kernel/events/hw_breakpoint.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * Copyright (C) 2007 Alan Stern
   4  * Copyright (C) IBM Corporation, 2009
   5  * Copyright (C) 2009, Frederic Weisbecker <fweisbec@gmail.com>
   6  *
   7  * Thanks to Ingo Molnar for his many suggestions.
   8  *
   9  * Authors: Alan Stern <stern@rowland.harvard.edu>
  10  *          K.Prasad <prasad@linux.vnet.ibm.com>
  11  *          Frederic Weisbecker <fweisbec@gmail.com>
  12  */
  13
  14 /*
  15  * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
  16  * using the CPU's debug registers.
  17  * This file contains the arch-independent routines.
  18  */
  19
  20 #include <linux/irqflags.h>
  21 #include <linux/kallsyms.h>
  22 #include <linux/notifier.h>
  23 #include <linux/kprobes.h>
  24 #include <linux/kdebug.h>
  25 #include <linux/kernel.h>
  26 #include <linux/module.h>
  27 #include <linux/percpu.h>
  28 #include <linux/sched.h>
  29 #include <linux/init.h>
  30 #include <linux/slab.h>
  31 #include <linux/list.h>
  32 #include <linux/cpu.h>
  33 #include <linux/smp.h>
  34 #include <linux/bug.h>
  35
  36 #include <linux/hw_breakpoint.h>
  37 /*
  38  * Constraints data
  39  */
  40 struct bp_cpuinfo {
  41         /* Number of pinned cpu breakpoints in a cpu */
  42         unsigned int    cpu_pinned;
  43         /* tsk_pinned[n] is the number of tasks having n+1 breakpoints */
  44         unsigned int    *tsk_pinned;
  45         /* Number of non-pinned cpu/task breakpoints in a cpu */
  46         unsigned int    flexible; /* XXX: placeholder, see fetch_this_slot() */
  47 };
  48
  49 static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
  50 static int nr_slots[TYPE_MAX];
  51
  52 static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
  53 {
  54         return per_cpu_ptr(bp_cpuinfo + type, cpu);
  55 }
  56
  57 /* Keep track of the breakpoints attached to tasks */
  58 static LIST_HEAD(bp_task_head);
  59
  60 static int constraints_initialized;
  61
  62 /* Gather the number of total pinned and un-pinned bp in a cpuset */
  63 struct bp_busy_slots {
  64         unsigned int pinned;
  65         unsigned int flexible;
  66 };
  67
  68 /* Serialize accesses to the above constraints */
  69 static DEFINE_MUTEX(nr_bp_mutex);
  70
  71 __weak int hw_breakpoint_weight(struct perf_event *bp)
  72 {
  73         return 1;
  74 }
  75
  76 static inline enum bp_type_idx find_slot_idx(u64 bp_type)
  77 {
  78         if (bp_type & HW_BREAKPOINT_RW)
  79                 return TYPE_DATA;
  80
  81         return TYPE_INST;
  82 }
  83
  84 /*
  85  * Report the maximum number of pinned breakpoints a task
  86  * have in this cpu
  87  */
  88 static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
  89 {
  90         unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
  91         int i;
  92
  93         for (i = nr_slots[type] - 1; i >= 0; i--) {
  94                 if (tsk_pinned[i] > 0)
  95                         return i + 1;
  96         }
  97
  98         return 0;
  99 }
 100
 101 /*
 102  * Count the number of breakpoints of the same type and same task.
 103  * The given event must be not on the list.
 104  */
 105 static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
 106 {
 107         struct task_struct *tsk = bp->hw.target;
 108         struct perf_event *iter;
 109         int count = 0;
 110
 111         list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
 112                 if (iter->hw.target == tsk &&
 113                     find_slot_idx(iter->attr.bp_type) == type &&
 114                     (iter->cpu < 0 || cpu == iter->cpu))
 115                         count += hw_breakpoint_weight(iter);
 116         }
 117
 118         return count;
 119 }
 120
 121 static const struct cpumask *cpumask_of_bp(struct perf_event *bp)
 122 {
 123         if (bp->cpu >= 0)
 124                 return cpumask_of(bp->cpu);
 125         return cpu_possible_mask;
 126 }
 127
 128 /*
 129  * Report the number of pinned/un-pinned breakpoints we have in
 130  * a given cpu (cpu > -1) or in all of them (cpu = -1).
