2 * Copyright (C) 2008 Mathieu Desnoyers
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.
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.
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.
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>
28 extern struct tracepoint __start___tracepoints[];
29 extern struct tracepoint __stop___tracepoints[];
31 /* Set to 1 to enable tracepoint debug output */
32 static const int tracepoint_debug;
35 * tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
36 * builtin and module tracepoints and the hash table.
38 static DEFINE_MUTEX(tracepoints_mutex);
41 * Tracepoint hash table, containing the active tracepoints.
42 * Protected by tracepoints_mutex.
44 #define TRACEPOINT_HASH_BITS 6
45 #define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
49 * It is used to to delay the free of multiple probes array until a quiescent
51 * Tracepoint entries modifications are protected by the tracepoints_mutex.
53 struct tracepoint_entry {
54 struct hlist_node hlist;
56 int refcount; /* Number of times armed. 0 if disarmed. */
59 unsigned char rcu_pending:1;
63 static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
65 static void free_old_closure(struct rcu_head *head)
67 struct tracepoint_entry *entry = container_of(head,
68 struct tracepoint_entry, rcu);
70 /* Make sure we free the data before setting the pending flag to 0 */
72 entry->rcu_pending = 0;
75 static void tracepoint_entry_free_old(struct tracepoint_entry *entry, void *old)
80 entry->rcu_pending = 1;
81 /* write rcu_pending before calling the RCU callback */
83 call_rcu_sched(&entry->rcu, free_old_closure);
86 static void debug_print_probes(struct tracepoint_entry *entry)
90 if (!tracepoint_debug)
93 for (i = 0; entry->funcs[i]; i++)
94 printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i]);
98 tracepoint_entry_add_probe(struct tracepoint_entry *entry, void *probe)
105 debug_print_probes(entry);
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);
113 /* + 2 : one for new probe, one for NULL func */
114 new = kzalloc((nr_probes + 2) * sizeof(void *), GFP_KERNEL);
116 return ERR_PTR(-ENOMEM);
118 memcpy(new, old, nr_probes * sizeof(void *));
119 new[nr_probes] = probe;
120 entry->refcount = nr_probes + 1;
122 debug_print_probes(entry);
127 tracepoint_entry_remove_probe(struct tracepoint_entry *entry, void *probe)
129 int nr_probes = 0, nr_del = 0, i;
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))
141 if (nr_probes - nr_del == 0) {
142 /* N -> 0, (N > 1) */
145 debug_print_probes(entry);
149 /* N -> M, (N > 1, M > 0) */
151 new = kzalloc((nr_probes - nr_del + 1)
152 * sizeof(void *), GFP_KERNEL);
154 return ERR_PTR(-ENOMEM);
155 for (i = 0; old[i]; i++)
156 if ((probe && old[i] != probe))
158 entry->refcount = nr_probes - nr_del;
161 debug_print_probes(entry);
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.
170 static struct tracepoint_entry *get_tracepoint(const char *name)
172 struct hlist_head *head;
173 struct hlist_node *node;
174 struct tracepoint_entry *e;
175 u32 hash = jhash(name, strlen(name), 0);
177 head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
178 hlist_for_each_entry(e, node, head, hlist) {
179 if (!strcmp(name, e->name))
186 * Add the tracepoint to the tracepoint hash table. Must be called with
187 * tracepoints_mutex held.
189 static struct tracepoint_entry *add_tracepoint(const char *name)
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);
197 head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
198 hlist_for_each_entry(e, node, head, hlist) {
199 if (!strcmp(name, e->name)) {
201 "tracepoint %s busy\n", name);
202 return ERR_PTR(-EEXIST); /* Already there */
206 * Using kmalloc here to allocate a variable length element. Could
207 * cause some memory fragmentation if overused.
209 e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
211 return ERR_PTR(-ENOMEM);
212 memcpy(&e->name[0], name, name_len);
216 hlist_add_head(&e->hlist, head);
221 * Remove the tracepoint from the tracepoint hash table. Must be called with
224 static int remove_tracepoint(const char *name)
226 struct hlist_head *head;
227 struct hlist_node *node;
228 struct tracepoint_entry *e;
230 size_t len = strlen(name) + 1;
231 u32 hash = jhash(name, len-1, 0);
233 head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
234 hlist_for_each_entry(e, node, head, hlist) {
235 if (!strcmp(name, e->name)) {
244 hlist_del(&e->hlist);
245 /* Make sure the call_rcu_sched has been executed */
253 * Sets the probe callback corresponding to one tracepoint.
255 static void set_tracepoint(struct tracepoint_entry **entry,
256 struct tracepoint *elem, int active)
258 WARN_ON(strcmp((*entry)->name, elem->name) != 0);
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()
267 rcu_assign_pointer(elem->funcs, (*entry)->funcs);
268 elem->state = active;
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.
277 static void disable_tracepoint(struct tracepoint *elem)
283 * tracepoint_update_probe_range - Update a probe range
284 * @begin: beginning of the range
285 * @end: end of the range
287 * Updates the probe callback corresponding to a range of tracepoints.
289 void tracepoint_update_probe_range(struct tracepoint *begin,
290 struct tracepoint *end)
292 struct tracepoint *iter;
293 struct tracepoint_entry *mark_entry;
295 mutex_lock(&tracepoints_mutex);
296 for (iter = begin; iter < end; iter++) {
297 mark_entry = get_tracepoint(iter->name);
299 set_tracepoint(&mark_entry, iter,
300 !!mark_entry->refcount);
302 disable_tracepoint(iter);
305 mutex_unlock(&tracepoints_mutex);
309 * Update probes, removing the faulty probes.
311 static void tracepoint_update_probes(void)
313 /* Core kernel tracepoints */
314 tracepoint_update_probe_range(__start___tracepoints,
315 __stop___tracepoints);
316 /* tracepoints in modules. */
317 module_update_tracepoints();
321 * tracepoint_probe_register - Connect a probe to a tracepoint
322 * @name: tracepoint name
323 * @probe: probe handler
325 * Returns 0 if ok, error value on error.
326 * The probe address must at least be aligned on the architecture pointer size.
328 int tracepoint_probe_register(const char *name, void *probe)
330 struct tracepoint_entry *entry;
334 mutex_lock(&tracepoints_mutex);
335 entry = get_tracepoint(name);
337 entry = add_tracepoint(name);
339 ret = PTR_ERR(entry);
344 * If we detect that a call_rcu_sched is pending for this tracepoint,
345 * make sure it's executed now.
347 if (entry->rcu_pending)
349 old = tracepoint_entry_add_probe(entry, probe);
354 mutex_unlock(&tracepoints_mutex);
355 tracepoint_update_probes(); /* may update entry */
356 mutex_lock(&tracepoints_mutex);
357 entry = get_tracepoint(name);
359 if (entry->rcu_pending)
361 tracepoint_entry_free_old(entry, old);
363 mutex_unlock(&tracepoints_mutex);
366 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
369 * tracepoint_probe_unregister - Disconnect a probe from a tracepoint
370 * @name: tracepoint name
371 * @probe: probe function pointer
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
378 int tracepoint_probe_unregister(const char *name, void *probe)
380 struct tracepoint_entry *entry;
384 mutex_lock(&tracepoints_mutex);
385 entry = get_tracepoint(name);
388 if (entry->rcu_pending)
390 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);
397 if (entry->rcu_pending)
399 tracepoint_entry_free_old(entry, old);
400 remove_tracepoint(name); /* Ignore busy error message */
403 mutex_unlock(&tracepoints_mutex);
406 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
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
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
418 int tracepoint_get_iter_range(struct tracepoint **tracepoint,
419 struct tracepoint *begin, struct tracepoint *end)
421 if (!*tracepoint && begin != end) {
425 if (*tracepoint >= begin && *tracepoint < end)
429 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
431 static void tracepoint_get_iter(struct tracepoint_iter *iter)
435 /* Core kernel tracepoints */
437 found = tracepoint_get_iter_range(&iter->tracepoint,
438 __start___tracepoints, __stop___tracepoints);
442 /* tracepoints in modules. */
443 found = module_get_iter_tracepoints(iter);
446 tracepoint_iter_reset(iter);
449 void tracepoint_iter_start(struct tracepoint_iter *iter)
451 tracepoint_get_iter(iter);
453 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
455 void tracepoint_iter_next(struct tracepoint_iter *iter)
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.
463 tracepoint_get_iter(iter);
465 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
467 void tracepoint_iter_stop(struct tracepoint_iter *iter)
470 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
472 void tracepoint_iter_reset(struct tracepoint_iter *iter)
475 iter->tracepoint = NULL;
477 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);