xref: /linux-6.15/kernel/events/ring_buffer.c (revision a8b0ca17) 
1 /*
2  * Performance events ring-buffer code:
3  *
4  *  Copyright (C) 2008 Thomas Gleixner <[email protected]>
5  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
6  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra <[email protected]>
7  *  Copyright  �  2009 Paul Mackerras, IBM Corp. <[email protected]>
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 		      int sample)
103 {
104 	struct ring_buffer *rb;
105 	unsigned long tail, offset, head;
106 	int have_lost;
107 	struct perf_sample_data sample_data;
108 	struct {
109 		struct perf_event_header header;
110 		u64			 id;
111 		u64			 lost;
112 	} lost_event;
113 
114 	rcu_read_lock();
115 	/*
116 	 * For inherited events we send all the output towards the parent.
117 	 */
118 	if (event->parent)
119 		event = event->parent;
120 
121 	rb = rcu_dereference(event->rb);
122 	if (!rb)
123 		goto out;
124 
125 	handle->rb	= rb;
126 	handle->event	= event;
127 	handle->sample	= sample;
128 
129 	if (!rb->nr_pages)
130 		goto out;
131 
132 	have_lost = local_read(&rb->lost);
133 	if (have_lost) {
134 		lost_event.header.size = sizeof(lost_event);
135 		perf_event_header__init_id(&lost_event.header, &sample_data,
136 					   event);
137 		size += lost_event.header.size;
138 	}
139 
140 	perf_output_get_handle(handle);
141 
142 	do {
143 		/*
144 		 * Userspace could choose to issue a mb() before updating the
145 		 * tail pointer. So that all reads will be completed before the
146 		 * write is issued.
147 		 */
148 		tail = ACCESS_ONCE(rb->user_page->data_tail);
149 		smp_rmb();
150 		offset = head = local_read(&rb->head);
151 		head += size;
152 		if (unlikely(!perf_output_space(rb, tail, offset, head)))
153 			goto fail;
154 	} while (local_cmpxchg(&rb->head, offset, head) != offset);
155 
156 	if (head - local_read(&rb->wakeup) > rb->watermark)
157 		local_add(rb->watermark, &rb->wakeup);
158 
159 	handle->page = offset >> (PAGE_SHIFT + page_order(rb));
160 	handle->page &= rb->nr_pages - 1;
161 	handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1);
162 	handle->addr = rb->data_pages[handle->page];
163 	handle->addr += handle->size;
164 	handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
165 
166 	if (have_lost) {
167 		lost_event.header.type = PERF_RECORD_LOST;
168 		lost_event.header.misc = 0;
169 		lost_event.id          = event->id;
170 		lost_event.lost        = local_xchg(&rb->lost, 0);
171 
172 		perf_output_put(handle, lost_event);
173 		perf_event__output_id_sample(event, handle, &sample_data);
174 	}
175 
176 	return 0;
177 
178 fail:
179 	local_inc(&rb->lost);
180 	perf_output_put_handle(handle);
181 out:
182 	rcu_read_unlock();
183 
184 	return -ENOSPC;
185 }
186 
187 void perf_output_copy(struct perf_output_handle *handle,
188 		      const void *buf, unsigned int len)
189 {
190 	__output_copy(handle, buf, len);
191 }
192 
193 void perf_output_end(struct perf_output_handle *handle)
194 {
195 	struct perf_event *event = handle->event;
196 	struct ring_buffer *rb = handle->rb;
197 
198 	if (handle->sample && !event->attr.watermark) {
199 		int wakeup_events = event->attr.wakeup_events;
200 
201 		if (wakeup_events) {
202 			int events = local_inc_return(&rb->events);
203 			if (events >= wakeup_events) {
204 				local_sub(wakeup_events, &rb->events);
205 				local_inc(&rb->wakeup);
206 			}
207 		}
208 	}
209 
210 	perf_output_put_handle(handle);
211 	rcu_read_unlock();
212 }
213 
214 static void
215 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
216 {
217 	long max_size = perf_data_size(rb);
218 
219 	if (watermark)
220 		rb->watermark = min(max_size, watermark);
221 
222 	if (!rb->watermark)
223 		rb->watermark = max_size / 2;
224 
225 	if (flags & RING_BUFFER_WRITABLE)
226 		rb->writable = 1;
227 
228 	atomic_set(&rb->refcount, 1);
229 }
230 
231 #ifndef CONFIG_PERF_USE_VMALLOC
232 
233 /*
234  * Back perf_mmap() with regular GFP_KERNEL-0 pages.
235  */
236 
237 struct page *
238 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
239 {
240 	if (pgoff > rb->nr_pages)
241 		return NULL;
242 
243 	if (pgoff == 0)
244 		return virt_to_page(rb->user_page);
245 
246 	return virt_to_page(rb->data_pages[pgoff - 1]);
247 }
248 
249 static void *perf_mmap_alloc_page(int cpu)
250 {
251 	struct page *page;
252 	int node;
253 
254 	node = (cpu == -1) ? cpu : cpu_to_node(cpu);
255 	page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
256 	if (!page)
257 		return NULL;
258 
259 	return page_address(page);
260 }
261 
262 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
263 {
264 	struct ring_buffer *rb;
265 	unsigned long size;
266 	int i;
267 
268 	size = sizeof(struct ring_buffer);
269 	size += nr_pages * sizeof(void *);
270 
271 	rb = kzalloc(size, GFP_KERNEL);
272 	if (!rb)
273 		goto fail;
274 
275 	rb->user_page = perf_mmap_alloc_page(cpu);
276 	if (!rb->user_page)
277 		goto fail_user_page;
278 
279 	for (i = 0; i < nr_pages; i++) {
280 		rb->data_pages[i] = perf_mmap_alloc_page(cpu);
281 		if (!rb->data_pages[i])
282 			goto fail_data_pages;
283 	}
284 
285 	rb->nr_pages = nr_pages;
286 
287 	ring_buffer_init(rb, watermark, flags);
288 
289 	return rb;
290 
291 fail_data_pages:
292 	for (i--; i >= 0; i--)
293 		free_page((unsigned long)rb->data_pages[i]);
294 
295 	free_page((unsigned long)rb->user_page);
296 
297 fail_user_page:
298 	kfree(rb);
299 
300 fail:
301 	return NULL;
302 }
303 
304 static void perf_mmap_free_page(unsigned long addr)
305 {
306 	struct page *page = virt_to_page((void *)addr);
307 
308 	page->mapping = NULL;
309 	__free_page(page);
310 }
311 
312 void rb_free(struct ring_buffer *rb)
313 {
314 	int i;
315 
316 	perf_mmap_free_page((unsigned long)rb->user_page);
317 	for (i = 0; i < rb->nr_pages; i++)
318 		perf_mmap_free_page((unsigned long)rb->data_pages[i]);
319 	kfree(rb);
320 }
321 
322 #else
323 
324 struct page *
325 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
326 {
327 	if (pgoff > (1UL << page_order(rb)))
328 		return NULL;
329 
330 	return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
331 }
332 
333 static void perf_mmap_unmark_page(void *addr)
334 {
335 	struct page *page = vmalloc_to_page(addr);
336 
337 	page->mapping = NULL;
338 }
339 
340 static void rb_free_work(struct work_struct *work)
341 {
342 	struct ring_buffer *rb;
343 	void *base;
344 	int i, nr;
345 
346 	rb = container_of(work, struct ring_buffer, work);
347 	nr = 1 << page_order(rb);
348 
349 	base = rb->user_page;
350 	for (i = 0; i < nr + 1; i++)
351 		perf_mmap_unmark_page(base + (i * PAGE_SIZE));
352 
353 	vfree(base);
354 	kfree(rb);
355 }
356 
357 void rb_free(struct ring_buffer *rb)
358 {
359 	schedule_work(&rb->work);
360 }
361 
362 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
363 {
364 	struct ring_buffer *rb;
365 	unsigned long size;
366 	void *all_buf;
367 
368 	size = sizeof(struct ring_buffer);
369 	size += sizeof(void *);
370 
371 	rb = kzalloc(size, GFP_KERNEL);
372 	if (!rb)
373 		goto fail;
374 
375 	INIT_WORK(&rb->work, rb_free_work);
376 
377 	all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
378 	if (!all_buf)
379 		goto fail_all_buf;
380 
381 	rb->user_page = all_buf;
382 	rb->data_pages[0] = all_buf + PAGE_SIZE;
383 	rb->page_order = ilog2(nr_pages);
384 	rb->nr_pages = 1;
385 
386 	ring_buffer_init(rb, watermark, flags);
387 
388 	return rb;
389 
390 fail_all_buf:
391 	kfree(rb);
392 
393 fail:
394 	return NULL;
395 }
396 
397 #endif
398