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e92f3e28 MD |
1 | #ifndef _LTTNG_RING_BUFFER_FRONTEND_API_H |
2 | #define _LTTNG_RING_BUFFER_FRONTEND_API_H | |
852c2936 MD |
3 | |
4 | /* | |
e92f3e28 | 5 | * libringbuffer/frontend_api.h |
852c2936 | 6 | * |
e92f3e28 MD |
7 | * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
8 | * | |
9 | * This library is free software; you can redistribute it and/or | |
10 | * modify it under the terms of the GNU Lesser General Public | |
11 | * License as published by the Free Software Foundation; only | |
12 | * version 2.1 of the License. | |
13 | * | |
14 | * This library is distributed in the hope that it will be useful, | |
15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
17 | * Lesser General Public License for more details. | |
18 | * | |
19 | * You should have received a copy of the GNU Lesser General Public | |
20 | * License along with this library; if not, write to the Free Software | |
21 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
852c2936 MD |
22 | * |
23 | * Ring Buffer Library Synchronization Header (buffer write API). | |
24 | * | |
25 | * Author: | |
e92f3e28 | 26 | * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
852c2936 | 27 | * |
e92f3e28 MD |
28 | * See ring_buffer_frontend.c for more information on wait-free |
29 | * algorithms. | |
30 | * See frontend.h for channel allocation and read-side API. | |
852c2936 MD |
31 | */ |
32 | ||
4931a13e | 33 | #include "frontend.h" |
9f3fdbc6 MD |
34 | #include <urcu-bp.h> |
35 | #include <urcu/compiler.h> | |
3ea36dea | 36 | #include "rseq.h" |
852c2936 | 37 | |
26cc635c MD |
38 | static inline |
39 | int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config) | |
40 | { | |
41 | return lttng_ust_get_cpu(); | |
42 | } | |
43 | ||
852c2936 | 44 | /** |
26cc635c | 45 | * lib_ring_buffer_begin - Precedes ring buffer reserve/commit. |
852c2936 | 46 | * |
36cb884c MD |
47 | * Keeps a ring buffer nesting count as supplementary safety net to |
48 | * ensure tracer client code will never trigger an endless recursion. | |
49 | * Returns the processor ID on success, -EPERM on failure (nesting count | |
50 | * too high). | |
852c2936 MD |
51 | * |
52 | * asm volatile and "memory" clobber prevent the compiler from moving | |
53 | * instructions out of the ring buffer nesting count. This is required to ensure | |
54 | * that probe side-effects which can cause recursion (e.g. unforeseen traps, | |
55 | * divisions by 0, ...) are triggered within the incremented nesting count | |
56 | * section. | |
57 | */ | |
58 | static inline | |
26cc635c | 59 | int lib_ring_buffer_begin(const struct lttng_ust_lib_ring_buffer_config *config) |
852c2936 | 60 | { |
26cc635c | 61 | int nesting; |
852c2936 | 62 | |
8c90a710 | 63 | nesting = ++URCU_TLS(lib_ring_buffer_nesting); |
9f3fdbc6 | 64 | cmm_barrier(); |
852c2936 | 65 | |
b5a3dfa5 | 66 | if (caa_unlikely(nesting > 4)) { |
852c2936 | 67 | WARN_ON_ONCE(1); |
8c90a710 | 68 | URCU_TLS(lib_ring_buffer_nesting)--; |
852c2936 | 69 | return -EPERM; |
26cc635c MD |
70 | } |
71 | return 0; | |
852c2936 MD |
72 | } |
73 | ||
74 | /** | |
26cc635c | 75 | * lib_ring_buffer_end - Follows ring buffer reserve/commit. |
852c2936 MD |
76 | */ |
77 | static inline | |
26cc635c | 78 | void lib_ring_buffer_end(const struct lttng_ust_lib_ring_buffer_config *config) |
852c2936 | 79 | { |
9f3fdbc6 | 80 | cmm_barrier(); |
8c90a710 | 81 | URCU_TLS(lib_ring_buffer_nesting)--; /* TLS */ |
852c2936 MD |
82 | } |
83 | ||
84 | /* | |
85 | * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not | |
86 | * part of the API per se. | |
