[PATCH] kretprobe spinlock deadlock patch
[linux-2.6.git] / kernel / kprobes.c
1 /*
2  *  Kernel Probes (KProbes)
3  *  kernel/kprobes.c
4  *
5  * This program is free software; you can redistribute it and/or modify
6  * it under the terms of the GNU General Public License as published by
7  * the Free Software Foundation; either version 2 of the License, or
8  * (at your option) any later version.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13  * GNU General Public License for more details.
14  *
15  * You should have received a copy of the GNU General Public License
16  * along with this program; if not, write to the Free Software
17  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18  *
19  * Copyright (C) IBM Corporation, 2002, 2004
20  *
21  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
22  *              Probes initial implementation (includes suggestions from
23  *              Rusty Russell).
24  * 2004-Aug     Updated by Prasanna S Panchamukhi <prasanna@in.ibm.com> with
25  *              hlists and exceptions notifier as suggested by Andi Kleen.
26  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
27  *              interface to access function arguments.
28  * 2004-Sep     Prasanna S Panchamukhi <prasanna@in.ibm.com> Changed Kprobes
29  *              exceptions notifier to be first on the priority list.
30  * 2005-May     Hien Nguyen <hien@us.ibm.com>, Jim Keniston
31  *              <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
32  *              <prasanna@in.ibm.com> added function-return probes.
33  */
34 #include <linux/kprobes.h>
35 #include <linux/hash.h>
36 #include <linux/init.h>
37 #include <linux/slab.h>
38 #include <linux/module.h>
39 #include <linux/moduleloader.h>
40 #include <linux/kallsyms.h>
41 #include <asm-generic/sections.h>
42 #include <asm/cacheflush.h>
43 #include <asm/errno.h>
44 #include <asm/kdebug.h>
45
46 #define KPROBE_HASH_BITS 6
47 #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
48
49
50 /*
51  * Some oddball architectures like 64bit powerpc have function descriptors
52  * so this must be overridable.
53  */
54 #ifndef kprobe_lookup_name
55 #define kprobe_lookup_name(name, addr) \
56         addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
57 #endif
58
59 static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
60 static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
61 static atomic_t kprobe_count;
62
63 DEFINE_MUTEX(kprobe_mutex);             /* Protects kprobe_table */
64 DEFINE_SPINLOCK(kretprobe_lock);        /* Protects kretprobe_inst_table */
65 static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
66
67 static struct notifier_block kprobe_page_fault_nb = {
68         .notifier_call = kprobe_exceptions_notify,
69         .priority = 0x7fffffff /* we need to notified first */
70 };
71
72 #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
73 /*
74  * kprobe->ainsn.insn points to the copy of the instruction to be
75  * single-stepped. x86_64, POWER4 and above have no-exec support and
76  * stepping on the instruction on a vmalloced/kmalloced/data page
77  * is a recipe for disaster
78  */
79 #define INSNS_PER_PAGE  (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
80
81 struct kprobe_insn_page {
82         struct hlist_node hlist;
83         kprobe_opcode_t *insns;         /* Page of instruction slots */
84         char slot_used[INSNS_PER_PAGE];
85         int nused;
86 };
87
88 static struct hlist_head kprobe_insn_pages;
89
90 /**
91  * get_insn_slot() - Find a slot on an executable page for an instruction.
92  * We allocate an executable page if there's no room on existing ones.
93  */
94 kprobe_opcode_t __kprobes *get_insn_slot(void)
95 {
96         struct kprobe_insn_page *kip;
97         struct hlist_node *pos;
98
99         hlist_for_each(pos, &kprobe_insn_pages) {
100                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
101                 if (kip->nused < INSNS_PER_PAGE) {
102                         int i;
103                         for (i = 0; i < INSNS_PER_PAGE; i++) {
104                                 if (!kip->slot_used[i]) {
105                                         kip->slot_used[i] = 1;
106                                         kip->nused++;
107                                         return kip->insns + (i * MAX_INSN_SIZE);
108                                 }
109                         }
110                         /* Surprise!  No unused slots.  Fix kip->nused. */
111                         kip->nused = INSNS_PER_PAGE;
112                 }
113         }
114
115         /* All out of space.  Need to allocate a new page. Use slot 0.*/
116         kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
117         if (!kip) {
118                 return NULL;
119         }
120
121         /*
122          * Use module_alloc so this page is within +/- 2GB of where the
123          * kernel image and loaded module images reside. This is required
124          * so x86_64 can correctly handle the %rip-relative fixups.
