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Linux/kernel/tracepoint.c

  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         int ret;
198 
199         if (tp->regfunc && !static_key_enabled(&tp->key)) {
200                 ret = tp->regfunc();
201                 if (ret < 0)
202                         return ret;
203         }
204 
205         tp_funcs = rcu_dereference_protected(tp->funcs,
206                         lockdep_is_held(&tracepoints_mutex));
207         old = func_add(&tp_funcs, func, prio);
208         if (IS_ERR(old)) {
209                 WARN_ON_ONCE(1);
210                 return PTR_ERR(old);
211         }
212 
213         /*
214          * rcu_assign_pointer has a smp_wmb() which makes sure that the new
215          * probe callbacks array is consistent before setting a pointer to it.
216          * This array is referenced by __DO_TRACE from
217          * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
218          * is used.
219          */
220         rcu_assign_pointer(tp->funcs, tp_funcs);
221         if (!static_key_enabled(&tp->key))
222                 static_key_slow_inc(&tp->key);
223         release_probes(old);
224         return 0;
225 }
226 
227 /*
228  * Remove a probe function from a tracepoint.
229  * Note: only waiting an RCU period after setting elem->call to the empty
230  * function insures that the original callback is not used anymore. This insured
231  * by preempt_disable around the call site.
232  */
233 static int tracepoint_remove_func(struct tracepoint *tp,
234                 struct tracepoint_func *func)
235 {
236         struct tracepoint_func *old, *tp_funcs;
237 
238         tp_funcs = rcu_dereference_protected(tp->funcs,
239                         lockdep_is_held(&tracepoints_mutex));
240         old = func_remove(&tp_funcs, func);
241         if (IS_ERR(old)) {
242                 WARN_ON_ONCE(1);
243                 return PTR_ERR(old);
244         }
245 
246         if (!tp_funcs) {
247                 /* Removed last function */
248                 if (tp->unregfunc && static_key_enabled(&tp->key))
249                         tp->unregfunc();
250 
251                 if (static_key_enabled(&tp->key))
252                         static_key_slow_dec(&tp->key);
253         }
254         rcu_assign_pointer(tp->funcs, tp_funcs);
255         release_probes(old);
256         return 0;
257 }
258 
259 /**
260  * tracepoint_probe_register -  Connect a probe to a tracepoint
261  * @tp: tracepoint
262  * @probe: probe handler
263  * @data: tracepoint data
264  * @prio: priority of this function over other registered functions
265  *
266  * Returns 0 if ok, error value on error.
267  * Note: if @tp is within a module, the caller is responsible for
268  * unregistering the probe before the module is gone. This can be
269  * performed either with a tracepoint module going notifier, or from
270  * within module exit functions.
271  */
272 int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
273                                    void *data, int prio)
274 {
275         struct tracepoint_func tp_func;
276         int ret;
277 
278         mutex_lock(&tracepoints_mutex);
279         tp_func.func = probe;
280         tp_func.data = data;
281         tp_func.prio = prio;
282         ret = tracepoint_add_func(tp, &tp_func, prio);
283         mutex_unlock(&tracepoints_mutex);
284         return ret;
285 }
286 EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);
287 
288 /**
289  * tracepoint_probe_register -  Connect a probe to a tracepoint
290  * @tp: tracepoint
291  * @probe: probe handler
292  * @data: tracepoint data
293  * @prio: priority of this function over other registered functions
294  *
295  * Returns 0 if ok, error value on error.
296  * Note: if @tp is within a module, the caller is responsible for
297  * unregistering the probe before the module is gone. This can be
298  * performed either with a tracepoint module going notifier, or from
299  * within module exit functions.
300  */
301 int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
302 {
303         return tracepoint_probe_register_prio(tp, probe, data, TRACEPOINT_DEFAULT_PRIO);
304 }
305 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
306 
307 /**
308  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
309  * @tp: tracepoint
310  * @probe: probe function pointer
311  * @data: tracepoint data
312  *
313  * Returns 0 if ok, error value on error.
314  */
315 int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
316 {
317         struct tracepoint_func tp_func;
318         int ret;
319 
320         mutex_lock(&tracepoints_mutex);
321         tp_func.func = probe;
322         tp_func.data = data;
323         ret = tracepoint_remove_func(tp, &tp_func);
324         mutex_unlock(&tracepoints_mutex);
325         return ret;
326 }
327 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
328 
329 #ifdef CONFIG_MODULES
330 bool trace_module_has_bad_taint(struct module *mod)
331 {
332         return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
333                                (1 << TAINT_UNSIGNED_MODULE));
334 }
335 
336 static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
337 
338 /**
339  * register_tracepoint_notifier - register tracepoint coming/going notifier
340  * @nb: notifier block
341  *
342  * Notifiers registered with this function are called on module
343  * coming/going with the tracepoint_module_list_mutex held.
344  * The notifier block callback should expect a "struct tp_module" data
345  * pointer.
346  */
347 int register_tracepoint_module_notifier(struct notifier_block *nb)
348 {
349         struct tp_module *tp_mod;
350         int ret;
351 
352         mutex_lock(&tracepoint_module_list_mutex);
353         ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
354         if (ret)
355                 goto end;
356         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
357                 (void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
358 end:
359         mutex_unlock(&tracepoint_module_list_mutex);
360         return ret;
361 }
362 EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);
363 
364 /**
365  * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
366  * @nb: notifier block
367  *
368  * The notifier block callback should expect a "struct tp_module" data
369  * pointer.
