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 #include <trace/power.h>
  14
  15 enum trace_type {
  16         __TRACE_FIRST_TYPE = 0,
  17
  18         TRACE_FN,
  19         TRACE_CTX,
  20         TRACE_WAKE,
  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         TRACE_BLK,
  37
  38         __TRACE_LAST_TYPE,
  39 };
  40
  41 /*
  42  * The trace entry - the most basic unit of tracing. This is what
  43  * is printed in the end as a single line in the trace output, such as:
  44  *
  45  *     bash-15816 [01]   235.197585: idle_cpu <- irq_enter
  46  */
  47 struct trace_entry {
  48         unsigned char           type;
  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  */
 203 enum trace_flag_type {
 204         TRACE_FLAG_IRQS_OFF             = 0x01,
 205         TRACE_FLAG_IRQS_NOSUPPORT       = 0x02,
 206         TRACE_FLAG_NEED_RESCHED         = 0x04,
 207         TRACE_FLAG_HARDIRQ              = 0x08,
 208         TRACE_FLAG_SOFTIRQ              = 0x10,
 209 };
 210
 211 #define TRACE_BUF_SIZE          1024
 212
 213 /*
 214  * The CPU trace array - it consists of thousands of trace entries
 215  * plus some other descriptor data: (for example which task started
 216  * the trace, etc.)
 217  */
 218 struct trace_array_cpu {
 219         atomic_t                disabled;
 220
 221         /* these fields get copied into max-trace: */
 222         unsigned long           trace_idx;
 223         unsigned long           overrun;
 224         unsigned long           saved_latency;
 225         unsigned long           critical_start;
 226         unsigned long           critical_end;
 227         unsigned long           critical_sequence;
 228         unsigned long           nice;
 229         unsigned long           policy;
 230         unsigned long           rt_priority;
 231         cycle_t                 preempt_timestamp;
 232         pid_t                   pid;
 233         uid_t                   uid;
 234         char                    comm[TASK_COMM_LEN];
 235 };
 236
 237 struct trace_iterator;
 238
 239 /*
 240  * The trace array - an array of per-CPU trace arrays. This is the
 241  * highest level data structure that individual tracers deal with.
 242  * They have on/off state as well:
 243  */
 244 struct trace_array {
 245         struct ring_buffer      *buffer;
 246         unsigned long           entries;
 247         int                     cpu;
 248         cycle_t                 time_start;
 249         struct task_struct      *waiter;
 250         struct trace_array_cpu  *data[NR_CPUS];
 251 };
 252
 253 #define FTRACE_CMP_TYPE(var, type) \
 254         __builtin_types_compatible_p(typeof(var), type *)
 255
 256 #undef IF_ASSIGN
 257 #define IF_ASSIGN(var, entry, etype, id)                \
 258         if (FTRACE_CMP_TYPE(var, etype)) {              \
 259                 var = (typeof(var))(entry);             \
 260                 WARN_ON(id && (entry)->type != id);     \
 261                 break;                                  \
 262         }
 263
 264 /* Will cause compile errors if type is not found. */
 265 extern void __ftrace_bad_type(void);
 266
 267 /*
 268  * The trace_assign_type is a verifier that the entry type is
 269  * the same as the type being assigned. To add new types simply
 270  * add a line with the following format:
 271  *
 272  * IF_ASSIGN(var, ent, type, id);
 273  *
 274  *  Where "type" is the trace type that includes the trace_entry
 275  *  as the "ent" item. And "id" is the trace identifier that is
 276  *  used in the trace_type enum.
 277  *
 278  *  If the type can have more than one id, then use zero.