 131  */
 132 static void
 133 fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
 134                     enum bp_type_idx type)
 135 {
 136         const struct cpumask *cpumask = cpumask_of_bp(bp);
 137         int cpu;
 138
 139         for_each_cpu(cpu, cpumask) {
 140                 struct bp_cpuinfo *info = get_bp_info(cpu, type);
 141                 int nr;
 142
 143                 nr = info->cpu_pinned;
 144                 if (!bp->hw.target)
 145                         nr += max_task_bp_pinned(cpu, type);
 146                 else
 147                         nr += task_bp_pinned(cpu, bp, type);
 148
 149                 if (nr > slots->pinned)
 150                         slots->pinned = nr;
 151
 152                 nr = info->flexible;
 153                 if (nr > slots->flexible)
 154                         slots->flexible = nr;
 155         }
 156 }
 157
 158 /*
 159  * For now, continue to consider flexible as pinned, until we can
 160  * ensure no flexible event can ever be scheduled before a pinned event
 161  * in a same cpu.
 162  */
 163 static void
 164 fetch_this_slot(struct bp_busy_slots *slots, int weight)
 165 {
 166         slots->pinned += weight;
 167 }
 168
 169 /*
 170  * Add a pinned breakpoint for the given task in our constraint table
 171  */
 172 static void toggle_bp_task_slot(struct perf_event *bp, int cpu,
 173                                 enum bp_type_idx type, int weight)
 174 {
 175         unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
 176         int old_idx, new_idx;
 177
 178         old_idx = task_bp_pinned(cpu, bp, type) - 1;
 179         new_idx = old_idx + weight;
 180
 181         if (old_idx >= 0)
 182                 tsk_pinned[old_idx]--;
 183         if (new_idx >= 0)
 184                 tsk_pinned[new_idx]++;
 185 }
 186
 187 /*
 188  * Add/remove the given breakpoint in our constraint table
 189  */
 190 static void
 191 toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
 192                int weight)
 193 {
 194         const struct cpumask *cpumask = cpumask_of_bp(bp);
 195         int cpu;
 196
 197         if (!enable)
 198                 weight = -weight;
 199
 200         /* Pinned counter cpu profiling */
 201         if (!bp->hw.target) {
 202                 get_bp_info(bp->cpu, type)->cpu_pinned += weight;
 203                 return;
 204         }
 205
 206         /* Pinned counter task profiling */
 207         for_each_cpu(cpu, cpumask)
 208                 toggle_bp_task_slot(bp, cpu, type, weight);
 209
 210         if (enable)
 211                 list_add_tail(&bp->hw.bp_list, &bp_task_head);
 212         else
 213                 list_del(&bp->hw.bp_list);
 214 }
 215
 216 __weak int arch_reserve_bp_slot(struct perf_event *bp)
 217 {
 218         return 0;
 219 }
 220
 221 __weak void arch_release_bp_slot(struct perf_event *bp)
 222 {
 223 }
 224
 225 /*
 226  * Function to perform processor-specific cleanup during unregistration
 227  */
 228 __weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
 229 {
 230         /*
 231          * A weak stub function here for those archs that don't define
 232          * it inside arch/.../kernel/hw_breakpoint.c
 233          */
 234 }
 235
 236 /*
 237  * Constraints to check before allowing this new breakpoint counter:
 238  *
 239  *  == Non-pinned counter == (Considered as pinned for now)
 240  *
 241  *   - If attached to a single cpu, check:
 242  *
 243  *       (per_cpu(info->flexible, cpu) || (per_cpu(info->cpu_pinned, cpu)
 244  *           + max(per_cpu(info->tsk_pinned, cpu)))) < HBP_NUM
 245  *
 246  *       -> If there are already non-pinned counters in this cpu, it means
 247  *          there is already a free slot for them.
