lttng-context-preemptible.c

   1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
   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-events.h>
  15 #include <wrapper/ringbuffer/frontend_types.h>
  16 #include <wrapper/vmalloc.h>
  17 #include <lttng-tracer.h>
  18
  19 /*
  20  * We nest twice in preempt disabling within LTTng: one nesting is done
  21  * by the instrumentation (tracepoint, kprobes, kretprobes, syscall
  22  * tracepoint), and the second is within the lib ring buffer
  23  * lib_ring_buffer_get_cpu().
  24  */
  25 #define LTTNG_PREEMPT_DISABLE_NESTING   2
  26
  27 static
  28 size_t preemptible_get_size(size_t offset)
  29 {
  30         size_t size = 0;
  31
  32         size += lib_ring_buffer_align(offset, lttng_alignof(uint8_t));
  33         size += sizeof(uint8_t);
  34         return size;
  35 }
  36
  37 static
  38 void preemptible_record(struct lttng_ctx_field *field,
  39                 struct lib_ring_buffer_ctx *ctx,
  40                 struct lttng_channel *chan)
  41 {
  42         int pc = preempt_count();
  43         uint8_t preemptible = 0;
  44
  45         WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
  46         if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
  47                 preemptible = 1;
  48         lib_ring_buffer_align_ctx(ctx, lttng_alignof(preemptible));
  49         chan->ops->event_write(ctx, &preemptible, sizeof(preemptible));
  50 }
  51
  52 static
  53 void preemptible_get_value(struct lttng_ctx_field *field,
  54                 struct lttng_probe_ctx *lttng_probe_ctx,
  55                 union lttng_ctx_value *value)
  56 {
  57         int pc = preempt_count();
  58
  59         WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
  60         if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
  61                 value->s64 = 1;
  62         else
  63                 value->s64 = 0;
  64 }
  65
  66 int lttng_add_preemptible_to_ctx(struct lttng_ctx **ctx)
  67 {
  68         struct lttng_ctx_field *field;
  69
  70         field = lttng_append_context(ctx);
  71         if (!field)
  72                 return -ENOMEM;
  73         if (lttng_find_context(*ctx, "preemptible")) {
  74                 lttng_remove_context_field(ctx, field);
  75                 return -EEXIST;
  76         }
  77         field->event_field.name = "preemptible";
  78         field->event_field.type.atype = atype_integer;
  79         field->event_field.type.u.basic.integer.size = sizeof(uint8_t) * CHAR_BIT;
  80         field->event_field.type.u.basic.integer.alignment = lttng_alignof(uint8_t) * CHAR_BIT;
  81         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(uint8_t);
  82         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
  83         field->event_field.type.u.basic.integer.base = 10;
  84         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
  85         field->get_size = preemptible_get_size;
  86         field->record = preemptible_record;
  87         field->get_value = preemptible_get_value;
  88         lttng_context_update(*ctx);
  89         wrapper_vmalloc_sync_mappings();
  90         return 0;
  91 }
  92 EXPORT_SYMBOL_GPL(lttng_add_preemptible_to_ctx);