include/ringbuffer/frontend_internal.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only)
   2  *
   3  * ringbuffer/frontend_internal.h
   4  *
   5  * Ring Buffer Library Synchronization Header (internal helpers).
   6  *
   7  * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * See ring_buffer_frontend.c for more information on wait-free algorithms.
  10  */
  11
  12 #ifndef _LIB_RING_BUFFER_FRONTEND_INTERNAL_H
  13 #define _LIB_RING_BUFFER_FRONTEND_INTERNAL_H
  14
  15 #include <ringbuffer/config.h>
  16 #include <ringbuffer/backend_types.h>
  17 #include <ringbuffer/frontend_types.h>
  18 #include <lttng/prio_heap.h>    /* For per-CPU read-side iterator */
  19
  20 /* Buffer offset macros */
  21
  22 /* buf_trunc mask selects only the buffer number. */
  23 static inline
  24 unsigned long buf_trunc(unsigned long offset, struct lttng_kernel_ring_buffer_channel *chan)
  25 {
  26         return offset & ~(chan->backend.buf_size - 1);
  27
  28 }
  29
  30 /* Select the buffer number value (counter). */
  31 static inline
  32 unsigned long buf_trunc_val(unsigned long offset, struct lttng_kernel_ring_buffer_channel *chan)
  33 {
  34         return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
  35 }
  36
  37 /* buf_offset mask selects only the offset within the current buffer. */
  38 static inline
  39 unsigned long buf_offset(unsigned long offset, struct lttng_kernel_ring_buffer_channel *chan)
  40 {
  41         return offset & (chan->backend.buf_size - 1);
  42 }
  43
  44 /* subbuf_offset mask selects the offset within the current subbuffer. */
  45 static inline
  46 unsigned long subbuf_offset(unsigned long offset, struct lttng_kernel_ring_buffer_channel *chan)
  47 {
  48         return offset & (chan->backend.subbuf_size - 1);
  49 }
  50
  51 /* subbuf_trunc mask selects the subbuffer number. */
  52 static inline
  53 unsigned long subbuf_trunc(unsigned long offset, struct lttng_kernel_ring_buffer_channel *chan)
  54 {
  55         return offset & ~(chan->backend.subbuf_size - 1);
  56 }
  57
  58 /* subbuf_align aligns the offset to the next subbuffer. */
  59 static inline
  60 unsigned long subbuf_align(unsigned long offset, struct lttng_kernel_ring_buffer_channel *chan)
  61 {
  62         return (offset + chan->backend.subbuf_size)
  63                & ~(chan->backend.subbuf_size - 1);
  64 }
  65
  66 /* subbuf_index returns the index of the current subbuffer within the buffer. */
  67 static inline
  68 unsigned long subbuf_index(unsigned long offset, struct lttng_kernel_ring_buffer_channel *chan)
  69 {
  70         return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
  71 }
  72
  73 /*
  74  * Last timestamp comparison functions. Check if the current timestamp
  75  * overflows timestamp_bits bits from the last timestamp read. When
  76  * overflows are detected, the full 64-bit timestamp counter should be
  77  * written in the record header. Reads and writes last_timestamp
  78  * atomically.
  79  */
  80
  81 #if (BITS_PER_LONG == 32)
  82 static inline
  83 void save_last_timestamp(const struct lttng_kernel_ring_buffer_config *config,
  84                    struct lttng_kernel_ring_buffer *buf, u64 timestamp)
  85 {
  86         if (config->timestamp_bits == 0 || config->timestamp_bits == 64)
  87                 return;
  88
  89         /*
  90          * Ensure the compiler performs this update in a single instruction.