125          */
126         kip->insns = module_alloc(PAGE_SIZE);
127         if (!kip->insns) {
128                 kfree(kip);
129                 return NULL;
130         }
131         INIT_HLIST_NODE(&kip->hlist);
132         hlist_add_head(&kip->hlist, &kprobe_insn_pages);
133         memset(kip->slot_used, 0, INSNS_PER_PAGE);
134         kip->slot_used[0] = 1;
135         kip->nused = 1;
136         return kip->insns;
137 }
138
139 void __kprobes free_insn_slot(kprobe_opcode_t *slot)
140 {
141         struct kprobe_insn_page *kip;
142         struct hlist_node *pos;
143
144         hlist_for_each(pos, &kprobe_insn_pages) {
145                 kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
146                 if (kip->insns <= slot &&
147                     slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
148                         int i = (slot - kip->insns) / MAX_INSN_SIZE;
149                         kip->slot_used[i] = 0;
150                         kip->nused--;
151                         if (kip->nused == 0) {
152                                 /*
153                                  * Page is no longer in use.  Free it unless
154                                  * it's the last one.  We keep the last one
155                                  * so as not to have to set it up again the
156                                  * next time somebody inserts a probe.
157                                  */
158                                 hlist_del(&kip->hlist);
159                                 if (hlist_empty(&kprobe_insn_pages)) {
160                                         INIT_HLIST_NODE(&kip->hlist);
161                                         hlist_add_head(&kip->hlist,
162                                                 &kprobe_insn_pages);
163                                 } else {
164                                         module_free(NULL, kip->insns);
165                                         kfree(kip);
166                                 }
167                         }
168                         return;
169                 }
170         }
171 }
172 #endif
173
174 /* We have preemption disabled.. so it is safe to use __ versions */
175 static inline void set_kprobe_instance(struct kprobe *kp)
176 {
177         __get_cpu_var(kprobe_instance) = kp;
178 }
179
180 static inline void reset_kprobe_instance(void)
181 {
182         __get_cpu_var(kprobe_instance) = NULL;
183 }
184
185 /*
186  * This routine is called either:
187  *      - under the kprobe_mutex - during kprobe_[un]register()
188  *                              OR
189  *      - with preemption disabled - from arch/xxx/kernel/kprobes.c
190  */
191 struct kprobe __kprobes *get_kprobe(void *addr)
192 {
193         struct hlist_head *head;
194         struct hlist_node *node;
195         struct kprobe *p;
196
197         head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
198         hlist_for_each_entry_rcu(p, node, head, hlist) {
199                 if (p->addr == addr)
200                         return p;
201         }
202         return NULL;
203 }
204
205 /*
206  * Aggregate handlers for multiple kprobes support - these handlers
207  * take care of invoking the individual kprobe handlers on p->list
208  */
209 static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
210 {
211         struct kprobe *kp;
212
213         list_for_each_entry_rcu(kp, &p->list, list) {
214                 if (kp->pre_handler) {
215                         set_kprobe_instance(kp);
216                         if (kp->pre_handler(kp, regs))
217                                 return 1;
218                 }
219                 reset_kprobe_instance();
220         }
221         return 0;
222 }
223
224 static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
225                                         unsigned long flags)
226 {
227         struct kprobe *kp;
228
229         list_for_each_entry_rcu(kp, &p->list, list) {
230                 if (kp->post_handler) {
231                         set_kprobe_instance(kp);
232                         kp->post_handler(kp, regs, flags);
