Root/kernel/tracepoint.c

1/*
2 * Copyright (C) 2008-2014 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/static_key.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#ifdef CONFIG_MODULES
37/*
38 * Tracepoint module list mutex protects the local module list.
39 */
40static DEFINE_MUTEX(tracepoint_module_list_mutex);
41
42/* Local list of struct tp_module */
43static LIST_HEAD(tracepoint_module_list);
44#endif /* CONFIG_MODULES */
45
46/*
47 * tracepoints_mutex protects the builtin and module tracepoints.
48 * tracepoints_mutex nests inside tracepoint_module_list_mutex.
49 */
50static DEFINE_MUTEX(tracepoints_mutex);
51
52/*
53 * Note about RCU :
54 * It is used to delay the free of multiple probes array until a quiescent
55 * state is reached.
56 */
57struct tp_probes {
58    struct rcu_head rcu;
59    struct tracepoint_func probes[0];
60};
61
62static inline void *allocate_probes(int count)
63{
64    struct tp_probes *p = kmalloc(count * sizeof(struct tracepoint_func)
65            + sizeof(struct tp_probes), GFP_KERNEL);
66    return p == NULL ? NULL : p->probes;
67}
68
69static void rcu_free_old_probes(struct rcu_head *head)
70{
71    kfree(container_of(head, struct tp_probes, rcu));
72}
73
74static inline void release_probes(struct tracepoint_func *old)
75{
76    if (old) {
77        struct tp_probes *tp_probes = container_of(old,
78            struct tp_probes, probes[0]);
79        call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes);
80    }
81}
82
83static void debug_print_probes(struct tracepoint_func *funcs)
84{
85    int i;
86
87    if (!tracepoint_debug || !funcs)
88        return;
89
90    for (i = 0; funcs[i].func; i++)
91        printk(KERN_DEBUG "Probe %d : %p\n", i, funcs[i].func);
92}
93
94static struct tracepoint_func *func_add(struct tracepoint_func **funcs,
95        struct tracepoint_func *tp_func)
96{
97    int nr_probes = 0;
98    struct tracepoint_func *old, *new;
99
100    if (WARN_ON(!tp_func->func))
101        return ERR_PTR(-EINVAL);
102
103    debug_print_probes(*funcs);
104    old = *funcs;
105    if (old) {
106        /* (N -> N+1), (N != 0, 1) probes */
107        for (nr_probes = 0; old[nr_probes].func; nr_probes++)
108            if (old[nr_probes].func == tp_func->func &&
109                old[nr_probes].data == tp_func->data)
110                return ERR_PTR(-EEXIST);
111    }
112    /* + 2 : one for new probe, one for NULL func */
113    new = allocate_probes(nr_probes + 2);
114    if (new == NULL)
115        return ERR_PTR(-ENOMEM);
116    if (old)
117        memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
118    new[nr_probes] = *tp_func;
119    new[nr_probes + 1].func = NULL;
120    *funcs = new;
121    debug_print_probes(*funcs);
122    return old;
123}
124
125static void *func_remove(struct tracepoint_func **funcs,
126        struct tracepoint_func *tp_func)
127{
128    int nr_probes = 0, nr_del = 0, i;
129    struct tracepoint_func *old, *new;
130
131    old = *funcs;
132
133    if (!old)
134        return ERR_PTR(-ENOENT);
135
136    debug_print_probes(*funcs);
137    /* (N -> M), (N > 1, M >= 0) probes */
138    if (tp_func->func) {
139        for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
140            if (old[nr_probes].func == tp_func->func &&
141                 old[nr_probes].data == tp_func->data)
142                nr_del++;
143        }
144    }
145
146    /*
147     * If probe is NULL, then nr_probes = nr_del = 0, and then the
148     * entire entry will be removed.
149     */
150    if (nr_probes - nr_del == 0) {
151        /* N -> 0, (N > 1) */
152        *funcs = NULL;
153        debug_print_probes(*funcs);
154        return old;
155    } else {
156        int j = 0;
157        /* N -> M, (N > 1, M > 0) */
158        /* + 1 for NULL */
159        new = allocate_probes(nr_probes - nr_del + 1);
160        if (new == NULL)
161            return ERR_PTR(-ENOMEM);
162        for (i = 0; old[i].func; i++)
163            if (old[i].func != tp_func->func
164                    || old[i].data != tp_func->data)
165                new[j++] = old[i];
166        new[nr_probes - nr_del].func = NULL;
167        *funcs = new;
168    }
169    debug_print_probes(*funcs);
170    return old;
171}
172
173/*
174 * Add the probe function to a tracepoint.
175 */
176static int tracepoint_add_func(struct tracepoint *tp,
177        struct tracepoint_func *func)
178{
179    struct tracepoint_func *old, *tp_funcs;
180
181    if (tp->regfunc && !static_key_enabled(&tp->key))
182        tp->regfunc();
183
184    tp_funcs = rcu_dereference_protected(tp->funcs,
185            lockdep_is_held(&tracepoints_mutex));
186    old = func_add(&tp_funcs, func);
187    if (IS_ERR(old)) {
188        WARN_ON_ONCE(1);
189        return PTR_ERR(old);
190    }
191
192    /*
193     * rcu_assign_pointer has a smp_wmb() which makes sure that the new
194     * probe callbacks array is consistent before setting a pointer to it.
195     * This array is referenced by __DO_TRACE from
196     * include/linux/tracepoints.h. A matching smp_read_barrier_depends()
197     * is used.
198     */
199    rcu_assign_pointer(tp->funcs, tp_funcs);
200    if (!static_key_enabled(&tp->key))
201        static_key_slow_inc(&tp->key);
202    release_probes(old);
203    return 0;
204}
205
206/*
207 * Remove a probe function from a tracepoint.
208 * Note: only waiting an RCU period after setting elem->call to the empty
209 * function insures that the original callback is not used anymore. This insured
210 * by preempt_disable around the call site.
211 */
212static int tracepoint_remove_func(struct tracepoint *tp,
213        struct tracepoint_func *func)
214{
215    struct tracepoint_func *old, *tp_funcs;
216
217    tp_funcs = rcu_dereference_protected(tp->funcs,
218            lockdep_is_held(&tracepoints_mutex));
219    old = func_remove(&tp_funcs, func);
220    if (IS_ERR(old)) {
221        WARN_ON_ONCE(1);
222        return PTR_ERR(old);
223    }
224
225    if (!tp_funcs) {
226        /* Removed last function */
227        if (tp->unregfunc && static_key_enabled(&tp->key))
228            tp->unregfunc();
229
230        if (static_key_enabled(&tp->key))
231            static_key_slow_dec(&tp->key);
232    }
233    rcu_assign_pointer(tp->funcs, tp_funcs);
234    release_probes(old);
235    return 0;
236}
237
238/**
239 * tracepoint_probe_register - Connect a probe to a tracepoint
240 * @tp: tracepoint
241 * @probe: probe handler
242 *
243 * Returns 0 if ok, error value on error.
244 * Note: if @tp is within a module, the caller is responsible for
245 * unregistering the probe before the module is gone. This can be
246 * performed either with a tracepoint module going notifier, or from
247 * within module exit functions.
248 */
249int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
250{
251    struct tracepoint_func tp_func;
252    int ret;
253
254    mutex_lock(&tracepoints_mutex);
255    tp_func.func = probe;
256    tp_func.data = data;
257    ret = tracepoint_add_func(tp, &tp_func);
258    mutex_unlock(&tracepoints_mutex);
259    return ret;
260}
261EXPORT_SYMBOL_GPL(tracepoint_probe_register);
262
263/**
264 * tracepoint_probe_unregister - Disconnect a probe from a tracepoint
265 * @tp: tracepoint
266 * @probe: probe function pointer
267 *
268 * Returns 0 if ok, error value on error.
269 */
270int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
271{
272    struct tracepoint_func tp_func;
273    int ret;
274
275    mutex_lock(&tracepoints_mutex);
276    tp_func.func = probe;
277    tp_func.data = data;
278    ret = tracepoint_remove_func(tp, &tp_func);
279    mutex_unlock(&tracepoints_mutex);
280    return ret;
281}
282EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
283
284#ifdef CONFIG_MODULES
285bool trace_module_has_bad_taint(struct module *mod)
286{
287    return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
288                   (1 << TAINT_UNSIGNED_MODULE));
289}
290
291static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
292
293/**
294 * register_tracepoint_notifier - register tracepoint coming/going notifier
295 * @nb: notifier block
296 *
297 * Notifiers registered with this function are called on module
298 * coming/going with the tracepoint_module_list_mutex held.
299 * The notifier block callback should expect a "struct tp_module" data
300 * pointer.
301 */
302int register_tracepoint_module_notifier(struct notifier_block *nb)
303{
304    struct tp_module *tp_mod;
305    int ret;
306
307    mutex_lock(&tracepoint_module_list_mutex);
308    ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
309    if (ret)
310        goto end;
311    list_for_each_entry(tp_mod, &tracepoint_module_list, list)
312        (void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
313end:
314    mutex_unlock(&tracepoint_module_list_mutex);
315    return ret;
316}
317EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);
318
319/**
320 * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
321 * @nb: notifier block
322 *
323 * The notifier block callback should expect a "struct tp_module" data
324 * pointer.
325 */
326int unregister_tracepoint_module_notifier(struct notifier_block *nb)
327{
328    struct tp_module *tp_mod;
329    int ret;
330
331    mutex_lock(&tracepoint_module_list_mutex);
332    ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
333    if (ret)
334        goto end;
335    list_for_each_entry(tp_mod, &tracepoint_module_list, list)
336        (void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
337end:
338    mutex_unlock(&tracepoint_module_list_mutex);
339    return ret;
340
341}
342EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
343
344/*
345 * Ensure the tracer unregistered the module's probes before the module
346 * teardown is performed. Prevents leaks of probe and data pointers.
347 */
348static void tp_module_going_check_quiescent(struct tracepoint * const *begin,
349        struct tracepoint * const *end)
350{
351    struct tracepoint * const *iter;
352
353    if (!begin)
354        return;
355    for (iter = begin; iter < end; iter++)
356        WARN_ON_ONCE((*iter)->funcs);
357}
358
359static int tracepoint_module_coming(struct module *mod)
360{
361    struct tp_module *tp_mod;
362    int ret = 0;
363
364    if (!mod->num_tracepoints)
365        return 0;
366
367    /*
368     * We skip modules that taint the kernel, especially those with different
369     * module headers (for forced load), to make sure we don't cause a crash.
370     * Staging, out-of-tree, and unsigned GPL modules are fine.
371     */
372    if (trace_module_has_bad_taint(mod))
373        return 0;
374    mutex_lock(&tracepoint_module_list_mutex);
375    tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
376    if (!tp_mod) {
377        ret = -ENOMEM;
378        goto end;
379    }
380    tp_mod->mod = mod;
381    list_add_tail(&tp_mod->list, &tracepoint_module_list);
382    blocking_notifier_call_chain(&tracepoint_notify_list,
383            MODULE_STATE_COMING, tp_mod);
384end:
385    mutex_unlock(&tracepoint_module_list_mutex);
386    return ret;
387}
388
389static void tracepoint_module_going(struct module *mod)
390{
391    struct tp_module *tp_mod;
392
393    if (!mod->num_tracepoints)
394        return;
395
396    mutex_lock(&tracepoint_module_list_mutex);
397    list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
398        if (tp_mod->mod == mod) {
399            blocking_notifier_call_chain(&tracepoint_notify_list,
400                    MODULE_STATE_GOING, tp_mod);
401            list_del(&tp_mod->list);
402            kfree(tp_mod);
403            /*
404             * Called the going notifier before checking for
405             * quiescence.
406             */
407            tp_module_going_check_quiescent(mod->tracepoints_ptrs,
408                mod->tracepoints_ptrs + mod->num_tracepoints);
409            break;
410        }
411    }
412    /*
413     * In the case of modules that were tainted at "coming", we'll simply
414     * walk through the list without finding it. We cannot use the "tainted"
415     * flag on "going", in case a module taints the kernel only after being
416     * loaded.
417     */
418    mutex_unlock(&tracepoint_module_list_mutex);
419}
420
421static int tracepoint_module_notify(struct notifier_block *self,
422        unsigned long val, void *data)
423{
424    struct module *mod = data;
425    int ret = 0;
426
427    switch (val) {
428    case MODULE_STATE_COMING:
429        ret = tracepoint_module_coming(mod);
430        break;
431    case MODULE_STATE_LIVE:
432        break;
433    case MODULE_STATE_GOING:
434        tracepoint_module_going(mod);
435        break;
436    case MODULE_STATE_UNFORMED:
437        break;
438    }
439    return ret;
440}
441
442static struct notifier_block tracepoint_module_nb = {
443    .notifier_call = tracepoint_module_notify,
444    .priority = 0,
445};
446
447static __init int init_tracepoints(void)
448{
449    int ret;
450
451    ret = register_module_notifier(&tracepoint_module_nb);
452    if (ret)
453        pr_warning("Failed to register tracepoint module enter notifier\n");
454
455    return ret;
456}
457__initcall(init_tracepoints);
458#endif /* CONFIG_MODULES */
459
460static void for_each_tracepoint_range(struct tracepoint * const *begin,
461        struct tracepoint * const *end,
462        void (*fct)(struct tracepoint *tp, void *priv),
463        void *priv)
464{
465    struct tracepoint * const *iter;
466
467    if (!begin)
468        return;
469    for (iter = begin; iter < end; iter++)
470        fct(*iter, priv);
471}
472
473/**
474 * for_each_kernel_tracepoint - iteration on all kernel tracepoints
475 * @fct: callback
476 * @priv: private data
477 */
478void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
479        void *priv)
480{
481    for_each_tracepoint_range(__start___tracepoints_ptrs,
482        __stop___tracepoints_ptrs, fct, priv);
483}
484EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
485
486#ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
487
488/* NB: reg/unreg are called while guarded with the tracepoints_mutex */
489static int sys_tracepoint_refcount;
490
491void syscall_regfunc(void)
492{
493    unsigned long flags;
494    struct task_struct *g, *t;
495
496    if (!sys_tracepoint_refcount) {
497        read_lock_irqsave(&tasklist_lock, flags);
498        do_each_thread(g, t) {
499            /* Skip kernel threads. */
500            if (t->mm)
501                set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
502        } while_each_thread(g, t);
503        read_unlock_irqrestore(&tasklist_lock, flags);
504    }
505    sys_tracepoint_refcount++;
506}
507
508void syscall_unregfunc(void)
509{
510    unsigned long flags;
511    struct task_struct *g, *t;
512
513    sys_tracepoint_refcount--;
514    if (!sys_tracepoint_refcount) {
515        read_lock_irqsave(&tasklist_lock, flags);
516        do_each_thread(g, t) {
517            clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
518        } while_each_thread(g, t);
519        read_unlock_irqrestore(&tasklist_lock, flags);
520    }
521}
522#endif
523

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