src/common/ringbuffer/frontend_internal.h

   1 /*
   2  * SPDX-License-Identifier: (LGPL-2.1-only or GPL-2.0-only)
   3  *
   4  * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * Ring Buffer Library Synchronization Header (internal helpers).
   7  *
   8  * See ring_buffer_frontend.c for more information on wait-free algorithms.
   9  */
  10
  11 #ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
  12 #define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
  13
  14 #include <urcu/compiler.h>
  15 #include <urcu/tls-compat.h>
  16 #include <signal.h>
  17 #include <stdint.h>
  18 #include <pthread.h>
  19
  20 #include <lttng/ust-ringbuffer-context.h>
  21 #include "ringbuffer-config.h"
  22 #include "backend_types.h"
  23 #include "backend_internal.h"
  24 #include "frontend_types.h"
  25 #include "shm.h"
  26
  27 /* Buffer offset macros */
  28
  29 /* buf_trunc mask selects only the buffer number. */
  30 static inline
  31 unsigned long buf_trunc(unsigned long offset,
  32                         struct lttng_ust_ring_buffer_channel *chan)
  33 {
  34         return offset & ~(chan->backend.buf_size - 1);
  35
  36 }
  37
  38 /* Select the buffer number value (counter). */
  39 static inline
  40 unsigned long buf_trunc_val(unsigned long offset,
  41                         struct lttng_ust_ring_buffer_channel *chan)
  42 {
  43         return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
  44 }
  45
  46 /* buf_offset mask selects only the offset within the current buffer. */
  47 static inline
  48 unsigned long buf_offset(unsigned long offset,
  49                         struct lttng_ust_ring_buffer_channel *chan)
  50 {
  51         return offset & (chan->backend.buf_size - 1);
  52 }
  53
  54 /* subbuf_offset mask selects the offset within the current subbuffer. */
  55 static inline
  56 unsigned long subbuf_offset(unsigned long offset,
  57                         struct lttng_ust_ring_buffer_channel *chan)
  58 {
  59         return offset & (chan->backend.subbuf_size - 1);
  60 }
  61
  62 /* subbuf_trunc mask selects the subbuffer number. */
  63 static inline
  64 unsigned long subbuf_trunc(unsigned long offset,
  65                         struct lttng_ust_ring_buffer_channel *chan)
  66 {
  67         return offset & ~(chan->backend.subbuf_size - 1);
  68 }
  69
  70 /* subbuf_align aligns the offset to the next subbuffer. */
  71 static inline
  72 unsigned long subbuf_align(unsigned long offset,
  73                         struct lttng_ust_ring_buffer_channel *chan)
  74 {
  75         return (offset + chan->backend.subbuf_size)
  76                & ~(chan->backend.subbuf_size - 1);
  77 }
  78
  79 /* subbuf_index returns the index of the current subbuffer within the buffer. */
  80 static inline
  81 unsigned long subbuf_index(unsigned long offset,
  82                         struct lttng_ust_ring_buffer_channel *chan)
  83 {
  84         return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
  85 }
  86
  87 /*
  88  * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
  89  * bits from the last TSC read. When overflows are detected, the full 64-bit
  90  * timestamp counter should be written in the record header. Reads and writes
  91  * last_tsc atomically.
  92  */
  93
  94 #if (CAA_BITS_PER_LONG == 32)
  95 static inline
  96 void save_last_tsc(const struct lttng_ust_ring_buffer_config *config,
  97                    struct lttng_ust_ring_buffer *buf, uint64_t tsc)
  98 {
  99         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 100                 return;
 101
 102         /*
 103          * Ensure the compiler performs this update in a single instruction.
 104          */
 105         v_set(config, &buf->last_tsc, (unsigned long)(tsc >> config->tsc_bits));
 106 }
 107
 108 static inline
 109 int last_tsc_overflow(const struct lttng_ust_ring_buffer_config *config,
 110                       struct lttng_ust_ring_buffer *buf, uint64_t tsc)
 111 {
 112         unsigned long tsc_shifted;
 113
 114         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 115                 return 0;
 116
 117         tsc_shifted = (unsigned long)(tsc >> config->tsc_bits);
 118         if (caa_unlikely(tsc_shifted
 119                      - (unsigned long)v_read(config, &buf->last_tsc)))
 120                 return 1;
 121         else
 122                 return 0;
 123 }
 124 #else
 125 static inline
 126 void save_last_tsc(const struct lttng_ust_ring_buffer_config *config,
 127                    struct lttng_ust_ring_buffer *buf, uint64_t tsc)
 128 {
 129         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 130                 return;
 131
 132         v_set(config, &buf->last_tsc, (unsigned long)tsc);
 133 }
 134
 135 static inline
 136 int last_tsc_overflow(const struct lttng_ust_ring_buffer_config *config,
 137                       struct lttng_ust_ring_buffer *buf, uint64_t tsc)
 138 {
 139         if (config->tsc_bits == 0 || config->tsc_bits == 64)
 140                 return 0;
 141
 142         if (caa_unlikely((tsc - v_read(config, &buf->last_tsc))
 143                      >> config->tsc_bits))
 144                 return 1;
 145         else
 146                 return 0;
 147 }
 148 #endif
 149
 150 extern
 151 int lib_ring_buffer_reserve_slow(struct lttng_ust_ring_buffer_ctx *ctx,
 152                 void *client_ctx)
 153         __attribute__((visibility("hidden")));
 154
 155 extern
 156 void lib_ring_buffer_switch_slow(struct lttng_ust_ring_buffer *buf,
 157                                  enum switch_mode mode,
 158                                  struct lttng_ust_shm_handle *handle)
 159         __attribute__((visibility("hidden")));
 160
 161 void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_ring_buffer_config *config,
 162                                    struct lttng_ust_ring_buffer *buf,
 163                                    struct lttng_ust_ring_buffer_channel *chan,
 164                                    unsigned long offset,
 165                                    unsigned long commit_count,
 166                                    unsigned long idx,
 167                                    struct lttng_ust_shm_handle *handle,
 168                                    uint64_t tsc)
 169         __attribute__((visibility("hidden")));
 170
 171 /* Buffer write helpers */
 172
 173 static inline
 174 void lib_ring_buffer_reserve_push_reader(struct lttng_ust_ring_buffer *buf,
 175                                          struct lttng_ust_ring_buffer_channel *chan,
 176                                          unsigned long offset)
 177 {
 178         unsigned long consumed_old, consumed_new;
 179
 180         do {
 181                 consumed_old = uatomic_read(&buf->consumed);
 182                 /*
 183                  * If buffer is in overwrite mode, push the reader consumed
 184                  * count if the write position has reached it and we are not
 185                  * at the first iteration (don't push the reader farther than
 186                  * the writer). This operation can be done concurrently by many
 187                  * writers in the same buffer, the writer being at the farthest
 188                  * write position sub-buffer index in the buffer being the one
 189                  * which will win this loop.
 190                  */
 191                 if (caa_unlikely(subbuf_trunc(offset, chan)
 192                               - subbuf_trunc(consumed_old, chan)
 193                              >= chan->backend.buf_size))
 194                         consumed_new = subbuf_align(consumed_old, chan);
 195                 else
 196                         return;
 197         } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
 198                                               consumed_new) != consumed_old));
 199 }
 200
 201 /*
 202  * Move consumed position to the beginning of subbuffer in which the
 203  * write offset is. Should only be used on ring buffers that are not
 204  * actively being written into, because clear_reader does not take into
 205  * account the commit counters when moving the consumed position, which
 206  * can make concurrent trace producers or consumers observe consumed
 207  * position further than the write offset, which breaks ring buffer
 208  * algorithm guarantees.
 209  */
 210 static inline
 211 void lib_ring_buffer_clear_reader(struct lttng_ust_ring_buffer *buf,
 212                                   struct lttng_ust_shm_handle *handle)
 213 {
 214         struct lttng_ust_ring_buffer_channel *chan;
 215         const struct lttng_ust_ring_buffer_config *config;
 216         unsigned long offset, consumed_old, consumed_new;
 217
 218         chan = shmp(handle, buf->backend.chan);
 219         if (!chan)
 220                 return;
 221         config = &chan->backend.config;
 222
 223         do {
 224                 offset = v_read(config, &buf->offset);
 225                 consumed_old = uatomic_read(&buf->consumed);
 226                 CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
 227                                 - subbuf_trunc(consumed_old, chan))
 228                                 < 0);
 229                 consumed_new = subbuf_trunc(offset, chan);
 230         } while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
 231                                               consumed_new) != consumed_old));
 232 }
 233
 234 static inline
 235 int lib_ring_buffer_pending_data(const struct lttng_ust_ring_buffer_config *config,
 236                                  struct lttng_ust_ring_buffer *buf,
 237                                  struct lttng_ust_ring_buffer_channel *chan)
 238 {
 239         return !!subbuf_offset(v_read(config, &buf->offset), chan);
 240 }
 241
 242 static inline
 243 unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_ring_buffer_config *config,
 244                                             struct lttng_ust_ring_buffer *buf,
 245                                             unsigned long idx,
 246                                             struct lttng_ust_shm_handle *handle)
 247 {
 248         return subbuffer_get_data_size(config, &buf->backend, idx, handle);
 249 }
 250
 251 /*
 252  * Check if all space reservation in a buffer have been committed. This helps
 253  * knowing if an execution context is nested (for per-cpu buffers only).
