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