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

   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 #include "../dm-bufio.h"
   9
  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
  17 #define DM_MSG_PREFIX "block manager"
  18
  19 /*----------------------------------------------------------------*/
  20
  21 #ifdef CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING
  22
  23 /*
  24  * This is a read/write semaphore with a couple of differences.
  25  *
  26  * i) There is a restriction on the number of concurrent read locks that
  27  * may be held at once.  This is just an implementation detail.
  28  *
  29  * ii) Recursive locking attempts are detected and return EINVAL.  A stack
  30  * trace is also emitted for the previous lock acquisition.
  31  *
  32  * iii) Priority is given to write locks.
  33  */
  34 #define MAX_HOLDERS 4
  35 #define MAX_STACK 10
  36
  37 typedef unsigned long stack_entries[MAX_STACK];
  38
  39 struct block_lock {
  40         spinlock_t lock;
  41         __s32 count;
  42         struct list_head waiters;
  43         struct task_struct *holders[MAX_HOLDERS];
  44
  45 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  46         struct stack_trace traces[MAX_HOLDERS];
  47         stack_entries entries[MAX_HOLDERS];
  48 #endif
  49 };
  50
  51 struct waiter {
  52         struct list_head list;
  53         struct task_struct *task;
  54         int wants_write;
  55 };
  56
  57 static unsigned __find_holder(struct block_lock *lock,
  58                               struct task_struct *task)
  59 {
  60         unsigned i;
  61
  62         for (i = 0; i < MAX_HOLDERS; i++)
  63                 if (lock->holders[i] == task)
  64                         break;
  65
  66         BUG_ON(i == MAX_HOLDERS);
  67         return i;
  68 }
  69
  70 /* call this *after* you increment lock->count */
  71 static void __add_holder(struct block_lock *lock, struct task_struct *task)
  72 {
  73         unsigned h = __find_holder(lock, NULL);
  74 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  75         struct stack_trace *t;
  76 #endif
  77
  78         get_task_struct(task);
  79         lock->holders[h] = task;
  80
  81 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  82         t = lock->traces + h;
  83         t->nr_entries = 0;
  84         t->max_entries = MAX_STACK;
  85         t->entries = lock->entries[h];
  86         t->skip = 2;
  87         save_stack_trace(t);
  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 h = __find_holder(lock, task);
  95         lock->holders[h] = NULL;
  96         put_task_struct(task);
  97 }
  98
  99 static int __check_holder(struct block_lock *lock)
 100 {
 101         unsigned i;
 102
 103         for (i = 0; i < MAX_HOLDERS; i++) {
 104                 if (lock->holders[i] == current) {
 105                         DMERR("recursive lock detected in metadata");
 106 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
 107                         DMERR("previously held here:");
 108                         print_stack_trace(lock->traces + i, 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 cache_size,
 381                                                  unsigned max_held_per_thread)
 382 {
 383         int r;
 384         struct dm_block_manager *bm;
 385
 386         bm = kmalloc(sizeof(*bm), GFP_KERNEL);
 387         if (!bm) {
 388                 r = -ENOMEM;
 389                 goto bad;
 390         }
 391
 392         bm->bufio = dm_bufio_client_create(bdev, block_size, max_held_per_thread,
 393                                            sizeof(struct buffer_aux),
 394                                            dm_block_manager_alloc_callback,
 395                                            dm_block_manager_write_callback);
 396         if (IS_ERR(bm->bufio)) {
 397                 r = PTR_ERR(bm->bufio);
 398                 kfree(bm);
 399                 goto bad;
 400         }
 401
 402         bm->read_only = false;
 403
 404         return bm;
 405
 406 bad:
 407         return ERR_PTR(r);
 408 }
 409 EXPORT_SYMBOL_GPL(dm_block_manager_create);
 410
 411 void dm_block_manager_destroy(struct dm_block_manager *bm)
 412 {
 413         dm_bufio_client_destroy(bm->bufio);
 414         kfree(bm);
 415 }
 416 EXPORT_SYMBOL_GPL(dm_block_manager_destroy);
 417
 418 unsigned dm_bm_block_size(struct dm_block_manager *bm)
 419 {
 420         return dm_bufio_get_block_size(bm->bufio);
 421 }
 422 EXPORT_SYMBOL_GPL(dm_bm_block_size);
 423
 424 dm_block_t dm_bm_nr_blocks(struct dm_block_manager *bm)
 425 {
 426         return dm_bufio_get_device_size(bm->bufio);
 427 }
 428
 429 static int dm_bm_validate_buffer(struct dm_block_manager *bm,
 430                                  struct dm_buffer *buf,
 431                                  struct buffer_aux *aux,
 432                                  struct dm_block_validator *v)
 433 {
 434         if (unlikely(!aux->validator)) {
 435                 int r;
 436                 if (!v)
 437                         return 0;
 438                 r = v->check(v, (struct dm_block *) buf, dm_bufio_get_block_size(bm->bufio));
 439                 if (unlikely(r)) {
 440                         DMERR_LIMIT("%s validator check failed for block %llu", v->name,
 441                                     (unsigned long long) dm_bufio_get_block_number(buf));
 442                         return r;
 443                 }
 444                 aux->validator = v;
 445         } else {
 446                 if (unlikely(aux->validator != v)) {
 447                         DMERR_LIMIT("validator mismatch (old=%s vs new=%s) for block %llu",
 448                                     aux->validator->name, v ? v->name : "NULL",
 449                                     (unsigned long long) dm_bufio_get_block_number(buf));
 450                         return -EINVAL;
 451                 }
 452         }
 453
 454         return 0;
 455 }
 456 int dm_bm_read_lock(struct dm_block_manager *bm, dm_block_t b,
 457                     struct dm_block_validator *v,
 458                     struct dm_block **result)
 459 {
 460         struct buffer_aux *aux;
 461         void *p;
 462         int r;
 463
 464         p = dm_bufio_read(bm->bufio, b, (struct dm_buffer **) result);
 465         if (unlikely(IS_ERR(p)))
 466                 return PTR_ERR(p);
 467
 468         aux = dm_bufio_get_aux_data(to_buffer(*result));
 469         r = bl_down_read(&aux->lock);
 470         if (unlikely(r)) {
 471                 dm_bufio_release(to_buffer(*result));
 472                 report_recursive_bug(b, r);
 473                 return r;
 474         }
 475
 476         aux->write_locked = 0;
 477
 478         r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
 479         if (unlikely(r)) {
 480                 bl_up_read(&aux->lock);
 481                 dm_bufio_release(to_buffer(*result));
 482                 return r;
 483         }
 484
 485         return 0;
 486 }
 487 EXPORT_SYMBOL_GPL(dm_bm_read_lock);
 488
 489 int dm_bm_write_lock(struct dm_block_manager *bm,
 490                      dm_block_t b, struct dm_block_validator *v,
 491                      struct dm_block **result)
 492 {
 493         struct buffer_aux *aux;
 494         void *p;
 495         int r;
 496
 497         if (bm->read_only)
 498                 return -EPERM;
 499
 500         p = dm_bufio_read(bm->bufio, b, (struct dm_buffer **) result);
 501         if (unlikely(IS_ERR(p)))
 502                 return PTR_ERR(p);
 503
 504         aux = dm_bufio_get_aux_data(to_buffer(*result));
 505         r = bl_down_write(&aux->lock);
 506         if (r) {
 507                 dm_bufio_release(to_buffer(*result));
 508                 report_recursive_bug(b, r);
 509                 return r;
 510         }
 511
 512         aux->write_locked = 1;
 513
 514         r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
 515         if (unlikely(r)) {
 516                 bl_up_write(&aux->lock);
 517                 dm_bufio_release(to_buffer(*result));
 518                 return r;
 519         }
 520
 521         return 0;
 522 }
 523 EXPORT_SYMBOL_GPL(dm_bm_write_lock);
 524
 525 int dm_bm_read_try_lock(struct dm_block_manager *bm,
 526                         dm_block_t b, struct dm_block_validator *v,
 527                         struct dm_block **result)
 528 {
 529         struct buffer_aux *aux;
 530         void *p;
 531         int r;
 532
 533         p = dm_bufio_get(bm->bufio, b, (struct dm_buffer **) result);
 534         if (unlikely(IS_ERR(p)))
 535                 return PTR_ERR(p);
 536         if (unlikely(!p))
 537                 return -EWOULDBLOCK;
 538
 539         aux = dm_bufio_get_aux_data(to_buffer(*result));
 540         r = bl_down_read_nonblock(&aux->lock);
 541         if (r < 0) {
 542                 dm_bufio_release(to_buffer(*result));
 543                 report_recursive_bug(b, r);
 544                 return r;
 545         }
 546         aux->write_locked = 0;
 547
 548         r = dm_bm_validate_buffer(bm, to_buffer(*result), aux, v);
 549         if (unlikely(r)) {
 550                 bl_up_read(&aux->lock);
 551                 dm_bufio_release(to_buffer(*result));
 552                 return r;
 553         }
 554
 555         return 0;
 556 }
 557
 558 int dm_bm_write_lock_zero(struct dm_block_manager *bm,
 559                           dm_block_t b, struct dm_block_validator *v,
 560                           struct dm_block **result)
 561 {
 562         int r;
 563         struct buffer_aux *aux;
 564         void *p;
 565
 566         if (bm->read_only)
 567                 return -EPERM;
 568
 569         p = dm_bufio_new(bm->bufio, b, (struct dm_buffer **) result);
 570         if (unlikely(IS_ERR(p)))
 571                 return PTR_ERR(p);
 572
 573         memset(p, 0, dm_bm_block_size(bm));
 574
 575         aux = dm_bufio_get_aux_data(to_buffer(*result));
 576         r = bl_down_write(&aux->lock);
 577         if (r) {
 578                 dm_bufio_release(to_buffer(*result));
 579                 return r;
 580         }
 581
 582         aux->write_locked = 1;
 583         aux->validator = v;
 584
 585         return 0;
 586 }
 587 EXPORT_SYMBOL_GPL(dm_bm_write_lock_zero);
 588
 589 void dm_bm_unlock(struct dm_block *b)
 590 {
 591         struct buffer_aux *aux;
 592         aux = dm_bufio_get_aux_data(to_buffer(b));
 593
 594         if (aux->write_locked) {
 595                 dm_bufio_mark_buffer_dirty(to_buffer(b));
 596                 bl_up_write(&aux->lock);
 597         } else
 598                 bl_up_read(&aux->lock);
 599
 600         dm_bufio_release(to_buffer(b));
 601 }
 602 EXPORT_SYMBOL_GPL(dm_bm_unlock);
 603
 604 int dm_bm_flush(struct dm_block_manager *bm)
 605 {
 606         if (bm->read_only)
 607                 return -EPERM;
 608
 609         return dm_bufio_write_dirty_buffers(bm->bufio);
 610 }
 611 EXPORT_SYMBOL_GPL(dm_bm_flush);
 612
 613 void dm_bm_prefetch(struct dm_block_manager *bm, dm_block_t b)
 614 {
 615         dm_bufio_prefetch(bm->bufio, b, 1);
 616 }
 617
 618 bool dm_bm_is_read_only(struct dm_block_manager *bm)
 619 {
 620         return bm->read_only;
 621 }
 622 EXPORT_SYMBOL_GPL(dm_bm_is_read_only);
 623
 624 void dm_bm_set_read_only(struct dm_block_manager *bm)
 625 {
 626         bm->read_only = true;
 627 }
 628 EXPORT_SYMBOL_GPL(dm_bm_set_read_only);
 629
 630 void dm_bm_set_read_write(struct dm_block_manager *bm)
 631 {
 632         bm->read_only = false;
 633 }
 634 EXPORT_SYMBOL_GPL(dm_bm_set_read_write);
 635
 636 u32 dm_bm_checksum(const void *data, size_t len, u32 init_xor)
 637 {
 638         return crc32c(~(u32) 0, data, len) ^ init_xor;
 639 }
 640 EXPORT_SYMBOL_GPL(dm_bm_checksum);
 641
 642 /*----------------------------------------------------------------*/
 643
 644 MODULE_LICENSE("GPL");
 645 MODULE_AUTHOR("Joe Thornber <dm-devel@redhat.com>");
 646 MODULE_DESCRIPTION("Immutable metadata library for dm");
 647
 648 /*----------------------------------------------------------------*/