 248  *          Otherwise, we check that the maximum number of per task
 249  *          breakpoints (for this cpu) plus the number of per cpu breakpoint
 250  *          (for this cpu) doesn't cover every registers.
 251  *
 252  *   - If attached to every cpus, check:
 253  *
 254  *       (per_cpu(info->flexible, *) || (max(per_cpu(info->cpu_pinned, *))
 255  *           + max(per_cpu(info->tsk_pinned, *)))) < HBP_NUM
 256  *
 257  *       -> This is roughly the same, except we check the number of per cpu
 258  *          bp for every cpu and we keep the max one. Same for the per tasks
 259  *          breakpoints.
 260  *
 261  *
 262  * == Pinned counter ==
 263  *
 264  *   - If attached to a single cpu, check:
 265  *
 266  *       ((per_cpu(info->flexible, cpu) > 1) + per_cpu(info->cpu_pinned, cpu)
 267  *            + max(per_cpu(info->tsk_pinned, cpu))) < HBP_NUM
 268  *
 269  *       -> Same checks as before. But now the info->flexible, if any, must keep
 270  *          one register at least (or they will never be fed).
 271  *
 272  *   - If attached to every cpus, check:
 273  *
 274  *       ((per_cpu(info->flexible, *) > 1) + max(per_cpu(info->cpu_pinned, *))
 275  *            + max(per_cpu(info->tsk_pinned, *))) < HBP_NUM
 276  */
 277 static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
 278 {
 279         struct bp_busy_slots slots = {0};
 280         enum bp_type_idx type;
 281         int weight;
 282         int ret;
 283
 284         /* We couldn't initialize breakpoint constraints on boot */
 285         if (!constraints_initialized)
 286                 return -ENOMEM;
 287
 288         /* Basic checks */
 289         if (bp_type == HW_BREAKPOINT_EMPTY ||
 290             bp_type == HW_BREAKPOINT_INVALID)
 291                 return -EINVAL;
 292
 293         type = find_slot_idx(bp_type);
 294         weight = hw_breakpoint_weight(bp);
 295
 296         fetch_bp_busy_slots(&slots, bp, type);
 297         /*
 298          * Simulate the addition of this breakpoint to the constraints
 299          * and see the result.
 300          */
 301         fetch_this_slot(&slots, weight);
 302
 303         /* Flexible counters need to keep at least one slot */
 304         if (slots.pinned + (!!slots.flexible) > nr_slots[type])
 305                 return -ENOSPC;
 306
 307         ret = arch_reserve_bp_slot(bp);
 308         if (ret)
 309                 return ret;
 310
 311         toggle_bp_slot(bp, true, type, weight);
 312
 313         return 0;
 314 }
 315
 316 int reserve_bp_slot(struct perf_event *bp)
 317 {
 318         int ret;
 319
 320         mutex_lock(&nr_bp_mutex);
 321
 322         ret = __reserve_bp_slot(bp, bp->attr.bp_type);
 323
 324         mutex_unlock(&nr_bp_mutex);
 325
 326         return ret;
 327 }
 328
 329 static void __release_bp_slot(struct perf_event *bp, u64 bp_type)
 330 {
 331         enum bp_type_idx type;
 332         int weight;
 333
 334         arch_release_bp_slot(bp);
 335
 336         type = find_slot_idx(bp_type);
 337         weight = hw_breakpoint_weight(bp);
 338         toggle_bp_slot(bp, false, type, weight);
 339 }
 340
 341 void release_bp_slot(struct perf_event *bp)
 342 {
 343         mutex_lock(&nr_bp_mutex);
 344
 345         arch_unregister_hw_breakpoint(bp);
 346         __release_bp_slot(bp, bp->attr.bp_type);
 347
 348         mutex_unlock(&nr_bp_mutex);
 349 }
 350
 351 static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
 352 {
 353         int err;
 354
 355         __release_bp_slot(bp, old_type);
 356
 357         err = __reserve_bp_slot(bp, new_type);
 358         if (err) {
 359                 /*
 360                  * Reserve the old_type slot back in case
 361                  * there's no space for the new type.
 362                  *
 363                  * This must succeed, because we just released
 364                  * the old_type slot in the __release_bp_slot
 365                  * call above. If not, something is broken.
 366                  */
 367                 WARN_ON(__reserve_bp_slot(bp, old_type));
 368         }
 369
 370         return err;
 371 }
 372
 373 static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
 374 {
 375         int ret;
 376
 377         mutex_lock(&nr_bp_mutex);
 378         ret = __modify_bp_slot(bp, old_type, new_type);
 379         mutex_unlock(&nr_bp_mutex);
 380         return ret;
 381 }
 382
 383 /*
 384  * Allow the kernel debugger to reserve breakpoint slots without
 385  * taking a lock using the dbg_* variant of for the reserve and
 386  * release breakpoint slots.
 387  */
 388 int dbg_reserve_bp_slot(struct perf_event *bp)
 389 {
 390         if (mutex_is_locked(&nr_bp_mutex))
 391                 return -1;
 392
 393         return __reserve_bp_slot(bp, bp->attr.bp_type);
 394 }
 395
 396 int dbg_release_bp_slot(struct perf_event *bp)
 397 {
 398         if (mutex_is_locked(&nr_bp_mutex))
 399                 return -1;
 400
 401         __release_bp_slot(bp, bp->attr.bp_type);
 402
 403         return 0;
 404 }
 405
 406 static int hw_breakpoint_parse(struct perf_event *bp,
 407                                const struct perf_event_attr *attr,
 408                                struct arch_hw_breakpoint *hw)
 409 {
 410         int err;
 411
 412         err = hw_breakpoint_arch_parse(bp, attr, hw);
 413         if (err)
 414                 return err;
 415
 416         if (arch_check_bp_in_kernelspace(hw)) {
 417                 if (attr->exclude_kernel)
 418                         return -EINVAL;
 419                 /*
 420                  * Don't let unprivileged users set a breakpoint in the trap
 421                  * path to avoid trap recursion attacks.
 422                  */
 423                 if (!capable(CAP_SYS_ADMIN))
 424                         return -EPERM;
 425         }
 426
 427         return 0;
 428 }
 429
 430 int register_perf_hw_breakpoint(struct perf_event *bp)
 431 {
 432         struct arch_hw_breakpoint hw = { };
 433         int err;
 434
 435         err = reserve_bp_slot(bp);
 436         if (err)
 437                 return err;
 438
 439         err = hw_breakpoint_parse(bp, &bp->attr, &hw);
 440         if (err) {
 441                 release_bp_slot(bp);
 442                 return err;
 443         }
 444
 445         bp->hw.info = hw;
 446
 447         return 0;
 448 }
 449
 450 /**
 451  * register_user_hw_breakpoint - register a hardware breakpoint for user space
 452  * @attr: breakpoint attributes
 453  * @triggered: callback to trigger when we hit the breakpoint
 454  * @context: context data could be used in the triggered callback
 455  * @tsk: pointer to 'task_struct' of the process to which the address belongs
 456  */
 457 struct perf_event *
 458 register_user_hw_breakpoint(struct perf_event_attr *attr,
 459                             perf_overflow_handler_t triggered,
 460                             void *context,
 461                             struct task_struct *tsk)
 462 {
 463         return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
 464                                                 context);
 465 }
 466 EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
 467
 468 static void hw_breakpoint_copy_attr(struct perf_event_attr *to,
 469                                     struct perf_event_attr *from)
 470 {
 471         to->bp_addr = from->bp_addr;
 472         to->bp_type = from->bp_type;
 473         to->bp_len  = from->bp_len;
 474         to->disabled = from->disabled;
 475 }
 476
 477 int
 478 modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
 479                                 bool check)
 480 {
 481         struct arch_hw_breakpoint hw = { };
 482         int err;
 483
 484         err = hw_breakpoint_parse(bp, attr, &hw);
 485         if (err)
 486                 return err;
 487
 488         if (check) {
 489                 struct perf_event_attr old_attr;
 490
 491                 old_attr = bp->attr;
 492                 hw_breakpoint_copy_attr(&old_attr, attr);
 493                 if (memcmp(&old_attr, attr, sizeof(*attr)))
 494                         return -EINVAL;
 495         }
 496
 497         if (bp->attr.bp_type != attr->bp_type) {
 498                 err = modify_bp_slot(bp, bp->attr.bp_type, attr->bp_type);
 499                 if (err)
 500                         return err;
 501         }
 502
 503         hw_breakpoint_copy_attr(&bp->attr, attr);
 504         bp->hw.info = hw;
 505
 506         return 0;
 507 }
 508
 509 /**
 510  * modify_user_hw_breakpoint - modify a user-space hardware breakpoint
 511  * @bp: the breakpoint structure to modify
 512  * @attr: new breakpoint attributes
 513  */
 514 int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
 515 {
 516         int err;
 517
 518         /*
 519          * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
 520          * will not be possible to raise IPIs that invoke __perf_event_disable.
 521          * So call the function directly after making sure we are targeting the
 522          * current task.
 523          */
 524         if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
 525                 perf_event_disable_local(bp);
 526         else
 527                 perf_event_disable(bp);
 528
 529         err = modify_user_hw_breakpoint_check(bp, attr, false);
 530
 531         if (!bp->attr.disabled)
 532                 perf_event_enable(bp);
 533
 534         return err;
 535 }
 536 EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
 537
 538 /**
 539  * unregister_hw_breakpoint - unregister a user-space hardware breakpoint
 540  * @bp: the breakpoint structure to unregister
 541  */
 542 void unregister_hw_breakpoint(struct perf_event *bp)
 543 {
 544         if (!bp)
 545                 return;
 546         perf_event_release_kernel(bp);
 547 }
 548 EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
 549
 550 /**
 551  * register_wide_hw_breakpoint - register a wide breakpoint in the kernel
 552  * @attr: breakpoint attributes
 553  * @triggered: callback to trigger when we hit the breakpoint
 554  * @context: context data could be used in the triggered callback
 555  *
 556  * @return a set of per_cpu pointers to perf events
 557  */
 558 struct perf_event * __percpu *
 559 register_wide_hw_breakpoint(struct perf_event_attr *attr,
 560                             perf_overflow_handler_t triggered,
 561                             void *context)
 562 {
 563         struct perf_event * __percpu *cpu_events, *bp;
 564         long err = 0;
 565         int cpu;
 566
 567         cpu_events = alloc_percpu(typeof(*cpu_events));
 568         if (!cpu_events)
 569                 return (void __percpu __force *)ERR_PTR(-ENOMEM);
 570
 571         cpus_read_lock();
 572         for_each_online_cpu(cpu) {
 573                 bp = perf_event_create_kernel_counter(attr, cpu, NULL,
 574                                                       triggered, context);
 575                 if (IS_ERR(bp)) {
 576                         err = PTR_ERR(bp);
 577                         break;
 578                 }
 579
 580                 per_cpu(*cpu_events, cpu) = bp;
 581         }
 582         cpus_read_unlock();
 583
 584         if (likely(!err))
 585                 return cpu_events;
 586
 587         unregister_wide_hw_breakpoint(cpu_events);
 588         return (void __percpu __force *)ERR_PTR(err);
 589 }
 590 EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);
 591
 592 /**
