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Mathieu Desnoyers97e1c182008-07-18 12:16:16 -04001/*
2 * Copyright (C) 2008 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
28extern struct tracepoint __start___tracepoints[];
29extern struct tracepoint __stop___tracepoints[];
30
31/* Set to 1 to enable tracepoint debug output */
32static const int tracepoint_debug;
33
34/*
35 * tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
36 * builtin and module tracepoints and the hash table.
37 */
38static DEFINE_MUTEX(tracepoints_mutex);
39
40/*
41 * Tracepoint hash table, containing the active tracepoints.
42 * Protected by tracepoints_mutex.
43 */
44#define TRACEPOINT_HASH_BITS 6
45#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
46
47/*
48 * Note about RCU :
49 * It is used to to delay the free of multiple probes array until a quiescent
50 * state is reached.
51 * Tracepoint entries modifications are protected by the tracepoints_mutex.
52 */
53struct tracepoint_entry {
54 struct hlist_node hlist;
55 void **funcs;
56 int refcount; /* Number of times armed. 0 if disarmed. */
57 struct rcu_head rcu;
58 void *oldptr;
59 unsigned char rcu_pending:1;
60 char name[0];
61};
62
63static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
64
65static void free_old_closure(struct rcu_head *head)
66{
67 struct tracepoint_entry *entry = container_of(head,
68 struct tracepoint_entry, rcu);
69 kfree(entry->oldptr);
70 /* Make sure we free the data before setting the pending flag to 0 */
71 smp_wmb();
72 entry->rcu_pending = 0;
73}
74
75static void tracepoint_entry_free_old(struct tracepoint_entry *entry, void *old)
76{
77 if (!old)
78 return;
79 entry->oldptr = old;
80 entry->rcu_pending = 1;
81 /* write rcu_pending before calling the RCU callback */
82 smp_wmb();
Mathieu Desnoyersca2db6c2008-09-30 01:49:39 -040083 call_rcu_sched(&entry->rcu, free_old_closure);
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -040084}
85
86static void debug_print_probes(struct tracepoint_entry *entry)
87{
88 int i;
89
90 if (!tracepoint_debug)
91 return;
92
93 for (i = 0; entry->funcs[i]; i++)
94 printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i]);
95}
96
97static void *
98tracepoint_entry_add_probe(struct tracepoint_entry *entry, void *probe)
99{
100 int nr_probes = 0;
101 void **old, **new;
102
103 WARN_ON(!probe);
104
105 debug_print_probes(entry);
106 old = entry->funcs;
107 if (old) {
108 /* (N -> N+1), (N != 0, 1) probes */
109 for (nr_probes = 0; old[nr_probes]; nr_probes++)
110 if (old[nr_probes] == probe)
111 return ERR_PTR(-EEXIST);
112 }
113 /* + 2 : one for new probe, one for NULL func */
114 new = kzalloc((nr_probes + 2) * sizeof(void *), GFP_KERNEL);
115 if (new == NULL)
116 return ERR_PTR(-ENOMEM);
117 if (old)
118 memcpy(new, old, nr_probes * sizeof(void *));
119 new[nr_probes] = probe;
120 entry->refcount = nr_probes + 1;
121 entry->funcs = new;
122 debug_print_probes(entry);
123 return old;
124}
125
126static void *
127tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
128{
129 int nr_probes = 0, nr_del = 0, i;
130 void **old, **new;
131
132 old = entry->funcs;
133
134 debug_print_probes(entry);
135 /* (N -> M), (N > 1, M >= 0) probes */
136 for (nr_probes = 0; old[nr_probes]; nr_probes++) {
137 if ((!probe || old[nr_probes] == probe))
138 nr_del++;
139 }
140
141 if (nr_probes - nr_del == 0) {
142 /* N -> 0, (N > 1) */
143 entry->funcs = NULL;
144 entry->refcount = 0;
145 debug_print_probes(entry);
146 return old;
147 } else {
148 int j = 0;
149 /* N -> M, (N > 1, M > 0) */
150 /* + 1 for NULL */
151 new = kzalloc((nr_probes - nr_del + 1)
152 * sizeof(void *), GFP_KERNEL);
153 if (new == NULL)
154 return ERR_PTR(-ENOMEM);
155 for (i = 0; old[i]; i++)
156 if ((probe && old[i] != probe))
157 new[j++] = old[i];
158 entry->refcount = nr_probes - nr_del;
159 entry->funcs = new;
160 }
161 debug_print_probes(entry);
162 return old;
163}
164
165/*
166 * Get tracepoint if the tracepoint is present in the tracepoint hash table.
