Root/kernel/notifier.c

1#include <linux/kdebug.h>
2#include <linux/kprobes.h>
3#include <linux/export.h>
4#include <linux/notifier.h>
5#include <linux/rcupdate.h>
6#include <linux/vmalloc.h>
7#include <linux/reboot.h>
8
9/*
10 * Notifier list for kernel code which wants to be called
11 * at shutdown. This is used to stop any idling DMA operations
12 * and the like.
13 */
14BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);
15
16/*
17 * Notifier chain core routines. The exported routines below
18 * are layered on top of these, with appropriate locking added.
19 */
20
21static int notifier_chain_register(struct notifier_block **nl,
22        struct notifier_block *n)
23{
24    while ((*nl) != NULL) {
25        if (n->priority > (*nl)->priority)
26            break;
27        nl = &((*nl)->next);
28    }
29    n->next = *nl;
30    rcu_assign_pointer(*nl, n);
31    return 0;
32}
33
34static int notifier_chain_cond_register(struct notifier_block **nl,
35        struct notifier_block *n)
36{
37    while ((*nl) != NULL) {
38        if ((*nl) == n)
39            return 0;
40        if (n->priority > (*nl)->priority)
41            break;
42        nl = &((*nl)->next);
43    }
44    n->next = *nl;
45    rcu_assign_pointer(*nl, n);
46    return 0;
47}
48
49static int notifier_chain_unregister(struct notifier_block **nl,
50        struct notifier_block *n)
51{
52    while ((*nl) != NULL) {
53        if ((*nl) == n) {
54            rcu_assign_pointer(*nl, n->next);
55            return 0;
56        }
57        nl = &((*nl)->next);
58    }
59    return -ENOENT;
60}
61
62/**
63 * notifier_call_chain - Informs the registered notifiers about an event.
64 * @nl: Pointer to head of the blocking notifier chain
65 * @val: Value passed unmodified to notifier function
66 * @v: Pointer passed unmodified to notifier function
67 * @nr_to_call: Number of notifier functions to be called. Don't care
68 * value of this parameter is -1.
69 * @nr_calls: Records the number of notifications sent. Don't care
70 * value of this field is NULL.
71 * @returns: notifier_call_chain returns the value returned by the
72 * last notifier function called.
73 */
74static int __kprobes notifier_call_chain(struct notifier_block **nl,
75                    unsigned long val, void *v,
76                    int nr_to_call, int *nr_calls)
77{
78    int ret = NOTIFY_DONE;
79    struct notifier_block *nb, *next_nb;
80
81    nb = rcu_dereference_raw(*nl);
82
83    while (nb && nr_to_call) {
84        next_nb = rcu_dereference_raw(nb->next);
85
86#ifdef CONFIG_DEBUG_NOTIFIERS
87        if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
88            WARN(1, "Invalid notifier called!");
89            nb = next_nb;
90            continue;
91        }
92#endif
93        ret = nb->notifier_call(nb, val, v);
94
95        if (nr_calls)
96            (*nr_calls)++;
97
98        if ((ret & NOTIFY_STOP_MASK) == NOTIFY_STOP_MASK)
99            break;
100        nb = next_nb;
101        nr_to_call--;
102    }
103    return ret;
104}
105
106/*
107 * Atomic notifier chain routines. Registration and unregistration
108 * use a spinlock, and call_chain is synchronized by RCU (no locks).
109 */
110
111/**
112 * atomic_notifier_chain_register - Add notifier to an atomic notifier chain
113 * @nh: Pointer to head of the atomic notifier chain
114 * @n: New entry in notifier chain
115 *
116 * Adds a notifier to an atomic notifier chain.
117 *
118 * Currently always returns zero.