 279  */
 280 #define trace_assign_type(var, ent)                                     \
 281         do {                                                            \
 282                 IF_ASSIGN(var, ent, struct ftrace_entry, TRACE_FN);     \
 283                 IF_ASSIGN(var, ent, struct ctx_switch_entry, 0);        \
 284                 IF_ASSIGN(var, ent, struct stack_entry, TRACE_STACK);   \
 285                 IF_ASSIGN(var, ent, struct userstack_entry, TRACE_USER_STACK);\
 286                 IF_ASSIGN(var, ent, struct print_entry, TRACE_PRINT);   \
 287                 IF_ASSIGN(var, ent, struct special_entry, 0);           \
 288                 IF_ASSIGN(var, ent, struct trace_mmiotrace_rw,          \
 289                           TRACE_MMIO_RW);                               \
 290                 IF_ASSIGN(var, ent, struct trace_mmiotrace_map,         \
 291                           TRACE_MMIO_MAP);                              \
 292                 IF_ASSIGN(var, ent, struct trace_boot_call, TRACE_BOOT_CALL);\
 293                 IF_ASSIGN(var, ent, struct trace_boot_ret, TRACE_BOOT_RET);\
 294                 IF_ASSIGN(var, ent, struct trace_branch, TRACE_BRANCH); \
 295                 IF_ASSIGN(var, ent, struct ftrace_graph_ent_entry,      \
 296                           TRACE_GRAPH_ENT);             \
 297                 IF_ASSIGN(var, ent, struct ftrace_graph_ret_entry,      \
 298                           TRACE_GRAPH_RET);             \
 299                 IF_ASSIGN(var, ent, struct hw_branch_entry, TRACE_HW_BRANCHES);\
 300                 IF_ASSIGN(var, ent, struct trace_power, TRACE_POWER); \
 301                 IF_ASSIGN(var, ent, struct kmemtrace_alloc_entry,       \
 302                           TRACE_KMEM_ALLOC);    \
 303                 IF_ASSIGN(var, ent, struct kmemtrace_free_entry,        \
 304                           TRACE_KMEM_FREE);     \
 305                 __ftrace_bad_type();                                    \
 306         } while (0)
 307
 308 /* Return values for print_line callback */
 309 enum print_line_t {
 310         TRACE_TYPE_PARTIAL_LINE = 0,    /* Retry after flushing the seq */
 311         TRACE_TYPE_HANDLED      = 1,
 312         TRACE_TYPE_UNHANDLED    = 2,    /* Relay to other output functions */
 313         TRACE_TYPE_NO_CONSUME   = 3     /* Handled but ask to not consume */
 314 };
 315
 316
 317 /*
 318  * An option specific to a tracer. This is a boolean value.
 319  * The bit is the bit index that sets its value on the
 320  * flags value in struct tracer_flags.
 321  */
 322 struct tracer_opt {
 323         const char      *name; /* Will appear on the trace_options file */
 324         u32             bit; /* Mask assigned in val field in tracer_flags */
 325 };
 326
 327 /*
 328  * The set of specific options for a tracer. Your tracer
 329  * have to set the initial value of the flags val.
 330  */
 331 struct tracer_flags {
 332         u32                     val;
 333         struct tracer_opt       *opts;
 334 };
 335
 336 /* Makes more easy to define a tracer opt */
 337 #define TRACER_OPT(s, b)        .name = #s, .bit = b
 338
 339
 340 /*
 341  * A specific tracer, represented by methods that operate on a trace array:
 342  */
 343 struct tracer {
 344         const char              *name;
 345         /* Your tracer should raise a warning if init fails */
 346         int                     (*init)(struct trace_array *tr);
 347         void                    (*reset)(struct trace_array *tr);
 348         void                    (*start)(struct trace_array *tr);
 349         void                    (*stop)(struct trace_array *tr);
 350         void                    (*open)(struct trace_iterator *iter);
 351         void                    (*pipe_open)(struct trace_iterator *iter);
 352         void                    (*close)(struct trace_iterator *iter);
 353         ssize_t                 (*read)(struct trace_iterator *iter,
 354                                         struct file *filp, char __user *ubuf,
 355                                         size_t cnt, loff_t *ppos);
 356         ssize_t                 (*splice_read)(struct trace_iterator *iter,
 357                                                struct file *filp,
 358                                                loff_t *ppos,
 359                                                struct pipe_inode_info *pipe,
 360                                                size_t len,
 361                                                unsigned int flags);
 362 #ifdef CONFIG_FTRACE_STARTUP_TEST
 363         int                     (*selftest)(struct tracer *trace,
 364                                             struct trace_array *tr);
 365 #endif
 366         void                    (*print_header)(struct seq_file *m);
 367         enum print_line_t       (*print_line)(struct trace_iterator *iter);
 368         /* If you handled the flag setting, return 0 */
 369         int                     (*set_flag)(u32 old_flags, u32 bit, int set);
 370         struct tracer           *next;
 371         int                     print_max;
 372         struct tracer_flags     *flags;
 373         struct tracer_stat      *stats;
 374 };
 375
 376 struct trace_seq {
 377         unsigned char           buffer[PAGE_SIZE];
 378         unsigned int            len;
 379         unsigned int            readpos;
 380 };
 381
 382 /*
 383  * Trace iterator - used by printout routines who present trace
 384  * results to users and which routines might sleep, etc:
 385  */
 386 struct trace_iterator {
 387         struct trace_array      *tr;
 388         struct tracer           *trace;
 389         void                    *private;
 390         struct ring_buffer_iter *buffer_iter[NR_CPUS];
 391
 392         /* The below is zeroed out in pipe_read */
 393         struct trace_seq        seq;
 394         struct trace_entry      *ent;
 395         int                     cpu;
 396         u64                     ts;
 397
 398         unsigned long           iter_flags;
 399         loff_t                  pos;
 400         long                    idx;
 401
 402         cpumask_var_t           started;
 403 };
 404
 405 int tracer_init(struct tracer *t, struct trace_array *tr);
 406 int tracing_is_enabled(void);
 407 void trace_wake_up(void);
 408 void tracing_reset(struct trace_array *tr, int cpu);
 409 void tracing_reset_online_cpus(struct trace_array *tr);
 410 int tracing_open_generic(struct inode *inode, struct file *filp);
 411 struct dentry *tracing_init_dentry(void);
 412 void init_tracer_sysprof_debugfs(struct dentry *d_tracer);
 413
 414 struct ring_buffer_event;
 415
 416 struct ring_buffer_event *trace_buffer_lock_reserve(struct trace_array *tr,
 417                                                     unsigned char type,
 418                                                     unsigned long len,
 419                                                     unsigned long flags,
 420                                                     int pc);
 421 void trace_buffer_unlock_commit(struct trace_array *tr,
 422                                 struct ring_buffer_event *event,
 423                                 unsigned long flags, int pc);
 424
 425 struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,
 426                                                 struct trace_array_cpu *data);
 427
 428 struct trace_entry *trace_find_next_entry(struct trace_iterator *iter,
 429                                           int *ent_cpu, u64 *ent_ts);
 430
 431 void tracing_generic_entry_update(struct trace_entry *entry,
 432                                   unsigned long flags,
 433                                   int pc);
 434
 435 void ftrace(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 void tracing_sched_switch_trace(struct trace_array *tr,
 441                                 struct task_struct *prev,
 442                                 struct task_struct *next,
 443                                 unsigned long flags, int pc);
 444 void tracing_record_cmdline(struct task_struct *tsk);
 445
 446 void tracing_sched_wakeup_trace(struct trace_array *tr,
 447                                 struct task_struct *wakee,
 448                                 struct task_struct *cur,
 449                                 unsigned long flags, int pc);
 450 void trace_special(struct trace_array *tr,
 451                    struct trace_array_cpu *data,
 452                    unsigned long arg1,
 453                    unsigned long arg2,
 454                    unsigned long arg3, int pc);
 455 void trace_function(struct trace_array *tr,
 456                     unsigned long ip,
 457                     unsigned long parent_ip,
 458                     unsigned long flags, int pc);
 459
 460 void trace_graph_return(struct ftrace_graph_ret *trace);
 461 int trace_graph_entry(struct ftrace_graph_ent *trace);
 462
 463 void tracing_start_cmdline_record(void);
 464 void tracing_stop_cmdline_record(void);
 465 void tracing_sched_switch_assign_trace(struct trace_array *tr);
 466 void tracing_stop_sched_switch_record(void);
 467 void tracing_start_sched_switch_record(void);
 468 int register_tracer(struct tracer *type);
 469 void unregister_tracer(struct tracer *type);
 470
 471 extern unsigned long nsecs_to_usecs(unsigned long nsecs);
 472
 473 extern unsigned long tracing_max_latency;
 474 extern unsigned long tracing_thresh;
 475
 476 void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu);
 477 void update_max_tr_single(struct trace_array *tr,
 478                           struct task_struct *tsk, int cpu);
 479
 480 void __trace_stack(struct trace_array *tr,
 481                    unsigned long flags,
 482                    int skip, int pc);
 483
 484 extern cycle_t ftrace_now(int cpu);
 485
 486 #ifdef CONFIG_CONTEXT_SWITCH_TRACER
 487 typedef void
 488 (*tracer_switch_func_t)(void *private,
 489                         void *__rq,
 490                         struct task_struct *prev,
 491                         struct task_struct *next);
 492
 493 struct tracer_switch_ops {
 494         tracer_switch_func_t            func;
 495         void                            *private;
 496         struct tracer_switch_ops        *next;
 497 };
 498 #endif /* CONFIG_CONTEXT_SWITCH_TRACER */
 499
 500 extern char *trace_find_cmdline(int pid);
 501
 502 #ifdef CONFIG_DYNAMIC_FTRACE
 503 extern unsigned long ftrace_update_tot_cnt;
 504 #define DYN_FTRACE_TEST_NAME trace_selftest_dynamic_test_func
 505 extern int DYN_FTRACE_TEST_NAME(void);
 506 #endif
 507
 508 #ifdef CONFIG_FTRACE_STARTUP_TEST
 509 extern int trace_selftest_startup_function(struct tracer *trace,
 510                                            struct trace_array *tr);
 511 extern int trace_selftest_startup_function_graph(struct tracer *trace,
 512                                                  struct trace_array *tr);
 513 extern int trace_selftest_startup_irqsoff(struct tracer *trace,
 514                                           struct trace_array *tr);
 515 extern int trace_selftest_startup_preemptoff(struct tracer *trace,
 516                                              struct trace_array *tr);
 517 extern int trace_selftest_startup_preemptirqsoff(struct tracer *trace,
 518                                                  struct trace_array *tr);
 519 extern int trace_selftest_startup_wakeup(struct tracer *trace,
 520                                          struct trace_array *tr);
 521 extern int trace_selftest_startup_nop(struct tracer *trace,
 522                                          struct trace_array *tr);
 523 extern int trace_selftest_startup_sched_switch(struct tracer *trace,
 524                                                struct trace_array *tr);
 525 extern int trace_selftest_startup_sysprof(struct tracer *trace,
 526                                                struct trace_array *tr);
 527 extern int trace_selftest_startup_branch(struct tracer *trace,
 528                                          struct trace_array *tr);
 529 #endif /* CONFIG_FTRACE_STARTUP_TEST */
 530
 531 extern void *head_page(struct trace_array_cpu *data);
 532 extern long ns2usecs(cycle_t nsec);
 533 extern int
 534 trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args);
 535
 536 extern unsigned long trace_flags;
 537
 538 /* Standard output formatting function used for function return traces */
 539 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 540 extern enum print_line_t print_graph_function(struct trace_iterator *iter);
 541
 542 #ifdef CONFIG_DYNAMIC_FTRACE
 543 /* TODO: make this variable */
 544 #define FTRACE_GRAPH_MAX_FUNCS          32
 545 extern int ftrace_graph_count;
 546 extern unsigned long ftrace_graph_funcs[FTRACE_GRAPH_MAX_FUNCS];
 547
 548 static inline int ftrace_graph_addr(unsigned long addr)
 549 {
 550         int i;
 551
 552         if (!ftrace_graph_count || test_tsk_trace_graph(current))
 553                 return 1;
 554
 555         for (i = 0; i < ftrace_graph_count; i++) {
 556                 if (addr == ftrace_graph_funcs[i])
 557                         return 1;
 558         }
 559
 560         return 0;
 561 }
 562 #else
 563 static inline int ftrace_trace_addr(unsigned long addr)
 564 {
 565         return 1;
 566 }
 567 static inline int ftrace_graph_addr(unsigned long addr)
 568 {
 569         return 1;
 570 }
 571 #endif /* CONFIG_DYNAMIC_FTRACE */
 572
 573 #else /* CONFIG_FUNCTION_GRAPH_TRACER */
 574 static inline enum print_line_t
 575 print_graph_function(struct trace_iterator *iter)
 576 {
 577         return TRACE_TYPE_UNHANDLED;
 578 }
 579 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 580
 581 extern struct pid *ftrace_pid_trace;
 582
 583 static inline int ftrace_trace_task(struct task_struct *task)
 584 {
 585         if (!ftrace_pid_trace)
 586                 return 1;
 587
 588         return test_tsk_trace_trace(task);
 589 }
 590
 591 /*
 592  * trace_iterator_flags is an enumeration that defines bit
 593  * positions into trace_flags that controls the output.
 594  *
 595  * NOTE: These bits must match the trace_options array in
 596  *       trace.c.
