kernel/bpf/stackmap.c

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This source file includes following definitions.
do_up_read
stack_map_use_build_id
stack_map_data_size
prealloc_elems_and_freelist
stack_map_alloc
stack_map_parse_build_id
stack_map_get_build_id_32
stack_map_get_build_id_64
stack_map_get_build_id
stack_map_get_build_id_offset
BPF_CALL_3
BPF_CALL_4
stack_map_lookup_elem
bpf_stackmap_copy
stack_map_get_next_key
stack_map_update_elem
stack_map_delete_elem
stack_map_free
stack_map_init
   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* Copyright (c) 2016 Facebook
   3  */
   4 #include <linux/bpf.h>
   5 #include <linux/jhash.h>
   6 #include <linux/filter.h>
   7 #include <linux/stacktrace.h>
   8 #include <linux/perf_event.h>
   9 #include <linux/elf.h>
  10 #include <linux/pagemap.h>
  11 #include <linux/irq_work.h>
  12 #include "percpu_freelist.h"
  13 
  14 #define STACK_CREATE_FLAG_MASK                                  \
  15         (BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY |        \
  16          BPF_F_STACK_BUILD_ID)
  17 
  18 struct stack_map_bucket {
  19         struct pcpu_freelist_node fnode;
  20         u32 hash;
  21         u32 nr;
  22         u64 data[];
  23 };
  24 
  25 struct bpf_stack_map {
  26         struct bpf_map map;
  27         void *elems;
  28         struct pcpu_freelist freelist;
  29         u32 n_buckets;
  30         struct stack_map_bucket *buckets[];
  31 };
  32 
  33 /* irq_work to run up_read() for build_id lookup in nmi context */
  34 struct stack_map_irq_work {
  35         struct irq_work irq_work;
  36         struct rw_semaphore *sem;
  37 };
  38 
  39 static void do_up_read(struct irq_work *entry)
  40 {
  41         struct stack_map_irq_work *work;
  42 
  43         work = container_of(entry, struct stack_map_irq_work, irq_work);
  44         up_read_non_owner(work->sem);
  45         work->sem = NULL;
  46 }
  47 
  48 static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work);
  49 
  50 static inline bool stack_map_use_build_id(struct bpf_map *map)
  51 {
  52         return (map->map_flags & BPF_F_STACK_BUILD_ID);
  53 }
  54 
  55 static inline int stack_map_data_size(struct bpf_map *map)
  56 {
  57         return stack_map_use_build_id(map) ?
  58                 sizeof(struct bpf_stack_build_id) : sizeof(u64);
  59 }
  60 
  61 static int prealloc_elems_and_freelist(struct bpf_stack_map *smap)
  62 {
  63         u32 elem_size = sizeof(struct stack_map_bucket) + smap->map.value_size;
  64         int err;
  65 
  66         smap->elems = bpf_map_area_alloc(elem_size * smap->map.max_entries,
  67                                          smap->map.numa_node);
  68         if (!smap->elems)
  69                 return -ENOMEM;
  70 
  71         err = pcpu_freelist_init(&smap->freelist);
  72         if (err)
  73                 goto free_elems;
  74 
  75         pcpu_freelist_populate(&smap->freelist, smap->elems, elem_size,
  76                                smap->map.max_entries);
  77         return 0;
  78 
  79 free_elems:
  80         bpf_map_area_free(smap->elems);
  81         return err;
  82 }
  83 
  84 /* Called from syscall */
  85 static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
  86 {
  87         u32 value_size = attr->value_size;
  88         struct bpf_stack_map *smap;
  89         struct bpf_map_memory mem;
  90         u64 cost, n_buckets;
  91         int err;
  92 
  93         if (!capable(CAP_SYS_ADMIN))
  94                 return ERR_PTR(-EPERM);
  95 
  96         if (attr->map_flags & ~STACK_CREATE_FLAG_MASK)
  97                 return ERR_PTR(-EINVAL);
  98 
  99         /* check sanity of attributes */
 100         if (attr->max_entries == 0 || attr->key_size != 4 ||
 101             value_size < 8 || value_size % 8)
 102                 return ERR_PTR(-EINVAL);
 103 
 104         BUILD_BUG_ON(sizeof(struct bpf_stack_build_id) % sizeof(u64));
 105         if (attr->map_flags & BPF_F_STACK_BUILD_ID) {
 106                 if (value_size % sizeof(struct bpf_stack_build_id) ||
 107                     value_size / sizeof(struct bpf_stack_build_id)
 108                     > sysctl_perf_event_max_stack)
 109                         return ERR_PTR(-EINVAL);
 110         } else if (value_size / 8 > sysctl_perf_event_max_stack)
 111                 return ERR_PTR(-EINVAL);
 112 
 113         /* hash table size must be power of 2 */
 114         n_buckets = roundup_pow_of_two(attr->max_entries);
 115 
 116         cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
 117         cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
 118         err = bpf_map_charge_init(&mem, cost);
 119         if (err)
 120                 return ERR_PTR(err);
 121 
 122         smap = bpf_map_area_alloc(cost, bpf_map_attr_numa_node(attr));
 123         if (!smap) {
 124                 bpf_map_charge_finish(&mem);
 125                 return ERR_PTR(-ENOMEM);
 126         }
 127 
 128         bpf_map_init_from_attr(&smap->map, attr);
 129         smap->map.value_size = value_size;
 130         smap->n_buckets = n_buckets;
 131 
 132         err = get_callchain_buffers(sysctl_perf_event_max_stack);
 133         if (err)
 134                 goto free_charge;
 135 
 136         err = prealloc_elems_and_freelist(smap);
 137         if (err)
 138                 goto put_buffers;
 139 
 140         bpf_map_charge_move(&smap->map.memory, &mem);
 141 
 142         return &smap->map;
 143 
 144 put_buffers:
 145         put_callchain_buffers();
 146 free_charge:
 147         bpf_map_charge_finish(&mem);
 148         bpf_map_area_free(smap);
 149         return ERR_PTR(err);
 150 }
 151 
 152 #define BPF_BUILD_ID 3
 153 /*
 154  * Parse build id from the note segment. This logic can be shared between
 155  * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
 156  * identical.
 157  */
 158 static inline int stack_map_parse_build_id(void *page_addr,
 159                                            unsigned char *build_id,
 160                                            void *note_start,
 161                                            Elf32_Word note_size)
 162 {
 163         Elf32_Word note_offs = 0, new_offs;
 164 
 165         /* check for overflow */
 166         if (note_start < page_addr || note_start + note_size < note_start)
 167                 return -EINVAL;
 168 
 169         /* only supports note that fits in the first page */
 170         if (note_start + note_size > page_addr + PAGE_SIZE)
 171                 return -EINVAL;
 172 
 173         while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
 174                 Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
 175 
 176                 if (nhdr->n_type == BPF_BUILD_ID &&
 177                     nhdr->n_namesz == sizeof("GNU") &&
 178                     nhdr->n_descsz > 0 &&
 179                     nhdr->n_descsz <= BPF_BUILD_ID_SIZE) {
 180                         memcpy(build_id,
 181                                note_start + note_offs +
 182                                ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
 183                                nhdr->n_descsz);
 184                         memset(build_id + nhdr->n_descsz, 0,
 185                                BPF_BUILD_ID_SIZE - nhdr->n_descsz);
 186                         return 0;
 187                 }
 188                 new_offs = note_offs + sizeof(Elf32_Nhdr) +
 189                         ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
 190                 if (new_offs <= note_offs)  /* overflow */
 191                         break;
 192                 note_offs = new_offs;
 193         }
 194         return -EINVAL;
 195 }
 196 
 197 /* Parse build ID from 32-bit ELF */
 198 static int stack_map_get_build_id_32(void *page_addr,
 199                                      unsigned char *build_id)
 200 {
 201         Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
 202         Elf32_Phdr *phdr;
 203         int i;
 204 
 205         /* only supports phdr that fits in one page */
 206         if (ehdr->e_phnum >
 207             (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
 208                 return -EINVAL;
 209 
 210         phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
 211 
 212         for (i = 0; i < ehdr->e_phnum; ++i)
 213                 if (phdr[i].p_type == PT_NOTE)
 214                         return stack_map_parse_build_id(page_addr, build_id,
 215                                         page_addr + phdr[i].p_offset,
 216                                         phdr[i].p_filesz);
 217         return -EINVAL;
 218 }
 219 
 220 /* Parse build ID from 64-bit ELF */
 221 static int stack_map_get_build_id_64(void *page_addr,
 222                                      unsigned char *build_id)
 223 {
 224         Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
 225         Elf64_Phdr *phdr;
 226         int i;
 227 
 228         /* only supports phdr that fits in one page */
 229         if (ehdr->e_phnum >
 230             (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
 231                 return -EINVAL;
 232 
 233         phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
 234 
 235         for (i = 0; i < ehdr->e_phnum; ++i)
 236                 if (phdr[i].p_type == PT_NOTE)
 237                         return stack_map_parse_build_id(page_addr, build_id,
 238                                         page_addr + phdr[i].p_offset,
 239                                         phdr[i].p_filesz);
 240         return -EINVAL;
 241 }
 242 
 243 /* Parse build ID of ELF file mapped to vma */
 244 static int stack_map_get_build_id(struct vm_area_struct *vma,
 245                                   unsigned char *build_id)
 246 {
 247         Elf32_Ehdr *ehdr;
 248         struct page *page;
 249         void *page_addr;
 250         int ret;
 251 
 252         /* only works for page backed storage  */
 253         if (!vma->vm_file)
 254                 return -EINVAL;
 255 
 256         page = find_get_page(vma->vm_file->f_mapping, 0);
 257         if (!page)
 258                 return -EFAULT; /* page not mapped */
 259 
 260         ret = -EINVAL;
 261         page_addr = kmap_atomic(page);
 262         ehdr = (Elf32_Ehdr *)page_addr;
 263 
 264         /* compare magic x7f "ELF" */
 265         if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
 266                 goto out;
 267 
 268         /* only support executable file and shared object file */
 269         if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
 270                 goto out;
 271 
 272         if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
 273                 ret = stack_map_get_build_id_32(page_addr, build_id);
 274         else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
 275                 ret = stack_map_get_build_id_64(page_addr, build_id);
 276 out:
 277         kunmap_atomic(page_addr);
 278         put_page(page);
 279         return ret;
 280 }
 281 
 282 static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
 283                                           u64 *ips, u32 trace_nr, bool user)
 284 {
 285         int i;
 286         struct vm_area_struct *vma;
 287         bool irq_work_busy = false;
 288         struct stack_map_irq_work *work = NULL;
 289 
 290         if (irqs_disabled()) {
 291                 work = this_cpu_ptr(&up_read_work);
 292                 if (work->irq_work.flags & IRQ_WORK_BUSY)
 293                         /* cannot queue more up_read, fallback */
 294                         irq_work_busy = true;
 295         }
 296 
 297         /*
 298          * We cannot do up_read() when the irq is disabled, because of
 299          * risk to deadlock with rq_lock. To do build_id lookup when the
 300          * irqs are disabled, 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                         memset(id_offs[i].build_id, 0, BPF_BUILD_ID_SIZE);
 314                 }
 315                 return;
 316         }
 317 
 318         for (i = 0; i < trace_nr; i++) {
 319                 vma = find_vma(current->mm, ips[i]);
 320                 if (!vma || stack_map_get_build_id(vma, id_offs[i].build_id)) {
 321                         /* per entry fall back to ips */
 322                         id_offs[i].status = BPF_STACK_BUILD_ID_IP;
 323                         id_offs[i].ip = ips[i];
 324                         memset(id_offs[i].build_id, 0, BPF_BUILD_ID_SIZE);
 325                         continue;
 326                 }
 327                 id_offs[i].offset = (vma->vm_pgoff << PAGE_SHIFT) + ips[i]
 328                         - vma->vm_start;
 329                 id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
 330         }
 331 
 332         if (!work) {
 333                 up_read(&current->mm->mmap_sem);
 334         } else {
 335                 work->sem = &current->mm->mmap_sem;
 336                 irq_work_queue(&work->irq_work);
 337                 /*
 338                  * The irq_work will release the mmap_sem with
 339                  * up_read_non_owner(). The rwsem_release() is called
 340                  * here to release the lock from lockdep's perspective.
 341                  */
 342                 rwsem_release(&current->mm->mmap_sem.dep_map, 1, _RET_IP_);
 343         }
 344 }
 345 
 346 BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
 347            u64, flags)
 348 {
 349         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 350         struct perf_callchain_entry *trace;
 351         struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
 352         u32 max_depth = map->value_size / stack_map_data_size(map);
 353         /* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */
 354         u32 init_nr = sysctl_perf_event_max_stack - max_depth;
 355         u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 356         u32 hash, id, trace_nr, trace_len;
 357         bool user = flags & BPF_F_USER_STACK;
 358         bool kernel = !user;
 359         u64 *ips;
 360         bool hash_matches;
 361 
 362         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 363                                BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
 364                 return -EINVAL;
 365 
 366         trace = get_perf_callchain(regs, init_nr, kernel, user,
 367                                    sysctl_perf_event_max_stack, false, false);
 368 
 369         if (unlikely(!trace))
 370                 /* couldn't fetch the stack trace */
 371                 return -EFAULT;
 372 
 373         /* get_perf_callchain() guarantees that trace->nr >= init_nr
 374          * and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth
 375          */
 376         trace_nr = trace->nr - init_nr;
 377 
 378         if (trace_nr <= skip)
 379                 /* skipping more than usable stack trace */
 380                 return -EFAULT;
 381 
 382         trace_nr -= skip;
 383         trace_len = trace_nr * sizeof(u64);
 384         ips = trace->ip + skip + init_nr;
 385         hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
 386         id = hash & (smap->n_buckets - 1);
 387         bucket = READ_ONCE(smap->buckets[id]);
 388 
 389         hash_matches = bucket && bucket->hash == hash;
 390         /* fast cmp */
 391         if (hash_matches && flags & BPF_F_FAST_STACK_CMP)
 392                 return id;
 393 
 394         if (stack_map_use_build_id(map)) {
 395                 /* for build_id+offset, pop a bucket before slow cmp */
 396                 new_bucket = (struct stack_map_bucket *)
 397                         pcpu_freelist_pop(&smap->freelist);
 398                 if (unlikely(!new_bucket))
 399                         return -ENOMEM;
 400                 new_bucket->nr = trace_nr;
 401                 stack_map_get_build_id_offset(
 402                         (struct bpf_stack_build_id *)new_bucket->data,
 403                         ips, trace_nr, user);
 404                 trace_len = trace_nr * sizeof(struct bpf_stack_build_id);
 405                 if (hash_matches && bucket->nr == trace_nr &&
 406                     memcmp(bucket->data, new_bucket->data, trace_len) == 0) {
 407                         pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 408                         return id;
 409                 }
 410                 if (bucket && !(flags & BPF_F_REUSE_STACKID)) {
 411                         pcpu_freelist_push(&smap->freelist, &new_bucket->fnode);
 412                         return -EEXIST;
 413                 }
 414         } else {
 415                 if (hash_matches && bucket->nr == trace_nr &&
 416                     memcmp(bucket->data, ips, trace_len) == 0)
 417                         return id;
 418                 if (bucket && !(flags & BPF_F_REUSE_STACKID))
 419                         return -EEXIST;
 420 
 421                 new_bucket = (struct stack_map_bucket *)
 422                         pcpu_freelist_pop(&smap->freelist);
 423                 if (unlikely(!new_bucket))
 424                         return -ENOMEM;
 425                 memcpy(new_bucket->data, ips, trace_len);
 426         }
 427 
 428         new_bucket->hash = hash;
 429         new_bucket->nr = trace_nr;
 430 
 431         old_bucket = xchg(&smap->buckets[id], new_bucket);
 432         if (old_bucket)
 433                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 434         return id;
 435 }
 436 
 437 const struct bpf_func_proto bpf_get_stackid_proto = {
 438         .func           = bpf_get_stackid,
 439         .gpl_only       = true,
 440         .ret_type       = RET_INTEGER,
 441         .arg1_type      = ARG_PTR_TO_CTX,
 442         .arg2_type      = ARG_CONST_MAP_PTR,
 443         .arg3_type      = ARG_ANYTHING,
 444 };
 445 
 446 BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
 447            u64, flags)
 448 {
 449         u32 init_nr, trace_nr, copy_len, elem_size, num_elem;
 450         bool user_build_id = flags & BPF_F_USER_BUILD_ID;
 451         u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
 452         bool user = flags & BPF_F_USER_STACK;
 453         struct perf_callchain_entry *trace;
 454         bool kernel = !user;
 455         int err = -EINVAL;
 456         u64 *ips;
 457 
 458         if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
 459                                BPF_F_USER_BUILD_ID)))
 460                 goto clear;
 461         if (kernel && user_build_id)
 462                 goto clear;
 463 
 464         elem_size = (user && user_build_id) ? sizeof(struct bpf_stack_build_id)
 465                                             : sizeof(u64);
 466         if (unlikely(size % elem_size))
 467                 goto clear;
 468 
 469         num_elem = size / elem_size;
 470         if (sysctl_perf_event_max_stack < num_elem)
 471                 init_nr = 0;
 472         else
 473                 init_nr = sysctl_perf_event_max_stack - num_elem;
 474         trace = get_perf_callchain(regs, init_nr, kernel, user,
 475                                    sysctl_perf_event_max_stack, false, false);
 476         if (unlikely(!trace))
 477                 goto err_fault;
 478 
 479         trace_nr = trace->nr - init_nr;
 480         if (trace_nr < skip)
 481                 goto err_fault;
 482 
 483         trace_nr -= skip;
 484         trace_nr = (trace_nr <= num_elem) ? trace_nr : num_elem;
 485         copy_len = trace_nr * elem_size;
 486         ips = trace->ip + skip + init_nr;
 487         if (user && user_build_id)
 488                 stack_map_get_build_id_offset(buf, ips, trace_nr, user);
 489         else
 490                 memcpy(buf, ips, copy_len);
 491 
 492         if (size > copy_len)
 493                 memset(buf + copy_len, 0, size - copy_len);
 494         return copy_len;
 495 
 496 err_fault:
 497         err = -EFAULT;
 498 clear:
 499         memset(buf, 0, size);
 500         return err;
 501 }
 502 
 503 const struct bpf_func_proto bpf_get_stack_proto = {
 504         .func           = bpf_get_stack,
 505         .gpl_only       = true,
 506         .ret_type       = RET_INTEGER,
 507         .arg1_type      = ARG_PTR_TO_CTX,
 508         .arg2_type      = ARG_PTR_TO_UNINIT_MEM,
 509         .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
 510         .arg4_type      = ARG_ANYTHING,
 511 };
 512 
 513 /* Called from eBPF program */
 514 static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
 515 {
 516         return ERR_PTR(-EOPNOTSUPP);
 517 }
 518 
 519 /* Called from syscall */
 520 int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
 521 {
 522         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 523         struct stack_map_bucket *bucket, *old_bucket;