233                         reset_kprobe_instance();
234                 }
235         }
236         return;
237 }
238
239 static int __kprobes aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
240                                         int trapnr)
241 {
242         struct kprobe *cur = __get_cpu_var(kprobe_instance);
243
244         /*
245          * if we faulted "during" the execution of a user specified
246          * probe handler, invoke just that probe's fault handler
247          */
248         if (cur && cur->fault_handler) {
249                 if (cur->fault_handler(cur, regs, trapnr))
250                         return 1;
251         }
252         return 0;
253 }
254
255 static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
256 {
257         struct kprobe *cur = __get_cpu_var(kprobe_instance);
258         int ret = 0;
259
260         if (cur && cur->break_handler) {
261                 if (cur->break_handler(cur, regs))
262                         ret = 1;
263         }
264         reset_kprobe_instance();
265         return ret;
266 }
267
268 /* Walks the list and increments nmissed count for multiprobe case */
269 void __kprobes kprobes_inc_nmissed_count(struct kprobe *p)
270 {
271         struct kprobe *kp;
272         if (p->pre_handler != aggr_pre_handler) {
273                 p->nmissed++;
274         } else {
275                 list_for_each_entry_rcu(kp, &p->list, list)
276                         kp->nmissed++;
277         }
278         return;
279 }
280
281 /* Called with kretprobe_lock held */
282 struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
283 {
284         struct hlist_node *node;
285         struct kretprobe_instance *ri;
286         hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
287                 return ri;
288         return NULL;
289 }
290
291 /* Called with kretprobe_lock held */
292 static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
293                                                               *rp)
294 {
295         struct hlist_node *node;
296         struct kretprobe_instance *ri;
297         hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
298                 return ri;
299         return NULL;
300 }
301
302 /* Called with kretprobe_lock held */
303 void __kprobes add_rp_inst(struct kretprobe_instance *ri)
304 {
305         /*
306          * Remove rp inst off the free list -
307          * Add it back when probed function returns
308          */
309         hlist_del(&ri->uflist);
310
311         /* Add rp inst onto table */
312         INIT_HLIST_NODE(&ri->hlist);
313         hlist_add_head(&ri->hlist,
314                         &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);
315
316         /* Also add this rp inst to the used list. */
317         INIT_HLIST_NODE(&ri->uflist);
318         hlist_add_head(&ri->uflist, &ri->rp->used_instances);
319 }
320
321 /* Called with kretprobe_lock held */
322 void __kprobes recycle_rp_inst(struct kretprobe_instance *ri,
323                                 struct hlist_head *head)
324 {
325         /* remove rp inst off the rprobe_inst_table */
326         hlist_del(&ri->hlist);
327         if (ri->rp) {
328                 /* remove rp inst off the used list */
329                 hlist_del(&ri->uflist);
330                 /* put rp inst back onto the free list */
331                 INIT_HLIST_NODE(&ri->uflist);
332                 hlist_add_head(&ri->uflist, &ri->rp->free_instances);
333         } else
334                 /* Unregistering */
335                 hlist_add_head(&ri->hlist, head);
336 }
337
338 struct hlist_head __kprobes *kretprobe_inst_table_head(struct task_struct *tsk)
339 {
340         return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
341 }
342
343 /*
344  * This function is called from finish_task_switch when task tk becomes dead,
345  * so that we can recycle any function-return probe instances associated
346  * with this task. These left over instances represent probed functions
347  * that have been called but will never return.
