SAFE public projects git trees. - safe/jmp/linux-2.6/blob - kernel/trace/trace.h

   1 #ifndef _LINUX_KERNEL_TRACE_H
   2 #define _LINUX_KERNEL_TRACE_H
   3
   4 #include <linux/fs.h>
   5 #include <asm/atomic.h>
   6 #include <linux/sched.h>
   7 #include <linux/clocksource.h>
   8 #include <linux/ring_buffer.h>
   9 #include <linux/mmiotrace.h>
  10 #include <linux/ftrace.h>
  11 #include <trace/boot.h>
  12 #include <trace/kmemtrace.h>
  13
  14 enum trace_type {
  15         __TRACE_FIRST_TYPE = 0,
  16
  17         TRACE_FN,
  18         TRACE_CTX,
  19         TRACE_WAKE,
  20         TRACE_CONT,
  21         TRACE_STACK,
  22         TRACE_PRINT,
  23         TRACE_SPECIAL,
  24         TRACE_MMIO_RW,
  25         TRACE_MMIO_MAP,
  26         TRACE_BRANCH,
  27         TRACE_BOOT_CALL,
  28         TRACE_BOOT_RET,
  29         TRACE_GRAPH_RET,
  30         TRACE_GRAPH_ENT,
  31         TRACE_USER_STACK,
  32         TRACE_HW_BRANCHES,
  33         TRACE_KMEM_ALLOC,
  34         TRACE_KMEM_FREE,
  35         TRACE_POWER,
  36
  37         __TRACE_LAST_TYPE
  38 };
  39
  40 /*
  41  * The trace entry - the most basic unit of tracing. This is what
  42  * is printed in the end as a single line in the trace output, such as:
  43  *
  44  *     bash-15816 [01]   235.197585: idle_cpu <- irq_enter
  45  */
  46 struct trace_entry {
  47         unsigned char           type;
  48         unsigned char           cpu;
  49         unsigned char           flags;
  50         unsigned char           preempt_count;
  51         int                     pid;
  52         int                     tgid;
  53 };
  54
  55 /*
  56  * Function trace entry - function address and parent function addres:
  57  */
  58 struct ftrace_entry {
  59         struct trace_entry      ent;
  60         unsigned long           ip;
  61         unsigned long           parent_ip;
  62 };
  63
  64 /* Function call entry */
  65 struct ftrace_graph_ent_entry {
  66         struct trace_entry                      ent;
  67         struct ftrace_graph_ent         graph_ent;
  68 };
  69
  70 /* Function return entry */
  71 struct ftrace_graph_ret_entry {
  72         struct trace_entry                      ent;
  73         struct ftrace_graph_ret         ret;
  74 };
  75 extern struct tracer boot_tracer;
  76
  77 /*
  78  * Context switch trace entry - which task (and prio) we switched from/to:
  79  */
  80 struct ctx_switch_entry {
  81         struct trace_entry      ent;
  82         unsigned int            prev_pid;
  83         unsigned char           prev_prio;
  84         unsigned char           prev_state;
  85         unsigned int            next_pid;
  86         unsigned char           next_prio;
  87         unsigned char           next_state;
  88         unsigned int            next_cpu;
  89 };
  90
  91 /*
  92  * Special (free-form) trace entry:
  93  */
  94 struct special_entry {
  95         struct trace_entry      ent;
  96         unsigned long           arg1;
  97         unsigned long           arg2;
  98         unsigned long           arg3;
  99 };
 100
 101 /*
 102  * Stack-trace entry:
 103  */
 104
 105 #define FTRACE_STACK_ENTRIES    8
 106
 107 struct stack_entry {
 108         struct trace_entry      ent;
 109         unsigned long           caller[FTRACE_STACK_ENTRIES];
 110 };
 111
 112 struct userstack_entry {
 113         struct trace_entry      ent;
 114         unsigned long           caller[FTRACE_STACK_ENTRIES];
 115 };
 116
 117 /*
 118  * ftrace_printk entry:
 119  */
 120 struct print_entry {
 121         struct trace_entry      ent;
 122         unsigned long           ip;
 123         int                     depth;
 124         char                    buf[];
 125 };
 126
 127 #define TRACE_OLD_SIZE          88
 128
 129 struct trace_field_cont {
 130         unsigned char           type;
