drivers/md/persistent-data/dm-block-manager.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2011 Red Hat, Inc.
   4  *
   5  * This file is released under the GPL.
   6  */
   7 #include "dm-block-manager.h"
   8 #include "dm-persistent-data-internal.h"
   9
  10 #include <linux/dm-bufio.h>
  11 #include <linux/crc32c.h>
  12 #include <linux/module.h>
  13 #include <linux/slab.h>
  14 #include <linux/rwsem.h>
  15 #include <linux/device-mapper.h>
  16 #include <linux/stacktrace.h>
  17 #include <linux/sched/task.h>
  18
  19 #define DM_MSG_PREFIX "block manager"
  20
  21 /*----------------------------------------------------------------*/
  22
  23 #ifdef CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING
  24
  25 /*
  26  * This is a read/write semaphore with a couple of differences.
  27  *
  28  * i) There is a restriction on the number of concurrent read locks that
  29  * may be held at once.  This is just an implementation detail.
  30  *
  31  * ii) Recursive locking attempts are detected and return EINVAL.  A stack
  32  * trace is also emitted for the previous lock acquisition.
  33  *
  34  * iii) Priority is given to write locks.
  35  */
  36 #define MAX_HOLDERS 4
  37 #define MAX_STACK 10
  38
  39 struct stack_store {
  40         unsigned int    nr_entries;
  41         unsigned long   entries[MAX_STACK];
  42 };
  43
  44 struct block_lock {
  45         spinlock_t lock;
  46         __s32 count;
  47         struct list_head waiters;
  48         struct task_struct *holders[MAX_HOLDERS];
  49
  50 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  51         struct stack_store traces[MAX_HOLDERS];
  52 #endif
  53 };
  54
  55 struct waiter {
  56         struct list_head list;
  57         struct task_struct *task;
  58         int wants_write;
  59 };
  60
  61 static unsigned int __find_holder(struct block_lock *lock,
  62                               struct task_struct *task)
  63 {
  64         unsigned int i;
  65
  66         for (i = 0; i < MAX_HOLDERS; i++)
  67                 if (lock->holders[i] == task)
  68                         break;
  69
  70         BUG_ON(i == MAX_HOLDERS);
  71         return i;
  72 }
  73
  74 /* call this *after* you increment lock->count */
  75 static void __add_holder(struct block_lock *lock, struct task_struct *task)
  76 {
  77         unsigned int h = __find_holder(lock, NULL);
  78 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  79         struct stack_store *t;
  80 #endif
  81
  82         get_task_struct(task);
  83         lock->holders[h] = task;
  84
  85 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  86         t = lock->traces + h;
  87         t->nr_entries = stack_trace_save(t->entries, MAX_STACK, 2);
  88 #endif
  89 }
  90
  91 /* call this *before* you decrement lock->count */
  92 static void __del_holder(struct block_lock *lock, struct task_struct *task)
  93 {
  94         unsigned int h = __find_holder(lock, task);
  95
  96         lock->holders[h] = NULL;
  97         put_task_struct(task);
  98 }
  99
 100 static int __check_holder(struct block_lock *lock)
 101 {
 102         unsigned int i;
 103
 104         for (i = 0; i < MAX_HOLDERS; i++) {
 105                 if (lock->holders[i] == current) {
 106                         DMERR("recursive lock detected in metadata");
 107 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
 108                         DMERR("previously held here:");
 109                         stack_trace_print(lock->traces[i].entries,
 110                                           lock->traces[i].nr_entries, 4);
 111
 112                         DMERR("subsequent acquisition attempted here:");
 113                         dump_stack();
 114 #endif
 115                         return -EINVAL;
 116                 }
 117         }
 118
 119         return 0;
 120 }
 121
 122 static void __wait(struct waiter *w)
 123 {
 124         for (;;) {
 125                 set_current_state(TASK_UNINTERRUPTIBLE);
 126
 127                 if (!w->task)
 128                         break;
 129
 130                 schedule();
 131         }
 132
 133         set_current_state(TASK_RUNNING);
 134 }
 135
 136 static void __wake_waiter(struct waiter *w)
 137 {
 138         struct task_struct *task;
 139
 140         list_del(&w->list);
 141         task = w->task;
 142         smp_mb();
 143         w->task = NULL;
 144         wake_up_process(task);
 145 }
 146
 147 /*
 148  * We either wake a few readers or a single writer.
 149  */
 150 static void __wake_many(struct block_lock *lock)
 151 {
 152         struct waiter *w, *tmp;
 153
 154         BUG_ON(lock->count < 0);
 155         list_for_each_entry_safe(w, tmp, &lock->waiters, list) {
 156                 if (lock->count >= MAX_HOLDERS)
 157                         return;
 158
 159                 if (w->wants_write) {
 160                         if (lock->count > 0)
 161                                 return; /* still read locked */
 162
 163                         lock->count = -1;
 164                         __add_holder(lock, w->task);
 165                         __wake_waiter(w);
 166                         return;
 167                 }
 168
 169                 lock->count++;
 170                 __add_holder(lock, w->task);
 171                 __wake_waiter(w);
 172         }
 173 }
 174
 175 static void bl_init(struct block_lock *lock)
 176 {
 177         int i;
 178
 179         spin_lock_init(&lock->lock);
 180         lock->count = 0;
 181         INIT_LIST_HEAD(&lock->waiters);
 182         for (i = 0; i < MAX_HOLDERS; i++)
 183                 lock->holders[i] = NULL;
 184 }
 185
 186 static int __available_for_read(struct block_lock *lock)
 187 {
 188         return lock->count >= 0 &&
 189                 lock->count < MAX_HOLDERS &&
 190                 list_empty(&lock->waiters);
 191 }
 192
 193 static int bl_down_read(struct block_lock *lock)
 194 {
 195         int r;
 196         struct waiter w;
 197
 198         spin_lock(&lock->lock);
 199         r = __check_holder(lock);
 200         if (r) {
 201                 spin_unlock(&lock->lock);
 202                 return r;
 203         }
 204
 205         if (__available_for_read(lock)) {
 206                 lock->count++;
 207                 __add_holder(lock, current);
 208                 spin_unlock(&lock->lock);
 209                 return 0;
 210         }
 211
 212         get_task_struct(current);
 213
 214         w.task = current;
 215         w.wants_write = 0;
 216         list_add_tail(&w.list, &lock->waiters);
 217         spin_unlock(&lock->lock);
 218
 219         __wait(&w);
 220         put_task_struct(current);
 221         return 0;
 222 }
 223
 224 static int bl_down_read_nonblock(struct block_lock *lock)
 225 {
 226         int r;
 227
 228         spin_lock(&lock->lock);
 229         r = __check_holder(lock);
 230         if (r)
 231                 goto out;
 232
 233         if (__available_for_read(lock)) {
 234                 lock->count++;
 235                 __add_holder(lock, current);
 236                 r = 0;
 237         } else
 238                 r = -EWOULDBLOCK;
 239
 240 out:
 241         spin_unlock(&lock->lock);
 242         return r;
 243 }
 244
 245 static void bl_up_read(struct block_lock *lock)
 246 {
 247         spin_lock(&lock->lock);
 248         BUG_ON(lock->count <= 0);
 249         __del_holder(lock, current);
 250         --lock->count;
 251         if (!list_empty(&lock->waiters))
 252                 __wake_many(lock);
 253         spin_unlock(&lock->lock);
 254 }
 255
 256 static int bl_down_write(struct block_lock *lock)
 257 {
 258         int r;
 259         struct waiter w;
 260
 261         spin_lock(&lock->lock);
 262         r = __check_holder(lock);
 263         if (r) {
 264                 spin_unlock(&lock->lock);
 265                 return r;
 266         }
 267
 268         if (lock->count == 0 && list_empty(&lock->waiters)) {
 269                 lock->count = -1;
 270                 __add_holder(lock, current);
 271                 spin_unlock(&lock->lock);
 272                 return 0;
 273         }
 274
 275         get_task_struct(current);
 276         w.task = current;
 277         w.wants_write = 1;
 278
 279         /*
 280          * Writers given priority. We know there's only one mutator in the
 281          * system, so ignoring the ordering reversal.
 282          */
 283         list_add(&w.list, &lock->waiters);
 284         spin_unlock(&lock->lock);
 285
 286         __wait(&w);
 287         put_task_struct(current);
 288
 289         return 0;
 290 }
 291
 292 static void bl_up_write(struct block_lock *lock)
 293 {
 294         spin_lock(&lock->lock);
 295         __del_holder(lock, current);
 296         lock->count = 0;
 297         if (!list_empty(&lock->waiters))
 298                 __wake_many(lock);
 299         spin_unlock(&lock->lock);
 300 }
 301
 302 static void report_recursive_bug(dm_block_t b, int r)
 303 {
 304         if (r == -EINVAL)
 305                 DMERR("recursive acquisition of block %llu requested.",
 306                       (unsigned long long) b);
 307 }
 308
 309 #else  /* !CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
 310
 311 #define bl_init(x) do { } while (0)
 312 #define bl_down_read(x) 0
 313 #define bl_down_read_nonblock(x) 0
 314 #define bl_up_read(x) do { } while (0)
 315 #define bl_down_write(x) 0
 316 #define bl_up_write(x) do { } while (0)
 317 #define report_recursive_bug(x, y) do { } while (0)
 318
 319 #endif /* CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
 320
 321 /*----------------------------------------------------------------*/
 322
 323 /*
 324  * Block manager is currently implemented using dm-bufio.  struct
 325  * dm_block_manager and struct dm_block map directly onto a couple of
 326  * structs in the bufio interface.  I want to retain the freedom to move
 327  * away from bufio in the future.  So these structs are just cast within
 328  * this .c file, rather than making it through to the public interface.
 329  */
 330 static struct dm_buffer *to_buffer(struct dm_block *b)
 331 {
 332         return (struct dm_buffer *) b;
 333 }
 334
 335 dm_block_t dm_block_location(struct dm_block *b)
 336 {
 337         return dm_bufio_get_block_number(to_buffer(b));
 338 }
 339 EXPORT_SYMBOL_GPL(dm_block_location);
 340
 341 void *dm_block_data(struct dm_block *b)
 342 {
 343         return dm_bufio_get_block_data(to_buffer(b));
 344 }
 345 EXPORT_SYMBOL_GPL(dm_block_data);
 346
 347 struct buffer_aux {
 348         struct dm_block_validator *validator;
 349         int write_locked;
 350
 351 #ifdef CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING
 352         struct block_lock lock;
 353 #endif
 354 };
 355
 356 static void dm_block_manager_alloc_callback(struct dm_buffer *buf)
 357 {
 358         struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
 359
 360         aux->validator = NULL;
 361         bl_init(&aux->lock);
 362 }
 363
 364 static void dm_block_manager_write_callback(struct dm_buffer *buf)
 365 {
 366         struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
 367
 368         if (aux->validator) {
 369                 aux->validator->prepare_for_write(aux->validator, (struct dm_block *) buf,
 370                          dm_bufio_get_block_size(dm_bufio_get_client(buf)));
 371         }
 372 }
 373
 374 /*
 375  * -------------------------------------------------------------
 376  * Public interface
 377  *--------------------------------------------------------------
 378  */
 379 struct dm_block_manager {
 380         struct dm_bufio_client *bufio;
 381         bool read_only:1;
 382 };
 383
 384 struct dm_block_manager *dm_block_manager_create(struct block_device *bdev,
 385                                                  unsigned int block_size,
 386                                                  unsigned int max_held_per_thread)
 387 {
 388         int r;
 389         struct dm_block_manager *bm;
 390
 391         bm = kmalloc(sizeof(*bm), GFP_KERNEL);
 392         if (!bm) {
 393                 r = -ENOMEM;
 394                 goto bad;
 395         }
 396
 397         bm->bufio = dm_bufio_client_create(bdev, block_size, max_held_per_thread,
 398                                            sizeof(struct buffer_aux),
 399                                            dm_block_manager_alloc_callback,
 400                                            dm_block_manager_write_callback,
 401                                            0);
 402         if (IS_ERR(bm->bufio)) {
 403                 r = PTR_ERR(bm->bufio);
