kernel/trace/fgraph.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Infrastructure to took into function calls and returns.
   4  * Copyright (c) 2008-2009 Frederic Weisbecker <[email protected]>
   5  * Mostly borrowed from function tracer which
   6  * is Copyright (c) Steven Rostedt <[email protected]>
   7  *
   8  * Highly modified by Steven Rostedt (VMware).
   9  */
  10 #include <linux/jump_label.h>
  11 #include <linux/suspend.h>
  12 #include <linux/ftrace.h>
  13 #include <linux/slab.h>
  14
  15 #include <trace/events/sched.h>
  16
  17 #include "ftrace_internal.h"
  18 #include "trace.h"
  19
  20 #ifdef CONFIG_DYNAMIC_FTRACE
  21 #define ASSIGN_OPS_HASH(opsname, val) \
  22         .func_hash              = val, \
  23         .local_hash.regex_lock  = __MUTEX_INITIALIZER(opsname.local_hash.regex_lock),
  24 #else
  25 #define ASSIGN_OPS_HASH(opsname, val)
  26 #endif
  27
  28 DEFINE_STATIC_KEY_FALSE(kill_ftrace_graph);
  29 int ftrace_graph_active;
  30
  31 /* Both enabled by default (can be cleared by function_graph tracer flags */
  32 static bool fgraph_sleep_time = true;
  33
  34 #ifdef CONFIG_DYNAMIC_FTRACE
  35 /*
  36  * archs can override this function if they must do something
  37  * to enable hook for graph tracer.
  38  */
  39 int __weak ftrace_enable_ftrace_graph_caller(void)
  40 {
  41         return 0;
  42 }
  43
  44 /*
  45  * archs can override this function if they must do something
  46  * to disable hook for graph tracer.
  47  */
  48 int __weak ftrace_disable_ftrace_graph_caller(void)
  49 {
  50         return 0;
  51 }
  52 #endif
  53
  54 /**
  55  * ftrace_graph_stop - set to permanently disable function graph tracing
  56  *
  57  * In case of an error int function graph tracing, this is called
  58  * to try to keep function graph tracing from causing any more harm.
  59  * Usually this is pretty severe and this is called to try to at least
  60  * get a warning out to the user.
  61  */
  62 void ftrace_graph_stop(void)
  63 {
  64         static_branch_enable(&kill_ftrace_graph);
  65 }
  66
  67 /* Add a function return address to the trace stack on thread info.*/
  68 static int
  69 ftrace_push_return_trace(unsigned long ret, unsigned long func,
  70                          unsigned long frame_pointer, unsigned long *retp)
  71 {
  72         unsigned long long calltime;
  73         int index;
  74
  75         if (unlikely(ftrace_graph_is_dead()))
  76                 return -EBUSY;
  77
  78         if (!current->ret_stack)
  79                 return -EBUSY;
  80
  81         /*
  82          * We must make sure the ret_stack is tested before we read
  83          * anything else.
  84          */
  85         smp_rmb();
  86
  87         /* The return trace stack is full */
  88         if (current->curr_ret_stack == FTRACE_RETFUNC_DEPTH - 1) {
  89                 atomic_inc(&current->trace_overrun);
  90                 return -EBUSY;
  91         }
  92
  93         calltime = trace_clock_local();
  94
  95         index = ++current->curr_ret_stack;
  96         barrier();
  97         current->ret_stack[index].ret = ret;
  98         current->ret_stack[index].func = func;
  99         current->ret_stack[index].calltime = calltime;
 100 #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
 101         current->ret_stack[index].fp = frame_pointer;
 102 #endif
 103 #ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 104         current->ret_stack[index].retp = retp;
 105 #endif
 106         return 0;
 107 }
 108
 109 /*
 110  * Not all archs define MCOUNT_INSN_SIZE which is used to look for direct
 111  * functions. But those archs currently don't support direct functions
 112  * anyway, and ftrace_find_rec_direct() is just a stub for them.
 113  * Define MCOUNT_INSN_SIZE to keep those archs compiling.
 114  */
 115 #ifndef MCOUNT_INSN_SIZE
 116 /* Make sure this only works without direct calls */
 117 # ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 118 #  error MCOUNT_INSN_SIZE not defined with direct calls enabled
 119 # endif
 120 # define MCOUNT_INSN_SIZE 0
 121 #endif
 122
 123 int function_graph_enter(unsigned long ret, unsigned long func,
 124                          unsigned long frame_pointer, unsigned long *retp)
 125 {
 126         struct ftrace_graph_ent trace;
 127
 128         trace.func = func;
 129         trace.depth = ++current->curr_ret_depth;
 130
 131         if (ftrace_push_return_trace(ret, func, frame_pointer, retp))
 132                 goto out;
 133
 134         /* Only trace if the calling function expects to */
 135         if (!ftrace_graph_entry(&trace))
 136                 goto out_ret;
 137
 138         return 0;
 139  out_ret:
 140         current->curr_ret_stack--;
 141  out:
 142         current->curr_ret_depth--;
 143         return -EBUSY;
 144 }
 145
 146 /* Retrieve a function return address to the trace stack on thread info.*/
 147 static void
 148 ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
 149                         unsigned long frame_pointer)
 150 {
 151         int index;
 152
 153         index = current->curr_ret_stack;
 154
 155         if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) {
 156                 ftrace_graph_stop();
 157                 WARN_ON(1);
 158                 /* Might as well panic, otherwise we have no where to go */
 159                 *ret = (unsigned long)panic;
 160                 return;
 161         }
 162
 163 #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
 164         /*
 165          * The arch may choose to record the frame pointer used
 166          * and check it here to make sure that it is what we expect it
 167          * to be. If gcc does not set the place holder of the return
 168          * address in the frame pointer, and does a copy instead, then
 169          * the function graph trace will fail. This test detects this
 170          * case.
 171          *
 172          * Currently, x86_32 with optimize for size (-Os) makes the latest
 173          * gcc do the above.
 174          *
 175          * Note, -mfentry does not use frame pointers, and this test
 176          *  is not needed if CC_USING_FENTRY is set.
 177          */
 178         if (unlikely(current->ret_stack[index].fp != frame_pointer)) {
 179                 ftrace_graph_stop();
 180                 WARN(1, "Bad frame pointer: expected %lx, received %lx\n"
 181                      "  from func %ps return to %lx\n",
 182                      current->ret_stack[index].fp,
 183                      frame_pointer,
 184                      (void *)current->ret_stack[index].func,
 185                      current->ret_stack[index].ret);
 186                 *ret = (unsigned long)panic;
 187                 return;
 188         }
 189 #endif
 190
 191         *ret = current->ret_stack[index].ret;
 192         trace->func = current->ret_stack[index].func;
 193         trace->calltime = current->ret_stack[index].calltime;
 194         trace->overrun = atomic_read(&current->trace_overrun);
 195         trace->depth = current->curr_ret_depth--;
 196         /*
 197          * We still want to trace interrupts coming in if
 198          * max_depth is set to 1. Make sure the decrement is
 199          * seen before ftrace_graph_return.
 200          */
 201         barrier();
 202 }
 203
 204 /*
 205  * Hibernation protection.
 206  * The state of the current task is too much unstable during
 207  * suspend/restore to disk. We want to protect against that.
 208  */
 209 static int
 210 ftrace_suspend_notifier_call(struct notifier_block *bl, unsigned long state,
 211                                                         void *unused)
 212 {
 213         switch (state) {
 214         case PM_HIBERNATION_PREPARE:
 215                 pause_graph_tracing();
 216                 break;
 217
 218         case PM_POST_HIBERNATION:
 219                 unpause_graph_tracing();
 220                 break;
 221         }
 222         return NOTIFY_DONE;
 223 }
 224
 225 static struct notifier_block ftrace_suspend_notifier = {
 226         .notifier_call = ftrace_suspend_notifier_call,
 227 };
 228
 229 /* fgraph_ret_regs is not defined without CONFIG_FUNCTION_GRAPH_RETVAL */
 230 struct fgraph_ret_regs;
 231
 232 /*
 233  * Send the trace to the ring-buffer.
