summaryrefslogtreecommitdiff
path: root/kernel/marker.c
blob: 05a25776f71fe4f802971323f3144733a8c14d8d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
/*
 * Copyright (C) 2007 Mathieu Desnoyers
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/types.h>
#include <linux/jhash.h>
#include <linux/list.h>
#include <linux/rcupdate.h>
#include <linux/marker.h>
#include <linux/err.h>
#include <linux/slab.h>

extern struct marker __start___markers[];
extern struct marker __stop___markers[];

/* Set to 1 to enable marker debug output */
static const int marker_debug;

/*
 * markers_mutex nests inside module_mutex. Markers mutex protects the builtin
 * and module markers and the hash table.
 */
static DEFINE_MUTEX(markers_mutex);

/*
 * Marker hash table, containing the active markers.
 * Protected by module_mutex.
 */
#define MARKER_HASH_BITS 6
#define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)

/*
 * Note about RCU :
 * It is used to make sure every handler has finished using its private data
 * between two consecutive operation (add or remove) on a given marker.  It is
 * also used to delay the free of multiple probes array until a quiescent state
 * is reached.
 * marker entries modifications are protected by the markers_mutex.
 */
struct marker_entry {
	struct hlist_node hlist;
	char *format;
			/* Probe wrapper */
	void (*call)(const struct marker *mdata, void *call_private, ...);
	struct marker_probe_closure single;
	struct marker_probe_closure *multi;
	int refcount;	/* Number of times armed. 0 if disarmed. */
	struct rcu_head rcu;
	void *oldptr;
	unsigned char rcu_pending:1;
	unsigned char ptype:1;
	char name[0];	/* Contains name'\0'format'\0' */
};

static struct hlist_head marker_table[MARKER_TABLE_SIZE];

/**
 * __mark_empty_function - Empty probe callback
 * @probe_private: probe private data
 * @call_private: call site private data
 * @fmt: format string
 * @...: variable argument list
 *
 * Empty callback provided as a probe to the markers. By providing this to a
 * disabled marker, we make sure the  execution flow is always valid even
 * though the function pointer change and the marker enabling are two distinct
 * operations that modifies the execution flow of preemptible code.
 */
void __mark_empty_function(void *probe_private, void *call_private,
	const char *fmt, va_list *args)
{
}
EXPORT_SYMBOL_GPL(__mark_empty_function);

/*
 * marker_probe_cb Callback that prepares the variable argument list for probes.
 * @mdata: pointer of type struct marker
 * @call_private: caller site private data
 * @...:  Variable argument list.
 *
 * Since we do not use "typical" pointer based RCU in the 1 argument case, we
 * need to put a full smp_rmb() in this branch. This is why we do not use
 * rcu_dereference() for the pointer read.
 */
void marker_probe_cb(const struct marker *mdata, void *call_private, ...)
{
	va_list args;
	char ptype;

	/*
	 * rcu_read_lock_sched does two things : disabling preemption to make
	 * sure the teardown of the callbacks can be done correctly when they
	 * are in modules and they insure RCU read coherency.
	 */
	rcu_read_lock_sched();
	ptype = mdata->ptype;
	if (likely(!ptype)) {
		marker_probe_func *func;
		/* Must read the ptype before ptr. They are not data dependant,
		 * so we put an explicit smp_rmb() here. */
		smp_rmb();
		func = mdata->single.func;
		/* Must read the ptr before private data. They are not data
		 * dependant, so we put an explicit smp_rmb() here. */
		smp_rmb();
		va_start(args, call_private);
		func(mdata->single.probe_private, call_private, mdata->format,
			&args);
		va_end(args);
	} else {
		struct marker_probe_closure *multi;
		int i;
		/*
		 * Read mdata->ptype before mdata->multi.
		 */
		smp_rmb();
		multi = mdata->multi;
		/*
		 * multi points to an array, therefore accessing the array
		 * depends on reading multi. However, even in this case,
		 * we must insure that the pointer is read _before_ the array
		 * data. Same as rcu_dereference, but we need a full smp_rmb()
		 * in the fast path, so put the explicit barrier here.
		 */
		smp_read_barrier_depends();
		for (i = 0; multi[i].func; i++) {
			va_start(args, call_private);
			multi[i].func(multi[i].probe_private, call_private,
				mdata->format, &args);
			va_end(args);
		}
	}
	rcu_read_unlock_sched();
}
EXPORT_SYMBOL_GPL(marker_probe_cb);

/*
 * marker_probe_cb Callback that does not prepare the variable argument list.
 * @mdata: pointer of type struct marker
 * @call_private: caller site private data
 * @...:  Variable argument list.
 *
 * Should be connected to markers "MARK_NOARGS".
 */
void marker_probe_cb_noarg(const struct marker *mdata, void *call_private, ...)
{
	va_list args;	/* not initialized */
	char ptype;

	rcu_read_lock_sched();
	ptype = mdata->ptype;
	if (likely(!ptype)) {
		marker_probe_func *func;
		/* Must read the ptype before ptr. They are not data dependant,
		 * so we put an explicit smp_rmb() here. */
		smp_rmb();
		func = mdata->single.func;
		/* Must read the ptr before private data. They are not data
		 * dependant, so we put an explicit smp_rmb() here. */
		smp_rmb();
		func(mdata->single.probe_private, call_private, mdata->format,
			&args);
	} else {
		struct marker_probe_closure *multi;
		int i;
		/*
		 * Read mdata->ptype before mdata->multi.
		 */
		smp_rmb();
		multi = mdata->multi;
		/*
		 * multi points to an array, therefore accessing the array
		 * depends on reading multi. However, even in this case,
		 * we must insure that the pointer is read _before_ the array
		 * data. Same as rcu_dereference, but we need a full smp_rmb()
		 * in the fast path, so put the explicit barrier here.
		 */
		smp_read_barrier_depends();
		for (i = 0; multi[i].func; i++)
			multi[i].func(multi[i].probe_private, call_private,
				mdata->format, &args);
	}
	rcu_read_unlock_sched();
}
EXPORT_SYMBOL_GPL(marker_probe_cb_noarg);

static void free_old_closure(struct rcu_head *head)
{
	struct marker_entry *entry = container_of(head,
		struct marker_entry, rcu);
	kfree(entry->oldptr);
	/* Make sure we free the data before setting the pending flag to 0 */
	smp_wmb();
	entry->rcu_pending = 0;
}

static void debug_print_probes(struct marker_entry *entry)
{
	int i;

	if (!marker_debug)
		return;

	if (!entry->ptype) {
		printk(KERN_DEBUG "Single probe : %p %p\n",
			entry->single.func,
			entry->single.probe_private);
	} else {
		for (i = 0; entry->multi[i].func; i++)
			printk(KERN_DEBUG "Multi probe %d : %p %p\n", i,
				entry->multi[i].func,
				entry->multi[i].probe_private);
	}
}

static struct marker_probe_closure *
marker_entry_add_probe(struct marker_entry *entry,
		marker_probe_func *probe, void *probe_private)
{
	int nr_probes = 0;
	struct marker_probe_closure *old, *new;

	WARN_ON(!probe);

	debug_print_probes(entry);
	old = entry->multi;
	if (!entry->ptype) {
		if (entry->single.func == probe &&
				entry->single.probe_private == probe_private)
			return ERR_PTR(-EBUSY);
		if (entry->single.func == __mark_empty_function) {
			/* 0 -> 1 probes */
			entry->single.func = probe;
			entry->single.probe_private = probe_private;
			entry->refcount = 1;
			entry->ptype = 0;
			debug_print_probes(entry);
			return NULL;
		} else {
			/* 1 -> 2 probes */
			nr_probes = 1;
			old = NULL;
		}
	} else {
		/* (N -> N+1), (N != 0, 1) probes */
		for (nr_probes = 0; old[nr_probes].func; nr_probes++)
			if (old[nr_probes].func == probe
					&& old[nr_probes].probe_private
						== probe_private)
				return ERR_PTR(-EBUSY);
	}
	/* + 2 : one for new probe, one for NULL func */
	new = kzalloc((nr_probes + 2) * sizeof(struct marker_probe_closure),
			GFP_KERNEL);
	if (new == NULL)
		return ERR_PTR(-ENOMEM);
	if (!old)
		new[0] = entry->single;
	else
		memcpy(new, old,
			nr_probes * sizeof(struct marker_probe_closure));
	new[nr_probes].func = probe;
	new[nr_probes].probe_private = probe_private;
	entry->refcount = nr_probes + 1;
	entry->multi = new;
	entry->ptype = 1;
	debug_print_probes(entry);
	return old;
}