348  */
349 void __kprobes kprobe_flush_task(struct task_struct *tk)
350 {
351         struct kretprobe_instance *ri;
352         struct hlist_head *head, empty_rp;
353         struct hlist_node *node, *tmp;
354         unsigned long flags = 0;
355
356         INIT_HLIST_HEAD(&empty_rp);
357         spin_lock_irqsave(&kretprobe_lock, flags);
358         head = kretprobe_inst_table_head(tk);
359         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
360                 if (ri->task == tk)
361                         recycle_rp_inst(ri, &empty_rp);
362         }
363         spin_unlock_irqrestore(&kretprobe_lock, flags);
364
365         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
366                 hlist_del(&ri->hlist);
367                 kfree(ri);
368         }
369 }
370
371 static inline void free_rp_inst(struct kretprobe *rp)
372 {
373         struct kretprobe_instance *ri;
374         while ((ri = get_free_rp_inst(rp)) != NULL) {
375                 hlist_del(&ri->uflist);
376                 kfree(ri);
377         }
378 }
379
380 /*
381  * Keep all fields in the kprobe consistent
382  */
383 static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
384 {
385         memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
386         memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
387 }
388
389 /*
390 * Add the new probe to old_p->list. Fail if this is the
391 * second jprobe at the address - two jprobes can't coexist
392 */
393 static int __kprobes add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
394 {
395         if (p->break_handler) {
396                 if (old_p->break_handler)
397                         return -EEXIST;
398                 list_add_tail_rcu(&p->list, &old_p->list);
399                 old_p->break_handler = aggr_break_handler;
400         } else
401                 list_add_rcu(&p->list, &old_p->list);
402         if (p->post_handler && !old_p->post_handler)
403                 old_p->post_handler = aggr_post_handler;
404         return 0;
405 }
406
407 /*
408  * Fill in the required fields of the "manager kprobe". Replace the
409  * earlier kprobe in the hlist with the manager kprobe
410  */
411 static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
412 {
413         copy_kprobe(p, ap);
414         flush_insn_slot(ap);
415         ap->addr = p->addr;
416         ap->pre_handler = aggr_pre_handler;
417         ap->fault_handler = aggr_fault_handler;
418         if (p->post_handler)
419                 ap->post_handler = aggr_post_handler;
420         if (p->break_handler)
421                 ap->break_handler = aggr_break_handler;
422
423         INIT_LIST_HEAD(&ap->list);
424         list_add_rcu(&p->list, &ap->list);
425
426         hlist_replace_rcu(&p->hlist, &ap->hlist);
427 }
428
429 /*
430  * This is the second or subsequent kprobe at the address - handle
431  * the intricacies
432  */
433 static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
434                                           struct kprobe *p)
435 {
436         int ret = 0;
437         struct kprobe *ap;
438
439         if (old_p->pre_handler == aggr_pre_handler) {
440                 copy_kprobe(old_p, p);
441                 ret = add_new_kprobe(old_p, p);
442         } else {
443                 ap = kzalloc(sizeof(struct kprobe), GFP_KERNEL);
444                 if (!ap)
445                         return -ENOMEM;
446                 add_aggr_kprobe(ap, old_p);
447                 copy_kprobe(ap, p);
448                 ret = add_new_kprobe(ap, p);
449         }
450         return ret;
451 }
452
453 static int __kprobes in_kprobes_functions(unsigned long addr)
454 {
455         if (addr >= (unsigned long)__kprobes_text_start
456                 && addr < (unsigned long)__kprobes_text_end)
457                 return -EINVAL;
458         return 0;
459 }
460
461 static int __kprobes __register_kprobe(struct kprobe *p,
462         unsigned long called_from)
463 {
464         int ret = 0;
465         struct kprobe *old_p;
466         struct module *probed_mod;
467
468         /*
469          * If we have a symbol_name argument look it up,
470          * and add it to the address.  That way the addr
471          * field can either be global or relative to a symbol.
472          */
473         if (p->symbol_name) {
474                 if (p->addr)
475                         return -EINVAL;
476                 kprobe_lookup_name(p->symbol_name, p->addr);
477         }
478
479         if (!p->addr)
480                 return -EINVAL;
481         p->addr = (kprobe_opcode_t *)(((char *)p->addr)+ p->offset);
482
483         if ((!kernel_text_address((unsigned long) p->addr)) ||
484                 in_kprobes_functions((unsigned long) p->addr))
485                 return -EINVAL;
486
487         p->mod_refcounted = 0;
488         /* Check are we probing a module */
489         if ((probed_mod = module_text_address((unsigned long) p->addr))) {
490                 struct module *calling_mod = module_text_address(called_from);
491                 /* We must allow modules to probe themself and
492                  * in this case avoid incrementing the module refcount,
493                  * so as to allow unloading of self probing modules.
