tracepoint: check if the probe has been registered
[linux-2.6.git] / kernel / tracepoint.c
1 /*
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
28 extern struct tracepoint __start___tracepoints[];
29 extern struct tracepoint __stop___tracepoints[];
30
31 /* Set to 1 to enable tracepoint debug output */
32 static 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  */
38 static 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  */
53 struct 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
63 static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
64
65 static 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
75 static 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();
83         call_rcu_sched(&entry->rcu, free_old_closure);
84 }
85
86 static 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
97 static void *
98 tracepoint_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
126 static void *
127 tracepoint_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         if (!old)
135                 return NULL;
136
137         debug_print_probes(entry);
138         /* (N -> M), (N > 1, M >= 0) probes */
139         for (nr_probes = 0; old[nr_probes]; nr_probes++) {
140                 if ((!probe || old[nr_probes] == probe))
141                         nr_del++;
142         }
143
144         if (nr_probes - nr_del == 0) {
145                 /* N -> 0, (N > 1) */
146                 entry->funcs = NULL;
147                 entry->refcount = 0;
148                 debug_print_probes(entry);
149                 return old;
150         } else {
151                 int j = 0;
152                 /* N -> M, (N > 1, M > 0) */
153                 /* + 1 for NULL */
154                 new = kzalloc((nr_probes - nr_del + 1)
155                         * sizeof(void *), GFP_KERNEL);
156                 if (new == NULL)
157                         return ERR_PTR(-ENOMEM);
158                 for (i = 0; old[i]; i++)
159                         if ((probe && old[i] != probe))
160                                 new[j++] = old[i];
161                 entry->refcount = nr_probes - nr_del;
162                 entry->funcs = new;
163         }
164         debug_print_probes(entry);
165         return old;
166 }
167
168 /*
169  * Get tracepoint if the tracepoint is present in the tracepoint hash table.
170  * Must be called with tracepoints_mutex held.
171  * Returns NULL if not present.
172  */
173 static struct tracepoint_entry *get_tracepoint(const char *name)
174 {
175         struct hlist_head *head;
176         struct hlist_node *node;
177         struct tracepoint_entry *e;
178         u32 hash = jhash(name, strlen(name), 0);
179
180         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
181         hlist_for_each_entry(e, node, head, hlist) {
182                 if (!strcmp(name, e->name))
183                         return e;
184         }
185         return NULL;
186 }
187
188 /*
189  * Add the tracepoint to the tracepoint hash table. Must be called with
190  * tracepoints_mutex held.
191  */
192 static struct tracepoint_entry *add_tracepoint(const char *name)
193 {
194         struct hlist_head *head;
195         struct hlist_node *node;
196         struct tracepoint_entry *e;
197         size_t name_len = strlen(name) + 1;
198         u32 hash = jhash(name, name_len-1, 0);
199
200         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
201         hlist_for_each_entry(e, node, head, hlist) {
202                 if (!strcmp(name, e->name)) {
203                         printk(KERN_NOTICE
204                                 "tracepoint %s busy\n", name);
205                         return ERR_PTR(-EEXIST);        /* Already there */
206                 }
207         }
208         /*
209          * Using kmalloc here to allocate a variable length element. Could
210          * cause some memory fragmentation if overused.
211          */
212         e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
213         if (!e)
214                 return ERR_PTR(-ENOMEM);
215         memcpy(&e->name[0], name, name_len);
216         e->funcs = NULL;
217         e->refcount = 0;
218         e->rcu_pending = 0;
219         hlist_add_head(&e->hlist, head);
220         return e;
221 }
222
223 /*
224  * Remove the tracepoint from the tracepoint hash table. Must be called with
225  * mutex_lock held.
226  */
227 static int remove_tracepoint(const char *name)
228 {
229         struct hlist_head *head;
230         struct hlist_node *node;
231         struct tracepoint_entry *e;
232         int found = 0;
233         size_t len = strlen(name) + 1;
234         u32 hash = jhash(name, len-1, 0);
235
236         head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
237         hlist_for_each_entry(e, node, head, hlist) {
238                 if (!strcmp(name, e->name)) {
239                         found = 1;
240                         break;
241                 }
242         }
243         if (!found)
244                 return -ENOENT;
245         if (e->refcount)
246                 return -EBUSY;
247         hlist_del(&e->hlist);
248         /* Make sure the call_rcu_sched has been executed */
249         if (e->rcu_pending)
250                 rcu_barrier_sched();
251         kfree(e);
252         return 0;
253 }
254
255 /*
256  * Sets the probe callback corresponding to one tracepoint.
257  */
258 static void set_tracepoint(struct tracepoint_entry **entry,
259         struct tracepoint *elem, int active)
260 {
261         WARN_ON(strcmp((*entry)->name, elem->name) != 0);
262
263         /*
264          * rcu_assign_pointer has a smp_wmb() which makes sure that the new
265          * probe callbacks array is consistent before setting a pointer to it.
266          * This array is referenced by __DO_TRACE from
267          * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
268          * is used.
269          */
270         rcu_assign_pointer(elem->funcs, (*entry)->funcs);
271         elem->state = active;
272 }
273
274 /*
275  * Disable a tracepoint and its probe callback.
276  * Note: only waiting an RCU period after setting elem->call to the empty
277  * function insures that the original callback is not used anymore. This insured
278  * by preempt_disable around the call site.
279  */
280 static void disable_tracepoint(struct tracepoint *elem)
281 {
282         elem->state = 0;
283 }
284
285 /**
286  * tracepoint_update_probe_range - Update a probe range
287  * @begin: beginning of the range
288  * @end: end of the range
289  *
290  * Updates the probe callback corresponding to a range of tracepoints.
291  */
292 void tracepoint_update_probe_range(struct tracepoint *begin,
293         struct tracepoint *end)
294 {
295         struct tracepoint *iter;
296         struct tracepoint_entry *mark_entry;
297
298         mutex_lock(&tracepoints_mutex);
299         for (iter = begin; iter < end; iter++) {
300                 mark_entry = get_tracepoint(iter->name);
301                 if (mark_entry) {
302                         set_tracepoint(&mark_entry, iter,
303                                         !!mark_entry->refcount);
304                 } else {
305                         disable_tracepoint(iter);
306                 }
307         }
308         mutex_unlock(&tracepoints_mutex);
309 }
310
311 /*
312  * Update probes, removing the faulty probes.
313  */
314 static void tracepoint_update_probes(void)
315 {
316         /* Core kernel tracepoints */
317         tracepoint_update_probe_range(__start___tracepoints,
318                 __stop___tracepoints);
319         /* tracepoints in modules. */
320         module_update_tracepoints();
321 }
322
323 /**
324  * tracepoint_probe_register -  Connect a probe to a tracepoint
325  * @name: tracepoint name
326  * @probe: probe handler
327  *
328  * Returns 0 if ok, error value on error.
329  * The probe address must at least be aligned on the architecture pointer size.
330  */
331 int tracepoint_probe_register(const char *name, void *probe)
332 {
333         struct tracepoint_entry *entry;
334         int ret = 0;
335         void *old;
336
337         mutex_lock(&tracepoints_mutex);
338         entry = get_tracepoint(name);
339         if (!entry) {
340                 entry = add_tracepoint(name);
341                 if (IS_ERR(entry)) {
342                         ret = PTR_ERR(entry);
343                         goto end;
344                 }
345         }
346         /*
347          * If we detect that a call_rcu_sched is pending for this tracepoint,
348          * make sure it's executed now.
349          */
350         if (entry->rcu_pending)
351                 rcu_barrier_sched();
352         old = tracepoint_entry_add_probe(entry, probe);
353         if (IS_ERR(old)) {
354                 ret = PTR_ERR(old);
355                 goto end;
356         }
357         mutex_unlock(&tracepoints_mutex);
358         tracepoint_update_probes();             /* may update entry */
359         mutex_lock(&tracepoints_mutex);
360         entry = get_tracepoint(name);
361         WARN_ON(!entry);
362         if (entry->rcu_pending)
363                 rcu_barrier_sched();
364         tracepoint_entry_free_old(entry, old);
365 end:
366         mutex_unlock(&tracepoints_mutex);
367         return ret;
368 }
369 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
370
371 /**
372  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
373  * @name: tracepoint name
374  * @probe: probe function pointer
375  *
376  * We do not need to call a synchronize_sched to make sure the probes have
377  * finished running before doing a module unload, because the module unload
378  * itself uses stop_machine(), which insures that every preempt disabled section
379  * have finished.
380  */
381 int tracepoint_probe_unregister(const char *name, void *probe)
382 {
383         struct tracepoint_entry *entry;
384         void *old;
385         int ret = -ENOENT;
386
387         mutex_lock(&tracepoints_mutex);
388         entry = get_tracepoint(name);
389         if (!entry)
390                 goto end;
391         if (entry->rcu_pending)
392                 rcu_barrier_sched();
393         old = tracepoint_entry_remove_probe(entry, probe);
394         if (!old) {
395                 printk(KERN_WARNING "Warning: Trying to unregister a probe"
396                                     "that doesn't exist\n");
397                 goto end;
398         }
399         mutex_unlock(&tracepoints_mutex);
400         tracepoint_update_probes();             /* may update entry */
401         mutex_lock(&tracepoints_mutex);
402         entry = get_tracepoint(name);
403         if (!entry)
404                 goto end;
405         if (entry->rcu_pending)
406                 rcu_barrier_sched();
407         tracepoint_entry_free_old(entry, old);
408         remove_tracepoint(name);        /* Ignore busy error message */
409         ret = 0;
410 end:
411         mutex_unlock(&tracepoints_mutex);
412         return ret;
413 }
414 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
415
416 /**
417  * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
418  * @tracepoint: current tracepoints (in), next tracepoint (out)
419  * @begin: beginning of the range
420  * @end: end of the range
421  *
422  * Returns whether a next tracepoint has been found (1) or not (0).
423  * Will return the first tracepoint in the range if the input tracepoint is
424  * NULL.
425  */
426 int tracepoint_get_iter_range(struct tracepoint **tracepoint,
427         struct tracepoint *begin, struct tracepoint *end)
428 {
429         if (!*tracepoint && begin != end) {
430                 *tracepoint = begin;
431                 return 1;
432         }
433         if (*tracepoint >= begin && *tracepoint < end)
434                 return 1;
435         return 0;
436 }
437 EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
438
439 static void tracepoint_get_iter(struct tracepoint_iter *iter)
440 {
441         int found = 0;
442
443         /* Core kernel tracepoints */
444         if (!iter->module) {
445                 found = tracepoint_get_iter_range(&iter->tracepoint,
446                                 __start___tracepoints, __stop___tracepoints);
447                 if (found)
448                         goto end;
449         }
450         /* tracepoints in modules. */
451         found = module_get_iter_tracepoints(iter);
452 end:
453         if (!found)
454                 tracepoint_iter_reset(iter);
455 }
456
457 void tracepoint_iter_start(struct tracepoint_iter *iter)
458 {
459         tracepoint_get_iter(iter);
460 }
461 EXPORT_SYMBOL_GPL(tracepoint_iter_start);
462
463 void tracepoint_iter_next(struct tracepoint_iter *iter)
464 {
465         iter->tracepoint++;
466         /*
467          * iter->tracepoint may be invalid because we blindly incremented it.
468          * Make sure it is valid by marshalling on the tracepoints, getting the
469          * tracepoints from following modules if necessary.
470          */
471         tracepoint_get_iter(iter);
472 }
473 EXPORT_SYMBOL_GPL(tracepoint_iter_next);
474
475 void tracepoint_iter_stop(struct tracepoint_iter *iter)
476 {
477 }
478 EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
479
480 void tracepoint_iter_reset(struct tracepoint_iter *iter)
481 {
482         iter->module = NULL;
483         iter->tracepoint = NULL;
484 }
485 EXPORT_SYMBOL_GPL(tracepoint_iter_reset);