static struct marker_probe_closure *
marker_entry_remove_probe(struct marker_entry *entry,
		marker_probe_func *probe, void *probe_private)
{
	int nr_probes = 0, nr_del = 0, i;
	struct marker_probe_closure *old, *new;

	old = entry->multi;

	debug_print_probes(entry);
	if (!entry->ptype) {
		/* 0 -> N is an error */
		WARN_ON(entry->single.func == __mark_empty_function);
		/* 1 -> 0 probes */
		WARN_ON(probe && entry->single.func != probe);
		WARN_ON(entry->single.probe_private != probe_private);
		entry->single.func = __mark_empty_function;
		entry->refcount = 0;
		entry->ptype = 0;
		debug_print_probes(entry);
		return NULL;
	} else {
		/* (N -> M), (N > 1, M >= 0) probes */
		for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
			if ((!probe || old[nr_probes].func == probe)
					&& old[nr_probes].probe_private
						== probe_private)
				nr_del++;
		}
	}

	if (nr_probes - nr_del == 0) {
		/* N -> 0, (N > 1) */
		entry->single.func = __mark_empty_function;
		entry->refcount = 0;
		entry->ptype = 0;
	} else if (nr_probes - nr_del == 1) {
		/* N -> 1, (N > 1) */
		for (i = 0; old[i].func; i++)
			if ((probe && old[i].func != probe) ||
					old[i].probe_private != probe_private)
				entry->single = old[i];
		entry->refcount = 1;
		entry->ptype = 0;
	} else {
		int j = 0;
		/* N -> M, (N > 1, M > 1) */
		/* + 1 for NULL */
		new = kzalloc((nr_probes - nr_del + 1)
			* sizeof(struct marker_probe_closure), GFP_KERNEL);
		if (new == NULL)
			return ERR_PTR(-ENOMEM);
		for (i = 0; old[i].func; i++)
			if ((probe && old[i].func != probe) ||
					old[i].probe_private != probe_private)
				new[j++] = old[i];
		entry->refcount = nr_probes - nr_del;
		entry->ptype = 1;
		entry->multi = new;
	}
	debug_print_probes(entry);
	return old;
}

/*
 * Get marker if the marker is present in the marker hash table.
 * Must be called with markers_mutex held.
 * Returns NULL if not present.
 */
static struct marker_entry *get_marker(const char *name)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct marker_entry *e;
	u32 hash = jhash(name, strlen(name), 0);

	head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name))
			return e;
	}
	return NULL;
}

/*
 * Add the marker to the marker hash table. Must be called with markers_mutex
 * held.
 */
static struct marker_entry *add_marker(const char *name, const char *format)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct marker_entry *e;
	size_t name_len = strlen(name) + 1;
	size_t format_len = 0;
	u32 hash = jhash(name, name_len-1, 0);

	if (format)
		format_len = strlen(format) + 1;
	head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name)) {
			printk(KERN_NOTICE
				"Marker %s busy\n", name);
			return ERR_PTR(-EBUSY);	/* Already there */
		}
	}
	/*
	 * Using kmalloc here to allocate a variable length element. Could
	 * cause some memory fragmentation if overused.
	 */
	e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
			GFP_KERNEL);
	if (!e)
		return ERR_PTR(-ENOMEM);
	memcpy(&e->name[0], name, name_len);
	if (format) {
		e->format = &e->name[name_len];
		memcpy(e->format, format, format_len);
		if (strcmp(e->format, MARK_NOARGS) == 0)
			e->call = marker_probe_cb_noarg;
		else
			e->call = marker_probe_cb;
		trace_mark(core_marker_format, "name %s format %s",
				e->name, e->format);
	} else {
		e->format = NULL;
		e->call = marker_probe_cb;
	}
	e->single.func = __mark_empty_function;
	e->single.probe_private = NULL;
	e->multi = NULL;
	e->ptype = 0;
	e->refcount = 0;
	e->rcu_pending = 0;
	hlist_add_head(&e->hlist, head);
	return e;
}

