aboutsummaryrefslogtreecommitdiff
path: root/kernel/tracepoint.c
blob: db39961a0d0377cf6e1d52edf14bb2949d2e79a2 (plain)
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
/*
 * Copyright (C) 2008 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>

extern struct tracepoint __start___tracepoints[];
extern struct tracepoint __stop___tracepoints[];

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

/*
 * tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
 * builtin and module tracepoints and the hash table.
 */
static DEFINE_MUTEX(tracepoints_mutex);

/*
 * Tracepoint hash table, containing the active tracepoints.
 * Protected by tracepoints_mutex.
 */
#define TRACEPOINT_HASH_BITS 6
#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)

/*
 * Note about RCU :
 * It is used to to delay the free of multiple probes array until a quiescent
 * state is reached.
 * Tracepoint entries modifications are protected by the tracepoints_mutex.
 */
struct tracepoint_entry {
	struct hlist_node hlist;
	void **funcs;
	int refcount;	/* Number of times armed. 0 if disarmed. */
	struct rcu_head rcu;
	void *oldptr;
	unsigned char rcu_pending:1;
	char name[0];
};

static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];

static void free_old_closure(struct rcu_head *head)
{
	struct tracepoint_entry *entry = container_of(head,
		struct tracepoint_entry, rcu);
	kfree(entry->oldptr);
	/* Make sure we free the data before setting the pending flag to 0 */
	smp_wmb();
	entry->rcu_pending = 0;
}

static void tracepoint_entry_free_old(struct tracepoint_entry *entry, void *old)
{
	if (!old)
		return;
	entry->oldptr = old;
	entry->rcu_pending = 1;
	/* write rcu_pending before calling the RCU callback */
	smp_wmb();
	call_rcu_sched(&entry->rcu, free_old_closure);
}

static void debug_print_probes(struct tracepoint_entry *entry)
{
	int i;

	if (!tracepoint_debug)
		return;

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

static void *
tracepoint_entry_add_probe(struct tracepoint_entry *entry, void *probe)
{
	int nr_probes = 0;
	void **old, **new;

	WARN_ON(!probe);

	debug_print_probes(entry);
	old = entry->funcs;
	if (old) {
		/* (N -> N+1), (N != 0, 1) probes */
		for (nr_probes = 0; old[nr_probes]; nr_probes++)
			if (old[nr_probes] == probe)
				return ERR_PTR(-EEXIST);
	}
	/* + 2 : one for new probe, one for NULL func */
	new = kzalloc((nr_probes + 2) * sizeof(void *), GFP_KERNEL);
	if (new == NULL)
		return ERR_PTR(-ENOMEM);
	if (old)
		memcpy(new, old, nr_probes * sizeof(void *));
	new[nr_probes] = probe;
	entry->refcount = nr_probes + 1;
	entry->funcs = new;
	debug_print_probes(entry);
	return old;
}

static void *
tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
{
	int nr_probes = 0, nr_del = 0, i;
	void **old, **new;

	old = entry->funcs;

	debug_print_probes(entry);
	/* (N -> M), (N > 1, M >= 0) probes */
	for (nr_probes = 0; old[nr_probes]; nr_probes++) {
		if ((!probe || old[nr_probes] == probe))
			nr_del++;
	}

	if (nr_probes - nr_del == 0) {
		/* N -> 0, (N > 1) */
		entry->funcs = NULL;
		entry->refcount = 0;
		debug_print_probes(entry);
		return old;
	} else {
		int j = 0;
		/* N -> M, (N > 1, M > 0) */
		/* + 1 for NULL */
		new = kzalloc((nr_probes - nr_del + 1)
			* sizeof(void *), GFP_KERNEL);
		if (new == NULL)
			return ERR_PTR(-ENOMEM);
		for (i = 0; old[i]; i++)
			if ((probe && old[i] != probe))
				new[j++] = old[i];
		entry->refcount = nr_probes - nr_del;
		entry->funcs = new;
	}
	debug_print_probes(entry);
	return old;
}

/*
 * Get tracepoint if the tracepoint is present in the tracepoint hash table.
 * Must be called with tracepoints_mutex held.
 * Returns NULL if not present.
 */
static struct tracepoint_entry *get_tracepoint(const char *name)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct tracepoint_entry *e;
	u32 hash = jhash(name, strlen(name), 0);

	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name))
			return e;
	}
	return NULL;
}

/*
 * Add the tracepoint to the tracepoint hash table. Must be called with
 * tracepoints_mutex held.
 */
static struct tracepoint_entry *add_tracepoint(const char *name)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct tracepoint_entry *e;
	size_t name_len = strlen(name) + 1;
	u32 hash = jhash(name, name_len-1, 0);

	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name)) {
			printk(KERN_NOTICE
				"tracepoint %s busy\n", name);
			return ERR_PTR(-EEXIST);	/* Already there */
		}
	}
	/*
	 * Using kmalloc here to allocate a variable length element. Could
	 * cause some memory fragmentation if overused.
	 */
	e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
	if (!e)
		return ERR_PTR(-ENOMEM);
	memcpy(&e->name[0], name, name_len);
	e->funcs = NULL;
	e->refcount = 0;
	e->rcu_pending = 0;
	hlist_add_head(&e->hlist, head);
	return e;
}

/*
 * Remove the tracepoint from the tracepoint hash table. Must be called with
 * mutex_lock held.
 */
static int remove_tracepoint(const char *name)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct tracepoint_entry *e;
	int found = 0;
	size_t len = strlen(name) + 1;
	u32 hash = jhash(name, len-1, 0);

	head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name)) {
			found = 1;
			break;
		}
	}
	if (!found)
		return -ENOENT;
	if (e->refcount)
		return -EBUSY;
	hlist_del(&e->hlist);
	/* Make sure the call_rcu_sched has been executed */
	if (e->rcu_pending)
		rcu_barrier_sched();
	kfree(e);
	return 0;
}

/*
 * Sets the probe callback corresponding to one tracepoint.
 */
static void set_tracepoint(struct tracepoint_entry **entry,
	struct tracepoint *elem, int active)
{
	WARN_ON(strcmp((*entry)->name, elem->name) != 0);

	/*
	 * 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(elem->funcs, (*entry)->funcs);
	elem->state = active;
}

/*
 * Disable a tracepoint and its probe callback.
 * 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 void disable_tracepoint(struct tracepoint *elem)
{
	elem->state = 0;
}

/**
 * tracepoint_update_probe_range - Update a probe range
 * @begin: beginning of the range
 * @end: end of the range
 *
 * Updates the probe callback corresponding to a range of tracepoints.
 */
void tracepoint_update_probe_range(struct tracepoint *begin,
	struct tracepoint *end)
{
	struct tracepoint *iter;
	struct tracepoint_entry *mark_entry;

	mutex_lock(&tracepoints_mutex);
	for (iter = begin; iter < end; iter++) {
		mark_entry = get_tracepoint(iter->name);
		if (mark_entry) {
			set_tracepoint(&mark_entry, iter,
					!!mark_entry->refcount);
		} else {
			disable_tracepoint(iter);
		}
	}
	mutex_unlock(&tracepoints_mutex);
}

/*
 * Update probes, removing the faulty probes.
 */
static void tracepoint_update_probes(void)
{
	/* Core kernel tracepoints */
	tracepoint_update_probe_range(__start___tracepoints,
		__stop___tracepoints);
	/* tracepoints in modules. */
	module_update_tracepoints();
}