  91          */
  92         v_set(config, &buf->last_timestamp, (unsigned long)(timestamp >> config->timestamp_bits));
  93 }
  94
  95 static inline
  96 int last_timestamp_overflow(const struct lttng_kernel_ring_buffer_config *config,
  97                       struct lttng_kernel_ring_buffer *buf, u64 timestamp)
  98 {
  99         unsigned long timestamp_shifted;
 100
 101         if (config->timestamp_bits == 0 || config->timestamp_bits == 64)
 102                 return 0;
 103
 104         timestamp_shifted = (unsigned long)(timestamp >> config->timestamp_bits);
 105         if (unlikely(timestamp_shifted
 106                      - (unsigned long)v_read(config, &buf->last_timestamp)))
 107                 return 1;
 108         else
 109                 return 0;
 110 }
 111 #else
 112 static inline
 113 void save_last_timestamp(const struct lttng_kernel_ring_buffer_config *config,
 114                    struct lttng_kernel_ring_buffer *buf, u64 timestamp)
 115 {
 116         if (config->timestamp_bits == 0 || config->timestamp_bits == 64)
 117                 return;
 118
 119         v_set(config, &buf->last_timestamp, (unsigned long)timestamp);
 120 }
 121
 122 static inline
 123 int last_timestamp_overflow(const struct lttng_kernel_ring_buffer_config *config,
 124                       struct lttng_kernel_ring_buffer *buf, u64 timestamp)
 125 {
 126         if (config->timestamp_bits == 0 || config->timestamp_bits == 64)
 127                 return 0;
 128
 129         if (unlikely((timestamp - v_read(config, &buf->last_timestamp))
 130                      >> config->timestamp_bits))
 131                 return 1;
 132         else
 133                 return 0;
 134 }
 135 #endif
 136
 137 extern
 138 int lib_ring_buffer_reserve_slow(struct lttng_kernel_ring_buffer_ctx *ctx,
 139                 void *client_ctx);
 140
 141 extern
 142 void lib_ring_buffer_switch_slow(struct lttng_kernel_ring_buffer *buf,
 143                                  enum switch_mode mode);
 144
 145 extern
 146 void lib_ring_buffer_check_deliver_slow(const struct lttng_kernel_ring_buffer_config *config,
 147                                    struct lttng_kernel_ring_buffer *buf,
 148                                    struct lttng_kernel_ring_buffer_channel *chan,
 149                                    unsigned long offset,
 150                                    unsigned long commit_count,
 151                                    unsigned long idx,
 152                                    const struct lttng_kernel_ring_buffer_ctx *ctx);
 153
 154 extern
 155 void lib_ring_buffer_switch_remote(struct lttng_kernel_ring_buffer *buf);
 156 extern
 157 void lib_ring_buffer_switch_remote_empty(struct lttng_kernel_ring_buffer *buf);
 158 extern
 159 void lib_ring_buffer_clear(struct lttng_kernel_ring_buffer *buf);
 160
 161 /* Buffer write helpers */
 162
 163 static inline
 164 void lib_ring_buffer_reserve_push_reader(struct lttng_kernel_ring_buffer *buf,
 165                                          struct lttng_kernel_ring_buffer_channel *chan,
 166                                          unsigned long offset)
 167 {
 168         unsigned long consumed_old, consumed_new;
 169
 170         do {
 171                 consumed_old = atomic_long_read(&buf->consumed);
 172                 /*
 173                  * If buffer is in overwrite mode, push the reader consumed
 174                  * count if the write position has reached it and we are not
 175                  * at the first iteration (don't push the reader farther than
 176                  * the writer). This operation can be done concurrently by many
 177                  * writers in the same buffer, the writer being at the farthest
 178                  * write position sub-buffer index in the buffer being the one
 179                  * which will win this loop.
 180                  */
 181                 if (unlikely(subbuf_trunc(offset, chan)
 182                               - subbuf_trunc(consumed_old, chan)
 183                              >= chan->backend.buf_size))
 184                         consumed_new = subbuf_align(consumed_old, chan);
 185                 else
 186                         return;
 187         } while (unlikely(atomic_long_cmpxchg(&buf->consumed, consumed_old,
 188                                               consumed_new) != consumed_old));
 189 }
 190
 191 /*
 192  * Move consumed position to the beginning of subbuffer in which the
 193  * write offset is. Should only be used on ring buffers that are not
 194  * actively being written into, because clear_reader does not take into
 195  * account the commit counters when moving the consumed position, which
 196  * can make concurrent trace producers or consumers observe consumed
 197  * position further than the write offset, which breaks ring buffer
 198  * algorithm guarantees.
 199  */
 200 static inline
 201 void lib_ring_buffer_clear_reader(struct lttng_kernel_ring_buffer *buf,
 202                                   struct lttng_kernel_ring_buffer_channel *chan)
 203 {
 204         const struct lttng_kernel_ring_buffer_config *config = &chan->backend.config;
 205         unsigned long offset, consumed_old, consumed_new;
 206
 207         do {
 208                 offset = v_read(config, &buf->offset);
 209                 consumed_old = atomic_long_read(&buf->consumed);
 210                 CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
 211                                 - subbuf_trunc(consumed_old, chan))
 212                                 < 0);
 213                 consumed_new = subbuf_trunc(offset, chan);
 214         } while (unlikely(atomic_long_cmpxchg(&buf->consumed, consumed_old,
 215                                               consumed_new) != consumed_old));
 216 }
 217
 218 static inline
 219 int lib_ring_buffer_pending_data(const struct lttng_kernel_ring_buffer_config *config,
 220                                  struct lttng_kernel_ring_buffer *buf,
 221                                  struct lttng_kernel_ring_buffer_channel *chan)
 222 {
 223         return !!subbuf_offset(v_read(config, &buf->offset), chan);
 224 }
 225
 226 static inline
 227 unsigned long lib_ring_buffer_get_data_size(const struct lttng_kernel_ring_buffer_config *config,
 228                                             struct lttng_kernel_ring_buffer *buf,
 229                                             unsigned long idx)
 230 {
 231         return subbuffer_get_data_size(config, &buf->backend, idx);
 232 }
 233
 234 /*
 235  * Check if all space reservation in a buffer have been committed. This helps
 236  * knowing if an execution context is nested (for per-cpu buffers only).
 237  * This is a very specific ftrace use-case, so we keep this as "internal" API.
 238  */
 239 static inline
 240 int lib_ring_buffer_reserve_committed(const struct lttng_kernel_ring_buffer_config *config,
 241                                       struct lttng_kernel_ring_buffer *buf,
 242                                       struct lttng_kernel_ring_buffer_channel *chan)
 243 {
 244         unsigned long offset, idx, commit_count;
 245
 246         CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 247         CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 248
 249         /*
 250          * Read offset and commit count in a loop so they are both read
 251          * atomically wrt interrupts. By deal with interrupt concurrency by
 252          * restarting both reads if the offset has been pushed. Note that given
 253          * we only have to deal with interrupt concurrency here, an interrupt
 254          * modifying the commit count will also modify "offset", so it is safe
 255          * to only check for offset modifications.
 256          */
 257         do {
 258                 offset = v_read(config, &buf->offset);
 259                 idx = subbuf_index(offset, chan);
 260                 commit_count = v_read(config, &buf->commit_hot[idx].cc);
 261         } while (offset != v_read(config, &buf->offset));
 262
 263         return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 264                      - (commit_count & chan->commit_count_mask) == 0);
 265 }
 266
 267 /*
 268  * Receive end of subbuffer timestamp as parameter. It has been read in the
 269  * space reservation loop of either reserve or switch, which ensures it
 270  * progresses monotonically with event records in the buffer. Therefore,
 271  * it ensures that the end timestamp of a subbuffer is <= begin
 272  * timestamp of the following subbuffers.
 273  */
 274 static inline
 275 void lib_ring_buffer_check_deliver(const struct lttng_kernel_ring_buffer_config *config,
 276                                    struct lttng_kernel_ring_buffer *buf,
 277                                    struct lttng_kernel_ring_buffer_channel *chan,
 278                                    unsigned long offset,
 279                                    unsigned long commit_count,
 280                                    unsigned long idx,
 281                                    const struct lttng_kernel_ring_buffer_ctx *ctx)
 282 {
 283         unsigned long old_commit_count = commit_count
 284                                          - chan->backend.subbuf_size;
 285
 286         /* Check if all commits have been done */
 287         if (unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
 288                      - (old_commit_count & chan->commit_count_mask) == 0))
 289                 lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
 290                         commit_count, idx, ctx);
 291 }
 292
 293 /*
 294  * lib_ring_buffer_write_commit_counter
 295  *
 296  * For flight recording. must be called after commit.
 297  * This function increments the subbuffer's commit_seq counter each time the
 298  * commit count reaches back the reserve offset (modulo subbuffer size). It is
 299  * useful for crash dump.
 300  */
 301 static inline
 302 void lib_ring_buffer_write_commit_counter(const struct lttng_kernel_ring_buffer_config *config,
 303                                           struct lttng_kernel_ring_buffer *buf,
 304                                           struct lttng_kernel_ring_buffer_channel *chan,
 305                                           unsigned long buf_offset,
 306                                           unsigned long commit_count,
 307                                           struct commit_counters_hot *cc_hot)
 308 {
 309         unsigned long commit_seq_old;
 310
 311         if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
 312                 return;
 313
 314         /*
 315          * subbuf_offset includes commit_count_mask. We can simply
 316          * compare the offsets within the subbuffer without caring about
 317          * buffer full/empty mismatch because offset is never zero here
 318          * (subbuffer header and record headers have non-zero length).
 319          */
 320         if (unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 321                 return;
 322
 323         commit_seq_old = v_read(config, &cc_hot->seq);
 324         if (likely((long) (commit_seq_old - commit_count) < 0))
 325                 v_set(config, &cc_hot->seq, commit_count);
 326 }
 327
 328 extern int lib_ring_buffer_create(struct lttng_kernel_ring_buffer *buf,
 329                                   struct channel_backend *chanb, int cpu);
 330 extern void lib_ring_buffer_free(struct lttng_kernel_ring_buffer *buf);
 331
 332 /* Keep track of trap nesting inside ring buffer code */
 333 DECLARE_PER_CPU(unsigned int, lib_ring_buffer_nesting);
 334
 335 #endif /* _LIB_RING_BUFFER_FRONTEND_INTERNAL_H */