494                  */
495                 if (calling_mod && (calling_mod != probed_mod)) {
496                         if (unlikely(!try_module_get(probed_mod)))
497                                 return -EINVAL;
498                         p->mod_refcounted = 1;
499                 } else
500                         probed_mod = NULL;
501         }
502
503         p->nmissed = 0;
504         mutex_lock(&kprobe_mutex);
505         old_p = get_kprobe(p->addr);
506         if (old_p) {
507                 ret = register_aggr_kprobe(old_p, p);
508                 if (!ret)
509                         atomic_inc(&kprobe_count);
510                 goto out;
511         }
512
513         if ((ret = arch_prepare_kprobe(p)) != 0)
514                 goto out;
515
516         INIT_HLIST_NODE(&p->hlist);
517         hlist_add_head_rcu(&p->hlist,
518                        &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
519
520         if (atomic_add_return(1, &kprobe_count) == \
521                                 (ARCH_INACTIVE_KPROBE_COUNT + 1))
522                 register_page_fault_notifier(&kprobe_page_fault_nb);
523
524         arch_arm_kprobe(p);
525
526 out:
527         mutex_unlock(&kprobe_mutex);
528
529         if (ret && probed_mod)
530                 module_put(probed_mod);
531         return ret;
532 }
533
534 int __kprobes register_kprobe(struct kprobe *p)
535 {
536         return __register_kprobe(p,
537                 (unsigned long)__builtin_return_address(0));
538 }
539
540 void __kprobes unregister_kprobe(struct kprobe *p)
541 {
542         struct module *mod;
543         struct kprobe *old_p, *list_p;
544         int cleanup_p;
545
546         mutex_lock(&kprobe_mutex);
547         old_p = get_kprobe(p->addr);
548         if (unlikely(!old_p)) {
549                 mutex_unlock(&kprobe_mutex);
550                 return;
551         }
552         if (p != old_p) {
553                 list_for_each_entry_rcu(list_p, &old_p->list, list)
554                         if (list_p == p)
555                         /* kprobe p is a valid probe */
556                                 goto valid_p;
557                 mutex_unlock(&kprobe_mutex);
558                 return;
559         }
560 valid_p:
561         if ((old_p == p) || ((old_p->pre_handler == aggr_pre_handler) &&
562                 (p->list.next == &old_p->list) &&
563                 (p->list.prev == &old_p->list))) {
564                 /* Only probe on the hash list */
565                 arch_disarm_kprobe(p);
566                 hlist_del_rcu(&old_p->hlist);
567                 cleanup_p = 1;
568         } else {
569                 list_del_rcu(&p->list);
570                 cleanup_p = 0;
571         }
572
573         mutex_unlock(&kprobe_mutex);
574
575         synchronize_sched();
576         if (p->mod_refcounted &&
577             (mod = module_text_address((unsigned long)p->addr)))
578                 module_put(mod);
579
580         if (cleanup_p) {
581                 if (p != old_p) {
582                         list_del_rcu(&p->list);
583                         kfree(old_p);
584                 }
585                 arch_remove_kprobe(p);
586         } else {
587                 mutex_lock(&kprobe_mutex);
588                 if (p->break_handler)
589                         old_p->break_handler = NULL;
590                 if (p->post_handler){
591                         list_for_each_entry_rcu(list_p, &old_p->list, list){
592                                 if (list_p->post_handler){
593                                         cleanup_p = 2;
594                                         break;
595                                 }
596                         }
597                         if (cleanup_p == 0)
598                                 old_p->post_handler = NULL;
599                 }
600                 mutex_unlock(&kprobe_mutex);
601         }
602
603         /* Call unregister_page_fault_notifier()
604          * if no probes are active
605          */
606         mutex_lock(&kprobe_mutex);
607         if (atomic_add_return(-1, &kprobe_count) == \
608                                 ARCH_INACTIVE_KPROBE_COUNT)
609                 unregister_page_fault_notifier(&kprobe_page_fault_nb);
610         mutex_unlock(&kprobe_mutex);
611         return;
612 }
613
614 static struct notifier_block kprobe_exceptions_nb = {
615         .notifier_call = kprobe_exceptions_notify,
616         .priority = 0x7fffffff /* we need to be notified first */
617 };
618
619
620 int __kprobes register_jprobe(struct jprobe *jp)
621 {
622         /* Todo: Verify probepoint is a function entry point */
623         jp->kp.pre_handler = setjmp_pre_handler;
624         jp->kp.break_handler = longjmp_break_handler;
625
626         return __register_kprobe(&jp->kp,
627                 (unsigned long)__builtin_return_address(0));
628 }
629
630 void __kprobes unregister_jprobe(struct jprobe *jp)
631 {
632         unregister_kprobe(&jp->kp);
633 }
634
635 #ifdef ARCH_SUPPORTS_KRETPROBES
636
637 /*
638  * This kprobe pre_handler is registered with every kretprobe. When probe
639  * hits it will set up the return probe.
