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TOMOYO Linux Cross Reference
Linux/kernel/events/ring_buffer.c

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  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 mask;
 22 
 23         if (!rb->writable)
 24                 return true;
 25 
 26         mask = perf_data_size(rb) - 1;
 27 
 28         offset = (offset - tail) & mask;
 29         head   = (head   - tail) & mask;
 30 
 31         if ((int)(head - offset) < 0)
 32                 return false;
 33 
 34         return true;
 35 }
 36 
 37 static void perf_output_wakeup(struct perf_output_handle *handle)
 38 {
 39         atomic_set(&handle->rb->poll, POLL_IN);
 40 
 41         handle->event->pending_wakeup = 1;
 42         irq_work_queue(&handle->event->pending);
 43 }
 44 
 45 /*
 46  * We need to ensure a later event_id doesn't publish a head when a former
 47  * event isn't done writing. However since we need to deal with NMIs we
 48  * cannot fully serialize things.
 49  *
 50  * We only publish the head (and generate a wakeup) when the outer-most
 51  * event completes.
 52  */
 53 static void perf_output_get_handle(struct perf_output_handle *handle)
 54 {
 55         struct ring_buffer *rb = handle->rb;
 56 
 57         preempt_disable();
 58         local_inc(&rb->nest);
 59         handle->wakeup = local_read(&rb->wakeup);
 60 }
 61 
 62 static void perf_output_put_handle(struct perf_output_handle *handle)
 63 {
 64         struct ring_buffer *rb = handle->rb;
 65         unsigned long head;
 66 
 67 again:
 68         head = local_read(&rb->head);
 69 
 70         /*
 71          * IRQ/NMI can happen here, which means we can miss a head update.
 72          */
 73 
 74         if (!local_dec_and_test(&rb->nest))
 75                 goto out;
 76 
 77         /*
 78          * Publish the known good head. Rely on the full barrier implied
 79          * by atomic_dec_and_test() order the rb->head read and this
 80          * write.
 81          */
 82         rb->user_page->data_head = head;
 83 
 84         /*
 85          * Now check if we missed an update, rely on the (compiler)
 86          * barrier in atomic_dec_and_test() to re-read rb->head.
 87          */
 88         if (unlikely(head != local_read(&rb->head))) {
 89                 local_inc(&rb->nest);
 90                 goto again;
 91         }
 92 
 93         if (handle->wakeup != local_read(&rb->wakeup))
 94                 perf_output_wakeup(handle);
 95 
 96 out:
 97         preempt_enable();
 98 }
 99 
100 int perf_output_begin(struct perf_output_handle *handle,
101                       struct perf_event *event, unsigned int size)
102 {
103         struct ring_buffer *rb;
104         unsigned long tail, offset, head;
105         int have_lost;
106         struct perf_sample_data sample_data;
107         struct {
108                 struct perf_event_header header;
109                 u64                      id;
110                 u64                      lost;
111         } lost_event;
112 
113         rcu_read_lock();
114         /*
115          * For inherited events we send all the output towards the parent.
116          */
117         if (event->parent)
118                 event = event->parent;
119 
120         rb = rcu_dereference(event->rb);
121         if (!rb)
122                 goto out;
123 
124         handle->rb      = rb;
125         handle->event   = event;
126 
127         if (!rb->nr_pages)
128                 goto out;
129 
130         have_lost = local_read(&rb->lost);
131         if (have_lost) {
132                 lost_event.header.size = sizeof(lost_event);
133                 perf_event_header__init_id(&lost_event.header, &sample_data,
134                                            event);
135                 size += lost_event.header.size;
136         }
137 
138         perf_output_get_handle(handle);
139 
140         do {
141                 /*
142                  * Userspace could choose to issue a mb() before updating the
143                  * tail pointer. So that all reads will be completed before the
144                  * write is issued.
145                  */
146                 tail = ACCESS_ONCE(rb->user_page->data_tail);
147                 smp_rmb();
148                 offset = head = local_read(&rb->head);
149                 head += size;
150                 if (unlikely(!perf_output_space(rb, tail, offset, head)))
151                         goto fail;
152         } while (local_cmpxchg(&rb->head, offset, head) != offset);
153 
154         if (head - local_read(&rb->wakeup) > rb->watermark)
155                 local_add(rb->watermark, &rb->wakeup);
156 
157         handle->page = offset >> (PAGE_SHIFT + page_order(rb));
158         handle->page &= rb->nr_pages - 1;
159         handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1);
160         handle->addr = rb->data_pages[handle->page];
161         handle->addr += handle->size;
162         handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
163 
164         if (have_lost) {
165                 lost_event.header.type = PERF_RECORD_LOST;
166                 lost_event.header.misc = 0;
167                 lost_event.id          = event->id;
168                 lost_event.lost        = local_xchg(&rb->lost, 0);
169 
170                 perf_output_put(handle, lost_event);
171                 perf_event__output_id_sample(event, handle, &sample_data);
172         }
173 
174         return 0;
175 
176 fail:
177         local_inc(&rb->lost);
178         perf_output_put_handle(handle);
179 out:
180         rcu_read_unlock();
181 
182         return -ENOSPC;
183 }
184 
185 void perf_output_copy(struct perf_output_handle *handle,
186                       const void *buf, unsigned int len)
187 {
188         __output_copy(handle, buf, len);
189 }
190 
191 void perf_output_end(struct perf_output_handle *handle)
192 {
193         perf_output_put_handle(handle);
194         rcu_read_unlock();
195 }
196 
197 static void
198 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
199 {
200         long max_size = perf_data_size(rb);
201 
202         if (watermark)
203                 rb->watermark = min(max_size, watermark);
204 
205         if (!rb->watermark)
206                 rb->watermark = max_size / 2;
207 
208         if (flags & RING_BUFFER_WRITABLE)
209                 rb->writable = 1;
210 
211         atomic_set(&rb->refcount, 1);
212 
213         INIT_LIST_HEAD(&rb->event_list);
214         spin_lock_init(&rb->event_lock);
215 }
216 
217 #ifndef CONFIG_PERF_USE_VMALLOC
218 
219 /*
220  * Back perf_mmap() with regular GFP_KERNEL-0 pages.
221  */
222 
223 struct page *
224 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
225 {
226         if (pgoff > rb->nr_pages)
227                 return NULL;
228 
229         if (pgoff == 0)
230                 return virt_to_page(rb->user_page);
231 
232         return virt_to_page(rb->data_pages[pgoff - 1]);
233 }
234 
235 static void *perf_mmap_alloc_page(int cpu)
236 {
237         struct page *page;
238         int node;
239 
240         node = (cpu == -1) ? cpu : cpu_to_node(cpu);
241         page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
242         if (!page)
243                 return NULL;
244 
245         return page_address(page);
246 }
247 
248 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
249 {
250         struct ring_buffer *rb;
251         unsigned long size;
252         int i;
253 
254         size = sizeof(struct ring_buffer);
255         size += nr_pages * sizeof(void *);
256 
257         rb = kzalloc(size, GFP_KERNEL);
258         if (!rb)
259                 goto fail;
260 
261         rb->user_page = perf_mmap_alloc_page(cpu);
262         if (!rb->user_page)
263                 goto fail_user_page;
264 
265         for (i = 0; i < nr_pages; i++) {
266                 rb->data_pages[i] = perf_mmap_alloc_page(cpu);
267                 if (!rb->data_pages[i])
268                         goto fail_data_pages;
269         }
270 
271         rb->nr_pages = nr_pages;
272 
273         ring_buffer_init(rb, watermark, flags);
274 
275         return rb;
276 
277 fail_data_pages:
278         for (i--; i >= 0; i--)
279                 free_page((unsigned long)rb->data_pages[i]);
280 
281         free_page((unsigned long)rb->user_page);
282 
283 fail_user_page:
284         kfree(rb);
285 
286 fail:
287         return NULL;
288 }
289 
290 static void perf_mmap_free_page(unsigned long addr)
291 {
292         struct page *page = virt_to_page((void *)addr);
293 
294         page->mapping = NULL;
295         __free_page(page);
296 }
297 
298 void rb_free(struct ring_buffer *rb)
299 {
300         int i;
301 
302         perf_mmap_free_page((unsigned long)rb->user_page);
303         for (i = 0; i < rb->nr_pages; i++)
304                 perf_mmap_free_page((unsigned long)rb->data_pages[i]);
305         kfree(rb);
306 }
307 
308 #else
309 
310 struct page *
311 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
312 {
313         if (pgoff > (1UL << page_order(rb)))
314                 return NULL;
315 
316         return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
317 }
318 
319 static void perf_mmap_unmark_page(void *addr)
320 {
321         struct page *page = vmalloc_to_page(addr);
322 
323         page->mapping = NULL;
324 }
325 
326 static void rb_free_work(struct work_struct *work)
327 {
328         struct ring_buffer *rb;
329         void *base;
330         int i, nr;
331 
332         rb = container_of(work, struct ring_buffer, work);
333         nr = 1 << page_order(rb);
334 
335         base = rb->user_page;
336         for (i = 0; i < nr + 1; i++)
337                 perf_mmap_unmark_page(base + (i * PAGE_SIZE));
338 
339         vfree(base);
340         kfree(rb);
341 }
342 
343 void rb_free(struct ring_buffer *rb)
344 {
345         schedule_work(&rb->work);
346 }
347 
348 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
349 {
350         struct ring_buffer *rb;
351         unsigned long size;
352         void *all_buf;
353 
354         size = sizeof(struct ring_buffer);
355         size += sizeof(void *);
356 
357         rb = kzalloc(size, GFP_KERNEL);
358         if (!rb)
359                 goto fail;
360 
361         INIT_WORK(&rb->work, rb_free_work);
362 
363         all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
364         if (!all_buf)
365                 goto fail_all_buf;
366 
367         rb->user_page = all_buf;
368         rb->data_pages[0] = all_buf + PAGE_SIZE;
369         rb->page_order = ilog2(nr_pages);
370         rb->nr_pages = 1;
371 
372         ring_buffer_init(rb, watermark, flags);
373 
374         return rb;
375 
376 fail_all_buf:
377         kfree(rb);
378 
379 fail:
380         return NULL;
381 }
382 
383 #endif
384 

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