lttng-context-callstack.c

   1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
   2  *
   3  * lttng-context-callstack.c
   4  *
   5  * LTTng callstack event context.
   6  *
   7  * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  * Copyright (C) 2014 Francis Giraldeau <francis.giraldeau@gmail.com>
   9  *
  10  * The callstack context can be added to any kernel event. It records
  11  * either the kernel or the userspace callstack, up to a max depth. The
  12  * context is a CTF sequence, such that it uses only the space required
  13  * for the number of callstack entries.
  14  *
  15  * It allocates callstack buffers per-CPU up to 4 interrupt nesting.
  16  * This nesting limit is the same as defined in the ring buffer. It
  17  * therefore uses a fixed amount of memory, proportional to the number
  18  * of CPUs:
  19  *
  20  *   size = cpus * nest * depth * sizeof(unsigned long)
  21  *
  22  * Which is 4096 bytes per CPU on 64-bit host and a depth of 128.
  23  * The allocation is done at the initialization to avoid memory
  24  * allocation overhead while tracing, using a shallow stack.
  25  *
  26  * The kernel callstack is recovered using save_stack_trace(), and the
  27  * userspace callstack uses save_stack_trace_user(). They rely on frame
  28  * pointers. These are usually available for the kernel, but the
  29  * compiler option -fomit-frame-pointer frequently used in popular Linux
  30  * distributions may cause the userspace callstack to be unreliable, and
  31  * is a known limitation of this approach. If frame pointers are not
  32  * available, it produces no error, but the callstack will be empty. We
  33  * still provide the feature, because it works well for runtime
  34  * environments having frame pointers. In the future, unwind support
  35  * and/or last branch record may provide a solution to this problem.
  36  *
  37  * The symbol name resolution is left to the trace reader.
  38  */
  39
  40 #include <linux/module.h>
  41 #include <linux/slab.h>
  42 #include <linux/sched.h>
  43 #include <linux/utsname.h>
  44 #include <linux/stacktrace.h>
  45 #include <linux/spinlock.h>
  46 #include "lttng-events.h"
  47 #include "wrapper/ringbuffer/backend.h"
  48 #include "wrapper/ringbuffer/frontend.h"
  49 #include "wrapper/vmalloc.h"
  50 #include "lttng-tracer.h"
  51
  52 #define MAX_ENTRIES 128
  53
  54 enum lttng_cs_ctx_modes {
  55         CALLSTACK_KERNEL = 0,
  56         CALLSTACK_USER = 1,
  57         NR_CALLSTACK_MODES,
  58 };
  59
  60 struct lttng_cs_dispatch {
  61         struct stack_trace stack_trace;
  62         unsigned long entries[MAX_ENTRIES];
  63 };
  64
  65 struct lttng_cs {
  66         struct lttng_cs_dispatch dispatch[RING_BUFFER_MAX_NESTING];
  67 };
  68
  69 struct field_data {
  70         struct lttng_cs __percpu *cs_percpu;
  71         enum lttng_cs_ctx_modes mode;
  72 };
  73
  74 struct lttng_cs_type {
  75         const char *name;
  76         const char *save_func_name;
  77         void (*save_func)(struct stack_trace *trace);
  78 };
  79
  80 static struct lttng_cs_type cs_types[] = {
  81         {
  82                 .name           = "callstack_kernel",
  83                 .save_func_name = "save_stack_trace",
  84                 .save_func      = NULL,
  85         },
  86         {
  87                 .name           = "callstack_user",
  88                 .save_func_name = "save_stack_trace_user",
  89                 .save_func      = NULL,
  90         },
  91 };
  92
  93 static
  94 int init_type(enum lttng_cs_ctx_modes mode)
  95 {
  96         unsigned long func;
  97
  98         if (cs_types[mode].save_func)
  99                 return 0;
 100         func = kallsyms_lookup_funcptr(cs_types[mode].save_func_name);
 101         if (!func) {
 102                 printk(KERN_WARNING "LTTng: symbol lookup failed: %s\n",
 103                                 cs_types[mode].save_func_name);
 104                 return -EINVAL;
 105         }
 106         cs_types[mode].save_func = (void *) func;
 107         return 0;
 108 }
 109
 110 /* Keep track of nesting inside userspace callstack context code */
 111 DEFINE_PER_CPU(int, callstack_user_nesting);
 112
 113 static
 114 struct stack_trace *stack_trace_context(struct lttng_ctx_field *field,
 115                                         struct lib_ring_buffer_ctx *ctx)
 116 {
 117         int buffer_nesting, cs_user_nesting;
 118         struct lttng_cs *cs;
 119         struct field_data *fdata = field->priv;
 120
 121         /*
 122          * Do not gather the userspace callstack context when the event was
 123          * triggered by the userspace callstack context saving mechanism.
 124          */
 125         cs_user_nesting = per_cpu(callstack_user_nesting, ctx->cpu);
 126
 127         if (fdata->mode == CALLSTACK_USER && cs_user_nesting >= 1)
 128                 return NULL;
 129
 130         /*
 131          * get_cpu() is not required, preemption is already
 132          * disabled while event is written.
 133          *
 134          * max nesting is checked in lib_ring_buffer_get_cpu().
 135          * Check it again as a safety net.
 136          */
 137         cs = per_cpu_ptr(fdata->cs_percpu, ctx->cpu);
 138         buffer_nesting = per_cpu(lib_ring_buffer_nesting, ctx->cpu) - 1;
 139         if (buffer_nesting >= RING_BUFFER_MAX_NESTING)
 140                 return NULL;
 141
 142         return &cs->dispatch[buffer_nesting].stack_trace;
 143 }
 144
 145 /*
 146  * In order to reserve the correct size, the callstack is computed. The
 147  * resulting callstack is saved to be accessed in the record step.
 148  */
 149 static
 150 size_t lttng_callstack_get_size(size_t offset, struct lttng_ctx_field *field,
 151                                 struct lib_ring_buffer_ctx *ctx,
 152                                 struct lttng_channel *chan)
 153 {
 154         struct stack_trace *trace;
 155         struct field_data *fdata = field->priv;
 156         size_t orig_offset = offset;
 157
 158         /* do not write data if no space is available */
 159         trace = stack_trace_context(field, ctx);
 160         if (unlikely(!trace)) {
 161                 offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
 162                 offset += sizeof(unsigned int);
 163                 offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 164                 return offset - orig_offset;
 165         }
 166
 167         /* reset stack trace, no need to clear memory */
 168         trace->nr_entries = 0;
 169
 170         if (fdata->mode == CALLSTACK_USER)
 171                 ++per_cpu(callstack_user_nesting, ctx->cpu);
 172
 173         /* do the real work and reserve space */
 174         cs_types[fdata->mode].save_func(trace);
 175
 176         if (fdata->mode == CALLSTACK_USER)
 177                 per_cpu(callstack_user_nesting, ctx->cpu)--;
 178
 179         /*
 180          * Remove final ULONG_MAX delimiter. If we cannot find it, add
 181          * our own marker to show that the stack is incomplete. This is
 182          * more compact for a trace.
 183          */
 184         if (trace->nr_entries > 0
 185                         && trace->entries[trace->nr_entries - 1] == ULONG_MAX) {
 186                 trace->nr_entries--;
 187         }
 188         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned int));
 189         offset += sizeof(unsigned int);
 190         offset += lib_ring_buffer_align(offset, lttng_alignof(unsigned long));
 191         offset += sizeof(unsigned long) * trace->nr_entries;
 192         /* Add our own ULONG_MAX delimiter to show incomplete stack. */
 193         if (trace->nr_entries == trace->max_entries)
 194                 offset += sizeof(unsigned long);
 195         return offset - orig_offset;
 196 }
 197
 198 static
 199 void lttng_callstack_record(struct lttng_ctx_field *field,
 200                         struct lib_ring_buffer_ctx *ctx,
 201                         struct lttng_channel *chan)
 202 {
 203         struct stack_trace *trace = stack_trace_context(field, ctx);
 204         unsigned int nr_seq_entries;
 205
 206         if (unlikely(!trace)) {
 207                 nr_seq_entries = 0;
 208                 lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
 209                 chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int));
 210                 lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
 211                 return;
 212         }
 213         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned int));
 214         nr_seq_entries = trace->nr_entries;
 215         if (trace->nr_entries == trace->max_entries)
 216                 nr_seq_entries++;
 217         chan->ops->event_write(ctx, &nr_seq_entries, sizeof(unsigned int));
 218         lib_ring_buffer_align_ctx(ctx, lttng_alignof(unsigned long));
 219         chan->ops->event_write(ctx, trace->entries,
 220                         sizeof(unsigned long) * trace->nr_entries);
 221         /* Add our own ULONG_MAX delimiter to show incomplete stack. */
 222         if (trace->nr_entries == trace->max_entries) {
 223                 unsigned long delim = ULONG_MAX;
 224
 225                 chan->ops->event_write(ctx, &delim, sizeof(unsigned long));
 226         }
 227 }
 228
 229 static
 230 void field_data_free(struct field_data *fdata)
 231 {
 232         if (!fdata)
 233                 return;
 234         free_percpu(fdata->cs_percpu);
 235         kfree(fdata);
 236 }
 237
 238 static
 239 struct field_data __percpu *field_data_create(enum lttng_cs_ctx_modes mode)
 240 {
 241         int cpu, i;
 242         struct lttng_cs __percpu *cs_set;
 243         struct field_data *fdata;
 244
 245         fdata = kzalloc(sizeof(*fdata), GFP_KERNEL);
 246         if (!fdata)
 247                 return NULL;
 248         cs_set = alloc_percpu(struct lttng_cs);
 249         if (!cs_set)
 250                 goto error_alloc;
 251
 252         fdata->cs_percpu = cs_set;
 253         for_each_possible_cpu(cpu) {
 254                 struct lttng_cs *cs;
 255
 256                 cs = per_cpu_ptr(cs_set, cpu);
 257                 for (i = 0; i < RING_BUFFER_MAX_NESTING; i++) {
 258                         struct lttng_cs_dispatch *dispatch;
 259
 260                         dispatch = &cs->dispatch[i];
 261                         dispatch->stack_trace.entries = dispatch->entries;
 262                         dispatch->stack_trace.max_entries = MAX_ENTRIES;
 263                 }
 264         }
 265         fdata->mode = mode;
 266         return fdata;
 267
 268 error_alloc:
 269         field_data_free(fdata);
 270         return NULL;
 271 }
 272
 273 static
 274 void lttng_callstack_destroy(struct lttng_ctx_field *field)
 275 {
 276         struct field_data *fdata = field->priv;
 277
 278         field_data_free(fdata);
 279 }
 280
 281 static
 282 int __lttng_add_callstack_generic(struct lttng_ctx **ctx,
 283                 enum lttng_cs_ctx_modes mode)
 284 {
 285         const char *ctx_name = cs_types[mode].name;
 286         struct lttng_ctx_field *field;
 287         struct field_data *fdata;
 288         int ret;
 289
 290         ret = init_type(mode);
 291         if (ret)
 292                 return ret;
 293         field = lttng_append_context(ctx);
 294         if (!field)
 295                 return -ENOMEM;
 296         if (lttng_find_context(*ctx, ctx_name)) {
 297                 ret = -EEXIST;
 298                 goto error_find;
 299         }
 300         fdata = field_data_create(mode);
 301         if (!fdata) {
 302                 ret = -ENOMEM;
 303                 goto error_create;
 304         }
 305
 306         field->event_field.name = ctx_name;
 307         field->event_field.type.atype = atype_sequence;
 308         field->event_field.type.u.sequence.elem_type.atype = atype_integer;
 309         field->event_field.type.u.sequence.elem_type.u.basic.integer.size = sizeof(unsigned long) * CHAR_BIT;
 310         field->event_field.type.u.sequence.elem_type.u.basic.integer.alignment = lttng_alignof(long) * CHAR_BIT;
 311         field->event_field.type.u.sequence.elem_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned long);
 312         field->event_field.type.u.sequence.elem_type.u.basic.integer.reverse_byte_order = 0;
 313         field->event_field.type.u.sequence.elem_type.u.basic.integer.base = 16;
 314         field->event_field.type.u.sequence.elem_type.u.basic.integer.encoding = lttng_encode_none;
 315
 316         field->event_field.type.u.sequence.length_type.atype = atype_integer;
 317         field->event_field.type.u.sequence.length_type.u.basic.integer.size = sizeof(unsigned int) * CHAR_BIT;
 318         field->event_field.type.u.sequence.length_type.u.basic.integer.alignment = lttng_alignof(unsigned int) * CHAR_BIT;
 319         field->event_field.type.u.sequence.length_type.u.basic.integer.signedness = lttng_is_signed_type(unsigned int);
 320         field->event_field.type.u.sequence.length_type.u.basic.integer.reverse_byte_order = 0;
 321         field->event_field.type.u.sequence.length_type.u.basic.integer.base = 10;
 322         field->event_field.type.u.sequence.length_type.u.basic.integer.encoding = lttng_encode_none;
 323
 324         field->get_size_arg = lttng_callstack_get_size;
 325         field->record = lttng_callstack_record;
 326         field->priv = fdata;
 327         field->destroy = lttng_callstack_destroy;
 328         wrapper_vmalloc_sync_all();
 329         return 0;
 330
 331 error_create:
 332         field_data_free(fdata);
 333 error_find:
 334         lttng_remove_context_field(ctx, field);
 335         return ret;
 336 }
 337
 338 /**
 339  *      lttng_add_callstack_to_ctx - add callstack event context
 340  *
 341  *      @ctx: the lttng_ctx pointer to initialize
 342  *      @type: the context type
 343  *
 344  *      Supported callstack type supported:
 345  *      LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL
 346  *              Records the callstack of the kernel
 347  *      LTTNG_KERNEL_CONTEXT_CALLSTACK_USER
 348  *              Records the callstack of the userspace program (from the kernel)
 349  *
 350  * Return 0 for success, or error code.
 351  */
 352 int lttng_add_callstack_to_ctx(struct lttng_ctx **ctx, int type)
 353 {
 354         switch (type) {
 355         case LTTNG_KERNEL_CONTEXT_CALLSTACK_KERNEL:
 356                 return __lttng_add_callstack_generic(ctx, CALLSTACK_KERNEL);
 357 #ifdef CONFIG_X86
 358         case LTTNG_KERNEL_CONTEXT_CALLSTACK_USER:
 359                 return __lttng_add_callstack_generic(ctx, CALLSTACK_USER);
 360 #endif
 361         default:
 362                 return -EINVAL;
 363         }
 364 }
 365 EXPORT_SYMBOL_GPL(lttng_add_callstack_to_ctx);