Root/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#include <linux/sched.h>
28#include <linux/jump_label.h>
29
30extern struct tracepoint * const __start___tracepoints_ptrs[];
31extern struct tracepoint * const __stop___tracepoints_ptrs[];
32
33/* Set to 1 to enable tracepoint debug output */
34static const int tracepoint_debug;
35
36/*
37 * tracepoints_mutex nests inside module_mutex. Tracepoints mutex protects the
38 * builtin and module tracepoints and the hash table.
39 */
40static DEFINE_MUTEX(tracepoints_mutex);
41
42/*
43 * Tracepoint hash table, containing the active tracepoints.
44 * Protected by tracepoints_mutex.
45 */
46#define TRACEPOINT_HASH_BITS 6
47#define TRACEPOINT_TABLE_SIZE (1 << TRACEPOINT_HASH_BITS)
48static struct hlist_head tracepoint_table[TRACEPOINT_TABLE_SIZE];
49
50/*
51 * Note about RCU :
52 * It is used to delay the free of multiple probes array until a quiescent
53 * state is reached.
54 * Tracepoint entries modifications are protected by the tracepoints_mutex.
55 */
56struct tracepoint_entry {
57    struct hlist_node hlist;
58    struct tracepoint_func *funcs;
59    int refcount; /* Number of times armed. 0 if disarmed. */
60    char name[0];
61};
62
63struct tp_probes {
64    union {
65        struct rcu_head rcu;
66        struct list_head list;
67    } u;
68    struct tracepoint_func probes[0];
69};
70
71static inline void *allocate_probes(int count)
72{
73    struct tp_probes *p = kmalloc(count * sizeof(struct tracepoint_func)
74            + sizeof(struct tp_probes), GFP_KERNEL);
75    return p == NULL ? NULL : p->probes;
76}
77
78static void rcu_free_old_probes(struct rcu_head *head)
79{
80    kfree(container_of(head, struct tp_probes, u.rcu));
81}
82
83static inline void release_probes(struct tracepoint_func *old)
84{
85    if (old) {
86        struct tp_probes *tp_probes = container_of(old,
87            struct tp_probes, probes[0]);
88        call_rcu_sched(&tp_probes->u.rcu, rcu_free_old_probes);
89    }
90}
91
92static void debug_print_probes(struct tracepoint_entry *entry)
93{
94    int i;
95
96    if (!tracepoint_debug || !entry->funcs)
97        return;
98
99    for (i = 0; entry->funcs[i].func; i++)
100        printk(KERN_DEBUG "Probe %d : %p\n", i, entry->funcs[i].func);
101}
102
103static struct tracepoint_func *
104tracepoint_entry_add_probe(struct tracepoint_entry *entry,
105               void *probe, void *data)
106{
107    int nr_probes = 0;
108    struct tracepoint_func *old, *new;
109
110    WARN_ON(!probe);
111
112    debug_print_probes(entry);
113    old = entry->funcs;
114    if (old) {
115        /* (N -> N+1), (N != 0, 1) probes */
116        for (nr_probes = 0; old[nr_probes].func; nr_probes++)
117            if (old[nr_probes].func == probe &&
118                old[nr_probes].data == data)
119                return ERR_PTR(-EEXIST);
120    }
121    /* + 2 : one for new probe, one for NULL func */
122    new = allocate_probes(nr_probes + 2);
123    if (new == NULL)
124        return ERR_PTR(-ENOMEM);
125    if (old)
126        memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
127    new[nr_probes].func = probe;
128    new[nr_probes].data = data;
129    new[nr_probes + 1].func = NULL;
130    entry->refcount = nr_probes + 1;
131    entry->funcs = new;
132    debug_print_probes(entry);
133    return old;
134}
135
136static void *
137tracepoint_entry_remove_probe(struct tracepoint_entry *entry,
138                  void *probe, void *data)
139{
140    int nr_probes = 0, nr_del = 0, i;
141    struct tracepoint_func *old, *new;
142
143    old = entry->funcs;
144
145    if (!old)
146        return ERR_PTR(-ENOENT);
147
148    debug_print_probes(entry);
149    /* (N -> M), (N > 1, M >= 0) probes */
150    for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
151        if (!probe ||
152            (old[nr_probes].func == probe &&
153             old[nr_probes].data == data))
154            nr_del++;
155    }
156
157    if (nr_probes - nr_del == 0) {
158        /* N -> 0, (N > 1) */
159        entry->funcs = NULL;
160        entry->refcount = 0;
161        debug_print_probes(entry);
162        return old;
163    } else {
164        int j = 0;
165        /* N -> M, (N > 1, M > 0) */
166        /* + 1 for NULL */
167        new = allocate_probes(nr_probes - nr_del + 1);
168        if (new == NULL)
169            return ERR_PTR(-ENOMEM);
170        for (i = 0; old[i].func; i++)
171            if (probe &&
172                (old[i].func != probe || old[i].data != data))
173                new[j++] = old[i];
174        new[nr_probes - nr_del].func = NULL;
175        entry->refcount = nr_probes - nr_del;
176        entry->funcs = new;
177    }
178    debug_print_probes(entry);
179    return old;
180}
181
182/*
183 * Get tracepoint if the tracepoint is present in the tracepoint hash table.
184 * Must be called with tracepoints_mutex held.
185 * Returns NULL if not present.
186 */
187static struct tracepoint_entry *get_tracepoint(const char *name)
188{
189    struct hlist_head *head;
190    struct hlist_node *node;
191    struct tracepoint_entry *e;
192    u32 hash = jhash(name, strlen(name), 0);
193
194    head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
195    hlist_for_each_entry(e, node, head, hlist) {
196        if (!strcmp(name, e->name))
197            return e;
198    }
199    return NULL;
200}
201
202/*
203 * Add the tracepoint to the tracepoint hash table. Must be called with
204 * tracepoints_mutex held.
205 */
206static struct tracepoint_entry *add_tracepoint(const char *name)
207{
208    struct hlist_head *head;
209    struct hlist_node *node;
210    struct tracepoint_entry *e;
211    size_t name_len = strlen(name) + 1;
212    u32 hash = jhash(name, name_len-1, 0);
213
214    head = &tracepoint_table[hash & (TRACEPOINT_TABLE_SIZE - 1)];
215    hlist_for_each_entry(e, node, head, hlist) {
216        if (!strcmp(name, e->name)) {
217            printk(KERN_NOTICE
218                "tracepoint %s busy\n", name);
219            return ERR_PTR(-EEXIST); /* Already there */
220        }
221    }
222    /*
223     * Using kmalloc here to allocate a variable length element. Could
224     * cause some memory fragmentation if overused.
225     */
226    e = kmalloc(sizeof(struct tracepoint_entry) + name_len, GFP_KERNEL);
227    if (!e)
228        return ERR_PTR(-ENOMEM);
229    memcpy(&e->name[0], name, name_len);
230    e->funcs = NULL;
231    e->refcount = 0;
232    hlist_add_head(&e->hlist, head);
233    return e;
234}
235
236/*
237 * Remove the tracepoint from the tracepoint hash table. Must be called with
238 * mutex_lock held.
239 */
240static inline void remove_tracepoint(struct tracepoint_entry *e)
241{
242    hlist_del(&e->hlist);
243    kfree(e);
244}
245
246/*
247 * Sets the probe callback corresponding to one tracepoint.
248 */
249static void set_tracepoint(struct tracepoint_entry **entry,
250    struct tracepoint *elem, int active)
251{
252    WARN_ON(strcmp((*entry)->name, elem->name) != 0);
253
254    if (elem->regfunc && !jump_label_enabled(&elem->key) && active)
255        elem->regfunc();
256    else if (elem->unregfunc && jump_label_enabled(&elem->key) && !active)
257        elem->unregfunc();
258
259    /*
260     * rcu_assign_pointer has a smp_wmb() which makes sure that the new
261     * probe callbacks array is consistent before setting a pointer to it.
262     * This array is referenced by __DO_TRACE from
263     * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
264     * is used.
265     */
266    rcu_assign_pointer(elem->funcs, (*entry)->funcs);
267    if (active && !jump_label_enabled(&elem->key))
268        jump_label_inc(&elem->key);
269    else if (!active && jump_label_enabled(&elem->key))
270        jump_label_dec(&elem->key);
271}
272
273/*
274 * Disable a tracepoint and its probe callback.
275 * Note: only waiting an RCU period after setting elem->call to the empty
276 * function insures that the original callback is not used anymore. This insured
277 * by preempt_disable around the call site.
278 */
279static void disable_tracepoint(struct tracepoint *elem)
280{
281    if (elem->unregfunc && jump_label_enabled(&elem->key))
282        elem->unregfunc();
283
284    if (jump_label_enabled(&elem->key))
285        jump_label_dec(&elem->key);
286    rcu_assign_pointer(elem->funcs, NULL);
287}
288
289/**
290 * tracepoint_update_probe_range - Update a probe range
291 * @begin: beginning of the range
292 * @end: end of the range
293 *
294 * Updates the probe callback corresponding to a range of tracepoints.
295 */
296void tracepoint_update_probe_range(struct tracepoint * const *begin,
297                   struct tracepoint * const *end)
298{
299    struct tracepoint * const *iter;
300    struct tracepoint_entry *mark_entry;
301
302    if (!begin)
303        return;
304
305    mutex_lock(&tracepoints_mutex);
306    for (iter = begin; iter < end; iter++) {
307        mark_entry = get_tracepoint((*iter)->name);
308        if (mark_entry) {
309            set_tracepoint(&mark_entry, *iter,
310                    !!mark_entry->refcount);
311        } else {
312            disable_tracepoint(*iter);
313        }
314    }
315    mutex_unlock(&tracepoints_mutex);
316}
317
318/*
319 * Update probes, removing the faulty probes.
320 */
321static void tracepoint_update_probes(void)
322{
323    /* Core kernel tracepoints */
324    tracepoint_update_probe_range(__start___tracepoints_ptrs,
325        __stop___tracepoints_ptrs);
326    /* tracepoints in modules. */
327    module_update_tracepoints();
328}
329
330static struct tracepoint_func *
331tracepoint_add_probe(const char *name, void *probe, void *data)
332{
333    struct tracepoint_entry *entry;
334    struct tracepoint_func *old;
335
336    entry = get_tracepoint(name);
337    if (!entry) {
338        entry = add_tracepoint(name);
339        if (IS_ERR(entry))
340            return (struct tracepoint_func *)entry;
341    }
342    old = tracepoint_entry_add_probe(entry, probe, data);
343    if (IS_ERR(old) && !entry->refcount)
344        remove_tracepoint(entry);
345    return old;
346}
347
348/**
349 * tracepoint_probe_register - Connect a probe to a tracepoint
350 * @name: tracepoint name
351 * @probe: probe handler
352 *
353 * Returns 0 if ok, error value on error.
354 * The probe address must at least be aligned on the architecture pointer size.
355 */
356int tracepoint_probe_register(const char *name, void *probe, void *data)
357{
358    struct tracepoint_func *old;
359
360    mutex_lock(&tracepoints_mutex);
361    old = tracepoint_add_probe(name, probe, data);
362    mutex_unlock(&tracepoints_mutex);
363    if (IS_ERR(old))
364        return PTR_ERR(old);
365
366    tracepoint_update_probes(); /* may update entry */
367    release_probes(old);
368    return 0;
369}
370EXPORT_SYMBOL_GPL(tracepoint_probe_register);
371
372static struct tracepoint_func *
373tracepoint_remove_probe(const char *name, void *probe, void *data)
374{
375    struct tracepoint_entry *entry;
376    struct tracepoint_func *old;
377
378    entry = get_tracepoint(name);
379    if (!entry)
380        return ERR_PTR(-ENOENT);
381    old = tracepoint_entry_remove_probe(entry, probe, data);
382    if (IS_ERR(old))
383        return old;
384    if (!entry->refcount)
385        remove_tracepoint(entry);
386    return old;
387}
388
389/**
390 * tracepoint_probe_unregister - Disconnect a probe from a tracepoint
391 * @name: tracepoint name
392 * @probe: probe function pointer
393 *
394 * We do not need to call a synchronize_sched to make sure the probes have
395 * finished running before doing a module unload, because the module unload
396 * itself uses stop_machine(), which insures that every preempt disabled section
397 * have finished.
398 */
399int tracepoint_probe_unregister(const char *name, void *probe, void *data)
400{
401    struct tracepoint_func *old;
402
403    mutex_lock(&tracepoints_mutex);
404    old = tracepoint_remove_probe(name, probe, data);
405    mutex_unlock(&tracepoints_mutex);
406    if (IS_ERR(old))
407        return PTR_ERR(old);
408
409    tracepoint_update_probes(); /* may update entry */
410    release_probes(old);
411    return 0;
412}
413EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
414
415static LIST_HEAD(old_probes);
416static int need_update;
417
418static void tracepoint_add_old_probes(void *old)
419{
420    need_update = 1;
421    if (old) {
422        struct tp_probes *tp_probes = container_of(old,
423            struct tp_probes, probes[0]);
424        list_add(&tp_probes->u.list, &old_probes);
425    }
426}
427
428/**
429 * tracepoint_probe_register_noupdate - register a probe but not connect
430 * @name: tracepoint name
431 * @probe: probe handler
432 *
433 * caller must call tracepoint_probe_update_all()
434 */
435int tracepoint_probe_register_noupdate(const char *name, void *probe,
436                       void *data)
437{
438    struct tracepoint_func *old;
439
440    mutex_lock(&tracepoints_mutex);
441    old = tracepoint_add_probe(name, probe, data);
442    if (IS_ERR(old)) {
443        mutex_unlock(&tracepoints_mutex);
444        return PTR_ERR(old);
445    }
446    tracepoint_add_old_probes(old);
447    mutex_unlock(&tracepoints_mutex);
448    return 0;
449}
450EXPORT_SYMBOL_GPL(tracepoint_probe_register_noupdate);
451
452/**
453 * tracepoint_probe_unregister_noupdate - remove a probe but not disconnect
454 * @name: tracepoint name
455 * @probe: probe function pointer
456 *
457 * caller must call tracepoint_probe_update_all()
458 */
459int tracepoint_probe_unregister_noupdate(const char *name, void *probe,
460                     void *data)
461{
462    struct tracepoint_func *old;
463
464    mutex_lock(&tracepoints_mutex);
465    old = tracepoint_remove_probe(name, probe, data);
466    if (IS_ERR(old)) {
467        mutex_unlock(&tracepoints_mutex);
468        return PTR_ERR(old);
469    }
470    tracepoint_add_old_probes(old);
471    mutex_unlock(&tracepoints_mutex);
472    return 0;
473}
474EXPORT_SYMBOL_GPL(tracepoint_probe_unregister_noupdate);
475
476/**
477 * tracepoint_probe_update_all - update tracepoints
478 */
479void tracepoint_probe_update_all(void)
480{
481    LIST_HEAD(release_probes);
482    struct tp_probes *pos, *next;
483
484    mutex_lock(&tracepoints_mutex);
485    if (!need_update) {
486        mutex_unlock(&tracepoints_mutex);
487        return;
488    }
489    if (!list_empty(&old_probes))
490        list_replace_init(&old_probes, &release_probes);
491    need_update = 0;
492    mutex_unlock(&tracepoints_mutex);
493
494    tracepoint_update_probes();
495    list_for_each_entry_safe(pos, next, &release_probes, u.list) {
496        list_del(&pos->u.list);
497        call_rcu_sched(&pos->u.rcu, rcu_free_old_probes);
498    }
499}
500EXPORT_SYMBOL_GPL(tracepoint_probe_update_all);
501
502/**
503 * tracepoint_get_iter_range - Get a next tracepoint iterator given a range.
504 * @tracepoint: current tracepoints (in), next tracepoint (out)
505 * @begin: beginning of the range
506 * @end: end of the range
507 *
508 * Returns whether a next tracepoint has been found (1) or not (0).
509 * Will return the first tracepoint in the range if the input tracepoint is
510 * NULL.
511 */
512int tracepoint_get_iter_range(struct tracepoint * const **tracepoint,
513    struct tracepoint * const *begin, struct tracepoint * const *end)
514{
515    if (!*tracepoint && begin != end) {
516        *tracepoint = begin;
517        return 1;
518    }
519    if (*tracepoint >= begin && *tracepoint < end)
520        return 1;
521    return 0;
522}
523EXPORT_SYMBOL_GPL(tracepoint_get_iter_range);
524
525static void tracepoint_get_iter(struct tracepoint_iter *iter)
526{
527    int found = 0;
528
529    /* Core kernel tracepoints */
530    if (!iter->module) {
531        found = tracepoint_get_iter_range(&iter->tracepoint,
532                __start___tracepoints_ptrs,
533                __stop___tracepoints_ptrs);
534        if (found)
535            goto end;
536    }
537    /* tracepoints in modules. */
538    found = module_get_iter_tracepoints(iter);
539end:
540    if (!found)
541        tracepoint_iter_reset(iter);
542}
543
544void tracepoint_iter_start(struct tracepoint_iter *iter)
545{
546    tracepoint_get_iter(iter);
547}
548EXPORT_SYMBOL_GPL(tracepoint_iter_start);
549
550void tracepoint_iter_next(struct tracepoint_iter *iter)
551{
552    iter->tracepoint++;
553    /*
554     * iter->tracepoint may be invalid because we blindly incremented it.
555     * Make sure it is valid by marshalling on the tracepoints, getting the
556     * tracepoints from following modules if necessary.
557     */
558    tracepoint_get_iter(iter);
559}
560EXPORT_SYMBOL_GPL(tracepoint_iter_next);
561
562void tracepoint_iter_stop(struct tracepoint_iter *iter)
563{
564}
565EXPORT_SYMBOL_GPL(tracepoint_iter_stop);
566
567void tracepoint_iter_reset(struct tracepoint_iter *iter)
568{
569    iter->module = NULL;
570    iter->tracepoint = NULL;
571}
572EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
573
574#ifdef CONFIG_MODULES
575
576int tracepoint_module_notify(struct notifier_block *self,
577                 unsigned long val, void *data)
578{
579    struct module *mod = data;
580
581    switch (val) {
582    case MODULE_STATE_COMING:
583    case MODULE_STATE_GOING:
584        tracepoint_update_probe_range(mod->tracepoints_ptrs,
585            mod->tracepoints_ptrs + mod->num_tracepoints);
586        break;
587    }
588    return 0;
589}
590
591struct notifier_block tracepoint_module_nb = {
592    .notifier_call = tracepoint_module_notify,
593    .priority = 0,
594};
595
596static int init_tracepoints(void)
597{
598    return register_module_notifier(&tracepoint_module_nb);
599}
600__initcall(init_tracepoints);
601
602#endif /* CONFIG_MODULES */
603
604#ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
605
606/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
607static int sys_tracepoint_refcount;
608
609void syscall_regfunc(void)
610{
611    unsigned long flags;
612    struct task_struct *g, *t;
613
614    if (!sys_tracepoint_refcount) {
615        read_lock_irqsave(&tasklist_lock, flags);
616        do_each_thread(g, t) {
617            /* Skip kernel threads. */
618            if (t->mm)
619                set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
620        } while_each_thread(g, t);
621        read_unlock_irqrestore(&tasklist_lock, flags);
622    }
623    sys_tracepoint_refcount++;
624}
625
626void syscall_unregfunc(void)
627{
628    unsigned long flags;
629    struct task_struct *g, *t;
630
631    sys_tracepoint_refcount--;
632    if (!sys_tracepoint_refcount) {
633        read_lock_irqsave(&tasklist_lock, flags);
634        do_each_thread(g, t) {
635            clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
636        } while_each_thread(g, t);
637        read_unlock_irqrestore(&tasklist_lock, flags);
638    }
639}
640#endif
641

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