/**
 * tracepoint_probe_register -  Connect a probe to a tracepoint
 * @name: tracepoint name
 * @probe: probe handler
 *
 * Returns 0 if ok, error value on error.
 * The probe address must at least be aligned on the architecture pointer size.
 */
int tracepoint_probe_register(const char *name, void *probe)
{
	struct tracepoint_entry *entry;
	int ret = 0;
	void *old;

	mutex_lock(&tracepoints_mutex);
	entry = get_tracepoint(name);
	if (!entry) {
		entry = add_tracepoint(name);
		if (IS_ERR(entry)) {
			ret = PTR_ERR(entry);
			goto end;
		}
	}
	/*
	 * If we detect that a call_rcu_sched is pending for this tracepoint,
	 * make sure it's executed now.
	 */
	if (entry->rcu_pending)
		rcu_barrier_sched();
	old = tracepoint_entry_add_probe(entry, probe);
	if (IS_ERR(old)) {
		ret = PTR_ERR(old);
		goto end;
	}
	mutex_unlock(&tracepoints_mutex);
	tracepoint_update_probes();		/* may update entry */
	mutex_lock(&tracepoints_mutex);
	entry = get_tracepoint(name);
	WARN_ON(!entry);
	tracepoint_entry_free_old(entry, old);
end:
	mutex_unlock(&tracepoints_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_register);

/**
 * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 * @name: tracepoint name
 * @probe: probe function pointer
 *
 * We do not need to call a synchronize_sched to make sure the probes have
 * finished running before doing a module unload, because the module unload
 * itself uses stop_machine(), which insures that every preempt disabled section
 * have finished.
 */
int tracepoint_probe_unregister(const char *name, void *probe)
{
	struct tracepoint_entry *entry;
	void *old;
	int ret = -ENOENT;

	mutex_lock(&tracepoints_mutex);
	entry = get_tracepoint(name);
	if (!entry)
		goto end;
	if (entry->rcu_pending)
		rcu_barrier_sched();
	old = tracepoint_entry_remove_probe(entry, probe);
	mutex_unlock(&tracepoints_mutex);
	tracepoint_update_probes();		/* may update entry */
	mutex_lock(&tracepoints_mutex);
	entry = get_tracepoint(name);
	if (!entry)
		goto end;
	tracepoint_entry_free_old(entry, old);
	remove_tracepoint(name);	/* Ignore busy error message */
	ret = 0;
end:
	mutex_unlock(&tracepoints_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);

/**
 * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
 * @tracepoint: current tracepoints (in), next tracepoint (out)
 * @begin: beginning of the range
 * @end: end of the range
 *
 * Returns whether a next tracepoint has been found (1) or not (0).
 * Will return the first tracepoint in the range if the input tracepoint is
 * NULL.
 */
int tracepoint_get_iter_range(struct tracepoint **tracepoint,
	struct tracepoint *begin, struct tracepoint *end)
{
	if (!*tracepoint && begin != end) {
		*tracepoint = begin;
		return 1;
	}
	if (*tracepoint >= begin && *tracepoint < end)
		return 1;
	return 0;
}
EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);

static void tracepoint_get_iter(struct tracepoint_iter *iter)
{
	int found = 0;

	/* Core kernel tracepoints */
	if (!iter->module) {
		found = tracepoint_get_iter_range(&iter->tracepoint,
				__start___tracepoints, __stop___tracepoints);
		if (found)
			goto end;
	}
	/* tracepoints in modules. */
	found = module_get_iter_tracepoints(iter);
end:
	if (!found)
		tracepoint_iter_reset(iter);
}

void tracepoint_iter_start(struct tracepoint_iter *iter)
{
	tracepoint_get_iter(iter);
}
EXPORT_SYMBOL_GPL(tracepoint_iter_start);

void tracepoint_iter_next(struct tracepoint_iter *iter)
{
	iter->tracepoint++;
	/*
	 * iter->tracepoint may be invalid because we blindly incremented it.
	 * Make sure it is valid by marshalling on the tracepoints, getting the
	 * tracepoints from following modules if necessary.
	 */
	tracepoint_get_iter(iter);
}
EXPORT_SYMBOL_GPL(tracepoint_iter_next);

void tracepoint_iter_stop(struct tracepoint_iter *iter)
{
}
EXPORT_SYMBOL_GPL(tracepoint_iter_stop);

void tracepoint_iter_reset(struct tracepoint_iter *iter)
{
	iter->module = NULL;
	iter->tracepoint = NULL;
}
EXPORT_SYMBOL_GPL(tracepoint_iter_reset);