 597  */
 598 enum trace_iterator_flags {
 599         TRACE_ITER_PRINT_PARENT         = 0x01,
 600         TRACE_ITER_SYM_OFFSET           = 0x02,
 601         TRACE_ITER_SYM_ADDR             = 0x04,
 602         TRACE_ITER_VERBOSE              = 0x08,
 603         TRACE_ITER_RAW                  = 0x10,
 604         TRACE_ITER_HEX                  = 0x20,
 605         TRACE_ITER_BIN                  = 0x40,
 606         TRACE_ITER_BLOCK                = 0x80,
 607         TRACE_ITER_STACKTRACE           = 0x100,
 608         TRACE_ITER_SCHED_TREE           = 0x200,
 609         TRACE_ITER_PRINTK               = 0x400,
 610         TRACE_ITER_PREEMPTONLY          = 0x800,
 611         TRACE_ITER_BRANCH               = 0x1000,
 612         TRACE_ITER_ANNOTATE             = 0x2000,
 613         TRACE_ITER_USERSTACKTRACE       = 0x4000,
 614         TRACE_ITER_SYM_USEROBJ          = 0x8000,
 615         TRACE_ITER_PRINTK_MSGONLY       = 0x10000,
 616         TRACE_ITER_CONTEXT_INFO         = 0x20000 /* Print pid/cpu/time */
 617 };
 618
 619 /*
 620  * TRACE_ITER_SYM_MASK masks the options in trace_flags that
 621  * control the output of kernel symbols.
 622  */
 623 #define TRACE_ITER_SYM_MASK \
 624         (TRACE_ITER_PRINT_PARENT|TRACE_ITER_SYM_OFFSET|TRACE_ITER_SYM_ADDR)
 625
 626 extern struct tracer nop_trace;
 627
 628 /**
 629  * ftrace_preempt_disable - disable preemption scheduler safe
 630  *
 631  * When tracing can happen inside the scheduler, there exists
 632  * cases that the tracing might happen before the need_resched
 633  * flag is checked. If this happens and the tracer calls
 634  * preempt_enable (after a disable), a schedule might take place
 635  * causing an infinite recursion.
 636  *
 637  * To prevent this, we read the need_resched flag before
 638  * disabling preemption. When we want to enable preemption we
 639  * check the flag, if it is set, then we call preempt_enable_no_resched.
 640  * Otherwise, we call preempt_enable.
 641  *
 642  * The rational for doing the above is that if need_resched is set
 643  * and we have yet to reschedule, we are either in an atomic location
 644  * (where we do not need to check for scheduling) or we are inside
 645  * the scheduler and do not want to resched.
 646  */
 647 static inline int ftrace_preempt_disable(void)
 648 {
 649         int resched;
 650
 651         resched = need_resched();
 652         preempt_disable_notrace();
 653
 654         return resched;
 655 }
 656
 657 /**
 658  * ftrace_preempt_enable - enable preemption scheduler safe
 659  * @resched: the return value from ftrace_preempt_disable
 660  *
 661  * This is a scheduler safe way to enable preemption and not miss
 662  * any preemption checks. The disabled saved the state of preemption.
 663  * If resched is set, then we are either inside an atomic or
 664  * are inside the scheduler (we would have already scheduled
 665  * otherwise). In this case, we do not want to call normal
 666  * preempt_enable, but preempt_enable_no_resched instead.
 667  */
 668 static inline void ftrace_preempt_enable(int resched)
 669 {
 670         if (resched)
 671                 preempt_enable_no_resched_notrace();
 672         else
 673                 preempt_enable_notrace();
 674 }
 675
 676 #ifdef CONFIG_BRANCH_TRACER
 677 extern int enable_branch_tracing(struct trace_array *tr);
 678 extern void disable_branch_tracing(void);
 679 static inline int trace_branch_enable(struct trace_array *tr)
 680 {
 681         if (trace_flags & TRACE_ITER_BRANCH)
 682                 return enable_branch_tracing(tr);
 683         return 0;
 684 }
 685 static inline void trace_branch_disable(void)
 686 {
 687         /* due to races, always disable */
 688         disable_branch_tracing();
 689 }
 690 #else
 691 static inline int trace_branch_enable(struct trace_array *tr)
 692 {
 693         return 0;
 694 }
 695 static inline void trace_branch_disable(void)
 696 {
 697 }
 698 #endif /* CONFIG_BRANCH_TRACER */
 699
 700 #endif /* _LINUX_KERNEL_TRACE_H */