kernel/bpf/stackmap.c

   1 /* Copyright (c) 2016 Facebook
   2  *
   3  * This program is free software; you can redistribute it and/or
   4  * modify it under the terms of version 2 of the GNU General Public
   5  * License as published by the Free Software Foundation.
   6  */
   7 #include <linux/bpf.h>
   8 #include <linux/jhash.h>
   9 #include <linux/filter.h>
  10 #include <linux/stacktrace.h>
  11 #include <linux/perf_event.h>
  12 #include <linux/elf.h>
  13 #include <linux/pagemap.h>
  14 #include <linux/irq_work.h>
  15 #include "percpu_freelist.h"
  16
  17 #define STACK_CREATE_FLAG_MASK                                  \
  18         (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY |        \
  19          BPF_F_STACK_BUILD_ID)
  20
  21 struct stack_map_bucket {
  22         struct pcpu_freelist_node fnode;
  23         u32 hash;
  24         u32 nr;
  25         u64 data[];
  26 };
  27
  28 struct bpf_stack_map {
  29         struct bpf_map map;
  30         void *elems;
  31         struct pcpu_freelist freelist;
  32         u32 n_buckets;
  33         struct stack_map_bucket *buckets[];
  34 };
  35
  36 /* irq_work to run up_read() for build_id lookup in nmi context */
  37 struct stack_map_irq_work {
  38         struct irq_work irq_work;
  39         struct rw_semaphore *sem;
  40 };
  41
  42 static void do_up_read(struct irq_work *entry)
  43 {
  44         struct stack_map_irq_work *work;
  45
  46         work = container_of(entry, struct stack_map_irq_work, irq_work);
  47         up_read(work->sem);
  48         work->sem = NULL;
  49 }
  50
  51 static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work);
  52
  53 static inline bool stack_map_use_build_id(struct bpf_map *map)
  54 {
  55         return (map->map_flags & BPF_F_STACK_BUILD_ID);
  56 }
  57
  58 static inline int stack_map_data_size(struct bpf_map *map)
  59 {
  60         return stack_map_use_build_id(map) ?
  61                 sizeof(struct bpf_stack_build_id) : sizeof(u64);
  62 }
  63
  64 static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
  65 {
  66         u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
  67         int err;
  68
  69         smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
  70                                          smap->map.numa_node);
  71         if (!smap->elems)
  72                 return -ENOMEM;
  73
  74         err = pcpu_freelist_init(&smap->freelist);
  75         if (err)
  76                 goto free_elems;
  77
  78         pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size,
  79                                smap->map.max_entries);
  80         return 0;
  81
  82 free_elems:
  83         bpf_map_area_free(smap->elems);
  84         return err;
  85 }
  86
  87 /* Called from syscall */
  88 static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
  89 {
  90         u32 value_size = attr->value_size;
  91         struct bpf_stack_map *smap;
  92         u64 cost, n_buckets;
  93         int err;
  94
  95         if (!capable(CAP_SYS_ADMIN))
  96                 return ERR_PTR(-EPERM);
  97
  98         if (attr->map_flags & ~STACK_CREATE_FLAG_MASK)
  99                 return ERR_PTR(-EINVAL);
 100
 101         /* check sanity of attributes */
 102         if (attr->max_entries == 0 || attr->key_size != 4 ||
 103             value_size < 8 || value_size % 8)
 104                 return ERR_PTR(-EINVAL);
 105
 106         BUILD_BUG_ON(sizeof(struct bpf_stack_build_id) % sizeof(u64));
 107         if (attr->map_flags & BPF_F_STACK_BUILD_ID) {
 108                 if (value_size % sizeof(struct bpf_stack_build_id) ||
 109                     value_size / sizeof(struct bpf_stack_build_id)
 110                     > sysctl_perf_event_max_stack)
 111                         return ERR_PTR(-EINVAL);
 112         } else if (value_size / 8 > sysctl_perf_event_max_stack)
 113                 return ERR_PTR(-EINVAL);
 114
 115         /* hash table size must be power of 2 */
 116         n_buckets = roundup_pow_of_two(attr->max_entries);
 117
 118         cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
 119         if (cost >= U32_MAX - PAGE_SIZE)
 120                 return ERR_PTR(-E2BIG);
 121
 122         smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr));
 123         if (!smap)
 124                 return ERR_PTR(-ENOMEM);
 125
 126         err = -E2BIG;
 127         cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
 128         if (cost >= U32_MAX - PAGE_SIZE)
 129                 goto free_smap;
 130
 131         bpf_map_init_from_attr(&smap->map, attr);
 132         smap->map.value_size = value_size;
 133         smap->n_buckets = n_buckets;
 134         smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
 135
 136         err = bpf_map_precharge_memlock(smap->map.pages);
 137         if (err)
 138                 goto free_smap;
 139
 140         err = get_callchain_buffers(sysctl_perf_event_max_stack);
 141         if (err)
 142                 goto free_smap;
 143
 144         err = prealloc_elems_and_freelist(smap);
 145         if (err)
 146                 goto put_buffers;
 147
 148         return &smap->map;
 149
 150 put_buffers:
 151         put_callchain_buffers();
 152 free_smap:
 153         bpf_map_area_free(smap);
 154         return ERR_PTR(err);
 155 }
 156
 157 #define BPF_BUILD_ID 3
 158 /*
 159  * Parse build id from the note segment. This logic can be shared between
 160  * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
 161  * identical.
 162  */
 163 static inline int stack_map_parse_build_id(void *page_addr,
 164                                            unsigned char *build_id,
 165                                            void *note_start,
 166                                            Elf32_Word note_size)
 167 {
 168         Elf32_Word note_offs = 0, new_offs;
 169
 170         /* check for overflow */
 171         if (note_start < page_addr || note_start + note_size < note_start)
 172                 return -EINVAL;
 173
 174         /* only supports note that fits in the first page */
 175         if (note_start + note_size > page_addr + PAGE_SIZE)
 176                 return -EINVAL;
 177
 178         while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
 179                 Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
 180
 181                 if (nhdr->n_type == BPF_BUILD_ID &&
 182                     nhdr->n_namesz == sizeof("GNU") &&
 183                     nhdr->n_descsz == BPF_BUILD_ID_SIZE) {
 184                         memcpy(build_id,
 185                                note_start + note_offs +
 186                                ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
 187                                BPF_BUILD_ID_SIZE);
 188                         return 0;
 189                 }
 190                 new_offs = note_offs + sizeof(Elf32_Nhdr) +
 191                         ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
 192                 if (new_offs <= note_offs)  /* overflow */
 193                         break;
 194                 note_offs = new_offs;
 195         }
 196         return -EINVAL;
 197 }
 198
 199 /* Parse build ID from 32-bit ELF */
 200 static int stack_map_get_build_id_32(void *page_addr,
 201                                      unsigned char *build_id)
 202 {
 203         Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
 204         Elf32_Phdr *phdr;
 205         int i;
 206
 207         /* only supports phdr that fits in one page */
 208         if (ehdr->e_phnum >
 209             (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
 210                 return -EINVAL;
 211
 212         phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
 213
 214         for (i = 0; i < ehdr->e_phnum; ++i)
 215                 if (phdr[i].p_type == PT_NOTE)
 216                         return stack_map_parse_build_id(page_addr, build_id,
 217                                         page_addr + phdr[i].p_offset,
 218                                         phdr[i].p_filesz);
 219         return -EINVAL;
 220 }
 221
 222 /* Parse build ID from 64-bit ELF */
 223 static int stack_map_get_build_id_64(void *page_addr,
 224                                      unsigned char *build_id)
 225 {
 226         Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
 227         Elf64_Phdr *phdr;
 228         int i;
 229
 230         /* only supports phdr that fits in one page */
 231         if (ehdr->e_phnum >
 232             (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
 233                 return -EINVAL;
 234
 235         phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
 236
 237         for (i = 0; i < ehdr->e_phnum; ++i)
 238                 if (phdr[i].p_type == PT_NOTE)
 239                         return stack_map_parse_build_id(page_addr, build_id,
 240                                         page_addr + phdr[i].p_offset,
 241                                         phdr[i].p_filesz);
 242         return -EINVAL;
 243 }
 244
 245 /* Parse build ID of ELF file mapped to vma */
 246 static int stack_map_get_build_id(struct vm_area_struct *vma,
 247                                   unsigned char *build_id)
 248 {
 249         Elf32_Ehdr *ehdr;
 250         struct page *page;
 251         void *page_addr;
 252         int ret;
 253
 254         /* only works for page backed storage  */
 255         if (!vma->vm_file)
 256                 return -EINVAL;
 257
 258         page = find_get_page(vma->vm_file->f_mapping, 0);
 259         if (!page)
 260                 return -EFAULT; /* page not mapped */
 261
 262         ret = -EINVAL;
 263         page_addr = page_address(page);
 264         ehdr = (Elf32_Ehdr *)page_addr;
 265
 266         /* compare magic x7f "ELF" */
 267         if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
 268                 goto out;
 269
 270         /* only support executable file and shared object file */
 271         if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
 272                 goto out;
 273
 274         if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
 275                 ret = stack_map_get_build_id_32(page_addr, build_id);
 276         else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
 277                 ret = stack_map_get_build_id_64(page_addr, build_id);
 278 out:
 279         put_page(page);
 280         return ret;
 281 }
 282
 283 static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
 284                                           u64 *ips, u32 trace_nr, bool user)
 285 {
 286         int i;
 287         struct vm_area_struct *vma;
 288         bool irq_work_busy = false;
 289         struct stack_map_irq_work *work = NULL;
 290
 291         if (in_nmi()) {
 292                 work = this_cpu_ptr(&up_read_work);
 293                 if (work->irq_work.flags & IRQ_WORK_BUSY)
 294                         /* cannot queue more up_read, fallback */
 295                         irq_work_busy = true;
 296         }
 297
 298         /*
 299          * We cannot do up_read() in nmi context. To do build_id lookup
 300          * in nmi context, we need to run up_read() in irq_work. We use
 301          * a percpu variable to do the irq_work. If the irq_work is
 302          * already used by another lookup, we fall back to report ips.
 303          *
 304          * Same fallback is used for kernel stack (!user) on a stackmap
 305          * with build_id.
 306          */
 307         if (!user || !current || !current->mm || irq_work_busy ||
 308             down_read_trylock(&current->mm->mmap_sem) == 0) {
 309                 /* cannot access current->mm, fall back to ips */
 310                 for (i = 0; i < trace_nr; i++) {
 311                         id_offs[i].status = BPF_STACK_BUILD_ID_IP;
 312                         id_offs[i].ip = ips[i];
 313                 }
 314                 return;
 315         }
 316
 317         for (i = 0; i < trace_nr; i++) {
 318                 vma = find_vma(current->mm, ips[i]);
 319                 if (!vma || stack_map_get_build_id(vma, id_offs[i].build_id)) {
 320                         /* per entry fall back to ips */
 321                         id_offs[i].status = BPF_STACK_BUILD_ID_IP;
 322                         id_offs[i].ip = ips[i];
 323                         continue;
 324                 }
 325                 id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i]
 326                         - vma->vm_start;
 327                 id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
 328         }
 329
 330         if (!work) {
 331                 up_read(&current->mm->mmap_sem);
 332         } else {
 333                 work->sem = &current->mm->mmap_sem;
 334                 irq_work_queue(&work->irq_work);
 335         }
 336 }
 337
 338 BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 339            u64, flags)
 340 {
 341         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 342         struct perf_callchain_entry *trace;
 343         struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
 344         u32 max_depth = map->value_size / stack_map_data_size(map);
 345         /* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */
 346         u32 init_nr = sysctl_perf_event_max_stack - max_depth;
 347         u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 348         u32 hash, id, trace_nr, trace_len;
 349         bool user = flags & BPF_F_USER_STACK;
 350         bool kernel = !user;
 351         u64 *ips;
 352         bool hash_matches;
 353
 354         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 355                                BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
 356                 return -EINVAL;
 357
 358         trace = get_perf_callchain(regs, init_nr, kernel, user,
 359                                    sysctl_perf_event_max_stack, false, false);
 360
 361         if (unlikely(!trace))
 362                 /* couldn't fetch the stack trace */
 363                 return -EFAULT;
 364
 365         /* get_perf_callchain() guarantees that trace->nr >= init_nr
 366          * and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth
 367          */
 368         trace_nr = trace->nr - init_nr;
 369
 370         if (trace_nr <= skip)
 371                 /* skipping more than usable stack trace */
 372                 return -EFAULT;
 373
 374         trace_nr -= skip;
 375         trace_len = trace_nr * sizeof(u64);
 376         ips = trace->ip + skip + init_nr;
 377         hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
 378         id = hash & (smap->n_buckets - 1);
 379         bucket = READ_ONCE(smap->buckets[id]);
 380
 381         hash_matches = bucket && bucket->hash == hash;
 382         /* fast cmp */
 383         if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
 384                 return id;
 385
 386         if (stack_map_use_build_id(map)) {
 387                 /* for build_id+offset, pop a bucket before slow cmp */
 388                 new_bucket = (struct stack_map_bucket *)
 389                         pcpu_freelist_pop(&smap->freelist);
 390                 if (unlikely(!new_bucket))
 391                         return -ENOMEM;
 392                 new_bucket->nr = trace_nr;
 393                 stack_map_get_build_id_offset(
 394                         (struct bpf_stack_build_id *)new_bucket->data,
 395                         ips, trace_nr, user);
 396                 trace_len = trace_nr * sizeof(struct bpf_stack_build_id);
 397                 if (hash_matches && bucket->nr == trace_nr &&
 398                     memcmp(bucket->data, new_bucket->data, trace_len) == 0) {
 399                         pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 400                         return id;
 401                 }
 402                 if (bucket && !(flags & BPF_F_REUSE_STACKID)) {
 403                         pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 404                         return -EEXIST;
 405                 }
 406         } else {
 407                 if (hash_matches && bucket->nr == trace_nr &&
 408                     memcmp(bucket->data, ips, trace_len) == 0)
 409                         return id;
 410                 if (bucket && !(flags & BPF_F_REUSE_STACKID))
 411                         return -EEXIST;
 412
 413                 new_bucket = (struct stack_map_bucket *)
 414                         pcpu_freelist_pop(&smap->freelist);
 415                 if (unlikely(!new_bucket))
 416                         return -ENOMEM;
 417                 memcpy(new_bucket->data, ips, trace_len);
 418         }
 419
 420         new_bucket->hash = hash;
 421         new_bucket->nr = trace_nr;
 422
 423         old_bucket = xchg(&smap->buckets[id], new_bucket);
 424         if (old_bucket)
 425                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 426         return id;
 427 }
 428
 429 const struct bpf_func_proto bpf_get_stackid_proto = {
 430         .func           = bpf_get_stackid,
 431         .gpl_only       = true,
 432         .ret_type       = RET_INTEGER,
 433         .arg1_type      = ARG_PTR_TO_CTX,
 434         .arg2_type      = ARG_CONST_MAP_PTR,
 435         .arg3_type      = ARG_ANYTHING,
 436 };
 437
 438 BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
 439            u64, flags)
 440 {
 441         u32 init_nr, trace_nr, copy_len, elem_size, num_elem;
 442         bool user_build_id = flags & BPF_F_USER_BUILD_ID;
 443         u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 444         bool user = flags & BPF_F_USER_STACK;
 445         struct perf_callchain_entry *trace;
 446         bool kernel = !user;
 447         int err = -EINVAL;
 448         u64 *ips;
 449
 450         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 451                                BPF_F_USER_BUILD_ID)))
 452                 goto clear;
 453         if (kernel && user_build_id)
 454                 goto clear;
 455
 456         elem_size = (user && user_build_id) ? sizeof(struct bpf_stack_build_id)
 457                                             : sizeof(u64);
 458         if (unlikely(size % elem_size))
 459                 goto clear;
 460
 461         num_elem = size / elem_size;
 462         if (sysctl_perf_event_max_stack < num_elem)
 463                 init_nr = 0;
 464         else
 465                 init_nr = sysctl_perf_event_max_stack - num_elem;
 466         trace = get_perf_callchain(regs, init_nr, kernel, user,
 467                                    sysctl_perf_event_max_stack, false, false);
 468         if (unlikely(!trace))
 469                 goto err_fault;
 470
 471         trace_nr = trace->nr - init_nr;
 472         if (trace_nr < skip)
 473                 goto err_fault;
 474
 475         trace_nr -= skip;
 476         trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
 477         copy_len = trace_nr * elem_size;
 478         ips = trace->ip + skip + init_nr;
 479         if (user && user_build_id)
 480                 stack_map_get_build_id_offset(buf, ips, trace_nr, user);
 481         else
 482                 memcpy(buf, ips, copy_len);
 483
 484         if (size > copy_len)
 485                 memset(buf + copy_len, 0, size - copy_len);
 486         return copy_len;
 487
 488 err_fault:
 489         err = -EFAULT;
 490 clear:
 491         memset(buf, 0, size);
 492         return err;
 493 }
 494
 495 const struct bpf_func_proto bpf_get_stack_proto = {
 496         .func           = bpf_get_stack,
 497         .gpl_only       = true,
 498         .ret_type       = RET_INTEGER,
 499         .arg1_type      = ARG_PTR_TO_CTX,
 500         .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
 501         .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
 502         .arg4_type      = ARG_ANYTHING,
 503 };
 504
 505 /* Called from eBPF program */
 506 static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
 507 {
 508         return ERR_PTR(-EOPNOTSUPP);
 509 }
 510
 511 /* Called from syscall */
 512 int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
 513 {
 514         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 515         struct stack_map_bucket *bucket, *old_bucket;
 516         u32 id = *(u32 *)key, trace_len;
 517
 518         if (unlikely(id >= smap->n_buckets))
 519                 return -ENOENT;
 520
 521         bucket = xchg(&smap->buckets[id], NULL);
 522         if (!bucket)
 523                 return -ENOENT;
 524
 525         trace_len = bucket->nr * stack_map_data_size(map);
 526         memcpy(value, bucket->data, trace_len);
 527         memset(value + trace_len, 0, map->value_size - trace_len);
 528
 529         old_bucket = xchg(&smap->buckets[id], bucket);
 530         if (old_bucket)
 531                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 532         return 0;
 533 }
 534
 535 static int stack_map_get_next_key(struct bpf_map *map, void *key,
 536                                   void *next_key)
 537 {
 538         struct bpf_stack_map *smap = container_of(map,
 539                                                   struct bpf_stack_map, map);
 540         u32 id;
 541
 542         WARN_ON_ONCE(!rcu_read_lock_held());
 543
 544         if (!key) {
 545                 id = 0;
 546         } else {
 547                 id = *(u32 *)key;
 548                 if (id >= smap->n_buckets || !smap->buckets[id])
 549                         id = 0;
 550                 else
 551                         id++;
 552         }
 553
 554         while (id < smap->n_buckets && !smap->buckets[id])
 555                 id++;
 556
 557         if (id >= smap->n_buckets)
 558                 return -ENOENT;
 559
 560         *(u32 *)next_key = id;
 561         return 0;
 562 }
 563
 564 static int stack_map_update_elem(struct bpf_map *map, void *key, void *value,
 565                                  u64 map_flags)
 566 {
 567         return -EINVAL;
 568 }
 569
 570 /* Called from syscall or from eBPF program */
 571 static int stack_map_delete_elem(struct bpf_map *map, void *key)
 572 {
 573         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 574         struct stack_map_bucket *old_bucket;
 575         u32 id = *(u32 *)key;
 576
 577         if (unlikely(id >= smap->n_buckets))
 578                 return -E2BIG;
 579
 580         old_bucket = xchg(&smap->buckets[id], NULL);
 581         if (old_bucket) {
 582                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 583                 return 0;
 584         } else {
 585                 return -ENOENT;
 586         }
 587 }
 588
 589 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
 590 static void stack_map_free(struct bpf_map *map)
 591 {
 592         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 593
 594         /* wait for bpf programs to complete before freeing stack map */
 595         synchronize_rcu();
 596
 597         bpf_map_area_free(smap->elems);
 598         pcpu_freelist_destroy(&smap->freelist);
 599         bpf_map_area_free(smap);
 600         put_callchain_buffers();
 601 }
 602
 603 const struct bpf_map_ops stack_trace_map_ops = {
 604         .map_alloc = stack_map_alloc,
 605         .map_free = stack_map_free,
 606         .map_get_next_key = stack_map_get_next_key,
 607         .map_lookup_elem = stack_map_lookup_elem,
 608         .map_update_elem = stack_map_update_elem,
 609         .map_delete_elem = stack_map_delete_elem,
 610         .map_check_btf = map_check_no_btf,
 611 };
 612
 613 static int __init stack_map_init(void)
 614 {
 615         int cpu;
 616         struct stack_map_irq_work *work;
 617
 618         for_each_possible_cpu(cpu) {
 619                 work = per_cpu_ptr(&up_read_work, cpu);
 620                 init_irq_work(&work->irq_work, do_up_read);
 621         }
 622         return 0;
 623 }
 624 subsys_initcall(stack_map_init);