119 */
120int atomic_notifier_chain_register(struct atomic_notifier_head *nh,
121        struct notifier_block *n)
122{
123    unsigned long flags;
124    int ret;
125
126    spin_lock_irqsave(&nh->lock, flags);
127    ret = notifier_chain_register(&nh->head, n);
128    spin_unlock_irqrestore(&nh->lock, flags);
129    return ret;
130}
131EXPORT_SYMBOL_GPL(atomic_notifier_chain_register);
132
133/**
134 * atomic_notifier_chain_unregister - Remove notifier from an atomic notifier chain
135 * @nh: Pointer to head of the atomic notifier chain
136 * @n: Entry to remove from notifier chain
137 *
138 * Removes a notifier from an atomic notifier chain.
139 *
140 * Returns zero on success or %-ENOENT on failure.
141 */
142int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
143        struct notifier_block *n)
144{
145    unsigned long flags;
146    int ret;
147
148    spin_lock_irqsave(&nh->lock, flags);
149    ret = notifier_chain_unregister(&nh->head, n);
150    spin_unlock_irqrestore(&nh->lock, flags);
151    synchronize_rcu();
152    return ret;
153}
154EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister);
155
156/**
157 * __atomic_notifier_call_chain - Call functions in an atomic notifier chain
158 * @nh: Pointer to head of the atomic notifier chain
159 * @val: Value passed unmodified to notifier function
160 * @v: Pointer passed unmodified to notifier function
161 * @nr_to_call: See the comment for notifier_call_chain.
162 * @nr_calls: See the comment for notifier_call_chain.
163 *
164 * Calls each function in a notifier chain in turn. The functions
165 * run in an atomic context, so they must not block.
166 * This routine uses RCU to synchronize with changes to the chain.
167 *
168 * If the return value of the notifier can be and'ed
169 * with %NOTIFY_STOP_MASK then atomic_notifier_call_chain()
170 * will return immediately, with the return value of
171 * the notifier function which halted execution.
172 * Otherwise the return value is the return value
173 * of the last notifier function called.
174 */
175int __kprobes __atomic_notifier_call_chain(struct atomic_notifier_head *nh,
176                    unsigned long val, void *v,
177                    int nr_to_call, int *nr_calls)
178{
179    int ret;
180
181    rcu_read_lock();
182    ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
183    rcu_read_unlock();
184    return ret;
185}
186EXPORT_SYMBOL_GPL(__atomic_notifier_call_chain);
187
188int __kprobes atomic_notifier_call_chain(struct atomic_notifier_head *nh,
189        unsigned long val, void *v)
190{
191    return __atomic_notifier_call_chain(nh, val, v, -1, NULL);
192}
193EXPORT_SYMBOL_GPL(atomic_notifier_call_chain);
194
195/*
196 * Blocking notifier chain routines. All access to the chain is
197 * synchronized by an rwsem.
198 */
199
200/**
201 * blocking_notifier_chain_register - Add notifier to a blocking notifier chain
202 * @nh: Pointer to head of the blocking notifier chain
203 * @n: New entry in notifier chain
204 *
205 * Adds a notifier to a blocking notifier chain.
206 * Must be called in process context.
207 *
208 * Currently always returns zero.
209 */
210int blocking_notifier_chain_register(struct blocking_notifier_head *nh,
211        struct notifier_block *n)
212{
213    int ret;
214
215    /*
216     * This code gets used during boot-up, when task switching is
217     * not yet working and interrupts must remain disabled. At
218     * such times we must not call down_write().
219     */
220    if (unlikely(system_state == SYSTEM_BOOTING))
221        return notifier_chain_register(&nh->head, n);
222
223    down_write(&nh->rwsem);
224    ret = notifier_chain_register(&nh->head, n);
225    up_write(&nh->rwsem);
226    return ret;
227}
228EXPORT_SYMBOL_GPL(blocking_notifier_chain_register);
229
230/**
231 * blocking_notifier_chain_cond_register - Cond add notifier to a blocking notifier chain
232 * @nh: Pointer to head of the blocking notifier chain
233 * @n: New entry in notifier chain
234 *
235 * Adds a notifier to a blocking notifier chain, only if not already
236 * present in the chain.
