lttng-context-preemptible.c

   1 /*
   2  * lttng-context-preemptible.c
   3  *
   4  * LTTng preemptible context.
   5  *
   6  * Copyright (C) 2009-2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; only
  11  * version 2.1 of the License.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include <linux/module.h>
  24 #include <linux/slab.h>
  25 #include <linux/sched.h>
  26 #include <linux/irqflags.h>
  27 #include <lttng-events.h>
  28 #include <wrapper/ringbuffer/frontend_types.h>
  29 #include <wrapper/vmalloc.h>
  30 #include <lttng-tracer.h>
  31
  32 /*
  33  * We nest twice in preempt disabling within LTTng: one nesting is done
  34  * by the instrumentation (tracepoint, kprobes, kretprobes, syscall
  35  * tracepoint), and the second is within the lib ring buffer
  36  * lib_ring_buffer_get_cpu().
  37  */
  38 #define LTTNG_PREEMPT_DISABLE_NESTING   2
  39
  40 static
  41 size_t preemptible_get_size(size_t offset)
  42 {
  43         size_t size = 0;
  44
  45         size += lib_ring_buffer_align(offset, lttng_alignof(uint8_t));
  46         size += sizeof(uint8_t);
  47         return size;
  48 }
  49
  50 static
  51 void preemptible_record(struct lttng_ctx_field *field,
  52                 struct lib_ring_buffer_ctx *ctx,
  53                 struct lttng_channel *chan)
  54 {
  55         int pc = preempt_count();
  56         uint8_t preemptible = 0;
  57
  58         WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
  59         if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
  60                 preemptible = 1;
  61         lib_ring_buffer_align_ctx(ctx, lttng_alignof(preemptible));
  62         chan->ops->event_write(ctx, &preemptible, sizeof(preemptible));
  63 }
  64
  65 static
  66 void preemptible_get_value(struct lttng_ctx_field *field,
  67                 struct lttng_probe_ctx *lttng_probe_ctx,
  68                 union lttng_ctx_value *value)
  69 {
  70         int pc = preempt_count();
  71
  72         WARN_ON_ONCE(pc < LTTNG_PREEMPT_DISABLE_NESTING);
  73         if (pc == LTTNG_PREEMPT_DISABLE_NESTING)
  74                 value->s64 = 1;
  75         else
  76                 value->s64 = 0;
  77 }
  78
  79 int lttng_add_preemptible_to_ctx(struct lttng_ctx **ctx)
  80 {
  81         struct lttng_ctx_field *field;
  82
  83         field = lttng_append_context(ctx);
  84         if (!field)
  85                 return -ENOMEM;
  86         if (lttng_find_context(*ctx, "preemptible")) {
  87                 lttng_remove_context_field(ctx, field);
  88                 return -EEXIST;
  89         }
  90         field->event_field.name = "preemptible";
  91         field->event_field.type.atype = atype_integer;
  92         field->event_field.type.u.basic.integer.size = sizeof(uint8_t) * CHAR_BIT;
  93         field->event_field.type.u.basic.integer.alignment = lttng_alignof(uint8_t) * CHAR_BIT;
  94         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(uint8_t);
  95         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
  96         field->event_field.type.u.basic.integer.base = 10;
  97         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
  98         field->get_size = preemptible_get_size;
  99         field->record = preemptible_record;
 100         field->get_value = preemptible_get_value;
 101         lttng_context_update(*ctx);
 102         wrapper_vmalloc_sync_all();
 103         return 0;
 104 }
 105 EXPORT_SYMBOL_GPL(lttng_add_preemptible_to_ctx);