640  */
641 static int __kprobes pre_handler_kretprobe(struct kprobe *p,
642                                            struct pt_regs *regs)
643 {
644         struct kretprobe *rp = container_of(p, struct kretprobe, kp);
645         unsigned long flags = 0;
646
647         /*TODO: consider to only swap the RA after the last pre_handler fired */
648         spin_lock_irqsave(&kretprobe_lock, flags);
649         arch_prepare_kretprobe(rp, regs);
650         spin_unlock_irqrestore(&kretprobe_lock, flags);
651         return 0;
652 }
653
654 int __kprobes register_kretprobe(struct kretprobe *rp)
655 {
656         int ret = 0;
657         struct kretprobe_instance *inst;
658         int i;
659
660         rp->kp.pre_handler = pre_handler_kretprobe;
661         rp->kp.post_handler = NULL;
662         rp->kp.fault_handler = NULL;
663         rp->kp.break_handler = NULL;
664
665         /* Pre-allocate memory for max kretprobe instances */
666         if (rp->maxactive <= 0) {
667 #ifdef CONFIG_PREEMPT
668                 rp->maxactive = max(10, 2 * NR_CPUS);
669 #else
670                 rp->maxactive = NR_CPUS;
671 #endif
672         }
673         INIT_HLIST_HEAD(&rp->used_instances);
674         INIT_HLIST_HEAD(&rp->free_instances);
675         for (i = 0; i < rp->maxactive; i++) {
676                 inst = kmalloc(sizeof(struct kretprobe_instance), GFP_KERNEL);
677                 if (inst == NULL) {
678                         free_rp_inst(rp);
679                         return -ENOMEM;
680                 }
681                 INIT_HLIST_NODE(&inst->uflist);
682                 hlist_add_head(&inst->uflist, &rp->free_instances);
683         }
684
685         rp->nmissed = 0;
686         /* Establish function entry probe point */
687         if ((ret = __register_kprobe(&rp->kp,
688                 (unsigned long)__builtin_return_address(0))) != 0)
689                 free_rp_inst(rp);
690         return ret;
691 }
692
693 #else /* ARCH_SUPPORTS_KRETPROBES */
694
695 int __kprobes register_kretprobe(struct kretprobe *rp)
696 {
697         return -ENOSYS;
698 }
699
700 #endif /* ARCH_SUPPORTS_KRETPROBES */
701
702 void __kprobes unregister_kretprobe(struct kretprobe *rp)
703 {
704         unsigned long flags;
705         struct kretprobe_instance *ri;
706
707         unregister_kprobe(&rp->kp);
708         /* No race here */
709         spin_lock_irqsave(&kretprobe_lock, flags);
710         while ((ri = get_used_rp_inst(rp)) != NULL) {
711                 ri->rp = NULL;
712                 hlist_del(&ri->uflist);
713         }
714         spin_unlock_irqrestore(&kretprobe_lock, flags);
715         free_rp_inst(rp);
716 }
717
718 static int __init init_kprobes(void)
719 {
720         int i, err = 0;
721
722         /* FIXME allocate the probe table, currently defined statically */
723         /* initialize all list heads */
724         for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
725                 INIT_HLIST_HEAD(&kprobe_table[i]);
726                 INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
727         }
728         atomic_set(&kprobe_count, 0);
729
730         err = arch_init_kprobes();
731         if (!err)
732                 err = register_die_notifier(&kprobe_exceptions_nb);
733
734         return err;
735 }
736
737 __initcall(init_kprobes);
738
739 EXPORT_SYMBOL_GPL(register_kprobe);
740 EXPORT_SYMBOL_GPL(unregister_kprobe);
741 EXPORT_SYMBOL_GPL(register_jprobe);
742 EXPORT_SYMBOL_GPL(unregister_jprobe);
743 EXPORT_SYMBOL_GPL(jprobe_return);
744 EXPORT_SYMBOL_GPL(register_kretprobe);
745 EXPORT_SYMBOL_GPL(unregister_kretprobe);
746