empty(h: &conn->list)) { |
661 | hlist_add_head_rcu(n: &mark->obj_list, h: &conn->list); |
662 | goto added; |
663 | } |
664 | |
665 | /* should mark be in the middle of the current list? */ |
666 | hlist_for_each_entry(lmark, &conn->list, obj_list) { |
667 | last = lmark; |
668 | |
669 | if ((lmark->group == mark->group) && |
670 | (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) && |
671 | !(mark->group->flags & FSNOTIFY_GROUP_DUPS)) { |
672 | err = -EEXIST; |
673 | goto out_err; |
674 | } |
675 | |
676 | cmp = fsnotify_compare_groups(a: lmark->group, b: mark->group); |
677 | if (cmp >= 0) { |
678 | hlist_add_before_rcu(n: &mark->obj_list, next: &lmark->obj_list); |
679 | goto added; |
680 | } |
681 | } |
682 | |
683 | BUG_ON(last == NULL); |
684 | /* mark should be the last entry. last is the current last entry */ |
685 | hlist_add_behind_rcu(n: &mark->obj_list, prev: &last->obj_list); |
686 | added: |
687 | /* |
688 | * Since connector is attached to object using cmpxchg() we are |
689 | * guaranteed that connector initialization is fully visible by anyone |
690 | * seeing mark->connector set. |
691 | */ |
692 | WRITE_ONCE(mark->connector, conn); |
693 | out_err: |
694 | spin_unlock(lock: &conn->lock); |
695 | spin_unlock(lock: &mark->lock); |
696 | return err; |
697 | } |
698 | |
699 | /* |
700 | * Attach an initialized mark to a given group and fs object. |
701 | * These marks may be used for the fsnotify backend to determine which |
702 | * event types should be delivered to which group. |
703 | */ |
704 | int fsnotify_add_mark_locked(struct fsnotify_mark *mark, |
705 | fsnotify_connp_t *connp, unsigned int obj_type, |
706 | int add_flags, __kernel_fsid_t *fsid) |
707 | { |
708 | struct fsnotify_group *group = mark->group; |
709 | int ret = 0; |
710 | |
711 | fsnotify_group_assert_locked(group); |
712 | |
713 | /* |
714 | * LOCKING ORDER!!!! |
715 | * group->mark_mutex |
716 | * mark->lock |
717 | * mark->connector->lock |
718 | */ |
719 | spin_lock(lock: &mark->lock); |
720 | mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED; |
721 | |
722 | list_add(new: &mark->g_list, head: &group->marks_list); |
723 | fsnotify_get_mark(mark); /* for g_list */ |
724 | spin_unlock(lock: &mark->lock); |
725 | |
726 | ret = fsnotify_add_mark_list(mark, connp, obj_type, add_flags, fsid); |
727 | if (ret) |
728 | goto err; |
729 | |
730 | fsnotify_recalc_mask(conn: mark->connector); |
731 | |
732 | return ret; |
733 | err: |
734 | spin_lock(lock: &mark->lock); |
735 | mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE | |
736 | FSNOTIFY_MARK_FLAG_ATTACHED); |
737 | list_del_init(entry: &mark->g_list); |
738 | spin_unlock(lock: &mark->lock); |
739 | |
740 | fsnotify_put_mark(mark); |
741 | return ret; |
742 | } |
743 | |
744 | int fsnotify_add_mark(struct fsnotify_mark *mark, fsnotify_connp_t *connp, |
745 | unsigned int obj_type, int add_flags, |
746 | __kernel_fsid_t *fsid) |
747 | { |
748 | int ret; |
749 | struct fsnotify_group *group = mark->group; |
750 | |
751 | fsnotify_group_lock(group); |
752 | ret = fsnotify_add_mark_locked(mark, connp, obj_type, add_flags, fsid); |
753 | fsnotify_group_unlock(group); |
754 | return ret; |
755 | } |
756 | EXPORT_SYMBOL_GPL(fsnotify_add_mark); |
757 | |
758 | /* |
759 | * Given a list of marks, find the mark associated with given group. If found |
760 | * take a reference to that mark and return it, else return NULL. |
761 | */ |
762 | struct fsnotify_mark *fsnotify_find_mark(fsnotify_connp_t *connp, |
763 | struct fsnotify_group *group) |
764 | { |
765 | struct fsnotify_mark_connector *conn; |
766 | struct fsnotify_mark *mark; |
767 | |
768 | conn = fsnotify_grab_connector(connp); |
769 | if (!conn) |
770 | return NULL; |
771 | |
772 | hlist_for_each_entry(mark, &conn->list, obj_list) { |
773 | if (mark->group == group && |
774 | (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) { |
775 | fsnotify_get_mark(mark); |
776 | spin_unlock(lock: &conn->lock); |
777 | return mark; |
778 | } |
779 | } |
780 | spin_unlock(lock: &conn->lock); |
781 | return NULL; |
782 | } |
783 | EXPORT_SYMBOL_GPL(fsnotify_find_mark); |
784 | |
785 | /* Clear any marks in a group with given type mask */ |
786 | void fsnotify_clear_marks_by_group(struct fsnotify_group *group, |
787 | unsigned int obj_type) |
788 | { |
789 | struct fsnotify_mark *lmark, *mark; |
790 | LIST_HEAD(to_free); |
791 | struct list_head *head = &to_free; |
