Free Electrons

Embedded Linux Experts

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
/*
 * Copyright (C) 2008-2014 Mathieu Desnoyers
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/types.h>
#include <linux/jhash.h>
#include <linux/list.h>
#include <linux/rcupdate.h>
#include <linux/tracepoint.h>
#include <linux/err.h>
#include <linux/slab.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
#include <linux/static_key.h>

extern struct tracepoint * const __start___tracepoints_ptrs[];
extern struct tracepoint * const __stop___tracepoints_ptrs[];

/* Set to 1 to enable tracepoint debug output */
static const int tracepoint_debug;

#ifdef CONFIG_MODULES
/*
 * Tracepoint module list mutex protects the local module list.
 */
static DEFINE_MUTEX(tracepoint_module_list_mutex);

/* Local list of struct tp_module */
static LIST_HEAD(tracepoint_module_list);
#endif /* CONFIG_MODULES */

/*
 * tracepoints_mutex protects the builtin and module tracepoints.
 * tracepoints_mutex nests inside tracepoint_module_list_mutex.
 */
static DEFINE_MUTEX(tracepoints_mutex);

/*
 * Note about RCU :
 * It is used to delay the free of multiple probes array until a quiescent
 * state is reached.
 */
struct tp_probes {
	struct rcu_head rcu;
	struct tracepoint_func probes[0];
};

static inline void *allocate_probes(int count)
{
	struct tp_probes *p  = kmalloc(count * sizeof(struct tracepoint_func)
			+ sizeof(struct tp_probes), GFP_KERNEL);
	return p == NULL ? NULL : p->probes;
}

static void rcu_free_old_probes(struct rcu_head *head)
{
	kfree(container_of(head, struct tp_probes, rcu));
}

static inline void release_probes(struct tracepoint_func *old)
{
	if (old) {
		struct tp_probes *tp_probes = container_of(old,
			struct tp_probes, probes[0]);
		call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes);
	}
}

static void debug_print_probes(struct tracepoint_func *funcs)
{
	int i;

	if (!tracepoint_debug || !funcs)
		return;

	for (i = 0; funcs[i].func; i++)
		printk(KERN_DEBUG "Probe %d : %p\n", i, funcs[i].func);
}

static struct tracepoint_func *
func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
	 int prio)
{
	struct tracepoint_func *old, *new;
	int nr_probes = 0;
	int pos = -1;

	if (WARN_ON(!tp_func->func))
		return ERR_PTR(-EINVAL);

	debug_print_probes(*funcs);
	old = *funcs;
	if (old) {
		/* (N -> N+1), (N != 0, 1) probes */
		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
			/* Insert before probes of lower priority */
			if (pos < 0 && old[nr_probes].prio < prio)
				pos = nr_probes;
			if (old[nr_probes].func == tp_func->func &&
			    old[nr_probes].data == tp_func->data)
				return ERR_PTR(-EEXIST);
		}
	}
	/* + 2 : one for new probe, one for NULL func */
	new = allocate_probes(nr_probes + 2);
	if (new == NULL)
		return ERR_PTR(-ENOMEM);
	if (old) {
		if (pos < 0) {
			pos = nr_probes;
			memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
		} else {
			/* Copy higher priority probes ahead of the new probe */
			memcpy(new, old, pos * sizeof(struct tracepoint_func));
			/* Copy the rest after it. */
			memcpy(new + pos + 1, old + pos,
			       (nr_probes - pos) * sizeof(struct tracepoint_func));
		}
	} else
		pos = 0;
	new[pos] = *tp_func;
	new[nr_probes + 1].func = NULL;
	*funcs = new;
	debug_print_probes(*funcs);
	return old;
}

static void *func_remove(struct tracepoint_func **funcs,
		struct tracepoint_func *tp_func)
{
	int nr_probes = 0, nr_del = 0, i;
	struct tracepoint_func *old, *new;

	old = *funcs;

	if (!old)
		return ERR_PTR(-ENOENT);

	debug_print_probes(*funcs);
	/* (N -> M), (N > 1, M >= 0) probes */
	if (tp_func->func) {
		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
			if (old[nr_probes].func == tp_func->func &&
			     old[nr_probes].data == tp_func->data)
				nr_del++;
		}
	}

	/*
	 * If probe is NULL, then nr_probes = nr_del = 0, and then the
	 * entire entry will be removed.
	 */
	if (nr_probes - nr_del == 0) {
		/* N -> 0, (N > 1) */
		*funcs = NULL;
		debug_print_probes(*funcs);
		return old;
	} else {
		int j = 0;
		/* N -> M, (N > 1, M > 0) */
		/* + 1 for NULL */
		new = allocate_probes(nr_probes - nr_del + 1);
		if (new == NULL)
			return ERR_PTR(-ENOMEM);
		for (i = 0; old[i].func; i++)
			if (old[i].func != tp_func->func
					|| old[i].data != tp_func->data)
				new[j++] = old[i];
		new[nr_probes - nr_del].func = NULL;
		*funcs = new;
	}
	debug_print_probes(*funcs);
	return old;
}

/*
 * Add the probe function to a tracepoint.
 */
static int tracepoint_add_func(struct tracepoint *tp,
			       struct tracepoint_func *func, int prio)
{
	struct tracepoint_func *old, *tp_funcs;
	int ret;

	if (tp->regfunc && !static_key_enabled(&tp->key)) {
		ret = tp->regfunc();
		if (ret < 0)
			return ret;
	}

	tp_funcs = rcu_dereference_protected(tp->funcs,
			lockdep_is_held(&tracepoints_mutex));
	old = func_add(&tp_funcs, func, prio);
	if (IS_ERR(old)) {
		WARN_ON_ONCE(1);
		return PTR_ERR(old);
	}

	/*
	 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
	 * probe callbacks array is consistent before setting a pointer to it.
	 * This array is referenced by __DO_TRACE from
	 * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
	 * is used.
	 */
	rcu_assign_pointer(tp->funcs, tp_funcs);
	if (!static_key_enabled(&tp->key))
		static_key_slow_inc(&tp->key);
	release_probes(old);
	return 0;
}

/*
 * Remove a probe function from a tracepoint.
 * Note: only waiting an RCU period after setting elem->call to the empty
 * function insures that the original callback is not used anymore. This insured
 * by preempt_disable around the call site.
 */
static int tracepoint_remove_func(struct tracepoint *tp,
		struct tracepoint_func *func)
{
	struct tracepoint_func *old, *tp_funcs;

	tp_funcs = rcu_dereference_protected(tp->funcs,
			lockdep_is_held(&tracepoints_mutex));
	old = func_remove(&tp_funcs, func);
	if (IS_ERR(old)) {
		WARN_ON_ONCE(1);
		return PTR_ERR(old);
	}

	if (!tp_funcs) {
		/* Removed last function */
		if (tp->unregfunc && static_key_enabled(&tp->key))
			tp->unregfunc();

		if (static_key_enabled(&tp->key))
			static_key_slow_dec(&tp->key);
	}
	rcu_assign_pointer(tp->funcs, tp_funcs);
	release_probes(old);
	return 0;
}

/**
 * tracepoint_probe_register -  Connect a probe to a tracepoint
 * @tp: tracepoint
 * @probe: probe handler
 * @data: tracepoint data
 * @prio: priority of this function over other registered functions
 *
 * Returns 0 if ok, error value on error.
 * Note: if @tp is within a module, the caller is responsible for
 * unregistering the probe before the module is gone. This can be
 * performed either with a tracepoint module going notifier, or from
 * within module exit functions.
 */
int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
				   void *data, int prio)
{
	struct tracepoint_func tp_func;
	int ret;

	mutex_lock(&tracepoints_mutex);
	tp_func.func = probe;
	tp_func.data = data;
	tp_func.prio = prio;
	ret = tracepoint_add_func(tp, &tp_func, prio);
	mutex_unlock(&tracepoints_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);

/**
 * tracepoint_probe_register -  Connect a probe to a tracepoint
 * @tp: tracepoint
 * @probe: probe handler
 * @data: tracepoint data
 * @prio: priority of this function over other registered functions
 *
 * Returns 0 if ok, error value on error.
 * Note: if @tp is within a module, the caller is responsible for
 * unregistering the probe before the module is gone. This can be
 * performed either with a tracepoint module going notifier, or from
 * within module exit functions.
 */
int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
{
	return tracepoint_probe_register_prio(tp, probe, data, TRACEPOINT_DEFAULT_PRIO);
}
EXPORT_SYMBOL_GPL(tracepoint_probe_register);

/**
 * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 * @tp: tracepoint
 * @probe: probe function pointer
 * @data: tracepoint data
 *
 * Returns 0 if ok, error value on error.
 */
int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
{
	struct tracepoint_func tp_func;
	int ret;

	mutex_lock(&tracepoints_mutex);
	tp_func.func = probe;
	tp_func.data = data;
	ret = tracepoint_remove_func(tp, &tp_func);
	mutex_unlock(&tracepoints_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);

#ifdef CONFIG_MODULES
bool trace_module_has_bad_taint(struct module *mod)
{
	return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
			       (1 << TAINT_UNSIGNED_MODULE));
}

static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);

/**
 * register_tracepoint_notifier - register tracepoint coming/going notifier
 * @nb: notifier block
 *
 * Notifiers registered with this function are called on module
 * coming/going with the tracepoint_module_list_mutex held.
 * The notifier block callback should expect a "struct tp_module" data
 * pointer.
 */
int register_tracepoint_module_notifier(struct notifier_block *nb)
{
	struct tp_module *tp_mod;
	int ret;

	mutex_lock(&tracepoint_module_list_mutex);
	ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
	if (ret)
		goto end;
	list_for_each_entry(tp_mod, &tracepoint_module_list, list)
		(void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
end:
	mutex_unlock(&tracepoint_module_list_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);

