kernel/trace/trace_event_perf.c

   1 /*
   2  * trace event based perf event profiling/tracing
   3  *
   4  * Copyright (C) 2009 Red Hat Inc, Peter Zijlstra <pzijlstr@redhat.com>
   5  * Copyright (C) 2009-2010 Frederic Weisbecker <fweisbec@gmail.com>
   6  */
   7
   8 #include <linux/module.h>
   9 #include <linux/kprobes.h>
  10 #include "trace.h"
  11
  12 DEFINE_PER_CPU(struct pt_regs, perf_trace_regs);
  13 EXPORT_PER_CPU_SYMBOL_GPL(perf_trace_regs);
  14
  15 EXPORT_SYMBOL_GPL(perf_arch_fetch_caller_regs);
  16
  17 static char *perf_trace_buf;
  18 static char *perf_trace_buf_nmi;
  19
  20 /*
  21  * Force it to be aligned to unsigned long to avoid misaligned accesses
  22  * suprises
  23  */
  24 typedef typeof(unsigned long [PERF_MAX_TRACE_SIZE / sizeof(unsigned long)])
  25         perf_trace_t;
  26
  27 /* Count the events in use (per event id, not per instance) */
  28 static int      total_ref_count;
  29
  30 static int perf_trace_event_enable(struct ftrace_event_call *event)
  31 {
  32         char *buf;
  33         int ret = -ENOMEM;
  34
  35         if (event->perf_refcount++ > 0)
  36                 return 0;
  37
  38         if (!total_ref_count) {
  39                 buf = (char *)alloc_percpu(perf_trace_t);
  40                 if (!buf)
  41                         goto fail_buf;
  42
  43                 rcu_assign_pointer(perf_trace_buf, buf);
  44
  45                 buf = (char *)alloc_percpu(perf_trace_t);
  46                 if (!buf)
  47                         goto fail_buf_nmi;
  48
  49                 rcu_assign_pointer(perf_trace_buf_nmi, buf);
  50         }
  51
  52         ret = event->perf_event_enable(event);
  53         if (!ret) {
  54                 total_ref_count++;
  55                 return 0;
  56         }
  57
  58 fail_buf_nmi:
  59         if (!total_ref_count) {
  60                 free_percpu(perf_trace_buf_nmi);
  61                 free_percpu(perf_trace_buf);
  62                 perf_trace_buf_nmi = NULL;
  63                 perf_trace_buf = NULL;
  64         }
  65 fail_buf:
  66         event->perf_refcount--;
  67
  68         return ret;
  69 }
  70
  71 int perf_trace_enable(int event_id)
  72 {
  73         struct ftrace_event_call *event;
  74         int ret = -EINVAL;
  75
  76         mutex_lock(&event_mutex);
  77         list_for_each_entry(event, &ftrace_events, list) {
  78                 if (event->id == event_id && event->perf_event_enable &&
  79                     try_module_get(event->mod)) {
  80                         ret = perf_trace_event_enable(event);
  81                         break;
  82                 }
  83         }
  84         mutex_unlock(&event_mutex);
  85
  86         return ret;
  87 }
  88
  89 static void perf_trace_event_disable(struct ftrace_event_call *event)
  90 {
  91         char *buf, *nmi_buf;
  92
  93         if (--event->perf_refcount > 0)
  94                 return;
  95
  96         event->perf_event_disable(event);
  97
  98         if (!--total_ref_count) {
  99                 buf = perf_trace_buf;
 100                 rcu_assign_pointer(perf_trace_buf, NULL);
 101
 102                 nmi_buf = perf_trace_buf_nmi;
 103                 rcu_assign_pointer(perf_trace_buf_nmi, NULL);
 104
 105                 /*
 106                  * Ensure every events in profiling have finished before
 107                  * releasing the buffers
 108                  */
 109                 synchronize_sched();
 110
 111                 free_percpu(buf);
 112                 free_percpu(nmi_buf);
 113         }
 114 }
 115
 116 void perf_trace_disable(int event_id)
 117 {
 118         struct ftrace_event_call *event;
 119
 120         mutex_lock(&event_mutex);
 121         list_for_each_entry(event, &ftrace_events, list) {
 122                 if (event->id == event_id) {
 123                         perf_trace_event_disable(event);
 124                         module_put(event->mod);
 125                         break;
 126                 }
 127         }
 128         mutex_unlock(&event_mutex);
 129 }
 130
 131 __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
 132                                        int *rctxp, unsigned long *irq_flags)
 133 {
 134         struct trace_entry *entry;
 135         char *trace_buf, *raw_data;
 136         int pc, cpu;
 137
 138         BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(unsigned long));
 139
 140         pc = preempt_count();
 141
 142         /* Protect the per cpu buffer, begin the rcu read side */
 143         local_irq_save(*irq_flags);
 144
 145         *rctxp = perf_swevent_get_recursion_context();
 146         if (*rctxp < 0)
 147                 goto err_recursion;
 148
 149         cpu = smp_processor_id();
 150
 151         if (in_nmi())
 152                 trace_buf = rcu_dereference_sched(perf_trace_buf_nmi);
 153         else
 154                 trace_buf = rcu_dereference_sched(perf_trace_buf);
 155
 156         if (!trace_buf)
 157                 goto err;
 158
 159         raw_data = per_cpu_ptr(trace_buf, cpu);
 160
 161         /* zero the dead bytes from align to not leak stack to user */
 162         memset(&raw_data[size - sizeof(u64)], 0, sizeof(u64));
 163
 164         entry = (struct trace_entry *)raw_data;
 165         tracing_generic_entry_update(entry, *irq_flags, pc);
 166         entry->type = type;
 167
 168         return raw_data;
 169 err:
 170         perf_swevent_put_recursion_context(*rctxp);
 171 err_recursion:
 172         local_irq_restore(*irq_flags);
 173         return NULL;
 174 }
 175 EXPORT_SYMBOL_GPL(perf_trace_buf_prepare);