87 | * | |
88 | * returns 0 if reserve ok, or 1 if the slow path must be taken. | |
89 | */ | |
90 | static inline | |
4cfec15c MD |
91 | int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
92 | struct lttng_ust_lib_ring_buffer_ctx *ctx, | |
852c2936 MD |
93 | unsigned long *o_begin, unsigned long *o_end, |
94 | unsigned long *o_old, size_t *before_hdr_pad) | |
95 | { | |
96 | struct channel *chan = ctx->chan; | |
4cfec15c | 97 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
98 | *o_begin = v_read(config, &buf->offset); |
99 | *o_old = *o_begin; | |
100 | ||
101 | ctx->tsc = lib_ring_buffer_clock_read(chan); | |
102 | if ((int64_t) ctx->tsc == -EIO) | |
103 | return 1; | |
104 | ||
105 | /* | |
106 | * Prefetch cacheline for read because we have to read the previous | |
107 | * commit counter to increment it and commit seq value to compare it to | |
108 | * the commit counter. | |
109 | */ | |
9f3fdbc6 | 110 | //prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]); |
852c2936 MD |
111 | |
112 | if (last_tsc_overflow(config, buf, ctx->tsc)) | |
113 | ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC; | |
114 | ||
b5a3dfa5 | 115 | if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0)) |
852c2936 MD |
116 | return 1; |
117 | ||
118 | ctx->slot_size = record_header_size(config, chan, *o_begin, | |
119 | before_hdr_pad, ctx); | |
120 | ctx->slot_size += | |
121 | lib_ring_buffer_align(*o_begin + ctx->slot_size, | |
122 | ctx->largest_align) + ctx->data_size; | |
b5a3dfa5 | 123 | if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size) |
852c2936 MD |
124 | > chan->backend.subbuf_size)) |
125 | return 1; | |
126 | ||
127 | /* | |
128 | * Record fits in the current buffer and we are not on a switch | |
129 | * boundary. It's safe to write. | |
130 | */ | |
131 | *o_end = *o_begin + ctx->slot_size; | |
1ad21f70 MD |
132 | |
133 | if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0)) | |
134 | /* | |
135 | * The offset_end will fall at the very beginning of the next | |
136 | * subbuffer. | |
137 | */ | |
138 | return 1; | |
139 | ||
852c2936 MD |
140 | return 0; |
141 | } | |
142 | ||
143 | /** | |
144 | * lib_ring_buffer_reserve - Reserve space in a ring buffer. | |
145 | * @config: ring buffer instance configuration. | |
146 | * @ctx: ring buffer context. (input and output) Must be already initialized. | |
147 | * | |
148 | * Atomic wait-free slot reservation. The reserved space starts at the context | |
149 | * "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc". | |
150 | * | |
151 | * Return : | |
152 | * 0 on success. | |
6fd21280 | 153 | * -EPERM if channel is disabled. |
852c2936 MD |
154 | * -ENOSPC if event size is too large for packet. |
155 | * -ENOBUFS if there is currently not enough space in buffer for the event. | |
156 | * -EIO if data cannot be written into the buffer for any other reason. | |
6fd21280 | 157 | * -EAGAIN reserve aborted, should be attempted again. |
852c2936 MD |
158 | */ |
159 | ||
160 | static inline | |
4cfec15c MD |
161 | int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
162 | struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 MD |
163 | { |
164 | struct channel *chan = ctx->chan; | |
38fae1d3 | 165 | struct lttng_ust_shm_handle *handle = ctx->handle; |
4cfec15c | 166 | struct lttng_ust_lib_ring_buffer *buf; |
852c2936 MD |
167 | unsigned long o_begin, o_end, o_old; |
168 | size_t before_hdr_pad = 0; | |
6fd21280 | 169 | struct lttng_rseq_state rseq_state; |
852c2936 | 170 | |
6fd21280 MD |
171 | if (caa_likely(ctx->ctx_len |
172 | >= sizeof(struct lttng_ust_lib_ring_buffer_ctx))) { | |
173 | rseq_state = ctx->rseq_state; | |
174 | } else { | |
175 | rseq_state.cpu_id = -2; | |
176 | rseq_state.event_counter = 0; | |
177 | rseq_state.rseqp = NULL; | |
178 | } | |
852c2936 | 179 | |
6fd21280 MD |
180 | if (caa_unlikely(uatomic_read(&chan->record_disabled))) |
181 | return -EPERM; | |
852c2936 | 182 | if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) |
1d498196 | 183 | buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp); |
852c2936 | 184 | else |
1d498196 | 185 | buf = shmp(handle, chan->backend.buf[0].shmp); |
15500a1b MD |
186 | if (caa_unlikely(!buf)) |
187 | return -EIO; | |
f52a5702 | 188 | if (caa_unlikely(uatomic_read(&buf->record_disabled))) |
6fd21280 | 189 | return -EPERM; |
852c2936 MD |
190 | ctx->buf = buf; |
191 | ||
192 | /* | |
193 | * Perform retryable operations. | |
194 | */ | |
b5a3dfa5 | 195 | if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, &o_begin, |
852c2936 MD |
196 | &o_end, &o_old, &before_hdr_pad))) |
197 | goto slow_path; | |
198 | ||
6fd21280 MD |
199 | if (caa_unlikely(config->sync == RING_BUFFER_SYNC_GLOBAL |
200 | || rseq_state.cpu_id < 0 | |
201 | || uatomic_read(&chan->u.reserve_fallback_ref))) { | |
202 | if (caa_unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, | |
203 | o_end) != o_old)) | |
204 | goto slow_path; | |
205 | } else { | |
206 | /* | |
207 | * Load reserve_fallback_ref before offset. Matches the | |
208 | * implicit memory barrier after v_cmpxchg of offset. | |
209 | */ | |
210 | cmm_smp_rmb(); | |
211 | if (caa_unlikely(ctx->buf->offset.a != o_old)) | |
212 | return -EAGAIN; | |
213 | if (caa_unlikely(!__rseq_finish(NULL, 0, NULL, NULL, 0, | |
214 | (intptr_t *) &ctx->buf->offset.a, | |
215 | (intptr_t) o_end, | |
216 | rseq_state, RSEQ_FINISH_SINGLE, false))) | |
217 | return -EAGAIN; | |
218 | } | |
852c2936 MD |
219 | /* |
220 | * Atomically update last_tsc. This update races against concurrent | |
221 | * atomic updates, but the race will always cause supplementary full TSC | |
222 | * record headers, never the opposite (missing a full TSC record header | |
223 | * when it would be needed). | |
224 | */ | |
225 | save_last_tsc(config, ctx->buf, ctx->tsc); | |
226 | ||
227 | /* | |
228 | * Push the reader if necessary | |
229 | */ | |
230 | lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1); | |
231 | ||
232 | /* | |
233 | * Clear noref flag for this subbuffer. | |
234 | */ | |
235 | lib_ring_buffer_clear_noref(config, &ctx->buf->backend, | |
1d498196 | 236 | subbuf_index(o_end - 1, chan), handle); |
852c2936 MD |
237 | |
238 | ctx->pre_offset = o_begin; | |
239 | ctx->buf_offset = o_begin + before_hdr_pad; | |
240 | return 0; | |
241 | slow_path: | |
242 | return lib_ring_buffer_reserve_slow(ctx); | |
243 | } | |
244 | ||
245 | /** | |
246 | * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer. | |
247 | * @config: ring buffer instance configuration. | |
248 | * @buf: buffer | |
249 | * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH) | |
250 | * | |
251 | * This operation is completely reentrant : can be called while tracing is | |
252 | * active with absolutely no lock held. | |
253 | * | |
254 | * Note, however, that as a v_cmpxchg is used for some atomic operations and | |
255 | * requires to be executed locally for per-CPU buffers, this function must be | |
256 | * called from the CPU which owns the buffer for a ACTIVE flush, with preemption | |
257 | * disabled, for RING_BUFFER_SYNC_PER_CPU configuration. | |
258 | */ | |
259 | static inline | |
4cfec15c MD |
260 | void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config, |
261 | struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode, | |
38fae1d3 | 262 | struct lttng_ust_shm_handle *handle) |
852c2936 | 263 | { |
1d498196 | 264 | lib_ring_buffer_switch_slow(buf, mode, handle); |
852c2936 MD |
265 | } |
266 | ||
267 | /* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */ | |
268 | ||
269 | /** | |
270 | * lib_ring_buffer_commit - Commit an record. | |
271 | * @config: ring buffer instance configuration. | |
272 | * @ctx: ring buffer context. (input arguments only) | |
273 | * | |
274 | * Atomic unordered slot commit. Increments the commit count in the | |
275 | * specified sub-buffer, and delivers it if necessary. | |
276 | */ | |
277 | static inline | |
4cfec15c MD |
278 | void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config, |
279 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 MD |
280 | { |
281 | struct channel *chan = ctx->chan; | |
38fae1d3 | 282 | struct lttng_ust_shm_handle *handle = ctx->handle; |
4cfec15c | 283 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
284 | unsigned long offset_end = ctx->buf_offset; |
285 | unsigned long endidx = subbuf_index(offset_end - 1, chan); | |
286 | unsigned long commit_count; | |
d2fe4771 MD |
287 | struct commit_counters_hot *cc_hot = shmp_index(handle, |
288 | buf->commit_hot, endidx); | |
3ea36dea MD |
289 | struct lttng_rseq_state rseq_state; |
290 | ||
291 | if (caa_likely(ctx->ctx_len | |
292 | >= sizeof(struct lttng_ust_lib_ring_buffer_ctx))) { | |
293 | rseq_state = ctx->rseq_state; | |
294 | } else { | |
295 | rseq_state.cpu_id = -2; | |
6fd21280 MD |
296 | rseq_state.event_counter = 0; |
297 | rseq_state.rseqp = NULL; | |
3ea36dea | 298 | } |
852c2936 | 299 | |
15500a1b MD |
300 | if (caa_unlikely(!cc_hot)) |
301 | return; | |
302 | ||
852c2936 MD |
303 | /* |
304 | * Must count record before incrementing the commit count. | |
305 | */ | |
15500a1b | 306 | subbuffer_count_record(config, ctx, &buf->backend, endidx, handle); |
852c2936 MD |
307 | |
308 | /* | |
309 | * Order all writes to buffer before the commit count update that will | |
310 | * determine that the subbuffer is full. | |
311 | */ | |
9f3fdbc6 | 312 | cmm_smp_wmb(); |
852c2936 | 313 | |
6fd21280 MD |
314 | if (caa_likely(config->sync == RING_BUFFER_SYNC_PER_CPU |
315 | && rseq_state.cpu_id >= 0)) { | |
3ea36dea MD |
316 | unsigned long newv; |
317 | ||
318 | newv = cc_hot->cc_rseq + ctx->slot_size; | |
319 | if (caa_likely(__rseq_finish(NULL, 0, NULL, NULL, 0, | |
320 | (intptr_t *)&cc_hot->cc_rseq, | |
321 | (intptr_t) newv, | |
322 | rseq_state, RSEQ_FINISH_SINGLE, false))) | |
323 | goto add_done; | |
324 | } | |
d2fe4771 | 325 | v_add(config, ctx->slot_size, &cc_hot->cc); |
3ea36dea | 326 | add_done: |
852c2936 MD |
327 | |
328 | /* | |
329 | * commit count read can race with concurrent OOO commit count updates. | |
330 | * This is only needed for lib_ring_buffer_check_deliver (for | |
331 | * non-polling delivery only) and for | |
332 | * lib_ring_buffer_write_commit_counter. The race can only cause the | |
333 | * counter to be read with the same value more than once, which could | |
334 | * cause : | |
335 | * - Multiple delivery for the same sub-buffer (which is handled | |
336 | * gracefully by the reader code) if the value is for a full | |
337 | * sub-buffer. It's important that we can never miss a sub-buffer | |
338 | * delivery. Re-reading the value after the v_add ensures this. | |
339 | * - Reading a commit_count with a higher value that what was actually | |
340 | * added to it for the lib_ring_buffer_write_commit_counter call | |
341 | * (again caused by a concurrent committer). It does not matter, | |
342 | * because this function is interested in the fact that the commit | |
343 | * count reaches back the reserve offset for a specific sub-buffer, | |
344 | * which is completely independent of the order. | |
345 | */ | |
d2fe4771 | 346 | commit_count = v_read(config, &cc_hot->cc); |
3ea36dea | 347 | commit_count += cc_hot->cc_rseq; |
852c2936 MD |
348 | |
349 | lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1, | |
1b7b0501 | 350 | commit_count, endidx, handle, ctx->tsc); |
852c2936 MD |
351 | /* |
352 | * Update used size at each commit. It's needed only for extracting | |
353 | * ring_buffer buffers from vmcore, after crash. | |
354 | */ | |
d2fe4771 MD |
355 | lib_ring_buffer_write_commit_counter(config, buf, chan, |
356 | offset_end, commit_count, handle, cc_hot); | |
852c2936 MD |
357 | } |
358 | ||
359 | /** | |
360 | * lib_ring_buffer_try_discard_reserve - Try discarding a record. | |
361 | * @config: ring buffer instance configuration. | |
362 | * @ctx: ring buffer context. (input arguments only) | |
363 | * | |
364 | * Only succeeds if no other record has been written after the record to | |
365 | * discard. If discard fails, the record must be committed to the buffer. | |
366 | * | |
367 | * Returns 0 upon success, -EPERM if the record cannot be discarded. | |
368 | */ | |
369 | static inline | |
4cfec15c MD |
370 | int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
371 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 | 372 | { |
4cfec15c | 373 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
374 | unsigned long end_offset = ctx->pre_offset + ctx->slot_size; |
375 | ||
376 | /* | |
377 | * We need to ensure that if the cmpxchg succeeds and discards the | |
378 | * record, the next record will record a full TSC, because it cannot | |
379 | * rely on the last_tsc associated with the discarded record to detect | |
380 | * overflows. The only way to ensure this is to set the last_tsc to 0 | |
381 | * (assuming no 64-bit TSC overflow), which forces to write a 64-bit | |
382 | * timestamp in the next record. | |
383 | * | |
384 | * Note: if discard fails, we must leave the TSC in the record header. | |
385 | * It is needed to keep track of TSC overflows for the following | |
386 | * records. | |
387 | */ | |
388 | save_last_tsc(config, buf, 0ULL); | |
389 | ||
b5a3dfa5 | 390 | if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset) |
852c2936 MD |
391 | != end_offset)) |
392 | return -EPERM; | |
393 | else | |
394 | return 0; | |
395 | } | |
396 | ||
397 | static inline | |
4cfec15c | 398 | void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
852c2936 MD |
399 | struct channel *chan) |
400 | { | |
9f3fdbc6 | 401 | uatomic_inc(&chan->record_disabled); |
852c2936 MD |
402 | } |
403 | ||
404 | static inline | |
4cfec15c | 405 | void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
852c2936 MD |
406 | struct channel *chan) |
407 | { | |
9f3fdbc6 | 408 | uatomic_dec(&chan->record_disabled); |
852c2936 MD |
409 | } |
410 | ||
411 | static inline | |
4cfec15c MD |
412 | void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
413 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 414 | { |
9f3fdbc6 | 415 | uatomic_inc(&buf->record_disabled); |
852c2936 MD |
416 | } |
417 | ||
418 | static inline | |
4cfec15c MD |
419 | void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
420 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 421 | { |
9f3fdbc6 | 422 | uatomic_dec(&buf->record_disabled); |
852c2936 MD |
423 | } |
424 | ||
e92f3e28 | 425 | #endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */ |