xref: /openbmc/linux/kernel/tracepoint.c (revision b34e08d5)
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 	release_probes(old);
192 
193 	/*
194 	 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
195 	 * probe callbacks array is consistent before setting a pointer to it.
196 	 * This array is referenced by __DO_TRACE from
197 	 * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
198 	 * is used.
199 	 */
200 	rcu_assign_pointer(tp->funcs, tp_funcs);
201 	if (!static_key_enabled(&tp->key))
202 		static_key_slow_inc(&tp->key);
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 	release_probes(old);
225 
226 	if (!tp_funcs) {
227 		/* Removed last function */
228 		if (tp->unregfunc && static_key_enabled(&tp->key))
229 			tp->unregfunc();
230 
231 		if (static_key_enabled(&tp->key))
232 			static_key_slow_dec(&tp->key);
233 	}
234 	rcu_assign_pointer(tp->funcs, tp_funcs);
235 	return 0;
236 }
237 
238 /**
239  * tracepoint_probe_register -  Connect a probe to a tracepoint
240  * @tp: tracepoint
241  * @probe: probe handler
242  *
243  * Returns 0 if ok, error value on error.
244  * Note: if @tp is within a module, the caller is responsible for
245  * unregistering the probe before the module is gone. This can be
246  * performed either with a tracepoint module going notifier, or from
247  * within module exit functions.
248  */
249 int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
250 {
251 	struct tracepoint_func tp_func;
252 	int ret;
253 
254 	mutex_lock(&tracepoints_mutex);
255 	tp_func.func = probe;
256 	tp_func.data = data;
257 	ret = tracepoint_add_func(tp, &tp_func);
258 	mutex_unlock(&tracepoints_mutex);
259 	return ret;
260 }
261 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
262 
263 /**
264  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
265  * @tp: tracepoint
266  * @probe: probe function pointer
267  *
268  * Returns 0 if ok, error value on error.
269  */
270 int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
271 {
272 	struct tracepoint_func tp_func;
273 	int ret;
274 
275 	mutex_lock(&tracepoints_mutex);
276 	tp_func.func = probe;
277 	tp_func.data = data;
278 	ret = tracepoint_remove_func(tp, &tp_func);
279 	mutex_unlock(&tracepoints_mutex);
280 	return ret;
281 }
282 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
283 
284 #ifdef CONFIG_MODULES
285 bool trace_module_has_bad_taint(struct module *mod)
286 {
287 	return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
288 			       (1 << TAINT_UNSIGNED_MODULE));
289 }
290 
291 static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
292 
293 /**
294  * register_tracepoint_notifier - register tracepoint coming/going notifier
295  * @nb: notifier block
296  *
297  * Notifiers registered with this function are called on module
298  * coming/going with the tracepoint_module_list_mutex held.
299  * The notifier block callback should expect a "struct tp_module" data
300  * pointer.
301  */
302 int register_tracepoint_module_notifier(struct notifier_block *nb)
303 {
304 	struct tp_module *tp_mod;
305 	int ret;
306 
307 	mutex_lock(&tracepoint_module_list_mutex);
308 	ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
309 	if (ret)
310 		goto end;
311 	list_for_each_entry(tp_mod, &tracepoint_module_list, list)
312 		(void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
313 end:
314 	mutex_unlock(&tracepoint_module_list_mutex);
315 	return ret;
316 }
317 EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);
318 
319 /**
320  * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
321  * @nb: notifier block
322  *
323  * The notifier block callback should expect a "struct tp_module" data
324  * pointer.
325  */
326 int unregister_tracepoint_module_notifier(struct notifier_block *nb)
327 {
328 	struct tp_module *tp_mod;
329 	int ret;
330 
331 	mutex_lock(&tracepoint_module_list_mutex);
332 	ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
333 	if (ret)
334 		goto end;
335 	list_for_each_entry(tp_mod, &tracepoint_module_list, list)
336 		(void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
337 end:
338 	mutex_unlock(&tracepoint_module_list_mutex);
339 	return ret;
340 
341 }
342 EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
343 
344 /*
345  * Ensure the tracer unregistered the module's probes before the module
346  * teardown is performed. Prevents leaks of probe and data pointers.
347  */
348 static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
349 		struct tracepoint * const *end)
350 {
351 	struct tracepoint * const *iter;
352 
353 	if (!begin)
354 		return;
355 	for (iter = begin; iter < end; iter++)
356 		WARN_ON_ONCE((*iter)->funcs);
357 }
358 
359 static int tracepoint_module_coming(struct module *mod)
360 {
361 	struct tp_module *tp_mod;
362 	int ret = 0;
363 
364 	if (!mod->num_tracepoints)
365 		return 0;
366 
367 	/*
368 	 * We skip modules that taint the kernel, especially those with different
369 	 * module headers (for forced load), to make sure we don't cause a crash.
370 	 * Staging, out-of-tree, and unsigned GPL modules are fine.