/*
 * Remove the marker from the marker hash table. Must be called with mutex_lock
 * held.
 */
static int remove_marker(const char *name)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct marker_entry *e;
	int found = 0;
	size_t len = strlen(name) + 1;
	u32 hash = jhash(name, len-1, 0);

	head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name)) {
			found = 1;
			break;
		}
	}
	if (!found)
		return -ENOENT;
	if (e->single.func != __mark_empty_function)
		return -EBUSY;
	hlist_del(&e->hlist);
	/* Make sure the call_rcu has been executed */
	if (e->rcu_pending)
		rcu_barrier_sched();
	kfree(e);
	return 0;
}

/*
 * Set the mark_entry format to the format found in the element.
 */
static int marker_set_format(struct marker_entry **entry, const char *format)
{
	struct marker_entry *e;
	size_t name_len = strlen((*entry)->name) + 1;
	size_t format_len = strlen(format) + 1;


	e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
			GFP_KERNEL);
	if (!e)
		return -ENOMEM;
	memcpy(&e->name[0], (*entry)->name, name_len);
	e->format = &e->name[name_len];
	memcpy(e->format, format, format_len);
	if (strcmp(e->format, MARK_NOARGS) == 0)
		e->call = marker_probe_cb_noarg;
	else
		e->call = marker_probe_cb;
	e->single = (*entry)->single;
	e->multi = (*entry)->multi;
	e->ptype = (*entry)->ptype;
	e->refcount = (*entry)->refcount;
	e->rcu_pending = 0;
	hlist_add_before(&e->hlist, &(*entry)->hlist);
	hlist_del(&(*entry)->hlist);
	/* Make sure the call_rcu has been executed */
	if ((*entry)->rcu_pending)
		rcu_barrier_sched();
	kfree(*entry);
	*entry = e;
	trace_mark(core_marker_format, "name %s format %s",
			e->name, e->format);
	return 0;
}

/*
 * Sets the probe callback corresponding to one marker.
 */
static int set_marker(struct marker_entry **entry, struct marker *elem,
		int active)
{
	int ret;
	WARN_ON(strcmp((*entry)->name, elem->name) != 0);

	if ((*entry)->format) {
		if (strcmp((*entry)->format, elem->format) != 0) {
			printk(KERN_NOTICE
				"Format mismatch for probe %s "
				"(%s), marker (%s)\n",
				(*entry)->name,
				(*entry)->format,
				elem->format);
			return -EPERM;
		}
	} else {
		ret = marker_set_format(entry, elem->format);
		if (ret)
			return ret;
	}

	/*
	 * probe_cb setup (statically known) is done here. It is
	 * asynchronous with the rest of execution, therefore we only
	 * pass from a "safe" callback (with argument) to an "unsafe"
	 * callback (does not set arguments).
	 */
	elem->call = (*entry)->call;
	/*
	 * Sanity check :
	 * We only update the single probe private data when the ptr is
	 * set to a _non_ single probe! (0 -> 1 and N -> 1, N != 1)
	 */
	WARN_ON(elem->single.func != __mark_empty_function
		&& elem->single.probe_private
		!= (*entry)->single.probe_private &&
		!elem->ptype);
	elem->single.probe_private = (*entry)->single.probe_private;
	/*
	 * Make sure the private data is valid when we update the
	 * single probe ptr.
	 */
	smp_wmb();
	elem->single.func = (*entry)->single.func;
	/*
	 * We also make sure that the new probe callbacks array is consistent
	 * before setting a pointer to it.
	 */
	rcu_assign_pointer(elem->multi, (*entry)->multi);
	/*
	 * Update the function or multi probe array pointer before setting the
	 * ptype.
	 */
	smp_wmb();
	elem->ptype = (*entry)->ptype;
	elem->state = active;

	return 0;
}

/*
 * Disable a marker and its probe callback.
 * Note: only waiting an RCU period after setting elem->call to the empty
 * function insures that the original callback is not used anymore. This insured
 * by rcu_read_lock_sched around the call site.
 */
static void disable_marker(struct marker *elem)
{
	/* leave "call" as is. It is known statically. */
	elem->state = 0;
	elem->single.func = __mark_empty_function;
	/* Update the function before setting the ptype */
	smp_wmb();
	elem->ptype = 0;	/* single probe */
	/*
	 * Leave the private data and id there, because removal is racy and
	 * should be done only after an RCU period. These are never used until
	 * the next initialization anyway.
	 */
}