370  */
371 int unregister_tracepoint_module_notifier(struct notifier_block *nb)
372 {
373         struct tp_module *tp_mod;
374         int ret;
375 
376         mutex_lock(&tracepoint_module_list_mutex);
377         ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
378         if (ret)
379                 goto end;
380         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
381                 (void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
382 end:
383         mutex_unlock(&tracepoint_module_list_mutex);
384         return ret;
385 
386 }
387 EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
388 
389 /*
390  * Ensure the tracer unregistered the module's probes before the module
391  * teardown is performed. Prevents leaks of probe and data pointers.
392  */
393 static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
394                 struct tracepoint * const *end)
395 {
396         struct tracepoint * const *iter;
397 
398         if (!begin)
399                 return;
400         for (iter = begin; iter < end; iter++)
401                 WARN_ON_ONCE((*iter)->funcs);
402 }
403 
404 static int tracepoint_module_coming(struct module *mod)
405 {
406         struct tp_module *tp_mod;
407         int ret = 0;
408 
409         if (!mod->num_tracepoints)
410                 return 0;
411 
412         /*
413          * We skip modules that taint the kernel, especially those with different
414          * module headers (for forced load), to make sure we don't cause a crash.
415          * Staging, out-of-tree, and unsigned GPL modules are fine.
416          */
417         if (trace_module_has_bad_taint(mod))
418                 return 0;
419         mutex_lock(&tracepoint_module_list_mutex);
420         tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
421         if (!tp_mod) {
422                 ret = -ENOMEM;
423                 goto end;
424         }
425         tp_mod->mod = mod;
426         list_add_tail(&tp_mod->list, &tracepoint_module_list);
427         blocking_notifier_call_chain(&tracepoint_notify_list,
428                         MODULE_STATE_COMING, tp_mod);
429 end:
430         mutex_unlock(&tracepoint_module_list_mutex);
431         return ret;
432 }
433 
434 static void tracepoint_module_going(struct module *mod)
435 {
436         struct tp_module *tp_mod;
437 
438         if (!mod->num_tracepoints)
439                 return;
440 
441         mutex_lock(&tracepoint_module_list_mutex);
442         list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
443                 if (tp_mod->mod == mod) {
444                         blocking_notifier_call_chain(&tracepoint_notify_list,
445                                         MODULE_STATE_GOING, tp_mod);
446                         list_del(&tp_mod->list);
447                         kfree(tp_mod);
448                         /*
449                          * Called the going notifier before checking for
450                          * quiescence.
451                          */
452                         tp_module_going_check_quiescent(mod->tracepoints_ptrs,
453                                 mod->tracepoints_ptrs + mod->num_tracepoints);
454                         break;
455                 }
456         }
457         /*
458          * In the case of modules that were tainted at "coming", we'll simply
459          * walk through the list without finding it. We cannot use the "tainted"
460          * flag on "going", in case a module taints the kernel only after being
461          * loaded.
462          */
463         mutex_unlock(&tracepoint_module_list_mutex);
464 }
465 
466 static int tracepoint_module_notify(struct notifier_block *self,
467                 unsigned long val, void *data)
468 {
469         struct module *mod = data;
470         int ret = 0;
471 
472         switch (val) {
473         case MODULE_STATE_COMING:
474                 ret = tracepoint_module_coming(mod);
475                 break;
476         case MODULE_STATE_LIVE:
477                 break;
478         case MODULE_STATE_GOING:
479                 tracepoint_module_going(mod);
480                 break;
481         case MODULE_STATE_UNFORMED:
482                 break;
483         }
484         return ret;
485 }
486 
487 static struct notifier_block tracepoint_module_nb = {
488         .notifier_call = tracepoint_module_notify,
489         .priority = 0,
490 };
491 
492 static __init int init_tracepoints(void)
493 {
494         int ret;
495 
496         ret = register_module_notifier(&tracepoint_module_nb);
497         if (ret)
498                 pr_warn("Failed to register tracepoint module enter notifier\n");
499 
500         return ret;
501 }
502 __initcall(init_tracepoints);
503 #endif /* CONFIG_MODULES */
504 
505 static void for_each_tracepoint_range(struct tracepoint * const *begin,
506                 struct tracepoint * const *end,
507                 void (*fct)(struct tracepoint *tp, void *priv),
508                 void *priv)
509 {
510         struct tracepoint * const *iter;
511 
512         if (!begin)
513                 return;
514         for (iter = begin; iter < end; iter++)
515                 fct(*iter, priv);
516 }
517 
518 /**
519  * for_each_kernel_tracepoint - iteration on all kernel tracepoints
520  * @fct: callback
521  * @priv: private data
522  */
523 void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
524                 void *priv)
525 {
526         for_each_tracepoint_range(__start___tracepoints_ptrs,
527                 __stop___tracepoints_ptrs, fct, priv);
528 }
529 EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
530 
531 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
532 
533 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
534 static int sys_tracepoint_refcount;
535 
536 int syscall_regfunc(void)
537 {
538         struct task_struct *p, *t;
539 
540         if (!sys_tracepoint_refcount) {
541                 read_lock(&tasklist_lock);
542                 for_each_process_thread(p, t) {
543                         set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
544                 }
545                 read_unlock(&tasklist_lock);
546         }
547         sys_tracepoint_refcount++;
548 
549         return 0;
550 }
551 
552 void syscall_unregfunc(void)
553 {
554         struct task_struct *p, *t;
555 
556         sys_tracepoint_refcount--;
557         if (!sys_tracepoint_refcount) {
558                 read_lock(&tasklist_lock);
559                 for_each_process_thread(p, t) {
560                         clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
561                 }
562                 read_unlock(&tasklist_lock);
563         }
564 }
565 #endif
566 

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