371 	 */
372 	if (trace_module_has_bad_taint(mod))
373 		return 0;
374 	mutex_lock(&tracepoint_module_list_mutex);
375 	tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
376 	if (!tp_mod) {
377 		ret = -ENOMEM;
378 		goto end;
379 	}
380 	tp_mod->mod = mod;
381 	list_add_tail(&tp_mod->list, &tracepoint_module_list);
382 	blocking_notifier_call_chain(&tracepoint_notify_list,
383 			MODULE_STATE_COMING, tp_mod);
384 end:
385 	mutex_unlock(&tracepoint_module_list_mutex);
386 	return ret;
387 }
388 
389 static void tracepoint_module_going(struct module *mod)
390 {
391 	struct tp_module *tp_mod;
392 
393 	if (!mod->num_tracepoints)
394 		return;
395 
396 	mutex_lock(&tracepoint_module_list_mutex);
397 	list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
398 		if (tp_mod->mod == mod) {
399 			blocking_notifier_call_chain(&tracepoint_notify_list,
400 					MODULE_STATE_GOING, tp_mod);
401 			list_del(&tp_mod->list);
402 			kfree(tp_mod);
403 			/*
404 			 * Called the going notifier before checking for
405 			 * quiescence.
406 			 */
407 			tp_module_going_check_quiescent(mod->tracepoints_ptrs,
408 				mod->tracepoints_ptrs + mod->num_tracepoints);
409 			break;
410 		}
411 	}
412 	/*
413 	 * In the case of modules that were tainted at "coming", we'll simply
414 	 * walk through the list without finding it. We cannot use the "tainted"
415 	 * flag on "going", in case a module taints the kernel only after being
416 	 * loaded.
417 	 */
418 	mutex_unlock(&tracepoint_module_list_mutex);
419 }
420 
421 static int tracepoint_module_notify(struct notifier_block *self,
422 		unsigned long val, void *data)
423 {
424 	struct module *mod = data;
425 	int ret = 0;
426 
427 	switch (val) {
428 	case MODULE_STATE_COMING:
429 		ret = tracepoint_module_coming(mod);
430 		break;
431 	case MODULE_STATE_LIVE:
432 		break;
433 	case MODULE_STATE_GOING:
434 		tracepoint_module_going(mod);
435 		break;
436 	case MODULE_STATE_UNFORMED:
437 		break;
438 	}
439 	return ret;
440 }
441 
442 static struct notifier_block tracepoint_module_nb = {
443 	.notifier_call = tracepoint_module_notify,
444 	.priority = 0,
445 };
446 
447 static __init int init_tracepoints(void)
448 {
449 	int ret;
450 
451 	ret = register_module_notifier(&tracepoint_module_nb);
452 	if (ret)
453 		pr_warning("Failed to register tracepoint module enter notifier\n");
454 
455 	return ret;
456 }
457 __initcall(init_tracepoints);
458 #endif /* CONFIG_MODULES */
459 
460 static void for_each_tracepoint_range(struct tracepoint * const *begin,
461 		struct tracepoint * const *end,
462 		void (*fct)(struct tracepoint *tp, void *priv),
463 		void *priv)
464 {
465 	struct tracepoint * const *iter;
466 
467 	if (!begin)
468 		return;
469 	for (iter = begin; iter < end; iter++)
470 		fct(*iter, priv);
471 }
472 
473 /**
474  * for_each_kernel_tracepoint - iteration on all kernel tracepoints
475  * @fct: callback
476  * @priv: private data
477  */
478 void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
479 		void *priv)
480 {
481 	for_each_tracepoint_range(__start___tracepoints_ptrs,
482 		__stop___tracepoints_ptrs, fct, priv);
483 }
484 EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
485 
486 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
487 
488 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
489 static int sys_tracepoint_refcount;
490 
491 void syscall_regfunc(void)
492 {
493 	unsigned long flags;
494 	struct task_struct *g, *t;
495 
496 	if (!sys_tracepoint_refcount) {
497 		read_lock_irqsave(&tasklist_lock, flags);
498 		do_each_thread(g, t) {
499 			/* Skip kernel threads. */
500 			if (t->mm)
501 				set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
502 		} while_each_thread(g, t);
503 		read_unlock_irqrestore(&tasklist_lock, flags);
504 	}
505 	sys_tracepoint_refcount++;
506 }
507 
508 void syscall_unregfunc(void)
509 {
510 	unsigned long flags;
511 	struct task_struct *g, *t;
512 
513 	sys_tracepoint_refcount--;
514 	if (!sys_tracepoint_refcount) {
515 		read_lock_irqsave(&tasklist_lock, flags);
516 		do_each_thread(g, t) {
517 			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
518 		} while_each_thread(g, t);
519 		read_unlock_irqrestore(&tasklist_lock, flags);
520 	}
521 }
522 #endif
523