1 /*
2  * Copyright (C) 2011 Red Hat, Inc.
3  *
4  * This file is released under the GPL.
5  */
6 #include "dm-block-manager.h"
7 #include "dm-persistent-data-internal.h"
8 
9 #include <linux/dm-bufio.h>
10 #include <linux/crc32c.h>
11 #include <linux/module.h>
12 #include <linux/slab.h>
13 #include <linux/rwsem.h>
14 #include <linux/device-mapper.h>
15 #include <linux/stacktrace.h>
16 #include <linux/sched/task.h>
17 
18 #define DM_MSG_PREFIX "block manager"
19 
20 /*----------------------------------------------------------------*/
21 
22 #ifdef CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING
23 
24 /*
25  * This is a read/write semaphore with a couple of differences.
26  *
27  * i) There is a restriction on the number of concurrent read locks that
28  * may be held at once.  This is just an implementation detail.
29  *
30  * ii) Recursive locking attempts are detected and return EINVAL.  A stack
31  * trace is also emitted for the previous lock acquisition.
32  *
33  * iii) Priority is given to write locks.
34  */
35 #define MAX_HOLDERS 4
36 #define MAX_STACK 10
37 
38 struct stack_store {
39 	unsigned int	nr_entries;
40 	unsigned long	entries[MAX_STACK];
41 };
42 
43 struct block_lock {
44 	spinlock_t lock;
45 	__s32 count;
46 	struct list_head waiters;
47 	struct task_struct *holders[MAX_HOLDERS];
48 
49 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
50 	struct stack_store traces[MAX_HOLDERS];
51 #endif
52 };
53 
54 struct waiter {
55 	struct list_head list;
56 	struct task_struct *task;
57 	int wants_write;
58 };
59 
60 static unsigned __find_holder(struct block_lock *lock,
61 			      struct task_struct *task)
62 {
63 	unsigned i;
64 
65 	for (i = 0; i < MAX_HOLDERS; i++)
66 		if (lock->holders[i] == task)
67 			break;
68 
69 	BUG_ON(i == MAX_HOLDERS);
70 	return i;
71 }
72 
73 /* call this *after* you increment lock->count */
74 static void __add_holder(struct block_lock *lock, struct task_struct *task)
75 {
76 	unsigned h = __find_holder(lock, NULL);
77 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
78 	struct stack_store *t;
79 #endif
80 
81 	get_task_struct(task);
82 	lock->holders[h] = task;
83 
84 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
85 	t = lock->traces + h;
86 	t->nr_entries = stack_trace_save(t->entries, MAX_STACK, 2);
87 #endif
88 }
89 
90 /* call this *before* you decrement lock->count */
91 static void __del_holder(struct block_lock *lock, struct task_struct *task)
92 {
93 	unsigned h = __find_holder(lock, task);
94 	lock->holders[h] = NULL;
95 	put_task_struct(task);
96 }
97 
98 static int __check_holder(struct block_lock *lock)
99 {
100 	unsigned i;
101 
102 	for (i = 0; i < MAX_HOLDERS; i++) {
103 		if (lock->holders[i] == current) {
104 			DMERR("recursive lock detected in metadata");
105 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
106 			DMERR("previously held here:");
107 			stack_trace_print(lock->traces[i].entries,
108 					  lock->traces[i].nr_entries, 4);
109 
110 			DMERR("subsequent acquisition attempted here:");
111 			dump_stack();
112 #endif
113 			return -EINVAL;
114 		}
115 	}
116 
117 	return 0;
118 }
119 
120 static void __wait(struct waiter *w)
121 {
122 	for (;;) {
123 		set_current_state(TASK_UNINTERRUPTIBLE);
124 
125 		if (!w->task)
126 			break;
127 
128 		schedule();
129 	}
130 
131 	set_current_state(TASK_RUNNING);
132 }
133 
134 static void __wake_waiter(struct waiter *w)
135 {
136 	struct task_struct *task;
137 
138 	list_del(&w->list);
139 	task = w->task;
140 	smp_mb();
141 	w->task = NULL;
142 	wake_up_process(task);
143 }
144 
145 /*
146  * We either wake a few readers or a single writer.
