1 /* 2 * Performance events ring-buffer code: 3 * 4 * Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de> 5 * Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar 6 * Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> 7 * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com> 8 * 9 * For licensing details see kernel-base/COPYING 10 */ 11 12 #include <linux/perf_event.h> 13 #include <linux/vmalloc.h> 14 #include <linux/slab.h> 15 16 #include "internal.h" 17 18 static bool perf_output_space(struct ring_buffer *rb, unsigned long tail, 19 unsigned long offset, unsigned long head) 20 { 21 unsigned long sz = perf_data_size(rb); 22 unsigned long mask = sz - 1; 23 24 /* 25 * check if user-writable 26 * overwrite : over-write its own tail 27 * !overwrite: buffer possibly drops events. 28 */ 29 if (rb->overwrite) 30 return true; 31 32 /* 33 * verify that payload is not bigger than buffer 34 * otherwise masking logic may fail to detect 35 * the "not enough space" condition 36 */ 37 if ((head - offset) > sz) 38 return false; 39 40 offset = (offset - tail) & mask; 41 head = (head - tail) & mask; 42 43 if ((int)(head - offset) < 0) 44 return false; 45 46 return true; 47 } 48 49 static void perf_output_wakeup(struct perf_output_handle *handle) 50 { 51 atomic_set(&handle->rb->poll, POLL_IN); 52 53 handle->event->pending_wakeup = 1; 54 irq_work_queue(&handle->event->pending); 55 } 56 57 /* 58 * We need to ensure a later event_id doesn't publish a head when a former 59 * event isn't done writing. However since we need to deal with NMIs we 60 * cannot fully serialize things. 61 * 62 * We only publish the head (and generate a wakeup) when the outer-most 63 * event completes. 64 */ 65 static void perf_output_get_handle(struct perf_output_handle *handle) 66 { 67 struct ring_buffer *rb = handle->rb; 68 69 preempt_disable(); 70 local_inc(&rb->nest); 71 handle->wakeup = local_read(&rb->wakeup); 72 } 73 74 static void perf_output_put_handle(struct perf_output_handle *handle) 75 { 76 struct ring_buffer *rb = handle->rb; 77 unsigned long head; 78 79 again: 80 head = local_read(&rb->head); 81 82 /* 83 * IRQ/NMI can happen here, which means we can miss a head update. 84 */ 85 86 if (!local_dec_and_test(&rb->nest)) 87 goto out; 88 89 /* 90 * Since the mmap() consumer (userspace) can run on a different CPU: 91 * 92 * kernel user 93 * 94 * READ ->data_tail READ ->data_head 95 * smp_mb() (A) smp_rmb() (C) 96 * WRITE $data READ $data 97 * smp_wmb() (B) smp_mb() (D) 98 * STORE ->data_head WRITE ->data_tail 99 * 100 * Where A pairs with D, and B pairs with C. 101 * 102 * I don't think A needs to be a full barrier because we won't in fact 103 * write data until we see the store from userspace. So we simply don't 104 * issue the data WRITE until we observe it. Be conservative for now. 105 * 106 * OTOH, D needs to be a full barrier since it separates the data READ 107 * from the tail WRITE. 108 * 109 * For B a WMB is sufficient since it separates two WRITEs, and for C 110 * an RMB is sufficient since it separates two READs. 111 * 112 * See perf_output_begin(). 