237 * Must be called in process context.
238 *
239 * Currently always returns zero.
240 */
241int blocking_notifier_chain_cond_register(struct blocking_notifier_head *nh,
242        struct notifier_block *n)
243{
244    int ret;
245
246    down_write(&nh->rwsem);
247    ret = notifier_chain_cond_register(&nh->head, n);
248    up_write(&nh->rwsem);
249    return ret;
250}
251EXPORT_SYMBOL_GPL(blocking_notifier_chain_cond_register);
252
253/**
254 * blocking_notifier_chain_unregister - Remove notifier from a blocking notifier chain
255 * @nh: Pointer to head of the blocking notifier chain
256 * @n: Entry to remove from notifier chain
257 *
258 * Removes a notifier from a blocking notifier chain.
259 * Must be called from process context.
260 *
261 * Returns zero on success or %-ENOENT on failure.
262 */
263int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,
264        struct notifier_block *n)
265{
266    int ret;
267
268    /*
269     * This code gets used during boot-up, when task switching is
270     * not yet working and interrupts must remain disabled. At
271     * such times we must not call down_write().
272     */
273    if (unlikely(system_state == SYSTEM_BOOTING))
274        return notifier_chain_unregister(&nh->head, n);
275
276    down_write(&nh->rwsem);
277    ret = notifier_chain_unregister(&nh->head, n);
278    up_write(&nh->rwsem);
279    return ret;
280}
281EXPORT_SYMBOL_GPL(blocking_notifier_chain_unregister);
282
283/**
284 * __blocking_notifier_call_chain - Call functions in a blocking notifier chain
285 * @nh: Pointer to head of the blocking notifier chain
286 * @val: Value passed unmodified to notifier function
287 * @v: Pointer passed unmodified to notifier function
288 * @nr_to_call: See comment for notifier_call_chain.
289 * @nr_calls: See comment for notifier_call_chain.
290 *
291 * Calls each function in a notifier chain in turn. The functions
292 * run in a process context, so they are allowed to block.
293 *
294 * If the return value of the notifier can be and'ed
295 * with %NOTIFY_STOP_MASK then blocking_notifier_call_chain()
296 * will return immediately, with the return value of
297 * the notifier function which halted execution.
298 * Otherwise the return value is the return value
299 * of the last notifier function called.
300 */
301int __blocking_notifier_call_chain(struct blocking_notifier_head *nh,
302                   unsigned long val, void *v,
303                   int nr_to_call, int *nr_calls)
304{
305    int ret = NOTIFY_DONE;
306
307    /*
308     * We check the head outside the lock, but if this access is
309     * racy then it does not matter what the result of the test
310     * is, we re-check the list after having taken the lock anyway:
311     */
312    if (rcu_dereference_raw(nh->head)) {
313        down_read(&nh->rwsem);
314        ret = notifier_call_chain(&nh->head, val, v, nr_to_call,
315                    nr_calls);
316        up_read(&nh->rwsem);
317    }
318    return ret;
319}
320EXPORT_SYMBOL_GPL(__blocking_notifier_call_chain);
321
322int blocking_notifier_call_chain(struct blocking_notifier_head *nh,
323        unsigned long val, void *v)
324{
325    return __blocking_notifier_call_chain(nh, val, v, -1, NULL);
326}
327EXPORT_SYMBOL_GPL(blocking_notifier_call_chain);
328
329/*
330 * Raw notifier chain routines. There is no protection;
331 * the caller must provide it. Use at your own risk!
332 */
333
334/**
335 * raw_notifier_chain_register - Add notifier to a raw notifier chain
336 * @nh: Pointer to head of the raw notifier chain
337 * @n: New entry in notifier chain
338 *
339 * Adds a notifier to a raw notifier chain.
340 * All locking must be provided by the caller.
341 *
342 * Currently always returns zero.