147  */
148 static void __wake_many(struct block_lock *lock)
149 {
150 	struct waiter *w, *tmp;
151 
152 	BUG_ON(lock->count < 0);
153 	list_for_each_entry_safe(w, tmp, &lock->waiters, list) {
154 		if (lock->count >= MAX_HOLDERS)
155 			return;
156 
157 		if (w->wants_write) {
158 			if (lock->count > 0)
159 				return; /* still read locked */
160 
161 			lock->count = -1;
162 			__add_holder(lock, w->task);
163 			__wake_waiter(w);
164 			return;
165 		}
166 
167 		lock->count++;
168 		__add_holder(lock, w->task);
169 		__wake_waiter(w);
170 	}
171 }
172 
173 static void bl_init(struct block_lock *lock)
174 {
175 	int i;
176 
177 	spin_lock_init(&lock->lock);
178 	lock->count = 0;
179 	INIT_LIST_HEAD(&lock->waiters);
180 	for (i = 0; i < MAX_HOLDERS; i++)
181 		lock->holders[i] = NULL;
182 }
183 
184 static int __available_for_read(struct block_lock *lock)
185 {
186 	return lock->count >= 0 &&
187 		lock->count < MAX_HOLDERS &&
188 		list_empty(&lock->waiters);
189 }
190 
191 static int bl_down_read(struct block_lock *lock)
192 {
193 	int r;
194 	struct waiter w;
195 
196 	spin_lock(&lock->lock);
197 	r = __check_holder(lock);
198 	if (r) {
199 		spin_unlock(&lock->lock);
200 		return r;
201 	}
202 
203 	if (__available_for_read(lock)) {
204 		lock->count++;
205 		__add_holder(lock, current);
206 		spin_unlock(&lock->lock);
207 		return 0;
208 	}
209 
210 	get_task_struct(current);
211 
212 	w.task = current;
213 	w.wants_write = 0;
214 	list_add_tail(&w.list, &lock->waiters);
215 	spin_unlock(&lock->lock);
216 
217 	__wait(&w);
218 	put_task_struct(current);
219 	return 0;
220 }
221 
222 static int bl_down_read_nonblock(struct block_lock *lock)
223 {
224 	int r;
225 
226 	spin_lock(&lock->lock);
227 	r = __check_holder(lock);
228 	if (r)
229 		goto out;
230 
231 	if (__available_for_read(lock)) {
232 		lock->count++;
233 		__add_holder(lock, current);
234 		r = 0;
235 	} else
236 		r = -EWOULDBLOCK;
237 
238 out:
239 	spin_unlock(&lock->lock);
240 	return r;
241 }
242 
243 static void bl_up_read(struct block_lock *lock)
244 {
245 	spin_lock(&lock->lock);
246 	BUG_ON(lock->count <= 0);
247 	__del_holder(lock, current);
248 	--lock->count;
249 	if (!list_empty(&lock->waiters))
250 		__wake_many(lock);
251 	spin_unlock(&lock->lock);
252 }
253 
254 static int bl_down_write(struct block_lock *lock)
255 {
256 	int r;
257 	struct waiter w;
258 
259 	spin_lock(&lock->lock);
260 	r = __check_holder(lock);
261 	if (r) {
262 		spin_unlock(&lock->lock);
263 		return r;
264 	}
265 
266 	if (lock->count == 0 && list_empty(&lock->waiters)) {
267 		lock->count = -1;
268 		__add_holder(lock, current);
269 		spin_unlock(&lock->lock);
270 		return 0;
271 	}
272 
273 	get_task_struct(current);
274 	w.task = current;
275 	w.wants_write = 1;
276 
277 	/*
278 	 * Writers given priority. We know there's only one mutator in the
279 	 * system, so ignoring the ordering reversal.