113 */ 114 smp_wmb(); 115 rb->user_page->data_head = head; 116 117 /* 118 * Now check if we missed an update, rely on the (compiler) 119 * barrier in atomic_dec_and_test() to re-read rb->head. 120 */ 121 if (unlikely(head != local_read(&rb->head))) { 122 local_inc(&rb->nest); 123 goto again; 124 } 125 126 if (handle->wakeup != local_read(&rb->wakeup)) 127 perf_output_wakeup(handle); 128 129 out: 130 preempt_enable(); 131 } 132 133 int perf_output_begin(struct perf_output_handle *handle, 134 struct perf_event *event, unsigned int size) 135 { 136 struct ring_buffer *rb; 137 unsigned long tail, offset, head; 138 int have_lost; 139 struct perf_sample_data sample_data; 140 struct { 141 struct perf_event_header header; 142 u64 id; 143 u64 lost; 144 } lost_event; 145 146 rcu_read_lock(); 147 /* 148 * For inherited events we send all the output towards the parent. 149 */ 150 if (event->parent) 151 event = event->parent; 152 153 rb = rcu_dereference(event->rb); 154 if (!rb) 155 goto out; 156 157 handle->rb = rb; 158 handle->event = event; 159 160 if (!rb->nr_pages) 161 goto out; 162 163 have_lost = local_read(&rb->lost); 164 if (have_lost) { 165 lost_event.header.size = sizeof(lost_event); 166 perf_event_header__init_id(&lost_event.header, &sample_data, 167 event); 168 size += lost_event.header.size; 169 } 170 171 perf_output_get_handle(handle); 172 173 do { 174 /* 175 * Userspace could choose to issue a mb() before updating the 176 * tail pointer. So that all reads will be completed before the 177 * write is issued. 178 * 179 * See perf_output_put_handle(). 180 */ 181 tail = ACCESS_ONCE(rb->user_page->data_tail); 182 smp_mb(); 183 offset = head = local_read(&rb->head); 184 head += size; 185 if (unlikely(!perf_output_space(rb, tail, offset, head))) 186 goto fail; 187 } while (local_cmpxchg(&rb->head, offset, head) != offset); 188 189 if (head - local_read(&rb->wakeup) > rb->watermark) 190 local_add(rb->watermark, &rb->wakeup); 191 192 handle->page = offset >> (PAGE_SHIFT + page_order(rb)); 193 handle->page &= rb->nr_pages - 1; 194 handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1); 195 handle->addr = rb->data_pages[handle->page]; 196 handle->addr += handle->size; 197 handle->size = (PAGE_SIZE << page_order(rb)) - handle->size; 198 199 if (have_lost) { 200 lost_event.header.type = PERF_RECORD_LOST; 201 lost_event.header.misc = 0; 202 lost_event.id = event->id; 203 lost_event.lost = local_xchg(&rb->lost, 0); 204 205 perf_output_put(handle, lost_event); 206 perf_event__output_id_sample(event, handle, &sample_data); 207 } 208 209 return 0; 210 211 fail: 212 local_inc(&rb->lost); 213 perf_output_put_handle(handle); 214 out: 215 rcu_read_unlock(); 216 217 return -ENOSPC; 218 } 219 220 unsigned int perf_output_copy(struct perf_output_handle *handle, 221 const void *buf, unsigned int len) 222 { 223 return __output_copy(handle, buf, len); 224 } 225 226 unsigned int perf_output_skip(struct perf_output_handle *handle, 227 unsigned int len) 228 { 229 return __output_skip(handle, NULL, len); 230 } 231 232 void perf_output_end(struct perf_output_handle *handle) 233 { 234 perf_output_put_handle(handle); 235 rcu_read_unlock(); 236 } 237 238 static void 239 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags) 240 { 241 long max_size = perf_data_size(rb); 242 243 if (watermark) 244 rb->watermark = min(max_size, watermark); 245 246 if (!rb->watermark) 247 rb->watermark = max_size / 2; 248 249 if (flags & RING_BUFFER_WRITABLE) 250 rb->overwrite = 0; 251 else 252 rb->overwrite = 1; 253 254 atomic_set(&rb->refcount, 1); 255 256 INIT_LIST_HEAD(&rb->event_list); 257 spin_lock_init(&rb->event_lock); 258 } 259 260 #ifndef CONFIG_PERF_USE_VMALLOC 261 262 /* 263 * Back perf_mmap() with regular GFP_KERNEL-0 pages. 264 */ 265 266 struct page * 267 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) 268 { 269 if (pgoff > rb->nr_pages) 270 return NULL; 271 272 if (pgoff == 0) 273 return virt_to_page(rb->user_page); 274 275 return virt_to_page(rb->data_pages[pgoff - 1]); 276 } 277 278 static void *perf_mmap_alloc_page(int cpu) 279 { 280 struct page *page; 281 int node; 282 283 node = (cpu == -1) ? cpu : cpu_to_node(cpu); 284 page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0); 285 if (!page) 286 return NULL; 287 288 return page_address(page); 289 } 290 291 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags) 292 { 293 struct ring_buffer *rb; 294 unsigned long size; 295 int i; 296 297 size = sizeof(struct ring_buffer); 298 size += nr_pages * sizeof(void *); 299 300 rb = kzalloc(size, GFP_KERNEL); 301 if (!rb) 302 goto fail; 303 304 rb->user_page = perf_mmap_alloc_page(cpu); 305 if (!rb->user_page) 306 goto fail_user_page; 307 308 for (i = 0; i < nr_pages; i++) { 309 rb->data_pages[i] = perf_mmap_alloc_page(cpu); 310 if (!rb->data_pages[i]) 311 goto fail_data_pages; 312 } 313 314 rb->nr_pages = nr_pages; 315 316 ring_buffer_init(rb, watermark, flags); 317 318 return rb; 319 320 fail_data_pages: 321 for (i--; i >= 0; i--) 322 free_page((unsigned long)rb->data_pages[i]); 323 324 free_page((unsigned long)rb->user_page); 325 326 fail_user_page: 327 kfree(rb); 328 329 fail: 330 return NULL; 331 } 332 333 static void perf_mmap_free_page(unsigned long addr) 334 { 335 struct page *page = virt_to_page((void *)addr); 336 337 page->mapping = NULL; 338 __free_page(page); 339 } 340 341 void rb_free(struct ring_buffer *rb) 342 { 343 int i; 344 345 perf_mmap_free_page((unsigned long)rb->user_page); 346 for (i = 0; i < rb->nr_pages; i++) 347 perf_mmap_free_page((unsigned long)rb->data_pages[i]); 348 kfree(rb); 349 } 350 351 #else 352 static int data_page_nr(struct ring_buffer *rb) 353 { 354 return rb->nr_pages << page_order(rb); 355 } 356 357 struct page * 358 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) 359 { 360 /* The '>' counts in the user page. */ 361 if (pgoff > data_page_nr(rb)) 362 return NULL; 363 364 return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE); 365 } 366 367 static void perf_mmap_unmark_page(void *addr) 368 { 369 struct page *page = vmalloc_to_page(addr); 370 371 page->mapping = NULL; 372 } 373 374 static void rb_free_work(struct work_struct *work) 375 { 376 struct ring_buffer *rb; 377 void *base; 378 int i, nr; 379 380 rb = container_of(work, struct ring_buffer, work); 381 nr = data_page_nr(rb); 382 383 base = rb->user_page; 384 /* The '<=' counts in the user page. */ 385 for (i = 0; i <= nr; i++) 386 perf_mmap_unmark_page(base + (i * PAGE_SIZE)); 387 388 vfree(base); 389 kfree(rb); 390 } 391 392 void rb_free(struct ring_buffer *rb) 393 { 394 schedule_work(&rb->work); 395 } 396 397 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags) 398 { 399 struct ring_buffer *rb; 400 unsigned long size; 401 void *all_buf; 402 403 size = sizeof(struct ring_buffer); 404 size += sizeof(void *); 405 406 rb = kzalloc(size, GFP_KERNEL); 407 if (!rb) 408 goto fail; 409 410 INIT_WORK(&rb->work, rb_free_work); 411 412 all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE); 413 if (!all_buf) 414 goto fail_all_buf; 415 416 rb->user_page = all_buf; 417 rb->data_pages[0] = all_buf + PAGE_SIZE; 418 rb->page_order = ilog2(nr_pages); 419 rb->nr_pages = !!nr_pages; 420 421 ring_buffer_init(rb, watermark, flags); 422 423 return rb; 424 425 fail_all_buf: 426 kfree(rb); 427 428 fail: 429 return NULL; 430 } 431 432 #endif 433