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

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