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 #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 typedef unsigned long stack_entries[MAX_STACK];
  39
  40 struct block_lock {
  41         spinlock_t lock;
  42         __s32 count;
  43         struct list_head waiters;
  44         struct task_struct *holders[MAX_HOLDERS];
  45
  46 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  47         struct stack_trace traces[MAX_HOLDERS];
  48         stack_entries entries[MAX_HOLDERS];
  49 #endif
  50 };
  51
  52 struct waiter {
  53         struct list_head list;
  54         struct task_struct *task;
  55         int wants_write;
  56 };
  57
  58 static unsigned __find_holder(struct block_lock *lock,
  59                               struct task_struct *task)
  60 {
  61         unsigned i;
  62
  63         for (i = 0; i < MAX_HOLDERS; i++)
  64                 if (lock->holders[i] == task)
  65                         break;
  66
  67         BUG_ON(i == MAX_HOLDERS);
  68         return i;
  69 }
  70
  71 /* call this *after* you increment lock->count */
  72 static void __add_holder(struct block_lock *lock, struct task_struct *task)
  73 {
  74         unsigned h = __find_holder(lock, NULL);
  75 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  76         struct stack_trace *t;
  77 #endif
  78
  79         get_task_struct(task);
  80         lock->holders[h] = task;
  81
  82 #ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
  83         t = lock->traces + h;
  84         t->nr_entries = 0;
  85         t->max_entries = MAX_STACK;
  86         t->entries = lock->entries[h];
  87         t->skip = 2;
  88         save_stack_trace(t);
  89 #endif
  90 }
  91
  92 /* call this *before* you decrement lock->count */
  93 static void __del_holder(struct block_lock *lock, struct task_struct *task)
  94 {
  95         unsigned h = __find_holder(lock, task);
  96         lock->holders[h] = NULL;
  97         put_task_struct(task);
  98 }
  99
 100 static int __check_holder(struct block_lock *lock)
 101 {
 102         unsigned 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                         print_stack_trace(lock->traces + i, 4);
 110
 111                         DMERR("subsequent acquisition attempted here:");
 112                         dump_stack();
 113 #endif
 114                         return -EINVAL;
 115                 }
 116         }
 117
 118         return 0;
 119 }
 120
 121 static void __wait(struct waiter *w)
 122 {
 123         for (;;) {
 124                 set_current_state(TASK_UNINTERRUPTIBLE);
 125
 126                 if (!w->task)
 127                         break;
 128
 129                 schedule();
 130         }
 131
 132         set_current_state(TASK_RUNNING);
 133 }
 134
 135 static void __wake_waiter(struct waiter *w)
 136 {
 137         struct task_struct *task;
 138
 139         list_del(&w->list);
 140         task = w->task;
 141         smp_mb();
 142         w->task = NULL;
 143         wake_up_process(task);
 144 }
 145
 146 /*
 147  * We either wake a few readers or a single writer.
 148  */
 149 static void __wake_many(struct block_lock *lock)
 150 {
 151         struct waiter *w, *tmp;
 152
 153         BUG_ON(lock->count < 0);
 154         list_for_each_entry_safe(w, tmp, &lock->waiters, list) {
 155                 if (lock->count >= MAX_HOLDERS)
 156                         return;
 157
 158                 if (w->wants_write) {
 159                         if (lock->count > 0)
 160                                 return; /* still read locked */
 161
 162                         lock->count = -1;
 163                         __add_holder(lock, w->task);
 164                         __wake_waiter(w);
 165                         return;
 166                 }
 167
 168                 lock->count++;
 169                 __add_holder(lock, w->task);
 170                 __wake_waiter(w);
 171         }
 172 }
 173
 174 static void bl_init(struct block_lock *lock)
 175 {
 176         int i;
 177
 178         spin_lock_init(&lock->lock);
 179         lock->count = 0;
 180         INIT_LIST_HEAD(&lock->waiters);
 181         for (i = 0; i < MAX_HOLDERS; i++)
 182                 lock->holders[i] = NULL;
 183 }
 184
 185 static int __available_for_read(struct block_lock *lock)
 186 {
 187         return lock->count >= 0 &&
 188                 lock->count < MAX_HOLDERS &&
 189                 list_empty(&lock->waiters);
 190 }
 191
 192 static int bl_down_read(struct block_lock *lock)
 193 {
 194         int r;
 195         struct waiter w;
 196
 197         spin_lock(&lock->lock);
 198         r = __check_holder(lock);
 199         if (r) {
 200                 spin_unlock(&lock->lock);
 201                 return r;
 202         }
 203
 204         if (__available_for_read(lock)) {
 205                 lock->count++;
 206                 __add_holder(lock, current);
 207                 spin_unlock(&lock->lock);
 208                 return 0;
 209         }
 210
 211         get_task_struct(current);
 212
 213         w.task = current;
 214         w.wants_write = 0;
 215         list_add_tail(&w.list, &lock->waiters);
 216         spin_unlock(&lock->lock);
 217
 218         __wait(&w);
 219         put_task_struct(current);
 220         return 0;
 221 }
 222
 223 static int bl_down_read_nonblock(struct block_lock *lock)
 224 {
 225         int r;
 226
 227         spin_lock(&lock->lock);
 228         r = __check_holder(lock);
 229         if (r)
 230                 goto out;
 231
 232         if (__available_for_read(lock)) {
 233                 lock->count++;
 234                 __add_holder(lock, current);
 235                 r = 0;
 236         } else
 237                 r = -EWOULDBLOCK;
 238
 239 out:
 240         spin_unlock(&lock->lock);
 241         return r;
 242 }
 243
 244 static void bl_up_read(struct block_lock *lock)
 245 {
 246         spin_lock(&lock->lock);
 247         BUG_ON(lock->count <= 0);
 248         __del_holder(lock, current);
 249         --lock->count;
 250         if (!list_empty(&lock->waiters))
 251                 __wake_many(lock);
 252         spin_unlock(&lock->lock);
 253 }
 254
 255 static int bl_down_write(struct block_lock *lock)
 256 {
 257         int r;
 258         struct waiter w;
 259
 260         spin_lock(&lock->lock);
 261         r = __check_holder(lock);
 262         if (r) {
 263                 spin_unlock(&lock->lock);
 264                 return r;
 265         }
 266
 267         if (lock->count == 0 && list_empty(&lock->waiters)) {
 268                 lock->count = -1;
 269                 __add_holder(lock, current);
 270                 spin_unlock(&lock->lock);
 271                 return 0;
 272         }
 273
 274         get_task_struct(current);
 275         w.task = current;
 276         w.wants_write = 1;
 277
 278         /*
 279          * Writers given priority. We know there's only one mutator in the
 280          * system, so ignoring the ordering reversal.
 281          */
 282         list_add(&w.list, &lock->waiters);
 283         spin_unlock(&lock->lock);
 284
 285         __wait(&w);
 286         put_task_struct(current);
 287
 288         return 0;
 289 }
 290
 291 static void bl_up_write(struct block_lock *lock)
 292 {
 293         spin_lock(&lock->lock);
 294         __del_holder(lock, current);
 295         lock->count = 0;
 296         if (!list_empty(&lock->waiters))
 297                 __wake_many(lock);
 298         spin_unlock(&lock->lock);
 299 }
 300
 301 static void report_recursive_bug(dm_block_t b, int r)
 302 {
 303         if (r == -EINVAL)
 304                 DMERR("recursive acquisition of block %llu requested.",
 305                       (unsigned long long) b);
 306 }
 307
 308 #else  /* !CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
 309
 310 #define bl_init(x) do { } while (0)
 311 #define bl_down_read(x) 0
 312 #define bl_down_read_nonblock(x) 0
 313 #define bl_up_read(x) do { } while (0)
 314 #define bl_down_write(x) 0
 315 #define bl_up_write(x) do { } while (0)
 316 #define report_recursive_bug(x, y) do { } while (0)
 317
 318 #endif /* CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING */
 319
 320 /*----------------------------------------------------------------*/
 321
 322 /*
 323  * Block manager is currently implemented using dm-bufio.  struct
 324  * dm_block_manager and struct dm_block map directly onto a couple of
 325  * structs in the bufio interface.  I want to retain the freedom to move
 326  * away from bufio in the future.  So these structs are just cast within
 327  * this .c file, rather than making it through to the public interface.
 328  */
 329 static struct dm_buffer *to_buffer(struct dm_block *b)
 330 {
 331         return (struct dm_buffer *) b;
 332 }
 333
 334 dm_block_t dm_block_location(struct dm_block *b)
 335 {
 336         return dm_bufio_get_block_number(to_buffer(b));
 337 }
 338 EXPORT_SYMBOL_GPL(dm_block_location);
 339
 340 void *dm_block_data(struct dm_block *b)
 341 {
 342         return dm_bufio_get_block_data(to_buffer(b));
 343 }
 344 EXPORT_SYMBOL_GPL(dm_block_data);
 345
 346 struct buffer_aux {
 347         struct dm_block_validator *validator;
 348         int write_locked;
 349
 350 #ifdef CONFIG_DM_DEBUG_BLOCK_MANAGER_LOCKING
 351         struct block_lock lock;
 352 #endif
 353 };
 354
 355 static void dm_block_manager_alloc_callback(struct dm_buffer *buf)
 356 {
 357         struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
 358         aux->validator = NULL;
 359         bl_init(&aux->lock);
 360 }
 361
 362 static void dm_block_manager_write_callback(struct dm_buffer *buf)
 363 {
 364         struct buffer_aux *aux = dm_bufio_get_aux_data(buf);
 365         if (aux->validator) {
 366                 aux->validator->prepare_for_write(aux->validator, (struct dm_block *) buf,
 367                          dm_bufio_get_block_size(dm_bufio_get_client(buf)));
 368         }
 369 }
 370
 371 /*----------------------------------------------------------------
 372  * Public interface
 373  *--------------------------------------------------------------*/
 374 struct dm_block_manager {
 375         struct dm_bufio_client *bufio;
 376         bool read_only:1;
 377 };
 378
 379 struct dm_block_manager *dm_block_manager_create(struct block_device *bdev,
 380                                                  unsigned block_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 /*----------------------------------------------------------------*/