792 | |
793 | /* Skip selection step if we want to clear all marks. */ |
794 | if (obj_type == FSNOTIFY_OBJ_TYPE_ANY) { |
795 | head = &group->marks_list; |
796 | goto clear; |
797 | } |
798 | /* |
799 | * We have to be really careful here. Anytime we drop mark_mutex, e.g. |
800 | * fsnotify_clear_marks_by_inode() can come and free marks. Even in our |
801 | * to_free list so we have to use mark_mutex even when accessing that |
802 | * list. And freeing mark requires us to drop mark_mutex. So we can |
803 | * reliably free only the first mark in the list. That's why we first |
804 | * move marks to free to to_free list in one go and then free marks in |
805 | * to_free list one by one. |
806 | */ |
807 | fsnotify_group_lock(group); |
808 | list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) { |
809 | if (mark->connector->type == obj_type) |
810 | list_move(list: &mark->g_list, head: &to_free); |
811 | } |
812 | fsnotify_group_unlock(group); |
813 | |
814 | clear: |
815 | while (1) { |
816 | fsnotify_group_lock(group); |
817 | if (list_empty(head)) { |
818 | fsnotify_group_unlock(group); |
819 | break; |
820 | } |
821 | mark = list_first_entry(head, struct fsnotify_mark, g_list); |
822 | fsnotify_get_mark(mark); |
823 | fsnotify_detach_mark(mark); |
824 | fsnotify_group_unlock(group); |
825 | fsnotify_free_mark(mark); |
826 | fsnotify_put_mark(mark); |
827 | } |
828 | } |
829 | |
830 | /* Destroy all marks attached to an object via connector */ |
831 | void fsnotify_destroy_marks(fsnotify_connp_t *connp) |
832 | { |
833 | struct fsnotify_mark_connector *conn; |
834 | struct fsnotify_mark *mark, *old_mark = NULL; |
835 | void *objp; |
836 | unsigned int type; |
837 | |
838 | conn = fsnotify_grab_connector(connp); |
839 | if (!conn) |
840 | return; |
841 | /* |
842 | * We have to be careful since we can race with e.g. |
843 | * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the |
844 | * list can get modified. However we are holding mark reference and |
845 | * thus our mark cannot be removed from obj_list so we can continue |
846 | * iteration after regaining conn->lock. |
847 | */ |
848 | hlist_for_each_entry(mark, &conn->list, obj_list) { |
849 | fsnotify_get_mark(mark); |
850 | spin_unlock(lock: &conn->lock); |
851 | if (old_mark) |
852 | fsnotify_put_mark(old_mark); |
853 | old_mark = mark; |
854 | fsnotify_destroy_mark(mark, mark->group); |
855 | spin_lock(lock: &conn->lock); |
856 | } |
857 | /* |
858 | * Detach list from object now so that we don't pin inode until all |
859 | * mark references get dropped. It would lead to strange results such |
860 | * as delaying inode deletion or blocking unmount. |
861 | */ |
862 | objp = fsnotify_detach_connector_from_object(conn, type: &type); |
863 | spin_unlock(lock: &conn->lock); |
864 | if (old_mark) |
865 | fsnotify_put_mark(old_mark); |
866 | fsnotify_drop_object(type, objp); |
867 | } |
868 | |
869 | /* |
870 | * Nothing fancy, just initialize lists and locks and counters. |
871 | */ |
872 | void fsnotify_init_mark(struct fsnotify_mark *mark, |
873 | struct fsnotify_group *group) |
874 | { |
875 | memset(mark, 0, sizeof(*mark)); |
876 | spin_lock_init(&mark->lock); |
877 | refcount_set(r: &mark->refcnt, n: 1); |
878 | fsnotify_get_group(group); |
879 | mark->group = group; |
880 | WRITE_ONCE(mark->connector, NULL); |
881 | } |
882 | EXPORT_SYMBOL_GPL(fsnotify_init_mark); |
883 | |
884 | /* |
885 | * Destroy all marks in destroy_list, waits for SRCU period to finish before |
886 | * actually freeing marks. |
887 | */ |
888 | static void fsnotify_mark_destroy_workfn(struct work_struct *work) |
889 | { |
890 | struct fsnotify_mark *mark, *next; |
891 | struct list_head private_destroy_list; |
892 | |
893 | spin_lock(lock: &destroy_lock); |
894 | /* exchange the list head */ |
895 | list_replace_init(old: &destroy_list, new: &private_destroy_list); |
896 | spin_unlock(lock: &destroy_lock); |
897 | |
898 | synchronize_srcu(ssp: &fsnotify_mark_srcu); |
899 | |
900 | list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) { |
901 | list_del_init(entry: &mark->g_list); |
902 | fsnotify_final_mark_destroy(mark); |
903 | } |
904 | } |
905 | |
906 | /* Wait for all marks queued for destruction to be actually destroyed */ |
907 | void fsnotify_wait_marks_destroyed(void) |
908 | { |
909 | flush_delayed_work(dwork: &reaper_work); |
910 | } |
911 | EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed); |
912 | |