 404                 kfree(bm);
 405                 goto bad;
 406         }
 407
 408         bm->read_only = false;
 409
 410         return bm;
 411
 412 bad:
 413         return ERR_PTR(r);
 414 }
 415 EXPORT_SYMBOL_GPL(dm_block_manager_create);
 416
 417 void dm_block_manager_destroy(struct dm_block_manager *bm)
 418 {
 419         dm_bufio_client_destroy(bm->bufio);
 420         kfree(bm);
 421 }
 422 EXPORT_SYMBOL_GPL(dm_block_manager_destroy);
 423
 424 void dm_block_manager_reset(struct dm_block_manager *bm)
 425 {
 426         dm_bufio_client_reset(bm->bufio);
 427 }
 428 EXPORT_SYMBOL_GPL(dm_block_manager_reset);
 429
 430 unsigned int dm_bm_block_size(struct dm_block_manager *bm)
 431 {
 432         return dm_bufio_get_block_size(bm->bufio);
 433 }
 434 EXPORT_SYMBOL_GPL(dm_bm_block_size);
 435
 436 dm_block_t dm_bm_nr_blocks(struct dm_block_manager *bm)
 437 {
 438         return dm_bufio_get_device_size(bm->bufio);
 439 }
 440
 441 static int dm_bm_validate_buffer(struct dm_block_manager *bm,
 442                                  struct dm_buffer *buf,
 443                                  struct buffer_aux *aux,
 444                                  struct dm_block_validator *v)
 445 {
 446         if (unlikely(!aux->validator)) {
 447                 int r;
 448
 449                 if (!v)
 450                         return 0;
 451                 r = v->check(v, (struct dm_block *) buf, dm_bufio_get_block_size(bm->bufio));
 452                 if (unlikely(r)) {
 453                         DMERR_LIMIT("%s validator check failed for block %llu", v->name,
 454                                     (unsigned long long) dm_bufio_get_block_number(buf));
 455                         return r;
 456                 }
 457                 aux->validator = v;
 458         } else {
 459                 if (unlikely(aux->validator != v)) {
 460                         DMERR_LIMIT("validator mismatch (old=%s vs new=%s) for block %llu",
 461                                     aux->validator->name, v ? v->name : "NULL",
 462                                     (unsigned long long) dm_bufio_get_block_number(buf));
 463                         return -EINVAL;
 464                 }
 465         }
 466
 467         return 0;
 468 }
 469 int dm_bm_read_lock(struct dm_block_manager *bm, dm_block_t b,
 470                     struct dm_block_validator *v,
 471                     struct dm_block **result)
 472 {
 473         struct buffer_aux *aux;
 474         void *p;
 475         int r;
 476
 477         p = dm_bufio_read(bm->bufio, b, (struct dm_buffer **) result);
 478         if (IS_ERR(p))
 479                 return PTR_ERR(p);
 480
 481         aux = dm_bufio_get_aux_data(to_buffer(*result));
 482         r = bl_down_read(&aux->lock);
 483         if (unlikely(r)) {
 484                 dm_bufio_release(to_buffer(*result));
 485                 report_recursive_bug(b, r);
 486                 return r;
 487         }
 488
 489         aux->write_locked = 0;
 490
 491         r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
 492         if (unlikely(r)) {
 493                 bl_up_read(&aux->lock);
 494                 dm_bufio_release(to_buffer(*result));
 495                 return r;
 496         }
 497
 498         return 0;
 499 }
 500 EXPORT_SYMBOL_GPL(dm_bm_read_lock);
 501
 502 int dm_bm_write_lock(struct dm_block_manager *bm,
 503                      dm_block_t b, struct dm_block_validator *v,
 504                      struct dm_block **result)
 505 {
 506         struct buffer_aux *aux;
 507         void *p;
 508         int r;
 509
 510         if (dm_bm_is_read_only(bm))
 511                 return -EPERM;
 512
 513         p = dm_bufio_read(bm->bufio, b, (struct dm_buffer **) result);
 514         if (IS_ERR(p))
 515                 return PTR_ERR(p);
 516
 517         aux = dm_bufio_get_aux_data(to_buffer(*result));
 518         r = bl_down_write(&aux->lock);
 519         if (r) {
 520                 dm_bufio_release(to_buffer(*result));
 521                 report_recursive_bug(b, r);
 522                 return r;
 523         }
 524
 525         aux->write_locked = 1;
 526
 527         r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
 528         if (unlikely(r)) {
 529                 bl_up_write(&aux->lock);
 530                 dm_bufio_release(to_buffer(*result));
 531                 return r;
 532         }
 533
 534         return 0;
 535 }
 536 EXPORT_SYMBOL_GPL(dm_bm_write_lock);
 537
 538 int dm_bm_read_try_lock(struct dm_block_manager *bm,
 539                         dm_block_t b, struct dm_block_validator *v,
 540                         struct dm_block **result)
 541 {
 542         struct buffer_aux *aux;
 543         void *p;
 544         int r;
 545
 546         p = dm_bufio_get(bm->bufio, b, (struct dm_buffer **) result);
 547         if (IS_ERR(p))
 548                 return PTR_ERR(p);
 549         if (unlikely(!p))
 550                 return -EWOULDBLOCK;
 551
 552         aux = dm_bufio_get_aux_data(to_buffer(*result));
 553         r = bl_down_read_nonblock(&aux->lock);
 554         if (r < 0) {
 555                 dm_bufio_release(to_buffer(*result));
 556                 report_recursive_bug(b, r);
 557                 return r;
 558         }
 559         aux->write_locked = 0;
 560
 561         r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
 562         if (unlikely(r)) {
 563                 bl_up_read(&aux->lock);
 564                 dm_bufio_release(to_buffer(*result));
 565                 return r;
 566         }
 567
 568         return 0;
 569 }
 570
 571 int dm_bm_write_lock_zero(struct dm_block_manager *bm,
 572                           dm_block_t b, struct dm_block_validator *v,
 573                           struct dm_block **result)
 574 {
 575         int r;
 576         struct buffer_aux *aux;
 577         void *p;
 578
 579         if (dm_bm_is_read_only(bm))
 580                 return -EPERM;
 581
 582         p = dm_bufio_new(bm->bufio, b, (struct dm_buffer **) result);
 583         if (IS_ERR(p))
 584                 return PTR_ERR(p);
 585
 586         memset(p, 0, dm_bm_block_size(bm));
 587
 588         aux = dm_bufio_get_aux_data(to_buffer(*result));
 589         r = bl_down_write(&aux->lock);
 590         if (r) {
 591                 dm_bufio_release(to_buffer(*result));
 592                 return r;
 593         }
 594
 595         aux->write_locked = 1;
 596         aux->validator = v;
 597
 598         return 0;
 599 }
 600 EXPORT_SYMBOL_GPL(dm_bm_write_lock_zero);
 601
 602 void dm_bm_unlock(struct dm_block *b)
 603 {
 604         struct buffer_aux *aux = dm_bufio_get_aux_data(to_buffer(b));
 605
 606         if (aux->write_locked) {
 607                 dm_bufio_mark_buffer_dirty(to_buffer(b));
 608                 bl_up_write(&aux->lock);
 609         } else
 610                 bl_up_read(&aux->lock);
 611
 612         dm_bufio_release(to_buffer(b));
 613 }
 614 EXPORT_SYMBOL_GPL(dm_bm_unlock);
 615
 616 int dm_bm_flush(struct dm_block_manager *bm)
 617 {
 618         if (dm_bm_is_read_only(bm))
 619                 return -EPERM;
 620
 621         return dm_bufio_write_dirty_buffers(bm->bufio);
 622 }
 623 EXPORT_SYMBOL_GPL(dm_bm_flush);
 624
 625 void dm_bm_prefetch(struct dm_block_manager *bm, dm_block_t b)
 626 {
 627         dm_bufio_prefetch(bm->bufio, b, 1);
 628 }
 629
 630 bool dm_bm_is_read_only(struct dm_block_manager *bm)
 631 {
 632         return bm ? bm->read_only : true;
 633 }
 634 EXPORT_SYMBOL_GPL(dm_bm_is_read_only);
 635
 636 void dm_bm_set_read_only(struct dm_block_manager *bm)
 637 {
 638         if (bm)
 639                 bm->read_only = true;
 640 }
 641 EXPORT_SYMBOL_GPL(dm_bm_set_read_only);
 642
 643 void dm_bm_set_read_write(struct dm_block_manager *bm)
 644 {
 645         if (bm)
 646                 bm->read_only = false;
 647 }
 648 EXPORT_SYMBOL_GPL(dm_bm_set_read_write);
 649
 650 u32 dm_bm_checksum(const void *data, size_t len, u32 init_xor)
 651 {
 652         return crc32c(~(u32) 0, data, len) ^ init_xor;
 653 }
 654 EXPORT_SYMBOL_GPL(dm_bm_checksum);
 655
 656 /*----------------------------------------------------------------*/
 657
 658 MODULE_LICENSE("GPL");
 659 MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
 660 MODULE_DESCRIPTION("Immutable metadata library for dm");
 661
 662 /*----------------------------------------------------------------*/