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852c2936 | 1 | /* |
c0c0989a | 2 | * SPDX-License-Identifier: LGPL-2.1-only |
852c2936 | 3 | * |
e92f3e28 MD |
4 | * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
5 | * | |
e92f3e28 MD |
6 | * See ring_buffer_frontend.c for more information on wait-free |
7 | * algorithms. | |
8 | * See frontend.h for channel allocation and read-side API. | |
852c2936 MD |
9 | */ |
10 | ||
c0c0989a MJ |
11 | #ifndef _LTTNG_RING_BUFFER_FRONTEND_API_H |
12 | #define _LTTNG_RING_BUFFER_FRONTEND_API_H | |
13 | ||
b4051ad8 FD |
14 | #include <stddef.h> |
15 | ||
9f3fdbc6 | 16 | #include <urcu/compiler.h> |
852c2936 | 17 | |
b4051ad8 FD |
18 | #include "frontend.h" |
19 | ||
852c2936 | 20 | /** |
7489fcb4 | 21 | * lib_ring_buffer_nesting_inc - Ring buffer recursive use protection. |
852c2936 | 22 | * |
7489fcb4 MD |
23 | * The rint buffer buffer nesting count is a safety net to ensure tracer |
24 | * client code will never trigger an endless recursion. | |
8936b6c0 MD |
25 | * Returns a nesting level >= 0 on success, -EPERM on failure (nesting |
26 | * count too high). | |
852c2936 MD |
27 | * |
28 | * asm volatile and "memory" clobber prevent the compiler from moving | |
29 | * instructions out of the ring buffer nesting count. This is required to ensure | |
30 | * that probe side-effects which can cause recursion (e.g. unforeseen traps, | |
31 | * divisions by 0, ...) are triggered within the incremented nesting count | |
32 | * section. | |
33 | */ | |
34 | static inline | |
7489fcb4 | 35 | int lib_ring_buffer_nesting_inc(const struct lttng_ust_lib_ring_buffer_config *config) |
852c2936 | 36 | { |
7489fcb4 | 37 | int nesting; |
852c2936 | 38 | |
8c90a710 | 39 | nesting = ++URCU_TLS(lib_ring_buffer_nesting); |
9f3fdbc6 | 40 | cmm_barrier(); |
8936b6c0 | 41 | if (caa_unlikely(nesting >= LIB_RING_BUFFER_MAX_NESTING)) { |
852c2936 | 42 | WARN_ON_ONCE(1); |
8c90a710 | 43 | URCU_TLS(lib_ring_buffer_nesting)--; |
852c2936 | 44 | return -EPERM; |
7489fcb4 | 45 | } |
8936b6c0 MD |
46 | return nesting - 1; |
47 | } | |
48 | ||
49 | static inline | |
50 | int lib_ring_buffer_nesting_count(const struct lttng_ust_lib_ring_buffer_config *config) | |
51 | { | |
52 | return URCU_TLS(lib_ring_buffer_nesting); | |
852c2936 MD |
53 | } |
54 | ||
852c2936 | 55 | static inline |
7489fcb4 | 56 | void lib_ring_buffer_nesting_dec(const struct lttng_ust_lib_ring_buffer_config *config) |
852c2936 | 57 | { |
9f3fdbc6 | 58 | cmm_barrier(); |
8c90a710 | 59 | URCU_TLS(lib_ring_buffer_nesting)--; /* TLS */ |
852c2936 MD |
60 | } |
61 | ||
62 | /* | |
63 | * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not | |
64 | * part of the API per se. | |
65 | * | |
66 | * returns 0 if reserve ok, or 1 if the slow path must be taken. | |
67 | */ | |
68 | static inline | |
4cfec15c MD |
69 | int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
70 | struct lttng_ust_lib_ring_buffer_ctx *ctx, | |
e56bb47c | 71 | void *client_ctx, |
852c2936 MD |
72 | unsigned long *o_begin, unsigned long *o_end, |
73 | unsigned long *o_old, size_t *before_hdr_pad) | |
74 | { | |
8936b6c0 MD |
75 | struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv; |
76 | struct lttng_ust_lib_ring_buffer_channel *chan = ctx_private->chan; | |
77 | struct lttng_ust_lib_ring_buffer *buf = ctx_private->buf; | |
852c2936 MD |
78 | *o_begin = v_read(config, &buf->offset); |
79 | *o_old = *o_begin; | |
80 | ||
8936b6c0 MD |
81 | ctx_private->tsc = lib_ring_buffer_clock_read(chan); |
82 | if ((int64_t) ctx_private->tsc == -EIO) | |
852c2936 MD |
83 | return 1; |
84 | ||
85 | /* | |
86 | * Prefetch cacheline for read because we have to read the previous | |
87 | * commit counter to increment it and commit seq value to compare it to | |
88 | * the commit counter. | |
89 | */ | |
9f3fdbc6 | 90 | //prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]); |
852c2936 | 91 | |
8936b6c0 MD |
92 | if (last_tsc_overflow(config, buf, ctx_private->tsc)) |
93 | ctx_private->rflags |= RING_BUFFER_RFLAG_FULL_TSC; | |
852c2936 | 94 | |