 234  * @return the original return address.
 235  */
 236 static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs,
 237                                                 unsigned long frame_pointer)
 238 {
 239         struct ftrace_graph_ret trace;
 240         unsigned long ret;
 241
 242         ftrace_pop_return_trace(&trace, &ret, frame_pointer);
 243 #ifdef CONFIG_FUNCTION_GRAPH_RETVAL
 244         trace.retval = fgraph_ret_regs_return_value(ret_regs);
 245 #endif
 246         trace.rettime = trace_clock_local();
 247         ftrace_graph_return(&trace);
 248         /*
 249          * The ftrace_graph_return() may still access the current
 250          * ret_stack structure, we need to make sure the update of
 251          * curr_ret_stack is after that.
 252          */
 253         barrier();
 254         current->curr_ret_stack--;
 255
 256         if (unlikely(!ret)) {
 257                 ftrace_graph_stop();
 258                 WARN_ON(1);
 259                 /* Might as well panic. What else to do? */
 260                 ret = (unsigned long)panic;
 261         }
 262
 263         return ret;
 264 }
 265
 266 /*
 267  * After all architecures have selected HAVE_FUNCTION_GRAPH_RETVAL, we can
 268  * leave only ftrace_return_to_handler(ret_regs).
 269  */
 270 #ifdef CONFIG_HAVE_FUNCTION_GRAPH_RETVAL
 271 unsigned long ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs)
 272 {
 273         return __ftrace_return_to_handler(ret_regs,
 274                                 fgraph_ret_regs_frame_pointer(ret_regs));
 275 }
 276 #else
 277 unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
 278 {
 279         return __ftrace_return_to_handler(NULL, frame_pointer);
 280 }
 281 #endif
 282
 283 /**
 284  * ftrace_graph_get_ret_stack - return the entry of the shadow stack
 285  * @task: The task to read the shadow stack from
 286  * @idx: Index down the shadow stack
 287  *
 288  * Return the ret_struct on the shadow stack of the @task at the
 289  * call graph at @idx starting with zero. If @idx is zero, it
 290  * will return the last saved ret_stack entry. If it is greater than
 291  * zero, it will return the corresponding ret_stack for the depth
 292  * of saved return addresses.
 293  */
 294 struct ftrace_ret_stack *
 295 ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
 296 {
 297         idx = task->curr_ret_stack - idx;
 298
 299         if (idx >= 0 && idx <= task->curr_ret_stack)
 300                 return &task->ret_stack[idx];
 301
 302         return NULL;
 303 }
 304
 305 /**
 306  * ftrace_graph_ret_addr - convert a potentially modified stack return address
 307  *                         to its original value
 308  *
 309  * This function can be called by stack unwinding code to convert a found stack
 310  * return address ('ret') to its original value, in case the function graph
 311  * tracer has modified it to be 'return_to_handler'.  If the address hasn't
 312  * been modified, the unchanged value of 'ret' is returned.
 313  *
 314  * 'idx' is a state variable which should be initialized by the caller to zero
 315  * before the first call.
 316  *
 317  * 'retp' is a pointer to the return address on the stack.  It's ignored if
 318  * the arch doesn't have HAVE_FUNCTION_GRAPH_RET_ADDR_PTR defined.
 319  */
 320 #ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 321 unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
 322                                     unsigned long ret, unsigned long *retp)
 323 {
 324         int index = task->curr_ret_stack;
 325         int i;
 326
 327         if (ret != (unsigned long)dereference_kernel_function_descriptor(return_to_handler))
 328                 return ret;
 329
 330         if (index < 0)
 331                 return ret;
 332
 333         for (i = 0; i <= index; i++)
 334                 if (task->ret_stack[i].retp == retp)
 335                         return task->ret_stack[i].ret;
 336
 337         return ret;
 338 }
 339 #else /* !HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */
 340 unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
 341                                     unsigned long ret, unsigned long *retp)
 342 {
 343         int task_idx;
 344
 345         if (ret != (unsigned long)dereference_kernel_function_descriptor(return_to_handler))
 346                 return ret;
 347
 348         task_idx = task->curr_ret_stack;
 349
 350         if (!task->ret_stack || task_idx < *idx)
 351                 return ret;
 352
 353         task_idx -= *idx;
 354         (*idx)++;
 355
 356         return task->ret_stack[task_idx].ret;
 357 }
 358 #endif /* HAVE_FUNCTION_GRAPH_RET_ADDR_PTR */
 359
 360 static struct ftrace_ops graph_ops = {
 361         .func                   = ftrace_graph_func,
 362         .flags                  = FTRACE_OPS_FL_INITIALIZED |
 363                                    FTRACE_OPS_FL_PID |
 364                                    FTRACE_OPS_GRAPH_STUB,
 365 #ifdef FTRACE_GRAPH_TRAMP_ADDR
 366         .trampoline             = FTRACE_GRAPH_TRAMP_ADDR,
 367         /* trampoline_size is only needed for dynamically allocated tramps */
 368 #endif
 369         ASSIGN_OPS_HASH(graph_ops, &global_ops.local_hash)
 370 };
 371
 372 void ftrace_graph_sleep_time_control(bool enable)
 373 {
 374         fgraph_sleep_time = enable;
 375 }
 376
 377 int ftrace_graph_entry_stub(struct ftrace_graph_ent *trace)
 378 {
 379         return 0;
 380 }
 381
 382 /*
 383  * Simply points to ftrace_stub, but with the proper protocol.
 384  * Defined by the linker script in linux/vmlinux.lds.h
 385  */
 386 extern void ftrace_stub_graph(struct ftrace_graph_ret *);
 387
 388 /* The callbacks that hook a function */
 389 trace_func_graph_ret_t ftrace_graph_return = ftrace_stub_graph;
 390 trace_func_graph_ent_t ftrace_graph_entry = ftrace_graph_entry_stub;
 391 static trace_func_graph_ent_t __ftrace_graph_entry = ftrace_graph_entry_stub;
 392
 393 /* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
 394 static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
 395 {
 396         int i;
 397         int ret = 0;
 398         int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE;
 399         struct task_struct *g, *t;
 400
 401         for (i = 0; i < FTRACE_RETSTACK_ALLOC_SIZE; i++) {
 402                 ret_stack_list[i] =
 403                         kmalloc_array(FTRACE_RETFUNC_DEPTH,
 404                                       sizeof(struct ftrace_ret_stack),
 405                                       GFP_KERNEL);
 406                 if (!ret_stack_list[i]) {
 407                         start = 0;
 408                         end = i;
 409                         ret = -ENOMEM;
 410                         goto free;
 411                 }
 412         }
 413
 414         rcu_read_lock();
 415         for_each_process_thread(g, t) {
 416                 if (start == end) {
 417                         ret = -EAGAIN;
 418                         goto unlock;
 419                 }
 420
 421                 if (t->ret_stack == NULL) {
 422                         atomic_set(&t->trace_overrun, 0);
 423                         t->curr_ret_stack = -1;
 424                         t->curr_ret_depth = -1;
 425                         /* Make sure the tasks see the -1 first: */
 426                         smp_wmb();
 427                         t->ret_stack = ret_stack_list[start++];
 428                 }
 429         }
 430
 431 unlock:
 432         rcu_read_unlock();
 433 free:
 434         for (i = start; i < end; i++)
 435                 kfree(ret_stack_list[i]);
 436         return ret;
 437 }
 438
 439 static void
 440 ftrace_graph_probe_sched_switch(void *ignore, bool preempt,
 441                                 struct task_struct *prev,
 442                                 struct task_struct *next,
 443                                 unsigned int prev_state)
 444 {
 445         unsigned long long timestamp;
 446         int index;
 447
 448         /*
 449          * Does the user want to count the time a function was asleep.
 450          * If so, do not update the time stamps.
 451          */
 452         if (fgraph_sleep_time)
 453                 return;
 454
 455         timestamp = trace_clock_local();
 456
 457         prev->ftrace_timestamp = timestamp;
 458
 459         /* only process tasks that we timestamped */
 460         if (!next->ftrace_timestamp)
 461                 return;
 462
 463         /*
 464          * Update all the counters in next to make up for the
 465          * time next was sleeping.
 466          */
 467         timestamp -= next->ftrace_timestamp;
 468
 469         for (index = next->curr_ret_stack; index >= 0; index--)
 470                 next->ret_stack[index].calltime += timestamp;
 471 }
 472
 473 static int ftrace_graph_entry_test(struct ftrace_graph_ent *trace)
 474 {
 475         if (!ftrace_ops_test(&global_ops, trace->func, NULL))
 476                 return 0;
 477         return __ftrace_graph_entry(trace);
 478 }
 479
 480 /*
 481  * The function graph tracer should only trace the functions defined
 482  * by set_ftrace_filter and set_ftrace_notrace. If another function
 483  * tracer ops is registered, the graph tracer requires testing the
 484  * function against the global ops, and not just trace any function
 485  * that any ftrace_ops registered.
 486  */
 487 void update_function_graph_func(void)
 488 {
 489         struct ftrace_ops *op;
 490         bool do_test = false;
 491
 492         /*
 493          * The graph and global ops share the same set of functions
 494          * to test. If any other ops is on the list, then
 495          * the graph tracing needs to test if its the function
 496          * it should call.
 497          */
 498         do_for_each_ftrace_op(op, ftrace_ops_list) {
 499                 if (op != &global_ops && op != &graph_ops &&
 500                     op != &ftrace_list_end) {
 501                         do_test = true;
 502                         /* in double loop, break out with goto */
 503                         goto out;
 504                 }
 505         } while_for_each_ftrace_op(op);
 506  out:
 507         if (do_test)
 508                 ftrace_graph_entry = ftrace_graph_entry_test;
 509         else
 510                 ftrace_graph_entry = __ftrace_graph_entry;
 511 }
 512
 513 static DEFINE_PER_CPU(struct ftrace_ret_stack *, idle_ret_stack);
 514
 515 static void
 516 graph_init_task(struct task_struct *t, struct ftrace_ret_stack *ret_stack)
 517 {
 518         atomic_set(&t->trace_overrun, 0);
 519         t->ftrace_timestamp = 0;
 520         /* make curr_ret_stack visible before we add the ret_stack */
 521         smp_wmb();
 522         t->ret_stack = ret_stack;
 523 }
 524
 525 /*
 526  * Allocate a return stack for the idle task. May be the first
 527  * time through, or it may be done by CPU hotplug online.
 528  */
 529 void ftrace_graph_init_idle_task(struct task_struct *t, int cpu)
 530 {
 531         t->curr_ret_stack = -1;
 532         t->curr_ret_depth = -1;
 533         /*
 534          * The idle task has no parent, it either has its own
 535          * stack or no stack at all.