167 * Must be called with tracepoints_mutex held.
168 * Returns NULL if not present.
169 */
170static struct tracepoint_entry *get_tracepoint(const char *name)
171{
172 struct hlist_head *head;
173 struct hlist_node *node;
174 struct tracepoint_entry *e;
175 u32 hash = jhash(name, strlen(name), 0);
176
Mathieu Desnoyers97953022008-07-24 16:37:23 -0400177 head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400178 hlist_for_each_entry(e, node, head, hlist) {
179 if (!strcmp(name, e->name))
180 return e;
181 }
182 return NULL;
183}
184
185/*
186 * Add the tracepoint to the tracepoint hash table. Must be called with
187 * tracepoints_mutex held.
188 */
189static struct tracepoint_entry *add_tracepoint(const char *name)
190{
191 struct hlist_head *head;
192 struct hlist_node *node;
193 struct tracepoint_entry *e;
194 size_t name_len = strlen(name) + 1;
195 u32 hash = jhash(name, name_len-1, 0);
196
Mathieu Desnoyers97953022008-07-24 16:37:23 -0400197 head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400198 hlist_for_each_entry(e, node, head, hlist) {
199 if (!strcmp(name, e->name)) {
200 printk(KERN_NOTICE
201 "tracepoint %s busy\n", name);
202 return ERR_PTR(-EEXIST); /* Already there */
203 }
204 }
205 /*
206 * Using kmalloc here to allocate a variable length element. Could
207 * cause some memory fragmentation if overused.
208 */
209 e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
210 if (!e)
211 return ERR_PTR(-ENOMEM);
212 memcpy(&e->name[0], name, name_len);
213 e->funcs = NULL;
214 e->refcount = 0;
215 e->rcu_pending = 0;
216 hlist_add_head(&e->hlist, head);
217 return e;
218}
219
220/*
221 * Remove the tracepoint from the tracepoint hash table. Must be called with
222 * mutex_lock held.
223 */
224static int remove_tracepoint(const char *name)
225{
226 struct hlist_head *head;
227 struct hlist_node *node;
228 struct tracepoint_entry *e;
229 int found = 0;
230 size_t len = strlen(name) + 1;
231 u32 hash = jhash(name, len-1, 0);
232
Mathieu Desnoyers97953022008-07-24 16:37:23 -0400233 head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400234 hlist_for_each_entry(e, node, head, hlist) {
235 if (!strcmp(name, e->name)) {
236 found = 1;
237 break;
238 }
239 }
240 if (!found)
241 return -ENOENT;
242 if (e->refcount)
243 return -EBUSY;
244 hlist_del(&e->hlist);
Mathieu Desnoyersca2db6c2008-09-30 01:49:39 -0400245 /* Make sure the call_rcu_sched has been executed */
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400246 if (e->rcu_pending)
Mathieu Desnoyersca2db6c2008-09-30 01:49:39 -0400247 rcu_barrier_sched();
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400248 kfree(e);
249 return 0;
250}
251
252/*
253 * Sets the probe callback corresponding to one tracepoint.
254 */
255static void set_tracepoint(struct tracepoint_entry **entry,
256 struct tracepoint *elem, int active)
257{
258 WARN_ON(strcmp((*entry)->name, elem->name) != 0);
259
260 /*
261 * rcu_assign_pointer has a smp_wmb() which makes sure that the new
262 * probe callbacks array is consistent before setting a pointer to it.
263 * This array is referenced by __DO_TRACE from
264 * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
265 * is used.
266 */
267 rcu_assign_pointer(elem->funcs, (*entry)->funcs);
268 elem->state = active;
269}
270
271/*
272 * Disable a tracepoint and its probe callback.
273 * Note: only waiting an RCU period after setting elem->call to the empty
274 * function insures that the original callback is not used anymore. This insured
275 * by preempt_disable around the call site.
276 */
277static void disable_tracepoint(struct tracepoint *elem)
278{
279 elem->state = 0;
280}
281
282/**
283 * tracepoint_update_probe_range - Update a probe range
284 * @begin: beginning of the range
285 * @end: end of the range
286 *
287 * Updates the probe callback corresponding to a range of tracepoints.
288 */
289void tracepoint_update_probe_range(struct tracepoint *begin,
290 struct tracepoint *end)
291{
292 struct tracepoint *iter;
293 struct tracepoint_entry *mark_entry;
294
295 mutex_lock(&tracepoints_mutex);
296 for (iter = begin; iter < end; iter++) {
297 mark_entry = get_tracepoint(iter->name);
298 if (mark_entry) {
299 set_tracepoint(&mark_entry, iter,
300 !!mark_entry->refcount);
301 } else {
302 disable_tracepoint(iter);
303 }
304 }
305 mutex_unlock(&tracepoints_mutex);
306}
307
308/*
309 * Update probes, removing the faulty probes.
310 */
311static void tracepoint_update_probes(void)
312{
313 /* Core kernel tracepoints */
314 tracepoint_update_probe_range(__start___tracepoints,
315 __stop___tracepoints);
316 /* tracepoints in modules. */
317 module_update_tracepoints();
318}
319
320/**
321 * tracepoint_probe_register - Connect a probe to a tracepoint
322 * @name: tracepoint name
323 * @probe: probe handler
324 *
325 * Returns 0 if ok, error value on error.
326 * The probe address must at least be aligned on the architecture pointer size.
327 */
328int tracepoint_probe_register(const char *name, void *probe)
329{
330 struct tracepoint_entry *entry;
331 int ret = 0;
332 void *old;
333
334 mutex_lock(&tracepoints_mutex);
335 entry = get_tracepoint(name);
336 if (!entry) {
337 entry = add_tracepoint(name);
338 if (IS_ERR(entry)) {
339 ret = PTR_ERR(entry);
340 goto end;
341 }
342 }
343 /*
Mathieu Desnoyersca2db6c2008-09-30 01:49:39 -0400344 * If we detect that a call_rcu_sched is pending for this tracepoint,
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400345 * make sure it's executed now.
346 */
347 if (entry->rcu_pending)
Mathieu Desnoyersca2db6c2008-09-30 01:49:39 -0400348 rcu_barrier_sched();
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400349 old = tracepoint_entry_add_probe(entry, probe);
350 if (IS_ERR(old)) {
351 ret = PTR_ERR(old);
352 goto end;
353 }
354 mutex_unlock(&tracepoints_mutex);
355 tracepoint_update_probes(); /* may update entry */
356 mutex_lock(&tracepoints_mutex);
357 entry = get_tracepoint(name);
358 WARN_ON(!entry);
Mathieu Desnoyers9a1e9692008-09-30 01:51:12 -0400359 if (entry->rcu_pending)
360 rcu_barrier_sched();
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400361 tracepoint_entry_free_old(entry, old);
362end:
363 mutex_unlock(&tracepoints_mutex);
364 return ret;
365}
366EXPORT_SYMBOL_GPL(tracepoint_probe_register);
367
368/**
369 * tracepoint_probe_unregister - Disconnect a probe from a tracepoint
370 * @name: tracepoint name
371 * @probe: probe function pointer
372 *
373 * We do not need to call a synchronize_sched to make sure the probes have
374 * finished running before doing a module unload, because the module unload
375 * itself uses stop_machine(), which insures that every preempt disabled section
376 * have finished.