343 */
344int raw_notifier_chain_register(struct raw_notifier_head *nh,
345        struct notifier_block *n)
346{
347    return notifier_chain_register(&nh->head, n);
348}
349EXPORT_SYMBOL_GPL(raw_notifier_chain_register);
350
351/**
352 * raw_notifier_chain_unregister - Remove notifier from a raw notifier chain
353 * @nh: Pointer to head of the raw notifier chain
354 * @n: Entry to remove from notifier chain
355 *
356 * Removes a notifier from a raw notifier chain.
357 * All locking must be provided by the caller.
358 *
359 * Returns zero on success or %-ENOENT on failure.
360 */
361int raw_notifier_chain_unregister(struct raw_notifier_head *nh,
362        struct notifier_block *n)
363{
364    return notifier_chain_unregister(&nh->head, n);
365}
366EXPORT_SYMBOL_GPL(raw_notifier_chain_unregister);
367
368/**
369 * __raw_notifier_call_chain - Call functions in a raw notifier chain
370 * @nh: Pointer to head of the raw notifier chain
371 * @val: Value passed unmodified to notifier function
372 * @v: Pointer passed unmodified to notifier function
373 * @nr_to_call: See comment for notifier_call_chain.
374 * @nr_calls: See comment for notifier_call_chain
375 *
376 * Calls each function in a notifier chain in turn. The functions
377 * run in an undefined context.
378 * All locking must be provided by the caller.
379 *
380 * If the return value of the notifier can be and'ed
381 * with %NOTIFY_STOP_MASK then raw_notifier_call_chain()
382 * will return immediately, with the return value of
383 * the notifier function which halted execution.
384 * Otherwise the return value is the return value
385 * of the last notifier function called.
386 */
387int __raw_notifier_call_chain(struct raw_notifier_head *nh,
388                  unsigned long val, void *v,
389                  int nr_to_call, int *nr_calls)
390{
391    return notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
392}
393EXPORT_SYMBOL_GPL(__raw_notifier_call_chain);
394
395int raw_notifier_call_chain(struct raw_notifier_head *nh,
396        unsigned long val, void *v)
397{
398    return __raw_notifier_call_chain(nh, val, v, -1, NULL);
399}
400EXPORT_SYMBOL_GPL(raw_notifier_call_chain);
401
402/*
403 * SRCU notifier chain routines. Registration and unregistration
404 * use a mutex, and call_chain is synchronized by SRCU (no locks).
405 */
406
407/**
408 * srcu_notifier_chain_register - Add notifier to an SRCU notifier chain
409 * @nh: Pointer to head of the SRCU notifier chain
410 * @n: New entry in notifier chain
411 *
412 * Adds a notifier to an SRCU notifier chain.
413 * Must be called in process context.
414 *
415 * Currently always returns zero.
416 */
417int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
418        struct notifier_block *n)
419{
420    int ret;
421
422    /*
423     * This code gets used during boot-up, when task switching is
424     * not yet working and interrupts must remain disabled. At
425     * such times we must not call mutex_lock().
426     */
427    if (unlikely(system_state == SYSTEM_BOOTING))
428        return notifier_chain_register(&nh->head, n);
429
430    mutex_lock(&nh->mutex);
431    ret = notifier_chain_register(&nh->head, n);
432    mutex_unlock(&nh->mutex);
433    return ret;
434}
435EXPORT_SYMBOL_GPL(srcu_notifier_chain_register);
436
437/**
438 * srcu_notifier_chain_unregister - Remove notifier from an SRCU notifier chain
439 * @nh: Pointer to head of the SRCU notifier chain
440 * @n: Entry to remove from notifier chain
441 *
442 * Removes a notifier from an SRCU notifier chain.
443 * Must be called from process context.
444 *
445 * Returns zero on success or %-ENOENT on failure.
446 */
447int srcu_notifier_chain_unregister(struct srcu_notifier_head *nh,
448        struct notifier_block *n)
449{
450    int ret;
451
452    /*
453     * This code gets used during boot-up, when task switching is
454     * not yet working and interrupts must remain disabled. At
455     * such times we must not call mutex_lock().
456     */
457    if (unlikely(system_state == SYSTEM_BOOTING))
458        return notifier_chain_unregister(&nh->head, n);
459
460    mutex_lock(&nh->mutex);
461    ret = notifier_chain_unregister(&nh->head, n);
462    mutex_unlock(&nh->mutex);
463    synchronize_srcu(&nh->srcu);
464    return ret;
465}
466EXPORT_SYMBOL_GPL(srcu_notifier_chain_unregister);
467
468/**
469 * __srcu_notifier_call_chain - Call functions in an SRCU notifier chain
470 * @nh: Pointer to head of the SRCU notifier chain
471 * @val: Value passed unmodified to notifier function
472 * @v: Pointer passed unmodified to notifier function
473 * @nr_to_call: See comment for notifier_call_chain.
474 * @nr_calls: See comment for notifier_call_chain
475 *
476 * Calls each function in a notifier chain in turn. The functions
477 * run in a process context, so they are allowed to block.
478 *
479 * If the return value of the notifier can be and'ed
480 * with %NOTIFY_STOP_MASK then srcu_notifier_call_chain()
481 * will return immediately, with the return value of
482 * the notifier function which halted execution.
483 * Otherwise the return value is the return value
484 * of the last notifier function called.
485 */
486int __srcu_notifier_call_chain(struct srcu_notifier_head *nh,
487                   unsigned long val, void *v,
488                   int nr_to_call, int *nr_calls)
489{
490    int ret;
491    int idx;
492
493    idx = srcu_read_lock(&nh->srcu);
494    ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls);
495    srcu_read_unlock(&nh->srcu, idx);
496    return ret;
497}
498EXPORT_SYMBOL_GPL(__srcu_notifier_call_chain);
499
500int srcu_notifier_call_chain(struct srcu_notifier_head *nh,
501        unsigned long val, void *v)
502{
503    return __srcu_notifier_call_chain(nh, val, v, -1, NULL);
504}
505EXPORT_SYMBOL_GPL(srcu_notifier_call_chain);
506
507/**
508 * srcu_init_notifier_head - Initialize an SRCU notifier head
509 * @nh: Pointer to head of the srcu notifier chain
510 *
511 * Unlike other sorts of notifier heads, SRCU notifier heads require
512 * dynamic initialization. Be sure to call this routine before
513 * calling any of the other SRCU notifier routines for this head.
514 *
515 * If an SRCU notifier head is deallocated, it must first be cleaned
516 * up by calling srcu_cleanup_notifier_head(). Otherwise the head's
517 * per-cpu data (used by the SRCU mechanism) will leak.
518 */
519void srcu_init_notifier_head(struct srcu_notifier_head *nh)
520{
521    mutex_init(&nh->mutex);
522    if (init_srcu_struct(&nh->srcu) < 0)
523        BUG();
524    nh->head = NULL;
525}
526EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
527
528static ATOMIC_NOTIFIER_HEAD(die_chain);
529
530int notrace __kprobes notify_die(enum die_val val, const char *str,
531           struct pt_regs *regs, long err, int trap, int sig)
532{
533    struct die_args args = {
534        .regs = regs,
535        .str = str,
536        .err = err,
537        .trapnr = trap,
538        .signr = sig,
539
540    };
541    return atomic_notifier_call_chain(&die_chain, val, &args);
542}
543
544int register_die_notifier(struct notifier_block *nb)
545{
546    vmalloc_sync_all();
547    return atomic_notifier_chain_register(&die_chain, nb);
548}
549EXPORT_SYMBOL_GPL(register_die_notifier);
550
551int unregister_die_notifier(struct notifier_block *nb)
552{
553    return atomic_notifier_chain_unregister(&die_chain, nb);
554}
555EXPORT_SYMBOL_GPL(unregister_die_notifier);
556

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