 536          */
 537         if (t->ret_stack)
 538                 WARN_ON(t->ret_stack != per_cpu(idle_ret_stack, cpu));
 539
 540         if (ftrace_graph_active) {
 541                 struct ftrace_ret_stack *ret_stack;
 542
 543                 ret_stack = per_cpu(idle_ret_stack, cpu);
 544                 if (!ret_stack) {
 545                         ret_stack =
 546                                 kmalloc_array(FTRACE_RETFUNC_DEPTH,
 547                                               sizeof(struct ftrace_ret_stack),
 548                                               GFP_KERNEL);
 549                         if (!ret_stack)
 550                                 return;
 551                         per_cpu(idle_ret_stack, cpu) = ret_stack;
 552                 }
 553                 graph_init_task(t, ret_stack);
 554         }
 555 }
 556
 557 /* Allocate a return stack for newly created task */
 558 void ftrace_graph_init_task(struct task_struct *t)
 559 {
 560         /* Make sure we do not use the parent ret_stack */
 561         t->ret_stack = NULL;
 562         t->curr_ret_stack = -1;
 563         t->curr_ret_depth = -1;
 564
 565         if (ftrace_graph_active) {
 566                 struct ftrace_ret_stack *ret_stack;
 567
 568                 ret_stack = kmalloc_array(FTRACE_RETFUNC_DEPTH,
 569                                           sizeof(struct ftrace_ret_stack),
 570                                           GFP_KERNEL);
 571                 if (!ret_stack)
 572                         return;
 573                 graph_init_task(t, ret_stack);
 574         }
 575 }
 576
 577 void ftrace_graph_exit_task(struct task_struct *t)
 578 {
 579         struct ftrace_ret_stack *ret_stack = t->ret_stack;
 580
 581         t->ret_stack = NULL;
 582         /* NULL must become visible to IRQs before we free it: */
 583         barrier();
 584
 585         kfree(ret_stack);
 586 }
 587
 588 /* Allocate a return stack for each task */
 589 static int start_graph_tracing(void)
 590 {
 591         struct ftrace_ret_stack **ret_stack_list;
 592         int ret, cpu;
 593
 594         ret_stack_list = kmalloc_array(FTRACE_RETSTACK_ALLOC_SIZE,
 595                                        sizeof(struct ftrace_ret_stack *),
 596                                        GFP_KERNEL);
 597
 598         if (!ret_stack_list)
 599                 return -ENOMEM;
 600
 601         /* The cpu_boot init_task->ret_stack will never be freed */
 602         for_each_online_cpu(cpu) {
 603                 if (!idle_task(cpu)->ret_stack)
 604                         ftrace_graph_init_idle_task(idle_task(cpu), cpu);
 605         }
 606
 607         do {
 608                 ret = alloc_retstack_tasklist(ret_stack_list);
 609         } while (ret == -EAGAIN);
 610
 611         if (!ret) {
 612                 ret = register_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
 613                 if (ret)
 614                         pr_info("ftrace_graph: Couldn't activate tracepoint"
 615                                 " probe to kernel_sched_switch\n");
 616         }
 617
 618         kfree(ret_stack_list);
 619         return ret;
 620 }
 621
 622 int register_ftrace_graph(struct fgraph_ops *gops)
 623 {
 624         int ret = 0;
 625
 626         mutex_lock(&ftrace_lock);
 627
 628         /* we currently allow only one tracer registered at a time */
 629         if (ftrace_graph_active) {
 630                 ret = -EBUSY;
 631                 goto out;
 632         }
 633
 634         register_pm_notifier(&ftrace_suspend_notifier);
 635
 636         ftrace_graph_active++;
 637         ret = start_graph_tracing();
 638         if (ret) {
 639                 ftrace_graph_active--;
 640                 goto out;
 641         }
 642
 643         ftrace_graph_return = gops->retfunc;
 644
 645         /*
 646          * Update the indirect function to the entryfunc, and the
 647          * function that gets called to the entry_test first. Then
 648          * call the update fgraph entry function to determine if
 649          * the entryfunc should be called directly or not.
 650          */
 651         __ftrace_graph_entry = gops->entryfunc;
 652         ftrace_graph_entry = ftrace_graph_entry_test;
 653         update_function_graph_func();
 654
 655         ret = ftrace_startup(&graph_ops, FTRACE_START_FUNC_RET);
 656 out:
 657         mutex_unlock(&ftrace_lock);
 658         return ret;
 659 }
 660
 661 void unregister_ftrace_graph(struct fgraph_ops *gops)
 662 {
 663         mutex_lock(&ftrace_lock);
 664
 665         if (unlikely(!ftrace_graph_active))
 666                 goto out;
 667
 668         ftrace_graph_active--;
 669         ftrace_graph_return = ftrace_stub_graph;
 670         ftrace_graph_entry = ftrace_graph_entry_stub;
 671         __ftrace_graph_entry = ftrace_graph_entry_stub;
 672         ftrace_shutdown(&graph_ops, FTRACE_STOP_FUNC_RET);
 673         unregister_pm_notifier(&ftrace_suspend_notifier);
 674         unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL);
 675
 676  out:
 677         mutex_unlock(&ftrace_lock);
 678 }