 254  * This is a very specific ftrace use-case, so we keep this as "internal" API.
 255  */
 256 static inline
 257 int lib_ring_buffer_reserve_committed(const struct lttng_ust_ring_buffer_config *config,
 258                                       struct lttng_ust_ring_buffer *buf,
 259                                       struct lttng_ust_ring_buffer_channel *chan,
 260                                       struct lttng_ust_shm_handle *handle)
 261 {
 262         unsigned long offset, idx, commit_count;
 263         struct commit_counters_hot *cc_hot;
 264
 265         CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 266         CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 267
 268         /*
 269          * Read offset and commit count in a loop so they are both read
 270          * atomically wrt interrupts. By deal with interrupt concurrency by
 271          * restarting both reads if the offset has been pushed. Note that given
 272          * we only have to deal with interrupt concurrency here, an interrupt
 273          * modifying the commit count will also modify "offset", so it is safe
 274          * to only check for offset modifications.
 275          */
 276         do {
 277                 offset = v_read(config, &buf->offset);
 278                 idx = subbuf_index(offset, chan);
 279                 cc_hot = shmp_index(handle, buf->commit_hot, idx);
 280                 if (caa_unlikely(!cc_hot))
 281                         return 0;
 282                 commit_count = v_read(config, &cc_hot->cc);
 283         } while (offset != v_read(config, &buf->offset));
 284
 285         return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 286                      - (commit_count & chan->commit_count_mask) == 0);
 287 }
 288
 289 /*
 290  * Receive end of subbuffer TSC as parameter. It has been read in the
 291  * space reservation loop of either reserve or switch, which ensures it
 292  * progresses monotonically with event records in the buffer. Therefore,
 293  * it ensures that the end timestamp of a subbuffer is <= begin
 294  * timestamp of the following subbuffers.
 295  */
 296 static inline
 297 void lib_ring_buffer_check_deliver(const struct lttng_ust_ring_buffer_config *config,
 298                                    struct lttng_ust_ring_buffer *buf,
 299                                    struct lttng_ust_ring_buffer_channel *chan,
 300                                    unsigned long offset,
 301                                    unsigned long commit_count,
 302                                    unsigned long idx,
 303                                    struct lttng_ust_shm_handle *handle,
 304                                    uint64_t tsc)
 305 {
 306         unsigned long old_commit_count = commit_count
 307                                          - chan->backend.subbuf_size;
 308
 309         /* Check if all commits have been done */
 310         if (caa_unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 311                      - (old_commit_count & chan->commit_count_mask) == 0))
 312                 lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
 313                         commit_count, idx, handle, tsc);
 314 }
 315
 316 /*
 317  * lib_ring_buffer_write_commit_counter
 318  *
 319  * For flight recording. must be called after commit.
 320  * This function increments the subbuffer's commit_seq counter each time the
 321  * commit count reaches back the reserve offset (modulo subbuffer size). It is
 322  * useful for crash dump.
 323  */
 324 static inline
 325 void lib_ring_buffer_write_commit_counter(
 326                 const struct lttng_ust_ring_buffer_config *config,
 327                 struct lttng_ust_ring_buffer *buf __attribute__((unused)),
 328                 struct lttng_ust_ring_buffer_channel *chan,
 329                 unsigned long buf_offset,
 330                 unsigned long commit_count,
 331                 struct lttng_ust_shm_handle *handle __attribute__((unused)),
 332                 struct commit_counters_hot *cc_hot)
 333 {
 334         unsigned long commit_seq_old;
 335
 336         if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
 337                 return;
 338
 339         /*
 340          * subbuf_offset includes commit_count_mask. We can simply
 341          * compare the offsets within the subbuffer without caring about
 342          * buffer full/empty mismatch because offset is never zero here
 343          * (subbuffer header and record headers have non-zero length).
 344          */
 345         if (caa_unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 346                 return;
 347
 348         commit_seq_old = v_read(config, &cc_hot->seq);
 349         if (caa_likely((long) (commit_seq_old - commit_count) < 0))
 350                 v_set(config, &cc_hot->seq, commit_count);
 351 }
 352
 353 extern int lib_ring_buffer_create(struct lttng_ust_ring_buffer *buf,
 354                                   struct channel_backend *chanb, int cpu,
 355                                   struct lttng_ust_shm_handle *handle,
 356                                   struct shm_object *shmobj)
 357         __attribute__((visibility("hidden")));
 358
 359 extern void lib_ring_buffer_free(struct lttng_ust_ring_buffer *buf,
 360                                  struct lttng_ust_shm_handle *handle)
 361         __attribute__((visibility("hidden")));
 362
 363 /* Keep track of trap nesting inside ring buffer code */
 364 extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting)
 365         __attribute__((visibility("hidden")));
 366
 367 #endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */