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

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