b5a3dfa5 | 95 | if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0)) |
852c2936 MD |
96 | return 1; |
97 | ||
8936b6c0 | 98 | ctx_private->slot_size = record_header_size(config, chan, *o_begin, |
e56bb47c | 99 | before_hdr_pad, ctx, client_ctx); |
8936b6c0 MD |
100 | ctx_private->slot_size += |
101 | lttng_ust_lib_ring_buffer_align(*o_begin + ctx_private->slot_size, | |
852c2936 | 102 | ctx->largest_align) + ctx->data_size; |
8936b6c0 | 103 | if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx_private->slot_size) |
852c2936 MD |
104 | > chan->backend.subbuf_size)) |
105 | return 1; | |
106 | ||
107 | /* | |
108 | * Record fits in the current buffer and we are not on a switch | |
109 | * boundary. It's safe to write. | |
110 | */ | |
8936b6c0 | 111 | *o_end = *o_begin + ctx_private->slot_size; |
1ad21f70 MD |
112 | |
113 | if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0)) | |
114 | /* | |
115 | * The offset_end will fall at the very beginning of the next | |
116 | * subbuffer. | |
117 | */ | |
118 | return 1; | |
119 | ||
852c2936 MD |
120 | return 0; |
121 | } | |
122 | ||
123 | /** | |
124 | * lib_ring_buffer_reserve - Reserve space in a ring buffer. | |
125 | * @config: ring buffer instance configuration. | |
126 | * @ctx: ring buffer context. (input and output) Must be already initialized. | |
127 | * | |
128 | * Atomic wait-free slot reservation. The reserved space starts at the context | |
129 | * "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc". | |
130 | * | |
131 | * Return : | |
132 | * 0 on success. | |
133 | * -EAGAIN if channel is disabled. | |
134 | * -ENOSPC if event size is too large for packet. | |
135 | * -ENOBUFS if there is currently not enough space in buffer for the event. | |
136 | * -EIO if data cannot be written into the buffer for any other reason. | |
137 | */ | |
138 | ||
139 | static inline | |
4cfec15c | 140 | int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
e56bb47c MD |
141 | struct lttng_ust_lib_ring_buffer_ctx *ctx, |
142 | void *client_ctx) | |
852c2936 | 143 | { |
8936b6c0 MD |
144 | struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv; |
145 | struct lttng_ust_lib_ring_buffer_channel *chan = ctx_private->chan; | |
146 | struct lttng_ust_shm_handle *handle = chan->handle; | |
4cfec15c | 147 | struct lttng_ust_lib_ring_buffer *buf; |
852c2936 MD |
148 | unsigned long o_begin, o_end, o_old; |
149 | size_t before_hdr_pad = 0; | |
150 | ||
f52a5702 | 151 | if (caa_unlikely(uatomic_read(&chan->record_disabled))) |
852c2936 MD |
152 | return -EAGAIN; |
153 | ||
7489fcb4 | 154 | if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) { |
8936b6c0 MD |
155 | ctx_private->reserve_cpu = lttng_ust_get_cpu(); |
156 | buf = shmp(handle, chan->backend.buf[ctx_private->reserve_cpu].shmp); | |
7489fcb4 | 157 | } else { |
1d498196 | 158 | buf = shmp(handle, chan->backend.buf[0].shmp); |
7489fcb4 | 159 | } |
15500a1b MD |
160 | if (caa_unlikely(!buf)) |
161 | return -EIO; | |
f52a5702 | 162 | if (caa_unlikely(uatomic_read(&buf->record_disabled))) |
852c2936 | 163 | return -EAGAIN; |
8936b6c0 | 164 | ctx_private->buf = buf; |
852c2936 MD |
165 | |
166 | /* | |
167 | * Perform retryable operations. | |
168 | */ | |
e56bb47c | 169 | if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, client_ctx, &o_begin, |
852c2936 MD |
170 | &o_end, &o_old, &before_hdr_pad))) |
171 | goto slow_path; | |
172 | ||
8936b6c0 | 173 | if (caa_unlikely(v_cmpxchg(config, &buf->offset, o_old, o_end) |
852c2936 MD |
174 | != o_old)) |
175 | goto slow_path; | |
176 | ||
177 | /* | |
178 | * Atomically update last_tsc. This update races against concurrent | |
179 | * atomic updates, but the race will always cause supplementary full TSC | |
180 | * record headers, never the opposite (missing a full TSC record header | |
181 | * when it would be needed). | |
182 | */ | |
8936b6c0 | 183 | save_last_tsc(config, buf, ctx_private->tsc); |
852c2936 MD |
184 | |
185 | /* | |
186 | * Push the reader if necessary | |
187 | */ | |