 524         u32 id = *(u32 *)key, trace_len;
 525 
 526         if (unlikely(id >= smap->n_buckets))
 527                 return -ENOENT;
 528 
 529         bucket = xchg(&smap->buckets[id], NULL);
 530         if (!bucket)
 531                 return -ENOENT;
 532 
 533         trace_len = bucket->nr * stack_map_data_size(map);
 534         memcpy(value, bucket->data, trace_len);
 535         memset(value + trace_len, 0, map->value_size - trace_len);
 536 
 537         old_bucket = xchg(&smap->buckets[id], bucket);
 538         if (old_bucket)
 539                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 540         return 0;
 541 }
 542 
 543 static int stack_map_get_next_key(struct bpf_map *map, void *key,
 544                                   void *next_key)
 545 {
 546         struct bpf_stack_map *smap = container_of(map,
 547                                                   struct bpf_stack_map, map);
 548         u32 id;
 549 
 550         WARN_ON_ONCE(!rcu_read_lock_held());
 551 
 552         if (!key) {
 553                 id = 0;
 554         } else {
 555                 id = *(u32 *)key;
 556                 if (id >= smap->n_buckets || !smap->buckets[id])
 557                         id = 0;
 558                 else
 559                         id++;
 560         }
 561 
 562         while (id < smap->n_buckets && !smap->buckets[id])
 563                 id++;
 564 
 565         if (id >= smap->n_buckets)
 566                 return -ENOENT;
 567 
 568         *(u32 *)next_key = id;
 569         return 0;
 570 }
 571 
 572 static int stack_map_update_elem(struct bpf_map *map, void *key, void *value,
 573                                  u64 map_flags)
 574 {
 575         return -EINVAL;
 576 }
 577 
 578 /* Called from syscall or from eBPF program */
 579 static int stack_map_delete_elem(struct bpf_map *map, void *key)
 580 {
 581         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 582         struct stack_map_bucket *old_bucket;
 583         u32 id = *(u32 *)key;
 584 
 585         if (unlikely(id >= smap->n_buckets))
 586                 return -E2BIG;
 587 
 588         old_bucket = xchg(&smap->buckets[id], NULL);
 589         if (old_bucket) {
 590                 pcpu_freelist_push(&smap->freelist, &old_bucket->fnode);
 591                 return 0;
 592         } else {
 593                 return -ENOENT;
 594         }
 595 }
 596 
 597 /* Called when map->refcnt goes to zero, either from workqueue or from syscall */
 598 static void stack_map_free(struct bpf_map *map)
 599 {
 600         struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
 601 
 602         /* wait for bpf programs to complete before freeing stack map */
 603         synchronize_rcu();
 604 
 605         bpf_map_area_free(smap->elems);
 606         pcpu_freelist_destroy(&smap->freelist);
 607         bpf_map_area_free(smap);
 608         put_callchain_buffers();
 609 }
 610 
 611 const struct bpf_map_ops stack_trace_map_ops = {
 612         .map_alloc = stack_map_alloc,
 613         .map_free = stack_map_free,
 614         .map_get_next_key = stack_map_get_next_key,
 615         .map_lookup_elem = stack_map_lookup_elem,
 616         .map_update_elem = stack_map_update_elem,
 617         .map_delete_elem = stack_map_delete_elem,
 618         .map_check_btf = map_check_no_btf,
 619 };
 620 
 621 static int __init stack_map_init(void)
 622 {
 623         int cpu;
 624         struct stack_map_irq_work *work;
 625 
 626         for_each_possible_cpu(cpu) {
 627                 work = per_cpu_ptr(&up_read_work, cpu);
 628                 init_irq_work(&work->irq_work, do_up_read);
 629         }
 630         return 0;
 631 }
 632 subsys_initcall(stack_map_init);
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root/kernel/bpf/stackmap.c

DEFINITIONS