 593  * unregister_wide_hw_breakpoint - unregister a wide breakpoint in the kernel
 594  * @cpu_events: the per cpu set of events to unregister
 595  */
 596 void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
 597 {
 598         int cpu;
 599
 600         for_each_possible_cpu(cpu)
 601                 unregister_hw_breakpoint(per_cpu(*cpu_events, cpu));
 602
 603         free_percpu(cpu_events);
 604 }
 605 EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);
 606
 607 static struct notifier_block hw_breakpoint_exceptions_nb = {
 608         .notifier_call = hw_breakpoint_exceptions_notify,
 609         /* we need to be notified first */
 610         .priority = 0x7fffffff
 611 };
 612
 613 static void bp_perf_event_destroy(struct perf_event *event)
 614 {
 615         release_bp_slot(event);
 616 }
 617
 618 static int hw_breakpoint_event_init(struct perf_event *bp)
 619 {
 620         int err;
 621
 622         if (bp->attr.type != PERF_TYPE_BREAKPOINT)
 623                 return -ENOENT;
 624
 625         /*
 626          * no branch sampling for breakpoint events
 627          */
 628         if (has_branch_stack(bp))
 629                 return -EOPNOTSUPP;
 630
 631         err = register_perf_hw_breakpoint(bp);
 632         if (err)
 633                 return err;
 634
 635         bp->destroy = bp_perf_event_destroy;
 636
 637         return 0;
 638 }
 639
 640 static int hw_breakpoint_add(struct perf_event *bp, int flags)
 641 {
 642         if (!(flags & PERF_EF_START))
 643                 bp->hw.state = PERF_HES_STOPPED;
 644
 645         if (is_sampling_event(bp)) {
 646                 bp->hw.last_period = bp->hw.sample_period;
 647                 perf_swevent_set_period(bp);
 648         }
 649
 650         return arch_install_hw_breakpoint(bp);
 651 }
 652
 653 static void hw_breakpoint_del(struct perf_event *bp, int flags)
 654 {
 655         arch_uninstall_hw_breakpoint(bp);
 656 }
 657
 658 static void hw_breakpoint_start(struct perf_event *bp, int flags)
 659 {
 660         bp->hw.state = 0;
 661 }
 662
 663 static void hw_breakpoint_stop(struct perf_event *bp, int flags)
 664 {
 665         bp->hw.state = PERF_HES_STOPPED;
 666 }
 667
 668 static struct pmu perf_breakpoint = {
 669         .task_ctx_nr    = perf_sw_context, /* could eventually get its own */
 670
 671         .event_init     = hw_breakpoint_event_init,
 672         .add            = hw_breakpoint_add,
 673         .del            = hw_breakpoint_del,
 674         .start          = hw_breakpoint_start,
 675         .stop           = hw_breakpoint_stop,
 676         .read           = hw_breakpoint_pmu_read,
 677 };
 678
 679 int __init init_hw_breakpoint(void)
 680 {
 681         int cpu, err_cpu;
 682         int i;
 683
 684         for (i = 0; i < TYPE_MAX; i++)
 685                 nr_slots[i] = hw_breakpoint_slots(i);
 686
 687         for_each_possible_cpu(cpu) {
 688                 for (i = 0; i < TYPE_MAX; i++) {
 689                         struct bp_cpuinfo *info = get_bp_info(cpu, i);
 690
 691                         info->tsk_pinned = kcalloc(nr_slots[i], sizeof(int),
 692                                                         GFP_KERNEL);
 693                         if (!info->tsk_pinned)
 694                                 goto err_alloc;
 695                 }
 696         }
 697
 698         constraints_initialized = 1;
 699
 700         perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
 701
 702         return register_die_notifier(&hw_breakpoint_exceptions_nb);
 703
 704  err_alloc:
 705         for_each_possible_cpu(err_cpu) {
 706                 for (i = 0; i < TYPE_MAX; i++)
 707                         kfree(get_bp_info(err_cpu, i)->tsk_pinned);
 708                 if (err_cpu == cpu)
 709                         break;
 710         }
 711
 712         return -ENOMEM;
 713 }
 714
 715