/**
 * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
 * @nb: notifier block
 *
 * The notifier block callback should expect a "struct tp_module" data
 * pointer.
 */
int unregister_tracepoint_module_notifier(struct notifier_block *nb)
{
	struct tp_module *tp_mod;
	int ret;

	mutex_lock(&tracepoint_module_list_mutex);
	ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
	if (ret)
		goto end;
	list_for_each_entry(tp_mod, &tracepoint_module_list, list)
		(void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
end:
	mutex_unlock(&tracepoint_module_list_mutex);
	return ret;

}
EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);

/*
 * Ensure the tracer unregistered the module's probes before the module
 * teardown is performed. Prevents leaks of probe and data pointers.
 */
static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
		struct tracepoint * const *end)
{
	struct tracepoint * const *iter;

	if (!begin)
		return;
	for (iter = begin; iter < end; iter++)
		WARN_ON_ONCE((*iter)->funcs);
}

static int tracepoint_module_coming(struct module *mod)
{
	struct tp_module *tp_mod;
	int ret = 0;

	if (!mod->num_tracepoints)
		return 0;

	/*
	 * We skip modules that taint the kernel, especially those with different
	 * module headers (for forced load), to make sure we don't cause a crash.
	 * Staging, out-of-tree, and unsigned GPL modules are fine.
	 */
	if (trace_module_has_bad_taint(mod))
		return 0;
	mutex_lock(&tracepoint_module_list_mutex);
	tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
	if (!tp_mod) {
		ret = -ENOMEM;
		goto end;
	}
	tp_mod->mod = mod;
	list_add_tail(&tp_mod->list, &tracepoint_module_list);
	blocking_notifier_call_chain(&tracepoint_notify_list,
			MODULE_STATE_COMING, tp_mod);
end:
	mutex_unlock(&tracepoint_module_list_mutex);
	return ret;
}

static void tracepoint_module_going(struct module *mod)
{
	struct tp_module *tp_mod;

	if (!mod->num_tracepoints)
		return;

	mutex_lock(&tracepoint_module_list_mutex);
	list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
		if (tp_mod->mod == mod) {
			blocking_notifier_call_chain(&tracepoint_notify_list,
					MODULE_STATE_GOING, tp_mod);
			list_del(&tp_mod->list);
			kfree(tp_mod);
			/*
			 * Called the going notifier before checking for
			 * quiescence.
			 */
			tp_module_going_check_quiescent(mod->tracepoints_ptrs,
				mod->tracepoints_ptrs + mod->num_tracepoints);
			break;
		}
	}
	/*
	 * In the case of modules that were tainted at "coming", we'll simply
	 * walk through the list without finding it. We cannot use the "tainted"
	 * flag on "going", in case a module taints the kernel only after being
	 * loaded.
	 */
	mutex_unlock(&tracepoint_module_list_mutex);
}

static int tracepoint_module_notify(struct notifier_block *self,
		unsigned long val, void *data)
{
	struct module *mod = data;
	int ret = 0;

	switch (val) {
	case MODULE_STATE_COMING:
		ret = tracepoint_module_coming(mod);
		break;
	case MODULE_STATE_LIVE:
		break;
	case MODULE_STATE_GOING:
		tracepoint_module_going(mod);
		break;
	case MODULE_STATE_UNFORMED:
		break;
	}
	return ret;
}

static struct notifier_block tracepoint_module_nb = {
	.notifier_call = tracepoint_module_notify,
	.priority = 0,
};

static __init int init_tracepoints(void)
{
	int ret;

	ret = register_module_notifier(&tracepoint_module_nb);
	if (ret)
		pr_warn("Failed to register tracepoint module enter notifier\n");

	return ret;
}
__initcall(init_tracepoints);
#endif /* CONFIG_MODULES */

static void for_each_tracepoint_range(struct tracepoint * const *begin,
		struct tracepoint * const *end,
		void (*fct)(struct tracepoint *tp, void *priv),
		void *priv)
{
	struct tracepoint * const *iter;

	if (!begin)
		return;
	for (iter = begin; iter < end; iter++)
		fct(*iter, priv);
}

/**
 * for_each_kernel_tracepoint - iteration on all kernel tracepoints
 * @fct: callback
 * @priv: private data
 */
void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
		void *priv)
{
	for_each_tracepoint_range(__start___tracepoints_ptrs,
		__stop___tracepoints_ptrs, fct, priv);
}
EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);

#ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS

/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
static int sys_tracepoint_refcount;

int syscall_regfunc(void)
{
	struct task_struct *p, *t;

	if (!sys_tracepoint_refcount) {
		read_lock(&tasklist_lock);
		for_each_process_thread(p, t) {
			set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
		}
		read_unlock(&tasklist_lock);
	}
	sys_tracepoint_refcount++;

	return 0;
}

void syscall_unregfunc(void)
{
	struct task_struct *p, *t;

	sys_tracepoint_refcount--;
	if (!sys_tracepoint_refcount) {
		read_lock(&tasklist_lock);
		for_each_process_thread(p, t) {
			clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
		}
		read_unlock(&tasklist_lock);
	}
}
#endif