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