280 	 */
281 	list_add(&w.list, &lock->waiters);
282 	spin_unlock(&lock->lock);
283 
284 	__wait(&w);
285 	put_task_struct(current);
286 
287 	return 0;
288 }
289 
290 static void bl_up_write(struct block_lock *lock)
291 {
292 	spin_lock(&lock->lock);
293 	__del_holder(lock, current);
294 	lock->count = 0;
295 	if (!list_empty(&lock->waiters))
296 		__wake_many(lock);
297 	spin_unlock(&lock->lock);
298 }
299 
300 static void report_recursive_bug(dm_block_t b, int r)
301 {
302 	if (r == -EINVAL)
303 		DMERR("recursive acquisition of block %llu requested.",
304 		      (unsigned long long) b);
305 }
306 
307 #else  /* !CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
308 
309 #define bl_init(x) do { } while (0)
310 #define bl_down_read(x) 0
311 #define bl_down_read_nonblock(x) 0
312 #define bl_up_read(x) do { } while (0)
313 #define bl_down_write(x) 0
314 #define bl_up_write(x) do { } while (0)
315 #define report_recursive_bug(x, y) do { } while (0)
316 
317 #endif /* CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
318 
319 /*----------------------------------------------------------------*/
320 
321 /*
322  * Block manager is currently implemented using dm-bufio.  struct
323  * dm_block_manager and struct dm_block map directly onto a couple of
324  * structs in the bufio interface.  I want to retain the freedom to move
325  * away from bufio in the future.  So these structs are just cast within
326  * this .c file, rather than making it through to the public interface.
327  */
328 static struct dm_buffer *to_buffer(struct dm_block *b)
329 {
330 	return (struct dm_buffer *) b;
331 }
332 
333 dm_block_t dm_block_location(struct dm_block *b)
334 {
335 	return dm_bufio_get_block_number(to_buffer(b));
336 }
337 EXPORT_SYMBOL_GPL(dm_block_location);
338 
339 void *dm_block_data(struct dm_block *b)
340 {
341 	return dm_bufio_get_block_data(to_buffer(b));
342 }
343 EXPORT_SYMBOL_GPL(dm_block_data);
344 
345 struct buffer_aux {
346 	struct dm_block_validator *validator;
347 	int write_locked;
348 
349 #ifdef CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING
350 	struct block_lock lock;
351 #endif
352 };
353 
354 static void dm_block_manager_alloc_callback(struct dm_buffer *buf)
355 {
356 	struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
357 	aux->validator = NULL;
358 	bl_init(&aux->lock);
359 }
360 
361 static void dm_block_manager_write_callback(struct dm_buffer *buf)
362 {
363 	struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
364 	if (aux->validator) {
365 		aux->validator->prepare_for_write(aux->validator, (struct dm_block *) buf,
366 			 dm_bufio_get_block_size(dm_bufio_get_client(buf)));
367 	}
368 }
369 
370 /*----------------------------------------------------------------
371  * Public interface
372  *--------------------------------------------------------------*/
373 struct dm_block_manager {
374 	struct dm_bufio_client *bufio;
375 	bool read_only:1;
376 };
377 
378 struct dm_block_manager *dm_block_manager_create(struct block_device *bdev,
379 						 unsigned block_size,
380 						 unsigned max_held_per_thread)
381 {
382 	int r;
383 	struct dm_block_manager *bm;
384 
385 	bm = kmalloc(sizeof(*bm), GFP_KERNEL);
386 	if (!bm) {
387 		r = -ENOMEM;
388 		goto bad;
389 	}
390 
391 	bm->bufio = dm_bufio_client_create(bdev, block_size, max_held_per_thread,
392 					   sizeof(struct buffer_aux),
393 					   dm_block_manager_alloc_callback,
394 					   dm_block_manager_write_callback);
395 	if (IS_ERR(bm->bufio)) {
396 		r = PTR_ERR(bm->bufio);
397 		kfree(bm);
398 		goto bad;
399 	}
400 
401 	bm->read_only = false;
402 
403 	return bm;
404 
405 bad:
406 	return ERR_PTR(r);
407 }
408 EXPORT_SYMBOL_GPL(dm_block_manager_create);
409 
410 void dm_block_manager_destroy(struct dm_block_manager *bm)
411 {
412 	dm_bufio_client_destroy(bm->bufio);
413 	kfree(bm);
414 }
415 EXPORT_SYMBOL_GPL(dm_block_manager_destroy);
416 
417 unsigned dm_bm_block_size(struct dm_block_manager *bm)
418 {
419 	return dm_bufio_get_block_size(bm->bufio);
420 }
421 EXPORT_SYMBOL_GPL(dm_bm_block_size);
422 
423 dm_block_t dm_bm_nr_blocks(struct dm_block_manager *bm)
424 {
425 	return dm_bufio_get_device_size(bm->bufio);
426 }
427 
428 static int dm_bm_validate_buffer(struct dm_block_manager *bm,
429 				 struct dm_buffer *buf,
430 				 struct buffer_aux *aux,
431 				 struct dm_block_validator *v)
432 {
433 	if (unlikely(!aux->validator)) {
434 		int r;
435 		if (!v)
436 			return 0;
437 		r = v->check(v, (struct dm_block *) buf, dm_bufio_get_block_size(bm->bufio));
438 		if (unlikely(r)) {
439 			DMERR_LIMIT("%s validator check failed for block %llu", v->name,
440 				    (unsigned long long) dm_bufio_get_block_number(buf));
441 			return r;
442 		}
443 		aux->validator = v;
444 	} else {
445 		if (unlikely(aux->validator != v)) {
446 			DMERR_LIMIT("validator mismatch (old=%s vs new=%s) for block %llu",
447 				    aux->validator->name, v ? v->name : "NULL",
448 				    (unsigned long long) dm_bufio_get_block_number(buf));
449 			return -EINVAL;
450 		}
451 	}
452 
453 	return 0;
454 }
455 int dm_bm_read_lock(struct dm_block_manager *bm, dm_block_t b,
456 		    struct dm_block_validator *v,
457 		    struct dm_block **result)
458 {
459 	struct buffer_aux *aux;
460 	void *p;
461 	int r;
462 
463 	p = dm_bufio_read(bm->bufio, b, (struct dm_buffer **) result);
464 	if (IS_ERR(p))
465 		return PTR_ERR(p);
466 
467 	aux = dm_bufio_get_aux_data(to_buffer(*result));
468 	r = bl_down_read(&aux->lock);
469 	if (unlikely(r)) {
470 		dm_bufio_release(to_buffer(*result));
471 		report_recursive_bug(b, r);
472 		return r;
473 	}
474 
475 	aux->write_locked = 0;
476 
477 	r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
478 	if (unlikely(r)) {
479 		bl_up_read(&aux->lock);
480 		dm_bufio_release(to_buffer(*result));
481 		return r;
482 	}
483 
484 	return 0;
485 }
486 EXPORT_SYMBOL_GPL(dm_bm_read_lock);
487 
488 int dm_bm_write_lock(struct dm_block_manager *bm,
489 		     dm_block_t b, struct dm_block_validator *v,
490 		     struct dm_block **result)
491 {
492 	struct buffer_aux *aux;
493 	void *p;
494 	int r;
495 
496 	if (bm->read_only)
497 		return -EPERM;
498 
499 	p = dm_bufio_read(bm->bufio, b, (struct dm_buffer **) result);
500 	if (IS_ERR(p))
501 		return PTR_ERR(p);
502 
503 	aux = dm_bufio_get_aux_data(to_buffer(*result));
504 	r = bl_down_write(&aux->lock);
505 	if (r) {
506 		dm_bufio_release(to_buffer(*result));
507 		report_recursive_bug(b, r);
508 		return r;
509 	}
510 
511 	aux->write_locked = 1;
512 
513 	r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
514 	if (unlikely(r)) {
515 		bl_up_write(&aux->lock);
516 		dm_bufio_release(to_buffer(*result));
517 		return r;
518 	}
519 
520 	return 0;
521 }
522 EXPORT_SYMBOL_GPL(dm_bm_write_lock);
523 
524 int dm_bm_read_try_lock(struct dm_block_manager *bm,
525 			dm_block_t b, struct dm_block_validator *v,
526 			struct dm_block **result)
527 {
528 	struct buffer_aux *aux;
529 	void *p;
530 	int r;
531 
532 	p = dm_bufio_get(bm->bufio, b, (struct dm_buffer **) result);
533 	if (IS_ERR(p))
534 		return PTR_ERR(p);
535 	if (unlikely(!p))
536 		return -EWOULDBLOCK;
537 
538 	aux = dm_bufio_get_aux_data(to_buffer(*result));
539 	r = bl_down_read_nonblock(&aux->lock);
540 	if (r < 0) {
541 		dm_bufio_release(to_buffer(*result));
542 		report_recursive_bug(b, r);
543 		return r;
544 	}
545 	aux->write_locked = 0;
546 
547 	r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
548 	if (unlikely(r)) {
549 		bl_up_read(&aux->lock);
550 		dm_bufio_release(to_buffer(*result));
551 		return r;
552 	}
553 
554 	return 0;
555 }
556 
557 int dm_bm_write_lock_zero(struct dm_block_manager *bm,
558 			  dm_block_t b, struct dm_block_validator *v,
559 			  struct dm_block **result)
560 {
561 	int r;
562 	struct buffer_aux *aux;
563 	void *p;
564 
565 	if (bm->read_only)
566 		return -EPERM;
567 
568 	p = dm_bufio_new(bm->bufio, b, (struct dm_buffer **) result);
569 	if (IS_ERR(p))
570 		return PTR_ERR(p);
571 
572 	memset(p, 0, dm_bm_block_size(bm));
573 
574 	aux = dm_bufio_get_aux_data(to_buffer(*result));
575 	r = bl_down_write(&aux->lock);
576 	if (r) {
577 		dm_bufio_release(to_buffer(*result));
578 		return r;
579 	}
580 
581 	aux->write_locked = 1;
582 	aux->validator = v;
583 
584 	return 0;
585 }
586 EXPORT_SYMBOL_GPL(dm_bm_write_lock_zero);
587 
588 void dm_bm_unlock(struct dm_block *b)
589 {
590 	struct buffer_aux *aux;
591 	aux = dm_bufio_get_aux_data(to_buffer(b));
592 
593 	if (aux->write_locked) {
594 		dm_bufio_mark_buffer_dirty(to_buffer(b));
595 		bl_up_write(&aux->lock);
596 	} else
597 		bl_up_read(&aux->lock);
598 
599 	dm_bufio_release(to_buffer(b));
600 }
601 EXPORT_SYMBOL_GPL(dm_bm_unlock);
602 
603 int dm_bm_flush(struct dm_block_manager *bm)
604 {
605 	if (bm->read_only)
606 		return -EPERM;
607 
608 	return dm_bufio_write_dirty_buffers(bm->bufio);
609 }
610 EXPORT_SYMBOL_GPL(dm_bm_flush);
611 
612 void dm_bm_prefetch(struct dm_block_manager *bm, dm_block_t b)
613 {
614 	dm_bufio_prefetch(bm->bufio, b, 1);
615 }
616 
617 bool dm_bm_is_read_only(struct dm_block_manager *bm)
618 {
619 	return bm->read_only;
620 }
621 EXPORT_SYMBOL_GPL(dm_bm_is_read_only);
622 
623 void dm_bm_set_read_only(struct dm_block_manager *bm)
624 {
625 	bm->read_only = true;
626 }
627 EXPORT_SYMBOL_GPL(dm_bm_set_read_only);
628 
629 void dm_bm_set_read_write(struct dm_block_manager *bm)
630 {
631 	bm->read_only = false;
632 }
633 EXPORT_SYMBOL_GPL(dm_bm_set_read_write);
634 
635 u32 dm_bm_checksum(const void *data, size_t len, u32 init_xor)
636 {
637 	return crc32c(~(u32) 0, data, len) ^ init_xor;
638 }
639 EXPORT_SYMBOL_GPL(dm_bm_checksum);
640 
641 /*----------------------------------------------------------------*/
642 
643 MODULE_LICENSE("GPL");
644 MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
645 MODULE_DESCRIPTION("Immutable metadata library for dm");
646 
647 /*----------------------------------------------------------------*/
648