kernel/bpf/bpf_local_storage.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Copyright (c) 2019 Facebook  */
   3 #include <linux/rculist.h>
   4 #include <linux/list.h>
   5 #include <linux/hash.h>
   6 #include <linux/types.h>
   7 #include <linux/spinlock.h>
   8 #include <linux/bpf.h>
   9 #include <linux/btf_ids.h>
  10 #include <linux/bpf_local_storage.h>
  11 #include <net/sock.h>
  12 #include <uapi/linux/sock_diag.h>
  13 #include <uapi/linux/btf.h>
  14 #include <linux/rcupdate.h>
  15 #include <linux/rcupdate_trace.h>
  16 #include <linux/rcupdate_wait.h>
  17
  18 #define BPF_LOCAL_STORAGE_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_CLONE)
  19
  20 static struct bpf_local_storage_map_bucket *
  21 select_bucket(struct bpf_local_storage_map *smap,
  22               struct bpf_local_storage_elem *selem)
  23 {
  24         return &smap->buckets[hash_ptr(selem, smap->bucket_log)];
  25 }
  26
  27 static int mem_charge(struct bpf_local_storage_map *smap, void *owner, u32 size)
  28 {
  29         struct bpf_map *map = &smap->map;
  30
  31         if (!map->ops->map_local_storage_charge)
  32                 return 0;
  33
  34         return map->ops->map_local_storage_charge(smap, owner, size);
  35 }
  36
  37 static void mem_uncharge(struct bpf_local_storage_map *smap, void *owner,
  38                          u32 size)
  39 {
  40         struct bpf_map *map = &smap->map;
  41
  42         if (map->ops->map_local_storage_uncharge)
  43                 map->ops->map_local_storage_uncharge(smap, owner, size);
  44 }
  45
  46 static struct bpf_local_storage __rcu **
  47 owner_storage(struct bpf_local_storage_map *smap, void *owner)
  48 {
  49         struct bpf_map *map = &smap->map;
  50
  51         return map->ops->map_owner_storage_ptr(owner);
  52 }
  53
  54 static bool selem_linked_to_storage_lockless(const struct bpf_local_storage_elem *selem)
  55 {
  56         return !hlist_unhashed_lockless(&selem->snode);
  57 }
  58
  59 static bool selem_linked_to_storage(const struct bpf_local_storage_elem *selem)
  60 {
  61         return !hlist_unhashed(&selem->snode);
  62 }
  63
  64 static bool selem_linked_to_map_lockless(const struct bpf_local_storage_elem *selem)
  65 {
  66         return !hlist_unhashed_lockless(&selem->map_node);
  67 }
  68
  69 static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
  70 {
  71         return !hlist_unhashed(&selem->map_node);
  72 }
  73
  74 struct bpf_local_storage_elem *
  75 bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
  76                 void *value, bool charge_mem, gfp_t gfp_flags)
  77 {
  78         struct bpf_local_storage_elem *selem;
  79
  80         if (charge_mem && mem_charge(smap, owner, smap->elem_size))
  81                 return NULL;
  82
  83         selem = bpf_map_kzalloc(&smap->map, smap->elem_size,
  84                                 gfp_flags | __GFP_NOWARN);
  85         if (selem) {
  86                 if (value)
  87                         copy_map_value(&smap->map, SDATA(selem)->data, value);
  88                 /* No need to call check_and_init_map_value as memory is zero init */
  89                 return selem;
  90         }
  91
  92         if (charge_mem)
  93                 mem_uncharge(smap, owner, smap->elem_size);
  94
  95         return NULL;
  96 }
  97
  98 static void bpf_local_storage_free_rcu(struct rcu_head *rcu)
  99 {
 100         struct bpf_local_storage *local_storage;
 101
 102         /* If RCU Tasks Trace grace period implies RCU grace period, do
 103          * kfree(), else do kfree_rcu().
 104          */
 105         local_storage = container_of(rcu, struct bpf_local_storage, rcu);
 106         if (rcu_trace_implies_rcu_gp())
 107                 kfree(local_storage);
 108         else
 109                 kfree_rcu(local_storage, rcu);
 110 }
 111
 112 static void bpf_selem_free_trace_rcu(struct rcu_head *rcu)
 113 {
 114         struct bpf_local_storage_elem *selem;
 115
 116         selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
 117         if (rcu_trace_implies_rcu_gp())
 118                 kfree(selem);
 119         else
 120                 kfree_rcu(selem, rcu);
 121 }
 122
 123 /* local_storage->lock must be held and selem->local_storage == local_storage.
 124  * The caller must ensure selem->smap is still valid to be
 125  * dereferenced for its smap->elem_size and smap->cache_idx.
 126  */
 127 static bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
 128                                             struct bpf_local_storage_elem *selem,
 129                                             bool uncharge_mem, bool reuse_now)
 130 {
 131         struct bpf_local_storage_map *smap;
 132         bool free_local_storage;
 133         void *owner;
 134
 135         smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());
 136         owner = local_storage->owner;
 137
 138         /* All uncharging on the owner must be done first.
 139          * The owner may be freed once the last selem is unlinked
 140          * from local_storage.
 141          */
 142         if (uncharge_mem)
 143                 mem_uncharge(smap, owner, smap->elem_size);
 144
 145         free_local_storage = hlist_is_singular_node(&selem->snode,
 146                                                     &local_storage->list);
 147         if (free_local_storage) {
 148                 mem_uncharge(smap, owner, sizeof(struct bpf_local_storage));
 149                 local_storage->owner = NULL;
 150
 151                 /* After this RCU_INIT, owner may be freed and cannot be used */
 152                 RCU_INIT_POINTER(*owner_storage(smap, owner), NULL);
 153
 154                 /* local_storage is not freed now.  local_storage->lock is
 155                  * still held and raw_spin_unlock_bh(&local_storage->lock)
 156                  * will be done by the caller.
 157                  *
 158                  * Although the unlock will be done under
 159                  * rcu_read_lock(),  it is more intuitive to
 160                  * read if the freeing of the storage is done
 161                  * after the raw_spin_unlock_bh(&local_storage->lock).
 162                  *
 163                  * Hence, a "bool free_local_storage" is returned
 164                  * to the caller which then calls then frees the storage after
 165                  * all the RCU grace periods have expired.
 166                  */
 167         }
 168         hlist_del_init_rcu(&selem->snode);
 169         if (rcu_access_pointer(local_storage->cache[smap->cache_idx]) ==
 170             SDATA(selem))
 171                 RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);
 172
 173         bpf_obj_free_fields(smap->map.record, SDATA(selem)->data);
 174         if (!reuse_now)
 175                 call_rcu_tasks_trace(&selem->rcu, bpf_selem_free_trace_rcu);
 176         else
 177                 kfree_rcu(selem, rcu);
 178
 179         if (rcu_access_pointer(local_storage->smap) == smap)
 180                 RCU_INIT_POINTER(local_storage->smap, NULL);
 181
 182         return free_local_storage;
 183 }
 184
 185 static void bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem,
 186                                      bool reuse_now)
 187 {
 188         struct bpf_local_storage *local_storage;
 189         bool free_local_storage = false;
 190         unsigned long flags;
 191
 192         if (unlikely(!selem_linked_to_storage_lockless(selem)))
 193                 /* selem has already been unlinked from sk */
 194                 return;
 195
 196         local_storage = rcu_dereference_check(selem->local_storage,
 197                                               bpf_rcu_lock_held());
 198         raw_spin_lock_irqsave(&local_storage->lock, flags);
 199         if (likely(selem_linked_to_storage(selem)))
 200                 free_local_storage = bpf_selem_unlink_storage_nolock(
 201                         local_storage, selem, true, reuse_now);
 202         raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 203
 204         if (free_local_storage) {
 205                 if (!reuse_now)
 206                         call_rcu_tasks_trace(&local_storage->rcu,
 207                                      bpf_local_storage_free_rcu);
 208                 else
 209                         kfree_rcu(local_storage, rcu);
 210         }
 211 }
 212
 213 void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
 214                                    struct bpf_local_storage_elem *selem)
 215 {
 216         RCU_INIT_POINTER(selem->local_storage, local_storage);
 217         hlist_add_head_rcu(&selem->snode, &local_storage->list);
 218 }
 219
 220 static void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
 221 {
 222         struct bpf_local_storage_map *smap;
 223         struct bpf_local_storage_map_bucket *b;
 224         unsigned long flags;
 225
 226         if (unlikely(!selem_linked_to_map_lockless(selem)))
 227                 /* selem has already be unlinked from smap */
 228                 return;
 229
 230         smap = rcu_dereference_check(SDATA(selem)->smap, bpf_rcu_lock_held());
 231         b = select_bucket(smap, selem);
 232         raw_spin_lock_irqsave(&b->lock, flags);
 233         if (likely(selem_linked_to_map(selem)))
 234                 hlist_del_init_rcu(&selem->map_node);
 235         raw_spin_unlock_irqrestore(&b->lock, flags);
 236 }
 237
 238 void bpf_selem_link_map(struct bpf_local_storage_map *smap,
 239                         struct bpf_local_storage_elem *selem)
 240 {
 241         struct bpf_local_storage_map_bucket *b = select_bucket(smap, selem);
 242         unsigned long flags;
 243
 244         raw_spin_lock_irqsave(&b->lock, flags);
 245         RCU_INIT_POINTER(SDATA(selem)->smap, smap);
 246         hlist_add_head_rcu(&selem->map_node, &b->list);
 247         raw_spin_unlock_irqrestore(&b->lock, flags);
 248 }
 249
 250 void bpf_selem_unlink(struct bpf_local_storage_elem *selem, bool reuse_now)
 251 {
 252         /* Always unlink from map before unlinking from local_storage
 253          * because selem will be freed after successfully unlinked from
 254          * the local_storage.
 255          */
 256         bpf_selem_unlink_map(selem);
 257         bpf_selem_unlink_storage(selem, reuse_now);
 258 }
 259
 260 /* If cacheit_lockit is false, this lookup function is lockless */
 261 struct bpf_local_storage_data *
 262 bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
 263                          struct bpf_local_storage_map *smap,
 264                          bool cacheit_lockit)
 265 {
 266         struct bpf_local_storage_data *sdata;
 267         struct bpf_local_storage_elem *selem;
 268
 269         /* Fast path (cache hit) */
 270         sdata = rcu_dereference_check(local_storage->cache[smap->cache_idx],
 271                                       bpf_rcu_lock_held());
 272         if (sdata && rcu_access_pointer(sdata->smap) == smap)
 273                 return sdata;
 274
 275         /* Slow path (cache miss) */
 276         hlist_for_each_entry_rcu(selem, &local_storage->list, snode,
 277                                   rcu_read_lock_trace_held())
 278                 if (rcu_access_pointer(SDATA(selem)->smap) == smap)
 279                         break;
 280
 281         if (!selem)
 282                 return NULL;
 283
 284         sdata = SDATA(selem);
 285         if (cacheit_lockit) {
 286                 unsigned long flags;
 287
 288                 /* spinlock is needed to avoid racing with the
 289                  * parallel delete.  Otherwise, publishing an already
 290                  * deleted sdata to the cache will become a use-after-free
 291                  * problem in the next bpf_local_storage_lookup().
 292                  */
 293                 raw_spin_lock_irqsave(&local_storage->lock, flags);
 294                 if (selem_linked_to_storage(selem))
 295                         rcu_assign_pointer(local_storage->cache[smap->cache_idx],
 296                                            sdata);
 297                 raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 298         }
 299
 300         return sdata;
 301 }
 302
 303 static int check_flags(const struct bpf_local_storage_data *old_sdata,
 304                        u64 map_flags)
 305 {
 306         if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
 307                 /* elem already exists */
 308                 return -EEXIST;
 309
 310         if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
 311                 /* elem doesn't exist, cannot update it */
 312                 return -ENOENT;
 313
 314         return 0;
 315 }
 316
 317 int bpf_local_storage_alloc(void *owner,
 318                             struct bpf_local_storage_map *smap,
 319                             struct bpf_local_storage_elem *first_selem,
 320                             gfp_t gfp_flags)
 321 {
 322         struct bpf_local_storage *prev_storage, *storage;
 323         struct bpf_local_storage **owner_storage_ptr;
 324         int err;
 325
 326         err = mem_charge(smap, owner, sizeof(*storage));
 327         if (err)
 328                 return err;
 329
 330         storage = bpf_map_kzalloc(&smap->map, sizeof(*storage),
 331                                   gfp_flags | __GFP_NOWARN);
 332         if (!storage) {
 333                 err = -ENOMEM;
 334                 goto uncharge;
 335         }
 336
 337         RCU_INIT_POINTER(storage->smap, smap);
 338         INIT_HLIST_HEAD(&storage->list);
 339         raw_spin_lock_init(&storage->lock);
 340         storage->owner = owner;
 341
 342         bpf_selem_link_storage_nolock(storage, first_selem);
 343         bpf_selem_link_map(smap, first_selem);
 344
 345         owner_storage_ptr =
 346                 (struct bpf_local_storage **)owner_storage(smap, owner);
 347         /* Publish storage to the owner.
 348          * Instead of using any lock of the kernel object (i.e. owner),
 349          * cmpxchg will work with any kernel object regardless what
 350          * the running context is, bh, irq...etc.
 351          *
 352          * From now on, the owner->storage pointer (e.g. sk->sk_bpf_storage)
 353          * is protected by the storage->lock.  Hence, when freeing
 354          * the owner->storage, the storage->lock must be held before
 355          * setting owner->storage ptr to NULL.
 356          */
 357         prev_storage = cmpxchg(owner_storage_ptr, NULL, storage);
 358         if (unlikely(prev_storage)) {
 359                 bpf_selem_unlink_map(first_selem);
 360                 err = -EAGAIN;
 361                 goto uncharge;
 362
 363                 /* Note that even first_selem was linked to smap's
 364                  * bucket->list, first_selem can be freed immediately
 365                  * (instead of kfree_rcu) because
 366                  * bpf_local_storage_map_free() does a
 367                  * synchronize_rcu_mult (waiting for both sleepable and
 368                  * normal programs) before walking the bucket->list.
 369                  * Hence, no one is accessing selem from the
 370                  * bucket->list under rcu_read_lock().
 371                  */
 372         }
 373
 374         return 0;
 375
 376 uncharge:
 377         kfree(storage);
 378         mem_uncharge(smap, owner, sizeof(*storage));
 379         return err;
 380 }
 381
 382 /* sk cannot be going away because it is linking new elem
 383  * to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
 384  * Otherwise, it will become a leak (and other memory issues
 385  * during map destruction).
 386  */
 387 struct bpf_local_storage_data *
 388 bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
 389                          void *value, u64 map_flags, gfp_t gfp_flags)
 390 {
 391         struct bpf_local_storage_data *old_sdata = NULL;
 392         struct bpf_local_storage_elem *selem = NULL;
 393         struct bpf_local_storage *local_storage;
 394         unsigned long flags;
 395         int err;
 396
 397         /* BPF_EXIST and BPF_NOEXIST cannot be both set */
 398         if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
 399             /* BPF_F_LOCK can only be used in a value with spin_lock */
 400             unlikely((map_flags & BPF_F_LOCK) &&
 401                      !btf_record_has_field(smap->map.record, BPF_SPIN_LOCK)))
 402                 return ERR_PTR(-EINVAL);
 403
 404         if (gfp_flags == GFP_KERNEL && (map_flags & ~BPF_F_LOCK) != BPF_NOEXIST)
 405                 return ERR_PTR(-EINVAL);
 406
 407         local_storage = rcu_dereference_check(*owner_storage(smap, owner),
 408                                               bpf_rcu_lock_held());
 409         if (!local_storage || hlist_empty(&local_storage->list)) {
 410                 /* Very first elem for the owner */
 411                 err = check_flags(NULL, map_flags);
 412                 if (err)
 413                         return ERR_PTR(err);
 414
 415                 selem = bpf_selem_alloc(smap, owner, value, true, gfp_flags);
 416                 if (!selem)
 417                         return ERR_PTR(-ENOMEM);
 418
 419                 err = bpf_local_storage_alloc(owner, smap, selem, gfp_flags);
 420                 if (err) {
 421                         kfree(selem);
 422                         mem_uncharge(smap, owner, smap->elem_size);
 423                         return ERR_PTR(err);
 424                 }
 425
 426                 return SDATA(selem);
 427         }
 428
 429         if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
 430                 /* Hoping to find an old_sdata to do inline update
 431                  * such that it can avoid taking the local_storage->lock
 432                  * and changing the lists.
 433                  */
 434                 old_sdata =
 435                         bpf_local_storage_lookup(local_storage, smap, false);
 436                 err = check_flags(old_sdata, map_flags);
 437                 if (err)
 438                         return ERR_PTR(err);
 439                 if (old_sdata && selem_linked_to_storage_lockless(SELEM(old_sdata))) {
 440                         copy_map_value_locked(&smap->map, old_sdata->data,
 441                                               value, false);
 442                         return old_sdata;
 443                 }
 444         }
 445
 446         if (gfp_flags == GFP_KERNEL) {
 447                 selem = bpf_selem_alloc(smap, owner, value, true, gfp_flags);
 448                 if (!selem)
 449                         return ERR_PTR(-ENOMEM);
 450         }
 451
 452         raw_spin_lock_irqsave(&local_storage->lock, flags);
 453
 454         /* Recheck local_storage->list under local_storage->lock */
 455         if (unlikely(hlist_empty(&local_storage->list))) {
 456                 /* A parallel del is happening and local_storage is going
 457                  * away.  It has just been checked before, so very
 458                  * unlikely.  Return instead of retry to keep things
 459                  * simple.
 460                  */
 461                 err = -EAGAIN;
 462                 goto unlock_err;
 463         }
 464
 465         old_sdata = bpf_local_storage_lookup(local_storage, smap, false);
 466         err = check_flags(old_sdata, map_flags);
 467         if (err)
 468                 goto unlock_err;
 469
 470         if (old_sdata && (map_flags & BPF_F_LOCK)) {
 471                 copy_map_value_locked(&smap->map, old_sdata->data, value,
 472                                       false);
 473                 selem = SELEM(old_sdata);
 474                 goto unlock;
 475         }
 476
 477         if (gfp_flags != GFP_KERNEL) {
 478                 /* local_storage->lock is held.  Hence, we are sure
 479                  * we can unlink and uncharge the old_sdata successfully
 480                  * later.  Hence, instead of charging the new selem now
 481                  * and then uncharge the old selem later (which may cause
 482                  * a potential but unnecessary charge failure),  avoid taking
 483                  * a charge at all here (the "!old_sdata" check) and the
 484                  * old_sdata will not be uncharged later during
 485                  * bpf_selem_unlink_storage_nolock().
 486                  */
 487                 selem = bpf_selem_alloc(smap, owner, value, !old_sdata, gfp_flags);
 488                 if (!selem) {
 489                         err = -ENOMEM;
 490                         goto unlock_err;
 491                 }
 492         }
 493
 494         /* First, link the new selem to the map */
 495         bpf_selem_link_map(smap, selem);
 496
 497         /* Second, link (and publish) the new selem to local_storage */
 498         bpf_selem_link_storage_nolock(local_storage, selem);
 499
 500         /* Third, remove old selem, SELEM(old_sdata) */
 501         if (old_sdata) {
 502                 bpf_selem_unlink_map(SELEM(old_sdata));
 503                 bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
 504                                                 false, false);
 505         }
 506
 507 unlock:
 508         raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 509         return SDATA(selem);
 510
 511 unlock_err:
 512         raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 513         if (selem) {
 514                 mem_uncharge(smap, owner, smap->elem_size);
 515                 kfree(selem);
 516         }
 517         return ERR_PTR(err);
 518 }
 519
 520 static u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
 521 {
 522         u64 min_usage = U64_MAX;
 523         u16 i, res = 0;
 524
 525         spin_lock(&cache->idx_lock);
 526
 527         for (i = 0; i < BPF_LOCAL_STORAGE_CACHE_SIZE; i++) {
 528                 if (cache->idx_usage_counts[i] < min_usage) {
 529                         min_usage = cache->idx_usage_counts[i];
 530                         res = i;
 531
 532                         /* Found a free cache_idx */
 533                         if (!min_usage)
 534                                 break;
 535                 }
 536         }
 537         cache->idx_usage_counts[res]++;
 538
 539         spin_unlock(&cache->idx_lock);
 540
 541         return res;
 542 }
 543
 544 static void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
 545                                              u16 idx)
 546 {
 547         spin_lock(&cache->idx_lock);
 548         cache->idx_usage_counts[idx]--;
 549         spin_unlock(&cache->idx_lock);
 550 }
 551
 552 int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
 553 {
 554         if (attr->map_flags & ~BPF_LOCAL_STORAGE_CREATE_FLAG_MASK ||
 555             !(attr->map_flags & BPF_F_NO_PREALLOC) ||
 556             attr->max_entries ||
 557             attr->key_size != sizeof(int) || !attr->value_size ||
 558             /* Enforce BTF for userspace sk dumping */
 559             !attr->btf_key_type_id || !attr->btf_value_type_id)
 560                 return -EINVAL;
 561
 562         if (!bpf_capable())
 563                 return -EPERM;
 564
 565         if (attr->value_size > BPF_LOCAL_STORAGE_MAX_VALUE_SIZE)
 566                 return -E2BIG;
 567
 568         return 0;
 569 }
 570
 571 int bpf_local_storage_map_check_btf(const struct bpf_map *map,
 572                                     const struct btf *btf,
 573                                     const struct btf_type *key_type,
 574                                     const struct btf_type *value_type)
 575 {
 576         u32 int_data;
 577
 578         if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
 579                 return -EINVAL;
 580
 581         int_data = *(u32 *)(key_type + 1);
 582         if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
 583                 return -EINVAL;
 584
 585         return 0;
 586 }
 587
 588 void bpf_local_storage_destroy(struct bpf_local_storage *local_storage)
 589 {
 590         struct bpf_local_storage_elem *selem;
 591         bool free_storage = false;
 592         struct hlist_node *n;
 593         unsigned long flags;
 594
 595         /* Neither the bpf_prog nor the bpf_map's syscall
 596          * could be modifying the local_storage->list now.
 597          * Thus, no elem can be added to or deleted from the
 598          * local_storage->list by the bpf_prog or by the bpf_map's syscall.
 599          *
 600          * It is racing with bpf_local_storage_map_free() alone
 601          * when unlinking elem from the local_storage->list and
 602          * the map's bucket->list.
 603          */
 604         raw_spin_lock_irqsave(&local_storage->lock, flags);
 605         hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
 606                 /* Always unlink from map before unlinking from
 607                  * local_storage.
 608                  */
 609                 bpf_selem_unlink_map(selem);
 610                 /* If local_storage list has only one element, the
 611                  * bpf_selem_unlink_storage_nolock() will return true.
 612                  * Otherwise, it will return false. The current loop iteration
 613                  * intends to remove all local storage. So the last iteration
 614                  * of the loop will set the free_cgroup_storage to true.
 615                  */
 616                 free_storage = bpf_selem_unlink_storage_nolock(
 617                         local_storage, selem, false, true);
 618         }
 619         raw_spin_unlock_irqrestore(&local_storage->lock, flags);
 620
 621         if (free_storage)
 622                 kfree_rcu(local_storage, rcu);
 623 }
 624
 625 u64 bpf_local_storage_map_mem_usage(const struct bpf_map *map)
 626 {
 627         struct bpf_local_storage_map *smap = (struct bpf_local_storage_map *)map;
 628         u64 usage = sizeof(*smap);
 629
 630         /* The dynamically callocated selems are not counted currently. */
 631         usage += sizeof(*smap->buckets) * (1ULL << smap->bucket_log);
 632         return usage;
 633 }
 634
 635 struct bpf_map *
 636 bpf_local_storage_map_alloc(union bpf_attr *attr,
 637                             struct bpf_local_storage_cache *cache)
 638 {
 639         struct bpf_local_storage_map *smap;
 640         unsigned int i;
 641         u32 nbuckets;
 642
 643         smap = bpf_map_area_alloc(sizeof(*smap), NUMA_NO_NODE);
 644         if (!smap)
 645                 return ERR_PTR(-ENOMEM);
 646         bpf_map_init_from_attr(&smap->map, attr);
 647
 648         nbuckets = roundup_pow_of_two(num_possible_cpus());
 649         /* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
 650         nbuckets = max_t(u32, 2, nbuckets);
 651         smap->bucket_log = ilog2(nbuckets);
 652
 653         smap->buckets = bpf_map_kvcalloc(&smap->map, sizeof(*smap->buckets),
 654                                          nbuckets, GFP_USER | __GFP_NOWARN);
 655         if (!smap->buckets) {
 656                 bpf_map_area_free(smap);
 657                 return ERR_PTR(-ENOMEM);
 658         }
 659
 660         for (i = 0; i < nbuckets; i++) {
 661                 INIT_HLIST_HEAD(&smap->buckets[i].list);
 662                 raw_spin_lock_init(&smap->buckets[i].lock);
 663         }
 664
 665         smap->elem_size = offsetof(struct bpf_local_storage_elem,
 666                                    sdata.data[attr->value_size]);
 667
 668         smap->cache_idx = bpf_local_storage_cache_idx_get(cache);
 669         return &smap->map;
 670 }
 671
 672 void bpf_local_storage_map_free(struct bpf_map *map,
 673                                 struct bpf_local_storage_cache *cache,
 674                                 int __percpu *busy_counter)
 675 {
 676         struct bpf_local_storage_map_bucket *b;
 677         struct bpf_local_storage_elem *selem;
 678         struct bpf_local_storage_map *smap;
 679         unsigned int i;
 680
 681         smap = (struct bpf_local_storage_map *)map;
 682         bpf_local_storage_cache_idx_free(cache, smap->cache_idx);
 683
 684         /* Note that this map might be concurrently cloned from
 685          * bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
 686          * RCU read section to finish before proceeding. New RCU
 687          * read sections should be prevented via bpf_map_inc_not_zero.
 688          */
 689         synchronize_rcu();
 690
 691         /* bpf prog and the userspace can no longer access this map
 692          * now.  No new selem (of this map) can be added
 693          * to the owner->storage or to the map bucket's list.
 694          *
 695          * The elem of this map can be cleaned up here
 696          * or when the storage is freed e.g.
 697          * by bpf_sk_storage_free() during __sk_destruct().
 698          */
 699         for (i = 0; i < (1U << smap->bucket_log); i++) {
 700                 b = &smap->buckets[i];
 701
 702                 rcu_read_lock();
 703                 /* No one is adding to b->list now */
 704                 while ((selem = hlist_entry_safe(
 705                                 rcu_dereference_raw(hlist_first_rcu(&b->list)),
 706                                 struct bpf_local_storage_elem, map_node))) {
 707                         if (busy_counter) {
 708                                 migrate_disable();
 709                                 this_cpu_inc(*busy_counter);
 710                         }
 711                         bpf_selem_unlink(selem, true);
 712                         if (busy_counter) {
 713                                 this_cpu_dec(*busy_counter);
 714                                 migrate_enable();
 715                         }
 716                         cond_resched_rcu();
 717                 }
 718                 rcu_read_unlock();
 719         }
 720
 721         /* While freeing the storage we may still need to access the map.
 722          *
 723          * e.g. when bpf_sk_storage_free() has unlinked selem from the map
 724          * which then made the above while((selem = ...)) loop
 725          * exit immediately.
 726          *
 727          * However, while freeing the storage one still needs to access the
 728          * smap->elem_size to do the uncharging in
 729          * bpf_selem_unlink_storage_nolock().
 730          *
 731          * Hence, wait another rcu grace period for the storage to be freed.
 732          */
 733         synchronize_rcu();
 734
 735         kvfree(smap->buckets);
 736         bpf_map_area_free(smap);
 737 }