/**
 * marker_update_probe_range - Update a probe range
 * @begin: beginning of the range
 * @end: end of the range
 *
 * Updates the probe callback corresponding to a range of markers.
 */
void marker_update_probe_range(struct marker *begin,
	struct marker *end)
{
	struct marker *iter;
	struct marker_entry *mark_entry;

	mutex_lock(&markers_mutex);
	for (iter = begin; iter < end; iter++) {
		mark_entry = get_marker(iter->name);
		if (mark_entry) {
			set_marker(&mark_entry, iter,
					!!mark_entry->refcount);
			/*
			 * ignore error, continue
			 */
		} else {
			disable_marker(iter);
		}
	}
	mutex_unlock(&markers_mutex);
}

/*
 * Update probes, removing the faulty probes.
 *
 * Internal callback only changed before the first probe is connected to it.
 * Single probe private data can only be changed on 0 -> 1 and 2 -> 1
 * transitions.  All other transitions will leave the old private data valid.
 * This makes the non-atomicity of the callback/private data updates valid.
 *
 * "special case" updates :
 * 0 -> 1 callback
 * 1 -> 0 callback
 * 1 -> 2 callbacks
 * 2 -> 1 callbacks
 * Other updates all behave the same, just like the 2 -> 3 or 3 -> 2 updates.
 * Site effect : marker_set_format may delete the marker entry (creating a
 * replacement).
 */
static void marker_update_probes(void)
{
	/* Core kernel markers */
	marker_update_probe_range(__start___markers, __stop___markers);
	/* Markers in modules. */
	module_update_markers();
}

/**
 * marker_probe_register -  Connect a probe to a marker
 * @name: marker name
 * @format: format string
 * @probe: probe handler
 * @probe_private: probe private data
 *
 * private data must be a valid allocated memory address, or NULL.
 * Returns 0 if ok, error value on error.
 * The probe address must at least be aligned on the architecture pointer size.
 */
int marker_probe_register(const char *name, const char *format,
			marker_probe_func *probe, void *probe_private)
{
	struct marker_entry *entry;
	int ret = 0;
	struct marker_probe_closure *old;

	mutex_lock(&markers_mutex);
	entry = get_marker(name);
	if (!entry) {
		entry = add_marker(name, format);
		if (IS_ERR(entry)) {
			ret = PTR_ERR(entry);
			goto end;
		}
	}
	/*
	 * If we detect that a call_rcu is pending for this marker,
	 * make sure it's executed now.
	 */
	if (entry->rcu_pending)
		rcu_barrier_sched();
	old = marker_entry_add_probe(entry, probe, probe_private);
	if (IS_ERR(old)) {
		ret = PTR_ERR(old);
		goto end;
	}
	mutex_unlock(&markers_mutex);
	marker_update_probes();		/* may update entry */
	mutex_lock(&markers_mutex);
	entry = get_marker(name);
	WARN_ON(!entry);
	if (entry->rcu_pending)
		rcu_barrier_sched();
	entry->oldptr = old;
	entry->rcu_pending = 1;
	/* write rcu_pending before calling the RCU callback */
	smp_wmb();
	call_rcu_sched(&entry->rcu, free_old_closure);
end:
	mutex_unlock(&markers_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(marker_probe_register);

/**
 * marker_probe_unregister -  Disconnect a probe from a marker
 * @name: marker name
 * @probe: probe function pointer
 * @probe_private: probe private data
 *
 * Returns the private data given to marker_probe_register, or an ERR_PTR().
 * We do not need to call a synchronize_sched to make sure the probes have
 * finished running before doing a module unload, because the module unload
 * itself uses stop_machine(), which insures that every preempt disabled section
 * have finished.
 */
int marker_probe_unregister(const char *name,
	marker_probe_func *probe, void *probe_private)
{
	struct marker_entry *entry;
	struct marker_probe_closure *old;
	int ret = -ENOENT;

	mutex_lock(&markers_mutex);
	entry = get_marker(name);
	if (!entry)
		goto end;
	if (entry->rcu_pending)
		rcu_barrier_sched();
	old = marker_entry_remove_probe(entry, probe, probe_private);
	mutex_unlock(&markers_mutex);
	marker_update_probes();		/* may update entry */
	mutex_lock(&markers_mutex);
	entry = get_marker(name);
	if (!entry)
		goto end;
	if (entry->rcu_pending)
		rcu_barrier_sched();
	entry->oldptr = old;
	entry->rcu_pending = 1;
	/* write rcu_pending before calling the RCU callback */
	smp_wmb();
	call_rcu_sched(&entry->rcu, free_old_closure);
	remove_marker(name);	/* Ignore busy error message */
	ret = 0;
end:
	mutex_unlock(&markers_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(marker_probe_unregister);

static struct marker_entry *
get_marker_from_private_data(marker_probe_func *probe, void *probe_private)
{
	struct marker_entry *entry;
	unsigned int i;
	struct hlist_head *head;
	struct hlist_node *node;

	for (i = 0; i < MARKER_TABLE_SIZE; i++) {
		head = &marker_table[i];
		hlist_for_each_entry(entry, node, head, hlist) {
			if (!entry->ptype) {
				if (entry->single.func == probe
						&& entry->single.probe_private
						== probe_private)
					return entry;
			} else {
				struct marker_probe_closure *closure;
				closure = entry->multi;
				for (i = 0; closure[i].func; i++) {
					if (closure[i].func == probe &&
							closure[i].probe_private
							== probe_private)
						return entry;
				}
			}
		}
	}
	return NULL;
}

/**
 * marker_probe_unregister_private_data -  Disconnect a probe from a marker
 * @probe: probe function
 * @probe_private: probe private data
 *
 * Unregister a probe by providing the registered private data.
 * Only removes the first marker found in hash table.
 * Return 0 on success or error value.
 * We do not need to call a synchronize_sched to make sure the probes have
 * finished running before doing a module unload, because the module unload
 * itself uses stop_machine(), which insures that every preempt disabled section
 * have finished.
 */
int marker_probe_unregister_private_data(marker_probe_func *probe,
		void *probe_private)
{
	struct marker_entry *entry;
	int ret = 0;
	struct marker_probe_closure *old;

	mutex_lock(&markers_mutex);
	entry = get_marker_from_private_data(probe, probe_private);
	if (!entry) {
		ret = -ENOENT;
		goto end;
	}
	if (entry->rcu_pending)
		rcu_barrier_sched();
	old = marker_entry_remove_probe(entry, NULL, probe_private);
	mutex_unlock(&markers_mutex);
	marker_update_probes();		/* may update entry */
	mutex_lock(&markers_mutex);
	entry = get_marker_from_private_data(probe, probe_private);
	WARN_ON(!entry);
	if (entry->rcu_pending)
		rcu_barrier_sched();
	entry->oldptr = old;
	entry->rcu_pending = 1;
	/* write rcu_pending before calling the RCU callback */
	smp_wmb();
	call_rcu_sched(&entry->rcu, free_old_closure);
	remove_marker(entry->name);	/* Ignore busy error message */
end:
	mutex_unlock(&markers_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);

/**
 * marker_get_private_data - Get a marker's probe private data
 * @name: marker name
 * @probe: probe to match
 * @num: get the nth matching probe's private data
 *
 * Returns the nth private data pointer (starting from 0) matching, or an
 * ERR_PTR.
 * Returns the private data pointer, or an ERR_PTR.
 * The private data pointer should _only_ be dereferenced if the caller is the
 * owner of the data, or its content could vanish. This is mostly used to
 * confirm that a caller is the owner of a registered probe.
 */
void *marker_get_private_data(const char *name, marker_probe_func *probe,
		int num)
{
	struct hlist_head *head;
	struct hlist_node *node;
	struct marker_entry *e;
	size_t name_len = strlen(name) + 1;
	u32 hash = jhash(name, name_len-1, 0);
	int i;

	head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
	hlist_for_each_entry(e, node, head, hlist) {
		if (!strcmp(name, e->name)) {
			if (!e->ptype) {
				if (num == 0 && e->single.func == probe)
					return e->single.probe_private;
				else
					break;
			} else {
				struct marker_probe_closure *closure;
				int match = 0;
				closure = e->multi;
				for (i = 0; closure[i].func; i++) {
					if (closure[i].func != probe)
						continue;
					if (match++ == num)
						return closure[i].probe_private;
				}
			}
		}
	}
	return ERR_PTR(-ENOENT);
}
EXPORT_SYMBOL_GPL(marker_get_private_data);