377 */
378int tracepoint_probe_unregister(const char *name, void *probe)
379{
380 struct tracepoint_entry *entry;
381 void *old;
382 int ret = -ENOENT;
383
384 mutex_lock(&tracepoints_mutex);
385 entry = get_tracepoint(name);
386 if (!entry)
387 goto end;
388 if (entry->rcu_pending)
Mathieu Desnoyersca2db6c2008-09-30 01:49:39 -0400389 rcu_barrier_sched();
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400390 old = tracepoint_entry_remove_probe(entry, probe);
391 mutex_unlock(&tracepoints_mutex);
392 tracepoint_update_probes(); /* may update entry */
393 mutex_lock(&tracepoints_mutex);
394 entry = get_tracepoint(name);
395 if (!entry)
396 goto end;
Mathieu Desnoyers9a1e9692008-09-30 01:51:12 -0400397 if (entry->rcu_pending)
398 rcu_barrier_sched();
Mathieu Desnoyers97e1c182008-07-18 12:16:16 -0400399 tracepoint_entry_free_old(entry, old);
400 remove_tracepoint(name); /* Ignore busy error message */
401 ret = 0;
402end:
403 mutex_unlock(&tracepoints_mutex);
404 return ret;
405}
406EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
407
408/**
409 * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
410 * @tracepoint: current tracepoints (in), next tracepoint (out)
411 * @begin: beginning of the range
412 * @end: end of the range
413 *
414 * Returns whether a next tracepoint has been found (1) or not (0).
415 * Will return the first tracepoint in the range if the input tracepoint is
416 * NULL.
417 */
418int tracepoint_get_iter_range(struct tracepoint **tracepoint,
419 struct tracepoint *begin, struct tracepoint *end)
420{
421 if (!*tracepoint && begin != end) {
422 *tracepoint = begin;
423 return 1;
424 }
425 if (*tracepoint >= begin && *tracepoint < end)
426 return 1;
427 return 0;
428}
429EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
430
431static void tracepoint_get_iter(struct tracepoint_iter *iter)
432{
433 int found = 0;
434
435 /* Core kernel tracepoints */
436 if (!iter->module) {
437 found = tracepoint_get_iter_range(&iter->tracepoint,
438 __start___tracepoints, __stop___tracepoints);
439 if (found)
440 goto end;
441 }
442 /* tracepoints in modules. */
443 found = module_get_iter_tracepoints(iter);
444end:
445 if (!found)
446 tracepoint_iter_reset(iter);
447}
448
449void tracepoint_iter_start(struct tracepoint_iter *iter)
450{
451 tracepoint_get_iter(iter);
452}
453EXPORT_SYMBOL_GPL(tracepoint_iter_start);
454
455void tracepoint_iter_next(struct tracepoint_iter *iter)
456{
457 iter->tracepoint++;
458 /*
459 * iter->tracepoint may be invalid because we blindly incremented it.
460 * Make sure it is valid by marshalling on the tracepoints, getting the
461 * tracepoints from following modules if necessary.
462 */
463 tracepoint_get_iter(iter);
464}
465EXPORT_SYMBOL_GPL(tracepoint_iter_next);
466
467void tracepoint_iter_stop(struct tracepoint_iter *iter)
468{
469}
470EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
471
472void tracepoint_iter_reset(struct tracepoint_iter *iter)
473{
474 iter->module = NULL;
475 iter->tracepoint = NULL;
476}
477EXPORT_SYMBOL_GPL(tracepoint_iter_reset);