git.sesse.net Git - bcachefs-tools-debian/blob - libbcachefs/btree_locking.c

   1 // SPDX-License-Identifier: GPL-2.0
   2
   3 #include "bcachefs.h"
   4 #include "btree_locking.h"
   5 #include "btree_types.h"
   6
   7 struct lock_class_key bch2_btree_node_lock_key;
   8
   9 /* Btree node locking: */
  10
  11 static inline void six_lock_readers_add(struct six_lock *lock, int nr)
  12 {
  13         if (lock->readers)
  14                 this_cpu_add(*lock->readers, nr);
  15         else if (nr > 0)
  16                 atomic64_add(__SIX_VAL(read_lock, nr), &lock->state.counter);
  17         else
  18                 atomic64_sub(__SIX_VAL(read_lock, -nr), &lock->state.counter);
  19 }
  20
  21 struct six_lock_count bch2_btree_node_lock_counts(struct btree_trans *trans,
  22                                                   struct btree_path *skip,
  23                                                   struct btree_bkey_cached_common *b,
  24                                                   unsigned level)
  25 {
  26         struct btree_path *path;
  27         struct six_lock_count ret;
  28
  29         memset(&ret, 0, sizeof(ret));
  30
  31         if (IS_ERR_OR_NULL(b))
  32                 return ret;
  33
  34         trans_for_each_path(trans, path)
  35                 if (path != skip && &path->l[level].b->c == b) {
  36                         int t = btree_node_locked_type(path, level);
  37
  38                         if (t != BTREE_NODE_UNLOCKED)
  39                                 ret.n[t]++;
  40                 }
  41
  42         return ret;
  43 }
  44
  45 /* unlock */
  46
  47 void bch2_btree_node_unlock_write(struct btree_trans *trans,
  48                         struct btree_path *path, struct btree *b)
  49 {
  50         bch2_btree_node_unlock_write_inlined(trans, path, b);
  51 }
  52
  53 /* lock */
  54
  55 /*
  56  * @trans wants to lock @b with type @type
  57  */
  58 struct trans_waiting_for_lock {
  59         struct btree_trans              *trans;
  60         struct btree_bkey_cached_common *node_want;
  61         enum six_lock_type              lock_want;
  62
  63         /* for iterating over held locks :*/
  64         u8                              path_idx;
  65         u8                              level;
  66         u64                             lock_start_time;
  67 };
  68
  69 struct lock_graph {
  70         struct trans_waiting_for_lock   g[8];
  71         unsigned                        nr;
  72 };
  73
  74 static noinline void print_cycle(struct printbuf *out, struct lock_graph *g)
  75 {
  76         struct trans_waiting_for_lock *i;
  77
  78         prt_printf(out, "Found lock cycle (%u entries):", g->nr);
  79         prt_newline(out);
  80
  81         for (i = g->g; i < g->g + g->nr; i++)
  82                 bch2_btree_trans_to_text(out, i->trans);
  83 }
  84
  85 static noinline void print_chain(struct printbuf *out, struct lock_graph *g)
  86 {
  87         struct trans_waiting_for_lock *i;
  88
  89         for (i = g->g; i != g->g + g->nr; i++) {
  90                 if (i != g->g)
  91                         prt_str(out, "<- ");
  92                 prt_printf(out, "%u ", i->trans->locking_wait.task->pid);
  93         }
  94         prt_newline(out);
  95 }
  96
  97 static void lock_graph_up(struct lock_graph *g)
  98 {
  99         closure_put(&g->g[--g->nr].trans->ref);
 100 }
 101
 102 static void lock_graph_down(struct lock_graph *g, struct btree_trans *trans)
 103 {
 104         closure_get(&trans->ref);
 105
 106         g->g[g->nr++] = (struct trans_waiting_for_lock) {
 107                 .trans          = trans,
 108                 .node_want      = trans->locking,
 109                 .lock_want      = trans->locking_wait.lock_want,
 110         };
 111 }
 112
 113 static bool lock_graph_remove_non_waiters(struct lock_graph *g)
 114 {
 115         struct trans_waiting_for_lock *i;
 116
 117         for (i = g->g + 1; i < g->g + g->nr; i++)
 118                 if (i->trans->locking != i->node_want ||
 119                     i->trans->locking_wait.start_time != i[-1].lock_start_time) {
 120                         while (g->g + g->nr > i)
 121                                 lock_graph_up(g);
 122                         return true;
 123                 }
 124
 125         return false;
 126 }
 127
 128 static int abort_lock(struct lock_graph *g, struct trans_waiting_for_lock *i)
 129 {
 130         if (i == g->g) {
 131                 trace_and_count(i->trans->c, trans_restart_would_deadlock, i->trans, _RET_IP_);
 132                 return btree_trans_restart(i->trans, BCH_ERR_transaction_restart_would_deadlock);
 133         } else {
 134                 i->trans->lock_must_abort = true;
 135                 wake_up_process(i->trans->locking_wait.task);
 136                 return 0;
 137         }
 138 }
 139
 140 static int btree_trans_abort_preference(struct btree_trans *trans)
 141 {
 142         if (trans->lock_may_not_fail)
 143                 return 0;
 144         if (trans->locking_wait.lock_want == SIX_LOCK_write)
 145                 return 1;
 146         if (!trans->in_traverse_all)
 147                 return 2;
 148         return 3;
 149 }
 150
 151 static noinline int break_cycle(struct lock_graph *g, struct printbuf *cycle)
 152 {
 153         struct trans_waiting_for_lock *i, *abort = NULL;
 154         unsigned best = 0, pref;
 155         int ret;
 156
 157         if (lock_graph_remove_non_waiters(g))
 158                 return 0;
 159
 160         /* Only checking, for debugfs: */
 161         if (cycle) {
 162                 print_cycle(cycle, g);
 163                 ret = -1;
 164                 goto out;
 165         }
 166
 167         for (i = g->g; i < g->g + g->nr; i++) {
 168                 pref = btree_trans_abort_preference(i->trans);
 169                 if (pref > best) {
 170                         abort = i;
 171                         best = pref;
 172                 }
 173         }
 174
 175         if (unlikely(!best)) {
 176                 struct printbuf buf = PRINTBUF;
 177
 178                 prt_printf(&buf, bch2_fmt(g->g->trans->c, "cycle of nofail locks"));
 179
 180                 for (i = g->g; i < g->g + g->nr; i++) {
 181                         struct btree_trans *trans = i->trans;
 182
 183                         bch2_btree_trans_to_text(&buf, trans);
 184
 185                         prt_printf(&buf, "backtrace:");
 186                         prt_newline(&buf);
 187                         printbuf_indent_add(&buf, 2);
 188                         bch2_prt_backtrace(&buf, trans->locking_wait.task);
 189                         printbuf_indent_sub(&buf, 2);
 190                         prt_newline(&buf);
 191                 }
 192
 193                 bch2_print_string_as_lines(KERN_ERR, buf.buf);
 194                 printbuf_exit(&buf);
 195                 BUG();
 196         }
 197
 198         ret = abort_lock(g, abort);
 199 out:
 200         if (ret)
 201                 while (g->nr)
 202                         lock_graph_up(g);
 203         return ret;
 204 }
 205
 206 static int lock_graph_descend(struct lock_graph *g, struct btree_trans *trans,
 207                               struct printbuf *cycle)
 208 {
 209         struct btree_trans *orig_trans = g->g->trans;
 210         struct trans_waiting_for_lock *i;
 211
 212         for (i = g->g; i < g->g + g->nr; i++)
 213                 if (i->trans == trans)
 214                         return break_cycle(g, cycle);
 215
 216         if (g->nr == ARRAY_SIZE(g->g)) {
 217                 if (orig_trans->lock_may_not_fail)
 218                         return 0;
 219
 220                 while (g->nr)
 221                         lock_graph_up(g);
 222                 trace_and_count(trans->c, trans_restart_would_deadlock_recursion_limit, trans, _RET_IP_);
 223                 return btree_trans_restart(orig_trans, BCH_ERR_transaction_restart_deadlock_recursion_limit);
 224         }
 225
 226         lock_graph_down(g, trans);
 227         return 0;
 228 }
 229
 230 static bool lock_type_conflicts(enum six_lock_type t1, enum six_lock_type t2)
 231 {
 232         return t1 + t2 > 1;
 233 }
 234
 235 int bch2_check_for_deadlock(struct btree_trans *trans, struct printbuf *cycle)
 236 {
 237         struct lock_graph g;
 238         struct trans_waiting_for_lock *top;
 239         struct btree_bkey_cached_common *b;
 240         struct btree_path *path;
 241         int ret;
 242
 243         if (trans->lock_must_abort) {
 244                 trace_and_count(trans->c, trans_restart_would_deadlock, trans, _RET_IP_);
 245                 return btree_trans_restart(trans, BCH_ERR_transaction_restart_would_deadlock);
 246         }
 247
 248         g.nr = 0;
 249         lock_graph_down(&g, trans);
 250 next:
 251         if (!g.nr)
 252                 return 0;
 253
 254         top = &g.g[g.nr - 1];
 255
 256         trans_for_each_path_from(top->trans, path, top->path_idx) {
 257                 if (!path->nodes_locked)
 258                         continue;
 259
 260                 if (top->path_idx != path->idx) {
 261                         top->path_idx           = path->idx;
 262                         top->level              = 0;
 263                         top->lock_start_time    = 0;
 264                 }
 265
 266                 for (;
 267                      top->level < BTREE_MAX_DEPTH;
 268                      top->level++, top->lock_start_time = 0) {
 269                         int lock_held = btree_node_locked_type(path, top->level);
 270
 271                         if (lock_held == BTREE_NODE_UNLOCKED)
 272                                 continue;
 273
 274                         b = &READ_ONCE(path->l[top->level].b)->c;
 275
 276                         if (IS_ERR_OR_NULL(b)) {
 277                                 BUG_ON(!lock_graph_remove_non_waiters(&g));
 278                                 goto next;
 279                         }
 280
 281                         if (list_empty_careful(&b->lock.wait_list))
 282                                 continue;
 283
 284                         raw_spin_lock(&b->lock.wait_lock);
 285                         list_for_each_entry(trans, &b->lock.wait_list, locking_wait.list) {
 286                                 BUG_ON(b != trans->locking);
 287
 288                                 if (top->lock_start_time &&
 289                                     time_after_eq64(top->lock_start_time, trans->locking_wait.start_time))
 290                                         continue;
 291
 292                                 top->lock_start_time = trans->locking_wait.start_time;
 293
 294                                 /* Don't check for self deadlock: */
 295                                 if (trans == top->trans ||
 296                                     !lock_type_conflicts(lock_held, trans->locking_wait.lock_want))
 297                                         continue;
 298
 299                                 ret = lock_graph_descend(&g, trans, cycle);
 300                                 raw_spin_unlock(&b->lock.wait_lock);
 301
 302                                 if (ret)
 303                                         return ret;
 304                                 goto next;
 305
 306                         }
 307                         raw_spin_unlock(&b->lock.wait_lock);
 308                 }
 309         }
 310
 311         if (g.nr > 1 && cycle)
 312                 print_chain(cycle, &g);
 313         lock_graph_up(&g);
 314         goto next;
 315 }
 316
 317 int bch2_six_check_for_deadlock(struct six_lock *lock, void *p)
 318 {
 319         struct btree_trans *trans = p;
 320
 321         return bch2_check_for_deadlock(trans, NULL);
 322 }
 323
 324 int __bch2_btree_node_lock_write(struct btree_trans *trans, struct btree_path *path,
 325                                  struct btree_bkey_cached_common *b,
 326                                  bool lock_may_not_fail)
 327 {
 328         int readers = bch2_btree_node_lock_counts(trans, NULL, b, b->level).n[SIX_LOCK_read];
 329         int ret;
 330
 331         /*
 332          * Must drop our read locks before calling six_lock_write() -
 333          * six_unlock() won't do wakeups until the reader count
 334          * goes to 0, and it's safe because we have the node intent
 335          * locked:
 336          */
 337         six_lock_readers_add(&b->lock, -readers);
 338         ret = __btree_node_lock_nopath(trans, b, SIX_LOCK_write, lock_may_not_fail);
 339         six_lock_readers_add(&b->lock, readers);
 340
 341         if (ret)
 342                 mark_btree_node_locked_noreset(path, b->level, SIX_LOCK_intent);
 343
 344         return ret;
 345 }
 346
 347 /* relock */
 348
 349 static inline bool btree_path_get_locks(struct btree_trans *trans,
 350                                         struct btree_path *path,
 351                                         bool upgrade)
 352 {
 353         unsigned l = path->level;
 354         int fail_idx = -1;
 355
 356         do {
 357                 if (!btree_path_node(path, l))
 358                         break;
 359
 360                 if (!(upgrade
 361                       ? bch2_btree_node_upgrade(trans, path, l)
 362                       : bch2_btree_node_relock(trans, path, l))) {
 363                         (upgrade
 364                          ? trace_node_upgrade_fail
 365                          : trace_node_relock_fail)(0, _RET_IP_,
 366                                         path->btree_id, &path->pos,
 367                                         l, path->l[l].lock_seq,
 368                                         path->l[l].b,
 369                                         is_btree_node(path, l)
 370                                         ? path->l[l].b->c.lock.state.seq
 371                                         : 0);
 372                         fail_idx = l;
 373                 }
 374
 375                 l++;
 376         } while (l < path->locks_want);
 377
 378         /*
 379          * When we fail to get a lock, we have to ensure that any child nodes
 380          * can't be relocked so bch2_btree_path_traverse has to walk back up to
 381          * the node that we failed to relock:
 382          */
 383         if (fail_idx >= 0) {
 384                 __bch2_btree_path_unlock(trans, path);
 385                 btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);
 386
 387                 do {
 388                         path->l[fail_idx].b = upgrade
 389                                 ? ERR_PTR(-BCH_ERR_no_btree_node_upgrade)
 390                                 : ERR_PTR(-BCH_ERR_no_btree_node_relock);
 391                         --fail_idx;
 392                 } while (fail_idx >= 0);
 393         }
 394
 395         if (path->uptodate == BTREE_ITER_NEED_RELOCK)
 396                 path->uptodate = BTREE_ITER_UPTODATE;
 397
 398         bch2_trans_verify_locks(trans);
 399
 400         return path->uptodate < BTREE_ITER_NEED_RELOCK;
 401 }
 402
 403 bool __bch2_btree_node_relock(struct btree_trans *trans,
 404                               struct btree_path *path, unsigned level,
 405                               bool trace)
 406 {
 407         struct btree *b = btree_path_node(path, level);
 408         int want = __btree_lock_want(path, level);
 409
 410         if (race_fault())
 411                 goto fail;
 412
 413         if (six_relock_type(&b->c.lock, want, path->l[level].lock_seq) ||
 414             (btree_node_lock_seq_matches(path, b, level) &&
 415              btree_node_lock_increment(trans, &b->c, level, want))) {
 416                 mark_btree_node_locked(trans, path, level, want);
 417                 return true;
 418         }
 419 fail:
 420         if (trace)
 421                 trace_and_count(trans->c, btree_path_relock_fail, trans, _RET_IP_, path, level);
 422         return false;
 423 }
 424
 425 /* upgrade */
 426
 427 bool bch2_btree_node_upgrade(struct btree_trans *trans,
 428                              struct btree_path *path, unsigned level)
 429 {
 430         struct btree *b = path->l[level].b;
 431         struct six_lock_count count = bch2_btree_node_lock_counts(trans, path, &b->c, level);
 432
 433         if (!is_btree_node(path, level))
 434                 return false;
 435
 436         switch (btree_lock_want(path, level)) {
 437         case BTREE_NODE_UNLOCKED:
 438                 BUG_ON(btree_node_locked(path, level));
 439                 return true;
 440         case BTREE_NODE_READ_LOCKED:
 441                 BUG_ON(btree_node_intent_locked(path, level));
 442                 return bch2_btree_node_relock(trans, path, level);
 443         case BTREE_NODE_INTENT_LOCKED:
 444                 break;
 445         case BTREE_NODE_WRITE_LOCKED:
 446                 BUG();
 447         }
 448
 449         if (btree_node_intent_locked(path, level))
 450                 return true;
 451
 452         if (race_fault())
 453                 return false;
 454
 455         if (btree_node_locked(path, level)) {
 456                 bool ret;
 457
 458                 six_lock_readers_add(&b->c.lock, -count.n[SIX_LOCK_read]);
 459                 ret = six_lock_tryupgrade(&b->c.lock);
 460                 six_lock_readers_add(&b->c.lock, count.n[SIX_LOCK_read]);
 461
 462                 if (ret)
 463                         goto success;
 464         } else {
 465                 if (six_relock_type(&b->c.lock, SIX_LOCK_intent, path->l[level].lock_seq))
 466                         goto success;
 467         }
 468
 469         /*
 470          * Do we already have an intent lock via another path? If so, just bump
 471          * lock count:
 472          */
 473         if (btree_node_lock_seq_matches(path, b, level) &&
 474             btree_node_lock_increment(trans, &b->c, level, BTREE_NODE_INTENT_LOCKED)) {
 475                 btree_node_unlock(trans, path, level);
 476                 goto success;
 477         }
 478
 479         trace_and_count(trans->c, btree_path_upgrade_fail, trans, _RET_IP_, path, level);
 480         return false;
 481 success:
 482         mark_btree_node_locked_noreset(path, level, SIX_LOCK_intent);
 483         return true;
 484 }
 485
 486 /* Btree path locking: */
 487
 488 /*
 489  * Only for btree_cache.c - only relocks intent locks
 490  */
 491 int bch2_btree_path_relock_intent(struct btree_trans *trans,
 492                                   struct btree_path *path)
 493 {
 494         unsigned l;
 495
 496         for (l = path->level;
 497              l < path->locks_want && btree_path_node(path, l);
 498              l++) {
 499                 if (!bch2_btree_node_relock(trans, path, l)) {
 500                         __bch2_btree_path_unlock(trans, path);
 501                         btree_path_set_dirty(path, BTREE_ITER_NEED_TRAVERSE);
 502                         trace_and_count(trans->c, trans_restart_relock_path_intent, trans, _RET_IP_, path);
 503                         return btree_trans_restart(trans, BCH_ERR_transaction_restart_relock_path_intent);
 504                 }
 505         }
 506
 507         return 0;
 508 }
 509
 510 __flatten
 511 bool bch2_btree_path_relock_norestart(struct btree_trans *trans,
 512                         struct btree_path *path, unsigned long trace_ip)
 513 {
 514         return btree_path_get_locks(trans, path, false);
 515 }
 516
 517 __flatten
 518 bool bch2_btree_path_upgrade_norestart(struct btree_trans *trans,
 519                         struct btree_path *path, unsigned long trace_ip)
 520 {
 521         return btree_path_get_locks(trans, path, true);
 522 }
 523
 524 bool bch2_btree_path_upgrade_noupgrade_sibs(struct btree_trans *trans,
 525                                struct btree_path *path,
 526                                unsigned new_locks_want)
 527 {
 528         EBUG_ON(path->locks_want >= new_locks_want);
 529
 530         path->locks_want = new_locks_want;
 531
 532         return btree_path_get_locks(trans, path, true);
 533 }
 534
 535 bool __bch2_btree_path_upgrade(struct btree_trans *trans,
 536                                struct btree_path *path,
 537                                unsigned new_locks_want)
 538 {
 539         struct btree_path *linked;
 540
 541         if (bch2_btree_path_upgrade_noupgrade_sibs(trans, path, new_locks_want))
 542                 return true;
 543
 544         /*
 545          * XXX: this is ugly - we'd prefer to not be mucking with other
 546          * iterators in the btree_trans here.
 547          *
 548          * On failure to upgrade the iterator, setting iter->locks_want and
 549          * calling get_locks() is sufficient to make bch2_btree_path_traverse()
 550          * get the locks we want on transaction restart.
 551          *
 552          * But if this iterator was a clone, on transaction restart what we did
 553          * to this iterator isn't going to be preserved.
 554          *
 555          * Possibly we could add an iterator field for the parent iterator when
 556          * an iterator is a copy - for now, we'll just upgrade any other
 557          * iterators with the same btree id.
 558          *
 559          * The code below used to be needed to ensure ancestor nodes get locked
 560          * before interior nodes - now that's handled by
 561          * bch2_btree_path_traverse_all().
 562          */
 563         if (!path->cached && !trans->in_traverse_all)
 564                 trans_for_each_path(trans, linked)
 565                         if (linked != path &&
 566                             linked->cached == path->cached &&
 567                             linked->btree_id == path->btree_id &&
 568                             linked->locks_want < new_locks_want) {
 569                                 linked->locks_want = new_locks_want;
 570                                 btree_path_get_locks(trans, linked, true);
 571                         }
 572
 573         return false;
 574 }
 575
 576 void __bch2_btree_path_downgrade(struct btree_trans *trans,
 577                                  struct btree_path *path,
 578                                  unsigned new_locks_want)
 579 {
 580         unsigned l;
 581
 582         EBUG_ON(path->locks_want < new_locks_want);
 583
 584         path->locks_want = new_locks_want;
 585
 586         while (path->nodes_locked &&
 587                (l = btree_path_highest_level_locked(path)) >= path->locks_want) {
 588                 if (l > path->level) {
 589                         btree_node_unlock(trans, path, l);
 590                 } else {
 591                         if (btree_node_intent_locked(path, l)) {
 592                                 six_lock_downgrade(&path->l[l].b->c.lock);
 593                                 mark_btree_node_locked_noreset(path, l, SIX_LOCK_read);
 594                         }
 595                         break;
 596                 }
 597         }
 598
 599         bch2_btree_path_verify_locks(path);
 600 }
 601
 602 /* Btree transaction locking: */
 603
 604 void bch2_trans_downgrade(struct btree_trans *trans)
 605 {
 606         struct btree_path *path;
 607
 608         trans_for_each_path(trans, path)
 609                 bch2_btree_path_downgrade(trans, path);
 610 }
 611
 612 int bch2_trans_relock(struct btree_trans *trans)
 613 {
 614         struct btree_path *path;
 615
 616         if (unlikely(trans->restarted))
 617                 return -((int) trans->restarted);
 618
 619         trans_for_each_path(trans, path)
 620                 if (path->should_be_locked &&
 621                     !bch2_btree_path_relock_norestart(trans, path, _RET_IP_)) {
 622                         trace_and_count(trans->c, trans_restart_relock, trans, _RET_IP_, path);
 623                         return btree_trans_restart(trans, BCH_ERR_transaction_restart_relock);
 624                 }
 625         return 0;
 626 }
 627
 628 void bch2_trans_unlock(struct btree_trans *trans)
 629 {
 630         struct btree_path *path;
 631
 632         trans_for_each_path(trans, path)
 633                 __bch2_btree_path_unlock(trans, path);
 634
 635         /*
 636          * bch2_gc_btree_init_recurse() doesn't use btree iterators for walking
 637          * btree nodes, it implements its own walking:
 638          */
 639         EBUG_ON(!trans->is_initial_gc &&
 640                 lock_class_is_held(&bch2_btree_node_lock_key));
 641 }
 642
 643 bool bch2_trans_locked(struct btree_trans *trans)
 644 {
 645         struct btree_path *path;
 646
 647         trans_for_each_path(trans, path)
 648                 if (path->nodes_locked)
 649                         return true;
 650         return false;
 651 }
 652
 653 /* Debug */
 654
 655 #ifdef CONFIG_BCACHEFS_DEBUG
 656
 657 void bch2_btree_path_verify_locks(struct btree_path *path)
 658 {
 659         unsigned l;
 660
 661         if (!path->nodes_locked) {
 662                 BUG_ON(path->uptodate == BTREE_ITER_UPTODATE &&
 663                        btree_path_node(path, path->level));
 664                 return;
 665         }
 666
 667         for (l = 0; l < BTREE_MAX_DEPTH; l++) {
 668                 int want = btree_lock_want(path, l);
 669                 int have = btree_node_locked_type(path, l);
 670
 671                 BUG_ON(!is_btree_node(path, l) && have != BTREE_NODE_UNLOCKED);
 672
 673                 BUG_ON(is_btree_node(path, l) &&
 674                        (want == BTREE_NODE_UNLOCKED ||
 675                         have != BTREE_NODE_WRITE_LOCKED) &&
 676                        want != have);
 677         }
 678 }
 679
 680 void bch2_trans_verify_locks(struct btree_trans *trans)
 681 {
 682         struct btree_path *path;
 683
 684         trans_for_each_path(trans, path)
 685                 bch2_btree_path_verify_locks(path);
 686 }
 687
 688 #endif