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