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Linux/kernel/tracepoint.c

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  1 /*
  2  * Copyright (C) 2008-2014 Mathieu Desnoyers
  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 of the License, or
  7  * (at your option) 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; if not, write to the Free Software
 16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 17  */
 18 #include <linux/module.h>
 19 #include <linux/mutex.h>
 20 #include <linux/types.h>
 21 #include <linux/jhash.h>
 22 #include <linux/list.h>
 23 #include <linux/rcupdate.h>
 24 #include <linux/tracepoint.h>
 25 #include <linux/err.h>
 26 #include <linux/slab.h>
 27 #include <linux/sched/signal.h>
 28 #include <linux/sched/task.h>
 29 #include <linux/static_key.h>
 30 
 31 extern struct tracepoint * const __start___tracepoints_ptrs[];
 32 extern struct tracepoint * const __stop___tracepoints_ptrs[];
 33 
 34 /* Set to 1 to enable tracepoint debug output */
 35 static const int tracepoint_debug;
 36 
 37 #ifdef CONFIG_MODULES
 38 /*
 39  * Tracepoint module list mutex protects the local module list.
 40  */
 41 static DEFINE_MUTEX(tracepoint_module_list_mutex);
 42 
 43 /* Local list of struct tp_module */
 44 static LIST_HEAD(tracepoint_module_list);
 45 #endif /* CONFIG_MODULES */
 46 
 47 /*
 48  * tracepoints_mutex protects the builtin and module tracepoints.
 49  * tracepoints_mutex nests inside tracepoint_module_list_mutex.
 50  */
 51 static DEFINE_MUTEX(tracepoints_mutex);
 52 
 53 /*
 54  * Note about RCU :
 55  * It is used to delay the free of multiple probes array until a quiescent
 56  * state is reached.
 57  */
 58 struct tp_probes {
 59         struct rcu_head rcu;
 60         struct tracepoint_func probes[0];
 61 };
 62 
 63 static inline void *allocate_probes(int count)
 64 {
 65         struct tp_probes *p  = kmalloc(count * sizeof(struct tracepoint_func)
 66                         + sizeof(struct tp_probes), GFP_KERNEL);
 67         return p == NULL ? NULL : p->probes;
 68 }
 69 
 70 static void rcu_free_old_probes(struct rcu_head *head)
 71 {
 72         kfree(container_of(head, struct tp_probes, rcu));
 73 }
 74 
 75 static inline void release_probes(struct tracepoint_func *old)
 76 {
 77         if (old) {
 78                 struct tp_probes *tp_probes = container_of(old,
 79                         struct tp_probes, probes[0]);
 80                 call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes);
 81         }
 82 }
 83 
 84 static void debug_print_probes(struct tracepoint_func *funcs)
 85 {
 86         int i;
 87 
 88         if (!tracepoint_debug || !funcs)
 89                 return;
 90 
 91         for (i = 0; funcs[i].func; i++)
 92                 printk(KERN_DEBUG "Probe %d : %p\n", i, funcs[i].func);
 93 }
 94 
 95 static struct tracepoint_func *
 96 func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
 97          int prio)
 98 {
 99         struct tracepoint_func *old, *new;
100         int nr_probes = 0;
101         int pos = -1;
102 
103         if (WARN_ON(!tp_func->func))
104                 return ERR_PTR(-EINVAL);
105 
106         debug_print_probes(*funcs);
107         old = *funcs;
108         if (old) {
109                 /* (N -> N+1), (N != 0, 1) probes */
110                 for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
111                         /* Insert before probes of lower priority */
112                         if (pos < 0 && old[nr_probes].prio < prio)
113                                 pos = nr_probes;
114                         if (old[nr_probes].func == tp_func->func &&
115                             old[nr_probes].data == tp_func->data)
116                                 return ERR_PTR(-EEXIST);
117                 }
118         }
119         /* + 2 : one for new probe, one for NULL func */
120         new = allocate_probes(nr_probes + 2);
121         if (new == NULL)
122                 return ERR_PTR(-ENOMEM);
123         if (old) {
124                 if (pos < 0) {
125                         pos = nr_probes;
126                         memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
127                 } else {
128                         /* Copy higher priority probes ahead of the new probe */
129                         memcpy(new, old, pos * sizeof(struct tracepoint_func));
130                         /* Copy the rest after it. */
131                         memcpy(new + pos + 1, old + pos,
132                                (nr_probes - pos) * sizeof(struct tracepoint_func));
133                 }
134         } else
135                 pos = 0;
136         new[pos] = *tp_func;
137         new[nr_probes + 1].func = NULL;
138         *funcs = new;
139         debug_print_probes(*funcs);
140         return old;
141 }
142 
143 static void *func_remove(struct tracepoint_func **funcs,
144                 struct tracepoint_func *tp_func)
145 {
146         int nr_probes = 0, nr_del = 0, i;
147         struct tracepoint_func *old, *new;
148 
149         old = *funcs;
150 
151         if (!old)
152                 return ERR_PTR(-ENOENT);
153 
154         debug_print_probes(*funcs);
155         /* (N -> M), (N > 1, M >= 0) probes */
156         if (tp_func->func) {
157                 for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
158                         if (old[nr_probes].func == tp_func->func &&
159                              old[nr_probes].data == tp_func->data)
160                                 nr_del++;
161                 }
162         }
163 
164         /*
165          * If probe is NULL, then nr_probes = nr_del = 0, and then the
166          * entire entry will be removed.
167          */
168         if (nr_probes - nr_del == 0) {
169                 /* N -> 0, (N > 1) */
170                 *funcs = NULL;
171                 debug_print_probes(*funcs);
172                 return old;
173         } else {
174                 int j = 0;
175                 /* N -> M, (N > 1, M > 0) */
176                 /* + 1 for NULL */
177                 new = allocate_probes(nr_probes - nr_del + 1);
178                 if (new == NULL)
179                         return ERR_PTR(-ENOMEM);
180                 for (i = 0; old[i].func; i++)
181                         if (old[i].func != tp_func->func
182                                         || old[i].data != tp_func->data)
183                                 new[j++] = old[i];
184                 new[nr_probes - nr_del].func = NULL;
185                 *funcs = new;
186         }
187         debug_print_probes(*funcs);
188         return old;
189 }
190 
191 /*
192  * Add the probe function to a tracepoint.
193  */
194 static int tracepoint_add_func(struct tracepoint *tp,
195                                struct tracepoint_func *func, int prio)
196 {
197         struct tracepoint_func *old, *tp_funcs;
198         int ret;
199 
200         if (tp->regfunc && !static_key_enabled(&tp->key)) {
201                 ret = tp->regfunc();
202                 if (ret < 0)
203                         return ret;
204         }
205 
206         tp_funcs = rcu_dereference_protected(tp->funcs,
207                         lockdep_is_held(&tracepoints_mutex));
208         old = func_add(&tp_funcs, func, prio);
209         if (IS_ERR(old)) {
210                 WARN_ON_ONCE(1);
211                 return PTR_ERR(old);
212         }
213 
214         /*
215          * rcu_assign_pointer has a smp_wmb() which makes sure that the new
216          * probe callbacks array is consistent before setting a pointer to it.
217          * This array is referenced by __DO_TRACE from
218          * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
219          * is used.
220          */
221         rcu_assign_pointer(tp->funcs, tp_funcs);
222         if (!static_key_enabled(&tp->key))
223                 static_key_slow_inc(&tp->key);
224         release_probes(old);
225         return 0;
226 }
227 
228 /*
229  * Remove a probe function from a tracepoint.
230  * Note: only waiting an RCU period after setting elem->call to the empty
231  * function insures that the original callback is not used anymore. This insured
232  * by preempt_disable around the call site.
233  */
234 static int tracepoint_remove_func(struct tracepoint *tp,
235                 struct tracepoint_func *func)
236 {
237         struct tracepoint_func *old, *tp_funcs;
238 
239         tp_funcs = rcu_dereference_protected(tp->funcs,
240                         lockdep_is_held(&tracepoints_mutex));
241         old = func_remove(&tp_funcs, func);
242         if (IS_ERR(old)) {
243                 WARN_ON_ONCE(1);
244                 return PTR_ERR(old);
245         }
246 
247         if (!tp_funcs) {
248                 /* Removed last function */
249                 if (tp->unregfunc && static_key_enabled(&tp->key))
250                         tp->unregfunc();
251 
252                 if (static_key_enabled(&tp->key))
253                         static_key_slow_dec(&tp->key);
254         }
255         rcu_assign_pointer(tp->funcs, tp_funcs);
256         release_probes(old);
257         return 0;
258 }
259 
260 /**
261  * tracepoint_probe_register -  Connect a probe to a tracepoint
262  * @tp: tracepoint
263  * @probe: probe handler
264  * @data: tracepoint data
265  * @prio: priority of this function over other registered functions
266  *
267  * Returns 0 if ok, error value on error.
268  * Note: if @tp is within a module, the caller is responsible for
269  * unregistering the probe before the module is gone. This can be
270  * performed either with a tracepoint module going notifier, or from
271  * within module exit functions.
272  */
273 int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
274                                    void *data, int prio)
275 {
276         struct tracepoint_func tp_func;
277         int ret;
278 
279         mutex_lock(&tracepoints_mutex);
280         tp_func.func = probe;
281         tp_func.data = data;
282         tp_func.prio = prio;
283         ret = tracepoint_add_func(tp, &tp_func, prio);
284         mutex_unlock(&tracepoints_mutex);
285         return ret;
286 }
287 EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);
288 
289 /**
290  * tracepoint_probe_register -  Connect a probe to a tracepoint
291  * @tp: tracepoint
292  * @probe: probe handler
293  * @data: tracepoint data
294  * @prio: priority of this function over other registered functions
295  *
296  * Returns 0 if ok, error value on error.
297  * Note: if @tp is within a module, the caller is responsible for
298  * unregistering the probe before the module is gone. This can be
299  * performed either with a tracepoint module going notifier, or from
300  * within module exit functions.
301  */
302 int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
303 {
304         return tracepoint_probe_register_prio(tp, probe, data, TRACEPOINT_DEFAULT_PRIO);
305 }
306 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
307 
308 /**
309  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
310  * @tp: tracepoint
311  * @probe: probe function pointer
312  * @data: tracepoint data
313  *
314  * Returns 0 if ok, error value on error.
315  */
316 int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
317 {
318         struct tracepoint_func tp_func;
319         int ret;
320 
321         mutex_lock(&tracepoints_mutex);
322         tp_func.func = probe;
323         tp_func.data = data;
324         ret = tracepoint_remove_func(tp, &tp_func);
325         mutex_unlock(&tracepoints_mutex);
326         return ret;
327 }
328 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
329 
330 #ifdef CONFIG_MODULES
331 bool trace_module_has_bad_taint(struct module *mod)
332 {
333         return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
334                                (1 << TAINT_UNSIGNED_MODULE));
335 }
336 
337 static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
338 
339 /**
340  * register_tracepoint_notifier - register tracepoint coming/going notifier
341  * @nb: notifier block
342  *
343  * Notifiers registered with this function are called on module
344  * coming/going with the tracepoint_module_list_mutex held.
345  * The notifier block callback should expect a "struct tp_module" data
346  * pointer.
347  */
348 int register_tracepoint_module_notifier(struct notifier_block *nb)
349 {
350         struct tp_module *tp_mod;
351         int ret;
352 
353         mutex_lock(&tracepoint_module_list_mutex);
354         ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
355         if (ret)
356                 goto end;
357         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
358                 (void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
359 end:
360         mutex_unlock(&tracepoint_module_list_mutex);
361         return ret;
362 }
363 EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);
364 
365 /**
366  * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
367  * @nb: notifier block
368  *
369  * The notifier block callback should expect a "struct tp_module" data
370  * pointer.
371  */
372 int unregister_tracepoint_module_notifier(struct notifier_block *nb)
373 {
374         struct tp_module *tp_mod;
375         int ret;
376 
377         mutex_lock(&tracepoint_module_list_mutex);
378         ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
379         if (ret)
380                 goto end;
381         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
382                 (void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
383 end:
384         mutex_unlock(&tracepoint_module_list_mutex);
385         return ret;
386 
387 }
388 EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
389 
390 /*
391  * Ensure the tracer unregistered the module's probes before the module
392  * teardown is performed. Prevents leaks of probe and data pointers.
393  */
394 static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
395                 struct tracepoint * const *end)
396 {
397         struct tracepoint * const *iter;
398 
399         if (!begin)
400                 return;
401         for (iter = begin; iter < end; iter++)
402                 WARN_ON_ONCE((*iter)->funcs);
403 }
404 
405 static int tracepoint_module_coming(struct module *mod)
406 {
407         struct tp_module *tp_mod;
408         int ret = 0;
409 
410         if (!mod->num_tracepoints)
411                 return 0;
412 
413         /*
414          * We skip modules that taint the kernel, especially those with different
415          * module headers (for forced load), to make sure we don't cause a crash.
416          * Staging, out-of-tree, and unsigned GPL modules are fine.
417          */
418         if (trace_module_has_bad_taint(mod))
419                 return 0;
420         mutex_lock(&tracepoint_module_list_mutex);
421         tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
422         if (!tp_mod) {
423                 ret = -ENOMEM;
424                 goto end;
425         }
426         tp_mod->mod = mod;
427         list_add_tail(&tp_mod->list, &tracepoint_module_list);
428         blocking_notifier_call_chain(&tracepoint_notify_list,
429                         MODULE_STATE_COMING, tp_mod);
430 end:
431         mutex_unlock(&tracepoint_module_list_mutex);
432         return ret;
433 }
434 
435 static void tracepoint_module_going(struct module *mod)
436 {
437         struct tp_module *tp_mod;
438 
439         if (!mod->num_tracepoints)
440                 return;
441 
442         mutex_lock(&tracepoint_module_list_mutex);
443         list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
444                 if (tp_mod->mod == mod) {
445                         blocking_notifier_call_chain(&tracepoint_notify_list,
446                                         MODULE_STATE_GOING, tp_mod);
447                         list_del(&tp_mod->list);
448                         kfree(tp_mod);
449                         /*
450                          * Called the going notifier before checking for
451                          * quiescence.
452                          */
453                         tp_module_going_check_quiescent(mod->tracepoints_ptrs,
454                                 mod->tracepoints_ptrs + mod->num_tracepoints);
455                         break;
456                 }
457         }
458         /*
459          * In the case of modules that were tainted at "coming", we'll simply
460          * walk through the list without finding it. We cannot use the "tainted"
461          * flag on "going", in case a module taints the kernel only after being
462          * loaded.
463          */
464         mutex_unlock(&tracepoint_module_list_mutex);
465 }
466 
467 static int tracepoint_module_notify(struct notifier_block *self,
468                 unsigned long val, void *data)
469 {
470         struct module *mod = data;
471         int ret = 0;
472 
473         switch (val) {
474         case MODULE_STATE_COMING:
475                 ret = tracepoint_module_coming(mod);
476                 break;
477         case MODULE_STATE_LIVE:
478                 break;
479         case MODULE_STATE_GOING:
480                 tracepoint_module_going(mod);
481                 break;
482         case MODULE_STATE_UNFORMED:
483                 break;
484         }
485         return ret;
486 }
487 
488 static struct notifier_block tracepoint_module_nb = {
489         .notifier_call = tracepoint_module_notify,
490         .priority = 0,
491 };
492 
493 static __init int init_tracepoints(void)
494 {
495         int ret;
496 
497         ret = register_module_notifier(&tracepoint_module_nb);
498         if (ret)
499                 pr_warn("Failed to register tracepoint module enter notifier\n");
500 
501         return ret;
502 }
503 __initcall(init_tracepoints);
504 #endif /* CONFIG_MODULES */
505 
506 static void for_each_tracepoint_range(struct tracepoint * const *begin,
507                 struct tracepoint * const *end,
508                 void (*fct)(struct tracepoint *tp, void *priv),
509                 void *priv)
510 {
511         struct tracepoint * const *iter;
512 
513         if (!begin)
514                 return;
515         for (iter = begin; iter < end; iter++)
516                 fct(*iter, priv);
517 }
518 
519 /**
520  * for_each_kernel_tracepoint - iteration on all kernel tracepoints
521  * @fct: callback
522  * @priv: private data
523  */
524 void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
525                 void *priv)
526 {
527         for_each_tracepoint_range(__start___tracepoints_ptrs,
528                 __stop___tracepoints_ptrs, fct, priv);
529 }
530 EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
531 
532 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
533 
534 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
535 static int sys_tracepoint_refcount;
536 
537 int syscall_regfunc(void)
538 {
539         struct task_struct *p, *t;
540 
541         if (!sys_tracepoint_refcount) {
542                 read_lock(&tasklist_lock);
543                 for_each_process_thread(p, t) {
544                         set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
545                 }
546                 read_unlock(&tasklist_lock);
547         }
548         sys_tracepoint_refcount++;
549 
550         return 0;
551 }
552 
553 void syscall_unregfunc(void)
554 {
555         struct task_struct *p, *t;
556 
557         sys_tracepoint_refcount--;
558         if (!sys_tracepoint_refcount) {
559                 read_lock(&tasklist_lock);
560                 for_each_process_thread(p, t) {
561                         clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
562                 }
563                 read_unlock(&tasklist_lock);
564         }
565 }
566 #endif
567 

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