8936b6c0 | 188 | lib_ring_buffer_reserve_push_reader(buf, chan, o_end - 1); |
852c2936 MD |
189 | |
190 | /* | |
191 | * Clear noref flag for this subbuffer. | |
192 | */ | |
8936b6c0 | 193 | lib_ring_buffer_clear_noref(config, &buf->backend, |
1d498196 | 194 | subbuf_index(o_end - 1, chan), handle); |
852c2936 | 195 | |
8936b6c0 MD |
196 | ctx_private->pre_offset = o_begin; |
197 | ctx_private->buf_offset = o_begin + before_hdr_pad; | |
852c2936 MD |
198 | return 0; |
199 | slow_path: | |
e56bb47c | 200 | return lib_ring_buffer_reserve_slow(ctx, client_ctx); |
852c2936 MD |
201 | } |
202 | ||
203 | /** | |
204 | * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer. | |
205 | * @config: ring buffer instance configuration. | |
206 | * @buf: buffer | |
207 | * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH) | |
208 | * | |
209 | * This operation is completely reentrant : can be called while tracing is | |
210 | * active with absolutely no lock held. | |
211 | * | |
212 | * Note, however, that as a v_cmpxchg is used for some atomic operations and | |
213 | * requires to be executed locally for per-CPU buffers, this function must be | |
214 | * called from the CPU which owns the buffer for a ACTIVE flush, with preemption | |
215 | * disabled, for RING_BUFFER_SYNC_PER_CPU configuration. | |
216 | */ | |
217 | static inline | |
4cfec15c MD |
218 | void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config, |
219 | struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode, | |
38fae1d3 | 220 | struct lttng_ust_shm_handle *handle) |
852c2936 | 221 | { |
1d498196 | 222 | lib_ring_buffer_switch_slow(buf, mode, handle); |
852c2936 MD |
223 | } |
224 | ||
225 | /* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */ | |
226 | ||
227 | /** | |
228 | * lib_ring_buffer_commit - Commit an record. | |
229 | * @config: ring buffer instance configuration. | |
230 | * @ctx: ring buffer context. (input arguments only) | |
231 | * | |
232 | * Atomic unordered slot commit. Increments the commit count in the | |
233 | * specified sub-buffer, and delivers it if necessary. | |
234 | */ | |
235 | static inline | |
4cfec15c MD |
236 | void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config, |
237 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 | 238 | { |
8936b6c0 MD |
239 | struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv; |
240 | struct lttng_ust_lib_ring_buffer_channel *chan = ctx_private->chan; | |
241 | struct lttng_ust_shm_handle *handle = chan->handle; | |
242 | struct lttng_ust_lib_ring_buffer *buf = ctx_private->buf; | |
243 | unsigned long offset_end = ctx_private->buf_offset; | |
852c2936 MD |
244 | unsigned long endidx = subbuf_index(offset_end - 1, chan); |
245 | unsigned long commit_count; | |
d2fe4771 MD |
246 | struct commit_counters_hot *cc_hot = shmp_index(handle, |
247 | buf->commit_hot, endidx); | |
852c2936 | 248 | |
15500a1b MD |
249 | if (caa_unlikely(!cc_hot)) |
250 | return; | |
251 | ||
852c2936 MD |
252 | /* |
253 | * Must count record before incrementing the commit count. | |
254 | */ | |
15500a1b | 255 | subbuffer_count_record(config, ctx, &buf->backend, endidx, handle); |
852c2936 MD |
256 | |
257 | /* | |
258 | * Order all writes to buffer before the commit count update that will | |
259 | * determine that the subbuffer is full. | |
260 | */ | |
9f3fdbc6 | 261 | cmm_smp_wmb(); |
852c2936 | 262 | |
8936b6c0 | 263 | v_add(config, ctx_private->slot_size, &cc_hot->cc); |
852c2936 MD |
264 | |
265 | /* | |
266 | * commit count read can race with concurrent OOO commit count updates. | |
267 | * This is only needed for lib_ring_buffer_check_deliver (for | |
268 | * non-polling delivery only) and for | |
269 | * lib_ring_buffer_write_commit_counter. The race can only cause the | |
270 | * counter to be read with the same value more than once, which could | |
271 | * cause : | |
272 | * - Multiple delivery for the same sub-buffer (which is handled | |
273 | * gracefully by the reader code) if the value is for a full | |
274 | * sub-buffer. It's important that we can never miss a sub-buffer | |
275 | * delivery. Re-reading the value after the v_add ensures this. | |
276 | * - Reading a commit_count with a higher value that what was actually | |
277 | * added to it for the lib_ring_buffer_write_commit_counter call | |
278 | * (again caused by a concurrent committer). It does not matter, | |
279 | * because this function is interested in the fact that the commit | |
280 | * count reaches back the reserve offset for a specific sub-buffer, | |
281 | * which is completely independent of the order. | |
282 | */ | |
d2fe4771 | 283 | commit_count = v_read(config, &cc_hot->cc); |
852c2936 MD |
284 | |
285 | lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1, | |
8936b6c0 | 286 | commit_count, endidx, handle, ctx_private->tsc); |
852c2936 MD |
287 | /* |
288 | * Update used size at each commit. It's needed only for extracting | |
289 | * ring_buffer buffers from vmcore, after crash. | |
290 | */ | |
d2fe4771 MD |
291 | lib_ring_buffer_write_commit_counter(config, buf, chan, |
292 | offset_end, commit_count, handle, cc_hot); | |
852c2936 MD |
293 | } |
294 | ||
295 | /** | |
296 | * lib_ring_buffer_try_discard_reserve - Try discarding a record. | |
297 | * @config: ring buffer instance configuration. | |
298 | * @ctx: ring buffer context. (input arguments only) | |
299 | * | |
300 | * Only succeeds if no other record has been written after the record to | |
301 | * discard. If discard fails, the record must be committed to the buffer. | |
302 | * | |
303 | * Returns 0 upon success, -EPERM if the record cannot be discarded. | |
304 | */ | |
305 | static inline | |
4cfec15c MD |
306 | int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
307 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 | 308 | { |
8936b6c0 MD |
309 | struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv; |
310 | struct lttng_ust_lib_ring_buffer *buf = ctx_private->buf; | |
311 | unsigned long end_offset = ctx_private->pre_offset + ctx_private->slot_size; | |
852c2936 MD |
312 | |
313 | /* | |
314 | * We need to ensure that if the cmpxchg succeeds and discards the | |
315 | * record, the next record will record a full TSC, because it cannot | |
316 | * rely on the last_tsc associated with the discarded record to detect | |
317 | * overflows. The only way to ensure this is to set the last_tsc to 0 | |
318 | * (assuming no 64-bit TSC overflow), which forces to write a 64-bit | |
319 | * timestamp in the next record. | |
320 | * | |
321 | * Note: if discard fails, we must leave the TSC in the record header. | |
322 | * It is needed to keep track of TSC overflows for the following | |
323 | * records. | |
324 | */ | |
325 | save_last_tsc(config, buf, 0ULL); | |
326 | ||
8936b6c0 | 327 | if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx_private->pre_offset) |
852c2936 MD |
328 | != end_offset)) |
329 | return -EPERM; | |
330 | else | |
331 | return 0; | |
332 | } | |
333 | ||
334 | static inline | |
4cfec15c | 335 | void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
5198080d | 336 | struct lttng_ust_lib_ring_buffer_channel *chan) |
852c2936 | 337 | { |
9f3fdbc6 | 338 | uatomic_inc(&chan->record_disabled); |
852c2936 MD |
339 | } |
340 | ||
341 | static inline | |
4cfec15c | 342 | void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
5198080d | 343 | struct lttng_ust_lib_ring_buffer_channel *chan) |
852c2936 | 344 | { |
9f3fdbc6 | 345 | uatomic_dec(&chan->record_disabled); |
852c2936 MD |
346 | } |
347 | ||
348 | static inline | |
4cfec15c MD |
349 | void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
350 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 351 | { |
9f3fdbc6 | 352 | uatomic_inc(&buf->record_disabled); |
852c2936 MD |
353 | } |
354 | ||
355 | static inline | |
4cfec15c MD |
356 | void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
357 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 358 | { |
9f3fdbc6 | 359 | uatomic_dec(&buf->record_disabled); |
852c2936 MD |
360 | } |
361 | ||
e92f3e28 | 362 | #endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */ |