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