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

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