 131         /* Temporary till we get rid of this completely */
 132         char                    buf[TRACE_OLD_SIZE - 1];
 133 };
 134
 135 struct trace_mmiotrace_rw {
 136         struct trace_entry      ent;
 137         struct mmiotrace_rw     rw;
 138 };
 139
 140 struct trace_mmiotrace_map {
 141         struct trace_entry      ent;
 142         struct mmiotrace_map    map;
 143 };
 144
 145 struct trace_boot_call {
 146         struct trace_entry      ent;
 147         struct boot_trace_call boot_call;
 148 };
 149
 150 struct trace_boot_ret {
 151         struct trace_entry      ent;
 152         struct boot_trace_ret boot_ret;
 153 };
 154
 155 #define TRACE_FUNC_SIZE 30
 156 #define TRACE_FILE_SIZE 20
 157 struct trace_branch {
 158         struct trace_entry      ent;
 159         unsigned                line;
 160         char                    func[TRACE_FUNC_SIZE+1];
 161         char                    file[TRACE_FILE_SIZE+1];
 162         char                    correct;
 163 };
 164
 165 struct hw_branch_entry {
 166         struct trace_entry      ent;
 167         u64                     from;
 168         u64                     to;
 169 };
 170
 171 struct trace_power {
 172         struct trace_entry      ent;
 173         struct power_trace      state_data;
 174 };
 175
 176 struct kmemtrace_alloc_entry {
 177         struct trace_entry      ent;
 178         enum kmemtrace_type_id type_id;
 179         unsigned long call_site;
 180         const void *ptr;
 181         size_t bytes_req;
 182         size_t bytes_alloc;
 183         gfp_t gfp_flags;
 184         int node;
 185 };
 186
 187 struct kmemtrace_free_entry {
 188         struct trace_entry      ent;
 189         enum kmemtrace_type_id type_id;
 190         unsigned long call_site;
 191         const void *ptr;
 192 };
 193
 194 /*
 195  * trace_flag_type is an enumeration that holds different
 196  * states when a trace occurs. These are:
 197  *  IRQS_OFF            - interrupts were disabled
 198  *  IRQS_NOSUPPORT      - arch does not support irqs_disabled_flags
 199  *  NEED_RESCED         - reschedule is requested
 200  *  HARDIRQ             - inside an interrupt handler
 201  *  SOFTIRQ             - inside a softirq handler
 202  *  CONT                - multiple entries hold the trace item
 203  */
 204 enum trace_flag_type {
 205         TRACE_FLAG_IRQS_OFF             = 0x01,
 206         TRACE_FLAG_IRQS_NOSUPPORT       = 0x02,
 207         TRACE_FLAG_NEED_RESCHED         = 0x04,
 208         TRACE_FLAG_HARDIRQ              = 0x08,
 209         TRACE_FLAG_SOFTIRQ              = 0x10,
 210         TRACE_FLAG_CONT                 = 0x20,
 211 };
 212
 213 #define TRACE_BUF_SIZE          1024
 214
 215 /*
 216  * The CPU trace array - it consists of thousands of trace entries
 217  * plus some other descriptor data: (for example which task started
 218  * the trace, etc.)
 219  */
 220 struct trace_array_cpu {
 221         atomic_t                disabled;
 222
 223         /* these fields get copied into max-trace: */
 224         unsigned long           trace_idx;
 225         unsigned long           overrun;
 226         unsigned long           saved_latency;
 227         unsigned long           critical_start;
 228         unsigned long           critical_end;
 229         unsigned long           critical_sequence;
 230         unsigned long           nice;
 231         unsigned long           policy;
 232         unsigned long           rt_priority;
 233         cycle_t                 preempt_timestamp;
 234         pid_t                   pid;
 235         uid_t                   uid;
 236         char                    comm[TASK_COMM_LEN];
 237 };
 238
 239 struct trace_iterator;
 240
 241 /*
 242  * The trace array - an array of per-CPU trace arrays. This is the
 243  * highest level data structure that individual tracers deal with.
 244  * They have on/off state as well:
 245  */
 246 struct trace_array {
 247         struct ring_buffer      *buffer;
 248         unsigned long           entries;
 249         int                     cpu;
 250         cycle_t                 time_start;
 251         struct task_struct      *waiter;
 252         struct trace_array_cpu  *data[NR_CPUS];
 253 };
 254
 255 #define FTRACE_CMP_TYPE(var, type) \
 256         __builtin_types_compatible_p(typeof(var), type *)
 257
 258 #undef IF_ASSIGN
 259 #define IF_ASSIGN(var, entry, etype, id)                \
 260         if (FTRACE_CMP_TYPE(var, etype)) {              \
 261                 var = (typeof(var))(entry);             \
 262                 WARN_ON(id && (entry)->type != id);     \
 263                 break;                                  \
 264         }
 265
 266 /* Will cause compile errors if type is not found. */
 267 extern void __ftrace_bad_type(void);
 268
 269 /*
 270  * The trace_assign_type is a verifier that the entry type is
 271  * the same as the type being assigned. To add new types simply
 272  * add a line with the following format:
 273  *
 274  * IF_ASSIGN(var, ent, type, id);
 275  *
 276  *  Where "type" is the trace type that includes the trace_entry
 277  *  as the "ent" item. And "id" is the trace identifier that is
 278  *  used in the trace_type enum.
 279  *
 280  *  If the type can have more than one id, then use zero.
 281  */
 282 #define trace_assign_type(var, ent)                                     \
 283         do {                                                            \
 284                 IF_ASSIGN(var, ent, struct ftrace_entry, TRACE_FN);     \
 285                 IF_ASSIGN(var, ent, struct ctx_switch_entry, 0);        \
 286                 IF_ASSIGN(var, ent, struct trace_field_cont, TRACE_CONT); \
 287                 IF_ASSIGN(var, ent, struct stack_entry, TRACE_STACK);   \
 288                 IF_ASSIGN(var, ent, struct userstack_entry, TRACE_USER_STACK);\
 289                 IF_ASSIGN(var, ent, struct print_entry, TRACE_PRINT);   \
 290                 IF_ASSIGN(var, ent, struct special_entry, 0);           \
 291                 IF_ASSIGN(var, ent, struct trace_mmiotrace_rw,          \
 292                           TRACE_MMIO_RW);                               \
 293                 IF_ASSIGN(var, ent, struct trace_mmiotrace_map,         \
 294                           TRACE_MMIO_MAP);                              \
 295                 IF_ASSIGN(var, ent, struct trace_boot_call, TRACE_BOOT_CALL);\
 296                 IF_ASSIGN(var, ent, struct trace_boot_ret, TRACE_BOOT_RET);\
 297                 IF_ASSIGN(var, ent, struct trace_branch, TRACE_BRANCH); \
 298                 IF_ASSIGN(var, ent, struct ftrace_graph_ent_entry,      \
 299                           TRACE_GRAPH_ENT);             \
 300                 IF_ASSIGN(var, ent, struct ftrace_graph_ret_entry,      \
 301                           TRACE_GRAPH_RET);             \
 302                 IF_ASSIGN(var, ent, struct hw_branch_entry, TRACE_HW_BRANCHES);\
 303                 IF_ASSIGN(var, ent, struct trace_power, TRACE_POWER); \
 304                 IF_ASSIGN(var, ent, struct kmemtrace_alloc_entry,       \
 305                           TRACE_KMEM_ALLOC);    \
 306                 IF_ASSIGN(var, ent, struct kmemtrace_free_entry,        \
 307                           TRACE_KMEM_FREE);     \
 308                 __ftrace_bad_type();                                    \
 309         } while (0)
 310
 311 /* Return values for print_line callback */
 312 enum print_line_t {
 313         TRACE_TYPE_PARTIAL_LINE = 0,    /* Retry after flushing the seq */
 314         TRACE_TYPE_HANDLED      = 1,
 315         TRACE_TYPE_UNHANDLED    = 2     /* Relay to other output functions */
 316 };
 317
 318
 319 /*
 320  * An option specific to a tracer. This is a boolean value.
 321  * The bit is the bit index that sets its value on the
 322  * flags value in struct tracer_flags.
 323  */
 324 struct tracer_opt {
 325         const char      *name; /* Will appear on the trace_options file */
 326         u32             bit; /* Mask assigned in val field in tracer_flags */
 327 };
 328
 329 /*
 330  * The set of specific options for a tracer. Your tracer
 331  * have to set the initial value of the flags val.
 332  */
 333 struct tracer_flags {
 334         u32                     val;
 335         struct tracer_opt       *opts;
 336 };
 337
 338 /* Makes more easy to define a tracer opt */
 339 #define TRACER_OPT(s, b)        .name = #s, .bit = b
 340
 341 /*
 342  * A specific tracer, represented by methods that operate on a trace array:
 343  */
 344 struct tracer {
 345         const char              *name;
 346         /* Your tracer should raise a warning if init fails */
 347         int                     (*init)(struct trace_array *tr);
 348         void                    (*reset)(struct trace_array *tr);
 349         void                    (*start)(struct trace_array *tr);
 350         void                    (*stop)(struct trace_array *tr);
 351         void                    (*open)(struct trace_iterator *iter);
 352         void                    (*pipe_open)(struct trace_iterator *iter);
 353         void                    (*close)(struct trace_iterator *iter);
 354         ssize_t                 (*read)(struct trace_iterator *iter,
 355                                         struct file *filp, char __user *ubuf,
 356                                         size_t cnt, loff_t *ppos);
 357 #ifdef CONFIG_FTRACE_STARTUP_TEST
 358         int                     (*selftest)(struct tracer *trace,
 359                                             struct trace_array *tr);
 360 #endif
 361         void                    (*print_header)(struct seq_file *m);
 362         enum print_line_t       (*print_line)(struct trace_iterator *iter);
 363         /* If you handled the flag setting, return 0 */
 364         int                     (*set_flag)(u32 old_flags, u32 bit, int set);
 365         struct tracer           *next;
 366         int                     print_max;
 367         struct tracer_flags     *flags;
 368 };
 369
 370 struct trace_seq {
 371         unsigned char           buffer[PAGE_SIZE];
 372         unsigned int            len;
 373         unsigned int            readpos;
 374 };
 375
 376 /*
 377  * Trace iterator - used by printout routines who present trace
 378  * results to users and which routines might sleep, etc:
 379  */
 380 struct trace_iterator {
 381         struct trace_array      *tr;
 382         struct tracer           *trace;
 383         void                    *private;
 384         struct ring_buffer_iter *buffer_iter[NR_CPUS];
 385
 386         /* The below is zeroed out in pipe_read */
 387         struct trace_seq        seq;
 388         struct trace_entry      *ent;
 389         int                     cpu;
 390         u64                     ts;
 391
 392         unsigned long           iter_flags;
 393         loff_t                  pos;
 394         long                    idx;
 395
 396         cpumask_t               started;
 397 };
 398
 399 int tracing_is_enabled(void);
 400 void trace_wake_up(void);
 401 void tracing_reset(struct trace_array *tr, int cpu);
 402 void tracing_reset_online_cpus(struct trace_array *tr);
 403 int tracing_open_generic(struct inode *inode, struct file *filp);
 404 struct dentry *tracing_init_dentry(void);
 405 void init_tracer_sysprof_debugfs(struct dentry *d_tracer);
 406
 407 struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,
 408                                                 struct trace_array_cpu *data);
 409 void tracing_generic_entry_update(struct trace_entry *entry,
 410                                   unsigned long flags,
 411                                   int pc);
 412
 413 void ftrace(struct trace_array *tr,
 414                             struct trace_array_cpu *data,
 415                             unsigned long ip,
 416                             unsigned long parent_ip,
 417                             unsigned long flags, int pc);
 418 void tracing_sched_switch_trace(struct trace_array *tr,
 419                                 struct trace_array_cpu *data,
 420                                 struct task_struct *prev,
 421                                 struct task_struct *next,
 422                                 unsigned long flags, int pc);
 423 void tracing_record_cmdline(struct task_struct *tsk);
 424
 425 void tracing_sched_wakeup_trace(struct trace_array *tr,
 426                                 struct trace_array_cpu *data,
 427                                 struct task_struct *wakee,
 428                                 struct task_struct *cur,
 429                                 unsigned long flags, int pc);
 430 void trace_special(struct trace_array *tr,
 431                    struct trace_array_cpu *data,
 432                    unsigned long arg1,
 433                    unsigned long arg2,
 434                    unsigned long arg3, int pc);
 435 void trace_function(struct trace_array *tr,
 436                     struct trace_array_cpu *data,
 437                     unsigned long ip,
 438                     unsigned long parent_ip,
 439                     unsigned long flags, int pc);
 440
 441 void trace_graph_return(struct ftrace_graph_ret *trace);
 442 int trace_graph_entry(struct ftrace_graph_ent *trace);
 443 void trace_hw_branch(struct trace_array *tr, u64 from, u64 to);
 444
 445 void tracing_start_cmdline_record(void);
 446 void tracing_stop_cmdline_record(void);
 447 void tracing_sched_switch_assign_trace(struct trace_array *tr);
 448 void tracing_stop_sched_switch_record(void);
 449 void tracing_start_sched_switch_record(void);
 450 int register_tracer(struct tracer *type);
 451 void unregister_tracer(struct tracer *type);
 452
 453 extern unsigned long nsecs_to_usecs(unsigned long nsecs);
 454
 455 extern unsigned long tracing_max_latency;
 456 extern unsigned long tracing_thresh;
 457
 458 void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu);
 459 void update_max_tr_single(struct trace_array *tr,
 460                           struct task_struct *tsk, int cpu);
 461
 462 extern cycle_t ftrace_now(int cpu);
 463
 464 #ifdef CONFIG_FUNCTION_TRACER
 465 void tracing_start_function_trace(void);
 466 void tracing_stop_function_trace(void);
 467 #else
 468 # define tracing_start_function_trace()         do { } while (0)
 469 # define tracing_stop_function_trace()          do { } while (0)
 470 #endif
 471
 472 #ifdef CONFIG_CONTEXT_SWITCH_TRACER
 473 typedef void
 474 (*tracer_switch_func_t)(void *private,
 475                         void *__rq,
 476                         struct task_struct *prev,
 477                         struct task_struct *next);
 478
 479 struct tracer_switch_ops {
 480         tracer_switch_func_t            func;
 481         void                            *private;
 482         struct tracer_switch_ops        *next;
 483 };
 484
 485 char *trace_find_cmdline(int pid);
 486 #endif /* CONFIG_CONTEXT_SWITCH_TRACER */
 487
 488 #ifdef CONFIG_DYNAMIC_FTRACE
 489 extern unsigned long ftrace_update_tot_cnt;
 490 #define DYN_FTRACE_TEST_NAME trace_selftest_dynamic_test_func
 491 extern int DYN_FTRACE_TEST_NAME(void);
 492 #endif
 493
 494 #ifdef CONFIG_FTRACE_STARTUP_TEST
 495 extern int trace_selftest_startup_function(struct tracer *trace,
 496                                            struct trace_array *tr);
 497 extern int trace_selftest_startup_irqsoff(struct tracer *trace,
 498                                           struct trace_array *tr);
 499 extern int trace_selftest_startup_preemptoff(struct tracer *trace,
 500                                              struct trace_array *tr);
 501 extern int trace_selftest_startup_preemptirqsoff(struct tracer *trace,
 502                                                  struct trace_array *tr);
 503 extern int trace_selftest_startup_wakeup(struct tracer *trace,
 504                                          struct trace_array *tr);
 505 extern int trace_selftest_startup_nop(struct tracer *trace,
 506                                          struct trace_array *tr);
 507 extern int trace_selftest_startup_sched_switch(struct tracer *trace,
 508                                                struct trace_array *tr);
 509 extern int trace_selftest_startup_sysprof(struct tracer *trace,
 510                                                struct trace_array *tr);
 511 extern int trace_selftest_startup_branch(struct tracer *trace,
 512                                          struct trace_array *tr);
 513 #endif /* CONFIG_FTRACE_STARTUP_TEST */
 514
 515 extern void *head_page(struct trace_array_cpu *data);
 516 extern int trace_seq_printf(struct trace_seq *s, const char *fmt, ...);
 517 extern void trace_seq_print_cont(struct trace_seq *s,
 518                                  struct trace_iterator *iter);
 519
 520 extern int
 521 seq_print_ip_sym(struct trace_seq *s, unsigned long ip,
 522                 unsigned long sym_flags);
 523 extern ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
 524                                  size_t cnt);
 525 extern long ns2usecs(cycle_t nsec);
 526 extern int
 527 trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args);
 528
 529 extern unsigned long trace_flags;
 530
 531 /* Standard output formatting function used for function return traces */
 532 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 533 extern enum print_line_t print_graph_function(struct trace_iterator *iter);
 534
 535 #ifdef CONFIG_DYNAMIC_FTRACE
 536 /* TODO: make this variable */
 537 #define FTRACE_GRAPH_MAX_FUNCS          32
 538 extern int ftrace_graph_count;
 539 extern unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS];
 540
 541 static inline int ftrace_graph_addr(unsigned long addr)
 542 {
 543         int i;
 544
 545         if (!ftrace_graph_count || test_tsk_trace_graph(current))
 546                 return 1;
 547
 548         for (i = 0; i < ftrace_graph_count; i++) {
 549                 if (addr == ftrace_graph_funcs[i])
 550                         return 1;
 551         }
 552
 553         return 0;
 554 }
 555 #else
 556 static inline int ftrace_trace_addr(unsigned long addr)
 557 {
 558         return 1;
 559 }
 560 static inline int ftrace_graph_addr(unsigned long addr)
 561 {
 562         return 1;
 563 }
 564 #endif /* CONFIG_DYNAMIC_FTRACE */
 565
 566 #else /* CONFIG_FUNCTION_GRAPH_TRACER */
 567 static inline enum print_line_t
 568 print_graph_function(struct trace_iterator *iter)
 569 {
 570         return TRACE_TYPE_UNHANDLED;
 571 }
 572 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 573
 574 extern struct pid *ftrace_pid_trace;
 575
 576 static inline int ftrace_trace_task(struct task_struct *task)
 577 {
 578         if (!ftrace_pid_trace)
 579                 return 1;
 580
 581         return test_tsk_trace_trace(task);
 582 }
 583
 584 /*
 585  * trace_iterator_flags is an enumeration that defines bit
 586  * positions into trace_flags that controls the output.
 587  *
 588  * NOTE: These bits must match the trace_options array in
 589  *       trace.c.
 590  */
 591 enum trace_iterator_flags {
 592         TRACE_ITER_PRINT_PARENT         = 0x01,
 593         TRACE_ITER_SYM_OFFSET           = 0x02,
 594         TRACE_ITER_SYM_ADDR             = 0x04,
 595         TRACE_ITER_VERBOSE              = 0x08,
 596         TRACE_ITER_RAW                  = 0x10,
 597         TRACE_ITER_HEX                  = 0x20,
 598         TRACE_ITER_BIN                  = 0x40,
 599         TRACE_ITER_BLOCK                = 0x80,
 600         TRACE_ITER_STACKTRACE           = 0x100,
 601         TRACE_ITER_SCHED_TREE           = 0x200,
 602         TRACE_ITER_PRINTK               = 0x400,
 603         TRACE_ITER_PREEMPTONLY          = 0x800,
 604         TRACE_ITER_BRANCH               = 0x1000,
 605         TRACE_ITER_ANNOTATE             = 0x2000,
 606         TRACE_ITER_USERSTACKTRACE       = 0x4000,
 607         TRACE_ITER_SYM_USEROBJ          = 0x8000,
 608         TRACE_ITER_PRINTK_MSGONLY       = 0x10000
 609 };
 610
 611 /*
 612  * TRACE_ITER_SYM_MASK masks the options in trace_flags that
 613  * control the output of kernel symbols.
 614  */
 615 #define TRACE_ITER_SYM_MASK \
 616         (TRACE_ITER_PRINT_PARENT|TRACE_ITER_SYM_OFFSET|TRACE_ITER_SYM_ADDR)
 617
 618 extern struct tracer nop_trace;
 619
 620 /**
 621  * ftrace_preempt_disable - disable preemption scheduler safe
 622  *
 623  * When tracing can happen inside the scheduler, there exists
 624  * cases that the tracing might happen before the need_resched
 625  * flag is checked. If this happens and the tracer calls
 626  * preempt_enable (after a disable), a schedule might take place
 627  * causing an infinite recursion.
 628  *
 629  * To prevent this, we read the need_recshed flag before
 630  * disabling preemption. When we want to enable preemption we
 631  * check the flag, if it is set, then we call preempt_enable_no_resched.
 632  * Otherwise, we call preempt_enable.
 633  *
 634  * The rational for doing the above is that if need resched is set
 635  * and we have yet to reschedule, we are either in an atomic location
 636  * (where we do not need to check for scheduling) or we are inside
 637  * the scheduler and do not want to resched.
 638  */
 639 static inline int ftrace_preempt_disable(void)
 640 {
 641         int resched;
 642
 643         resched = need_resched();
 644         preempt_disable_notrace();
 645
 646         return resched;
 647 }
 648
 649 /**
 650  * ftrace_preempt_enable - enable preemption scheduler safe
 651  * @resched: the return value from ftrace_preempt_disable
 652  *
 653  * This is a scheduler safe way to enable preemption and not miss
 654  * any preemption checks. The disabled saved the state of preemption.
 655  * If resched is set, then we were either inside an atomic or
 656  * are inside the scheduler (we would have already scheduled
 657  * otherwise). In this case, we do not want to call normal
 658  * preempt_enable, but preempt_enable_no_resched instead.
 659  */
 660 static inline void ftrace_preempt_enable(int resched)
 661 {
 662         if (resched)
 663                 preempt_enable_no_resched_notrace();
 664         else
 665                 preempt_enable_notrace();
 666 }
 667
 668 #ifdef CONFIG_BRANCH_TRACER
 669 extern int enable_branch_tracing(struct trace_array *tr);
 670 extern void disable_branch_tracing(void);
 671 static inline int trace_branch_enable(struct trace_array *tr)
 672 {
 673         if (trace_flags & TRACE_ITER_BRANCH)
 674                 return enable_branch_tracing(tr);
 675         return 0;
 676 }
 677 static inline void trace_branch_disable(void)
 678 {
 679         /* due to races, always disable */
 680         disable_branch_tracing();
 681 }
 682 #else
 683 static inline int trace_branch_enable(struct trace_array *tr)
 684 {
 685         return 0;
 686 }
 687 static inline void trace_branch_disable(void)
 688 {
 689 }
 690 #endif /* CONFIG_BRANCH_TRACER */
 691
 692 #endif /* _LINUX_KERNEL_TRACE_H */