lttng-context-preemptible.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * lttng-context-preemptible.c
   4  *
   5  * LTTng preemptible context.
   6  *
   7  * Copyright (C) 2009-2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/slab.h>
  12 #include <linux/sched.h>
  13 #include <linux/irqflags.h>
  14 #include <lttng/lttng-events.h>
  15 #include <ringbuffer/frontend_types.h>
  16 #include <lttng/lttng-tracer.h>
  17
  18 /*
  19  * We nest twice in preempt disabling within LTTng: one nesting is done
  20  * by the instrumentation (tracepoint, kprobes, kretprobes, syscall
  21  * tracepoint), and the second is within the lib ring buffer
  22  * lib_ring_buffer_get_cpu().
  23  */
  24 #define LTTNG_PREEMPT_DISABLE_NESTING   2
  25
  26 static
  27 size_t preemptible_get_size(size_t offset)
  28 {
  29         size_t size = 0;
  30
  31         size += lib_ring_buffer_align(offset, lttng_alignof(uint8_t));
  32         size += sizeof(uint8_t);
  33         return size;
  34 }
  35
  36 static
  37 void preemptible_record(struct lttng_ctx_field *field,
  38                 struct lib_ring_buffer_ctx *ctx,
  39                 struct lttng_channel *chan)
  40 {
  41         int pc = preempt_count();
  42         uint8_t preemptible = 0;
  43
  44         WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
  45         if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
  46                 preemptible = 1;
  47         lib_ring_buffer_align_ctx(ctx, lttng_alignof(preemptible));
  48         chan->ops->event_write(ctx, &preemptible, sizeof(preemptible));
  49 }
  50
  51 static
  52 void preemptible_get_value(struct lttng_ctx_field *field,
  53                 struct lttng_probe_ctx *lttng_probe_ctx,
  54                 union lttng_ctx_value *value)
  55 {
  56         int pc = preempt_count();
  57
  58         WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
  59         if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
  60                 value->s64 = 1;
  61         else
  62                 value->s64 = 0;
  63 }
  64
  65 int lttng_add_preemptible_to_ctx(struct lttng_ctx **ctx)
  66 {
  67         struct lttng_ctx_field *field;
  68
  69         field = lttng_append_context(ctx);
  70         if (!field)
  71                 return -ENOMEM;
  72         if (lttng_find_context(*ctx, "preemptible")) {
  73                 lttng_remove_context_field(ctx, field);
  74                 return -EEXIST;
  75         }
  76         field->event_field.name = "preemptible";
  77         field->event_field.type.atype = atype_integer;
  78         field->event_field.type.u.integer.size = sizeof(uint8_t) * CHAR_BIT;
  79         field->event_field.type.u.integer.alignment = lttng_alignof(uint8_t) * CHAR_BIT;
  80         field->event_field.type.u.integer.signedness = lttng_is_signed_type(uint8_t);
  81         field->event_field.type.u.integer.reverse_byte_order = 0;
  82         field->event_field.type.u.integer.base = 10;
  83         field->event_field.type.u.integer.encoding = lttng_encode_none;
  84         field->get_size = preemptible_get_size;
  85         field->record = preemptible_record;
  86         field->get_value = preemptible_get_value;
  87         lttng_context_update(*ctx);
  88         return 0;
  89 }
  90 EXPORT_SYMBOL_GPL(lttng_add_preemptible_to_ctx);