kernel/events/ring_buffer.c - codeaurora/cp-linux - Gitiles

 /*
  * Performance events ring-buffer code:
  *
  *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
  *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
  *
  * For licensing details see kernel-base/COPYING
  */

 #include <linux/perf_event.h>
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
 #include <linux/circ_buf.h>
 #include <linux/poll.h>

 #include "internal.h"

 static void perf_output_wakeup(struct perf_output_handle *handle)
 {
 	atomic_set(&handle->rb->poll, POLLIN);

 	handle->event->pending_wakeup = 1;
 	irq_work_queue(&handle->event->pending);
 }

 /*
  * We need to ensure a later event_id doesn't publish a head when a former
  * event isn't done writing. However since we need to deal with NMIs we
  * cannot fully serialize things.
  *
  * We only publish the head (and generate a wakeup) when the outer-most
  * event completes.
  */
 static void perf_output_get_handle(struct perf_output_handle *handle)
 {
 	struct ring_buffer *rb = handle->rb;

 	preempt_disable();
 	local_inc(&rb->nest);
 	handle->wakeup = local_read(&rb->wakeup);
 }

 static void perf_output_put_handle(struct perf_output_handle *handle)
 {
 	struct ring_buffer *rb = handle->rb;
 	unsigned long head;

 again:
 	head = local_read(&rb->head);

 	/*
 	 * IRQ/NMI can happen here, which means we can miss a head update.
 	 */

 	if (!local_dec_and_test(&rb->nest))
 		goto out;

 	/*
 	 * Since the mmap() consumer (userspace) can run on a different CPU:
 	 *
 	 *   kernel				user
 	 *
 	 *   if (LOAD ->data_tail) {		LOAD ->data_head
 	 *			(A)		smp_rmb()	(C)
 	 *	STORE $data			LOAD $data
 	 *	smp_wmb()	(B)		smp_mb()	(D)
 	 *	STORE ->data_head		STORE ->data_tail
 	 *   }
 	 *
 	 * Where A pairs with D, and B pairs with C.
 	 *
 	 * In our case (A) is a control dependency that separates the load of
 	 * the ->data_tail and the stores of $data. In case ->data_tail
 	 * indicates there is no room in the buffer to store $data we do not.
 	 *
 	 * D needs to be a full barrier since it separates the data READ
 	 * from the tail WRITE.
 	 *
 	 * For B a WMB is sufficient since it separates two WRITEs, and for C
 	 * an RMB is sufficient since it separates two READs.
 	 *
 	 * See perf_output_begin().
 	 */
 	smp_wmb(); /* B, matches C */
 	rb->user_page->data_head = head;

 	/*
 	 * Now check if we missed an update -- rely on previous implied
 	 * compiler barriers to force a re-read.
 	 */
 	if (unlikely(head != local_read(&rb->head))) {
 		local_inc(&rb->nest);
 		goto again;
 	}

 	if (handle->wakeup != local_read(&rb->wakeup))
 		perf_output_wakeup(handle);

 out:
 	preempt_enable();
 }

 int perf_output_begin(struct perf_output_handle *handle,
 		      struct perf_event *event, unsigned int size)
 {
 	struct ring_buffer *rb;
 	unsigned long tail, offset, head;
 	int have_lost, page_shift;
 	struct {
 		struct perf_event_header header;
 		u64			 id;
 		u64			 lost;
 	} lost_event;

 	rcu_read_lock();
 	/*
 	 * For inherited events we send all the output towards the parent.
 	 */
 	if (event->parent)
 		event = event->parent;

 	rb = rcu_dereference(event->rb);
 	if (unlikely(!rb))
 		goto out;

 	if (unlikely(!rb->nr_pages))
 		goto out;

 	handle->rb    = rb;
 	handle->event = event;

 	have_lost = local_read(&rb->lost);
 	if (unlikely(have_lost)) {
 		size += sizeof(lost_event);
 		if (event->attr.sample_id_all)
 			size += event->id_header_size;
 	}

 	perf_output_get_handle(handle);

 	do {
 		tail = READ_ONCE(rb->user_page->data_tail);
 		offset = head = local_read(&rb->head);
 		if (!rb->overwrite &&
 		    unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
 			goto fail;

 		/*
 		 * The above forms a control dependency barrier separating the
 		 * @tail load above from the data stores below. Since the @tail
 		 * load is required to compute the branch to fail below.
 		 *
 		 * A, matches D; the full memory barrier userspace SHOULD issue
 		 * after reading the data and before storing the new tail
 		 * position.
 		 *
 		 * See perf_output_put_handle().
 		 */

 		head += size;
 	} while (local_cmpxchg(&rb->head, offset, head) != offset);

 	/*
 	 * We rely on the implied barrier() by local_cmpxchg() to ensure
 	 * none of the data stores below can be lifted up by the compiler.
 	 */

 	if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
 		local_add(rb->watermark, &rb->wakeup);

 	page_shift = PAGE_SHIFT + page_order(rb);

 	handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
 	offset &= (1UL << page_shift) - 1;
 	handle->addr = rb->data_pages[handle->page] + offset;
 	handle->size = (1UL << page_shift) - offset;

 	if (unlikely(have_lost)) {
 		struct perf_sample_data sample_data;

 		lost_event.header.size = sizeof(lost_event);
 		lost_event.header.type = PERF_RECORD_LOST;
 		lost_event.header.misc = 0;
 		lost_event.id          = event->id;
 		lost_event.lost        = local_xchg(&rb->lost, 0);

 		perf_event_header__init_id(&lost_event.header,
 					   &sample_data, event);
 		perf_output_put(handle, lost_event);
 		perf_event__output_id_sample(event, handle, &sample_data);
 	}

 	return 0;

 fail:
 	local_inc(&rb->lost);
 	perf_output_put_handle(handle);
 out:
 	rcu_read_unlock();

 	return -ENOSPC;
 }

 unsigned int perf_output_copy(struct perf_output_handle *handle,
 		      const void *buf, unsigned int len)
 {
 	return __output_copy(handle, buf, len);
 }

 unsigned int perf_output_skip(struct perf_output_handle *handle,
 			      unsigned int len)
 {
 	return __output_skip(handle, NULL, len);
 }

 void perf_output_end(struct perf_output_handle *handle)
 {
 	perf_output_put_handle(handle);
 	rcu_read_unlock();
 }

 static void rb_irq_work(struct irq_work *work);

 static void
 ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
 {
 	long max_size = perf_data_size(rb);

 	if (watermark)
 		rb->watermark = min(max_size, watermark);

 	if (!rb->watermark)
 		rb->watermark = max_size / 2;

 	if (flags & RING_BUFFER_WRITABLE)
 		rb->overwrite = 0;
 	else
 		rb->overwrite = 1;

 	atomic_set(&rb->refcount, 1);

 	INIT_LIST_HEAD(&rb->event_list);
 	spin_lock_init(&rb->event_lock);
 	init_irq_work(&rb->irq_work, rb_irq_work);
 }

 static void ring_buffer_put_async(struct ring_buffer *rb)
 {
 	if (!atomic_dec_and_test(&rb->refcount))
 		return;

 	rb->rcu_head.next = (void *)rb;
 	irq_work_queue(&rb->irq_work);
 }

 /*
  * This is called before hardware starts writing to the AUX area to
  * obtain an output handle and make sure there's room in the buffer.
  * When the capture completes, call perf_aux_output_end() to commit
  * the recorded data to the buffer.
  *
  * The ordering is similar to that of perf_output_{begin,end}, with
  * the exception of (B), which should be taken care of by the pmu
  * driver, since ordering rules will differ depending on hardware.
  */
 void *perf_aux_output_begin(struct perf_output_handle *handle,
 			    struct perf_event *event)
 {
 	struct perf_event *output_event = event;
 	unsigned long aux_head, aux_tail;
 	struct ring_buffer *rb;

 	if (output_event->parent)
 		output_event = output_event->parent;

 	/*
 	 * Since this will typically be open across pmu::add/pmu::del, we
 	 * grab ring_buffer's refcount instead of holding rcu read lock
 	 * to make sure it doesn't disappear under us.
 	 */
 	rb = ring_buffer_get(output_event);
 	if (!rb)
 		return NULL;

 	if (!rb_has_aux(rb) || !atomic_inc_not_zero(&rb->aux_refcount))
 		goto err;

 	/*
 	 * Nesting is not supported for AUX area, make sure nested
 	 * writers are caught early
 	 */
 	if (WARN_ON_ONCE(local_xchg(&rb->aux_nest, 1)))
 		goto err_put;

 	aux_head = local_read(&rb->aux_head);

 	handle->rb = rb;
 	handle->event = event;
 	handle->head = aux_head;
 	handle->size = 0;

 	/*
 	 * In overwrite mode, AUX data stores do not depend on aux_tail,
 	 * therefore (A) control dependency barrier does not exist. The
 	 * (B) <-> (C) ordering is still observed by the pmu driver.
 	 */
 	if (!rb->aux_overwrite) {
 		aux_tail = ACCESS_ONCE(rb->user_page->aux_tail);
 		handle->wakeup = local_read(&rb->aux_wakeup) + rb->aux_watermark;
 		if (aux_head - aux_tail < perf_aux_size(rb))
 			handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb));

 		/*
 		 * handle->size computation depends on aux_tail load; this forms a
 		 * control dependency barrier separating aux_tail load from aux data
 		 * store that will be enabled on successful return
 		 */
 		if (!handle->size) { /* A, matches D */
 			event->pending_disable = 1;
 			perf_output_wakeup(handle);
 			local_set(&rb->aux_nest, 0);
 			goto err_put;
 		}
 	}

 	return handle->rb->aux_priv;

 err_put:
 	rb_free_aux(rb);

 err:
 	ring_buffer_put_async(rb);
 	handle->event = NULL;

 	return NULL;
 }

 /*
  * Commit the data written by hardware into the ring buffer by adjusting
  * aux_head and posting a PERF_RECORD_AUX into the perf buffer. It is the
  * pmu driver's responsibility to observe ordering rules of the hardware,
  * so that all the data is externally visible before this is called.
  */
 void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
 			 bool truncated)
 {
 	struct ring_buffer *rb = handle->rb;
 	bool wakeup = truncated;
 	unsigned long aux_head;
 	u64 flags = 0;

 	if (truncated)
 		flags |= PERF_AUX_FLAG_TRUNCATED;

 	/* in overwrite mode, driver provides aux_head via handle */
 	if (rb->aux_overwrite) {
 		flags |= PERF_AUX_FLAG_OVERWRITE;

 		aux_head = handle->head;
 		local_set(&rb->aux_head, aux_head);
 	} else {
 		aux_head = local_read(&rb->aux_head);
 		local_add(size, &rb->aux_head);
 	}

 	if (size || flags) {
 		/*
 		 * Only send RECORD_AUX if we have something useful to communicate
 		 */

 		perf_event_aux_event(handle->event, aux_head, size, flags);
 	}

 	aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);

 	if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
 		wakeup = true;
 		local_add(rb->aux_watermark, &rb->aux_wakeup);
 	}

 	if (wakeup) {
 		if (truncated)
 			handle->event->pending_disable = 1;
 		perf_output_wakeup(handle);
 	}

 	handle->event = NULL;

 	local_set(&rb->aux_nest, 0);
 	rb_free_aux(rb);
 	ring_buffer_put_async(rb);
 }

 /*
  * Skip over a given number of bytes in the AUX buffer, due to, for example,
  * hardware's alignment constraints.
  */
 int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)
 {
 	struct ring_buffer *rb = handle->rb;
 	unsigned long aux_head;

 	if (size > handle->size)
 		return -ENOSPC;

 	local_add(size, &rb->aux_head);

 	aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
 	if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
 		perf_output_wakeup(handle);
 		local_add(rb->aux_watermark, &rb->aux_wakeup);
 		handle->wakeup = local_read(&rb->aux_wakeup) +
 				 rb->aux_watermark;
 	}

 	handle->head = aux_head;
 	handle->size -= size;

 	return 0;
 }

 void *perf_get_aux(struct perf_output_handle *handle)
 {
 	/* this is only valid between perf_aux_output_begin and *_end */
 	if (!handle->event)
 		return NULL;

 	return handle->rb->aux_priv;
 }

 #define PERF_AUX_GFP	(GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY)

 static struct page *rb_alloc_aux_page(int node, int order)
 {
 	struct page *page;

 	if (order > MAX_ORDER)
 		order = MAX_ORDER;

 	do {
 		page = alloc_pages_node(node, PERF_AUX_GFP, order);
 	} while (!page && order--);

 	if (page && order) {
 		/*
 		 * Communicate the allocation size to the driver:
 		 * if we managed to secure a high-order allocation,
 		 * set its first page's private to this order;
 		 * !PagePrivate(page) means it's just a normal page.
 		 */
 		split_page(page, order);
 		SetPagePrivate(page);
 		set_page_private(page, order);
 	}

 	return page;
 }

 static void rb_free_aux_page(struct ring_buffer *rb, int idx)
 {
 	struct page *page = virt_to_page(rb->aux_pages[idx]);

 	ClearPagePrivate(page);
 	page->mapping = NULL;
 	__free_page(page);
 }

 int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
 		 pgoff_t pgoff, int nr_pages, long watermark, int flags)
 {
 	bool overwrite = !(flags & RING_BUFFER_WRITABLE);
 	int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
 	int ret = -ENOMEM, max_order = 0;

 	if (!has_aux(event))
 		return -ENOTSUPP;

 	if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
 		/*
 		 * We need to start with the max_order that fits in nr_pages,
 		 * not the other way around, hence ilog2() and not get_order.
 		 */
 		max_order = ilog2(nr_pages);

 		/*
 		 * PMU requests more than one contiguous chunks of memory
 		 * for SW double buffering
 		 */
 		if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_SW_DOUBLEBUF) &&
 		    !overwrite) {
 			if (!max_order)
 				return -EINVAL;

 			max_order--;
 		}
 	}

 	rb->aux_pages = kzalloc_node(nr_pages * sizeof(void *), GFP_KERNEL, node);
 	if (!rb->aux_pages)
 		return -ENOMEM;

 	rb->free_aux = event->pmu->free_aux;
 	for (rb->aux_nr_pages = 0; rb->aux_nr_pages < nr_pages;) {
 		struct page *page;
 		int last, order;

 		order = min(max_order, ilog2(nr_pages - rb->aux_nr_pages));
 		page = rb_alloc_aux_page(node, order);
 		if (!page)
 			goto out;

 		for (last = rb->aux_nr_pages + (1 << page_private(page));
 		     last > rb->aux_nr_pages; rb->aux_nr_pages++)
 			rb->aux_pages[rb->aux_nr_pages] = page_address(page++);
 	}

 	/*
 	 * In overwrite mode, PMUs that don't support SG may not handle more
 	 * than one contiguous allocation, since they rely on PMI to do double
 	 * buffering. In this case, the entire buffer has to be one contiguous
 	 * chunk.
 	 */
 	if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) &&
 	    overwrite) {
 		struct page *page = virt_to_page(rb->aux_pages[0]);

 		if (page_private(page) != max_order)
 			goto out;
 	}

 	rb->aux_priv = event->pmu->setup_aux(event->cpu, rb->aux_pages, nr_pages,
 					     overwrite);
 	if (!rb->aux_priv)
 		goto out;

 	ret = 0;

 	/*
 	 * aux_pages (and pmu driver's private data, aux_priv) will be
 	 * referenced in both producer's and consumer's contexts, thus
 	 * we keep a refcount here to make sure either of the two can
 	 * reference them safely.
 	 */
 	atomic_set(&rb->aux_refcount, 1);

 	rb->aux_overwrite = overwrite;
 	rb->aux_watermark = watermark;

 	if (!rb->aux_watermark && !rb->aux_overwrite)
 		rb->aux_watermark = nr_pages << (PAGE_SHIFT - 1);

 out:
 	if (!ret)
 		rb->aux_pgoff = pgoff;
 	else
 		rb_free_aux(rb);

 	return ret;
 }

 static void __rb_free_aux(struct ring_buffer *rb)
 {
 	int pg;

 	if (rb->aux_priv) {
 		rb->free_aux(rb->aux_priv);
 		rb->free_aux = NULL;
 		rb->aux_priv = NULL;
 	}

 	if (rb->aux_nr_pages) {
 		for (pg = 0; pg < rb->aux_nr_pages; pg++)
 			rb_free_aux_page(rb, pg);

 		kfree(rb->aux_pages);
 		rb->aux_nr_pages = 0;
 	}
 }

 void rb_free_aux(struct ring_buffer *rb)
 {
 	if (atomic_dec_and_test(&rb->aux_refcount))
 		irq_work_queue(&rb->irq_work);
 }

 static void rb_irq_work(struct irq_work *work)
 {
 	struct ring_buffer *rb = container_of(work, struct ring_buffer, irq_work);

 	if (!atomic_read(&rb->aux_refcount))
 		__rb_free_aux(rb);

 	if (rb->rcu_head.next == (void *)rb)
 		call_rcu(&rb->rcu_head, rb_free_rcu);
 }

 #ifndef CONFIG_PERF_USE_VMALLOC

 /*
  * Back perf_mmap() with regular GFP_KERNEL-0 pages.
  */

 static struct page *
 __perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
 {
 	if (pgoff > rb->nr_pages)
 		return NULL;

 	if (pgoff == 0)
 		return virt_to_page(rb->user_page);

 	return virt_to_page(rb->data_pages[pgoff - 1]);
 }

 static void *perf_mmap_alloc_page(int cpu)
 {
 	struct page *page;
 	int node;

 	node = (cpu == -1) ? cpu : cpu_to_node(cpu);
 	page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
 	if (!page)
 		return NULL;

 	return page_address(page);
 }

 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
 {
 	struct ring_buffer *rb;
 	unsigned long size;
 	int i;

 	size = sizeof(struct ring_buffer);
 	size += nr_pages * sizeof(void *);

 	rb = kzalloc(size, GFP_KERNEL);
 	if (!rb)
 		goto fail;

 	rb->user_page = perf_mmap_alloc_page(cpu);
 	if (!rb->user_page)
 		goto fail_user_page;

 	for (i = 0; i < nr_pages; i++) {
 		rb->data_pages[i] = perf_mmap_alloc_page(cpu);
 		if (!rb->data_pages[i])
 			goto fail_data_pages;
 	}

 	rb->nr_pages = nr_pages;

 	ring_buffer_init(rb, watermark, flags);

 	return rb;

 fail_data_pages:
 	for (i--; i >= 0; i--)
 		free_page((unsigned long)rb->data_pages[i]);

 	free_page((unsigned long)rb->user_page);

 fail_user_page:
 	kfree(rb);

 fail:
 	return NULL;
 }

 static void perf_mmap_free_page(unsigned long addr)
 {
 	struct page *page = virt_to_page((void *)addr);

 	page->mapping = NULL;
 	__free_page(page);
 }

 void rb_free(struct ring_buffer *rb)
 {
 	int i;

 	perf_mmap_free_page((unsigned long)rb->user_page);
 	for (i = 0; i < rb->nr_pages; i++)
 		perf_mmap_free_page((unsigned long)rb->data_pages[i]);
 	kfree(rb);
 }

 #else
 static int data_page_nr(struct ring_buffer *rb)
 {
 	return rb->nr_pages << page_order(rb);
 }

 static struct page *
 __perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
 {
 	/* The '>' counts in the user page. */
 	if (pgoff > data_page_nr(rb))
 		return NULL;

 	return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
 }

 static void perf_mmap_unmark_page(void *addr)
 {
 	struct page *page = vmalloc_to_page(addr);

 	page->mapping = NULL;
 }

 static void rb_free_work(struct work_struct *work)
 {
 	struct ring_buffer *rb;
 	void *base;
 	int i, nr;

 	rb = container_of(work, struct ring_buffer, work);
 	nr = data_page_nr(rb);

 	base = rb->user_page;
 	/* The '<=' counts in the user page. */
 	for (i = 0; i <= nr; i++)
 		perf_mmap_unmark_page(base + (i * PAGE_SIZE));

 	vfree(base);
 	kfree(rb);
 }

 void rb_free(struct ring_buffer *rb)
 {
 	schedule_work(&rb->work);
 }

 struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
 {
 	struct ring_buffer *rb;
 	unsigned long size;
 	void *all_buf;

 	size = sizeof(struct ring_buffer);
 	size += sizeof(void *);

 	rb = kzalloc(size, GFP_KERNEL);
 	if (!rb)
 		goto fail;

 	INIT_WORK(&rb->work, rb_free_work);

 	all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
 	if (!all_buf)
 		goto fail_all_buf;

 	rb->user_page = all_buf;
 	rb->data_pages[0] = all_buf + PAGE_SIZE;
 	rb->page_order = ilog2(nr_pages);
 	rb->nr_pages = !!nr_pages;

 	ring_buffer_init(rb, watermark, flags);

 	return rb;

 fail_all_buf:
 	kfree(rb);

 fail:
 	return NULL;
 }

 #endif

 struct page *
 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
 {
 	if (rb->aux_nr_pages) {
 		/* above AUX space */
 		if (pgoff > rb->aux_pgoff + rb->aux_nr_pages)
 			return NULL;

 		/* AUX space */
 		if (pgoff >= rb->aux_pgoff)
 			return virt_to_page(rb->aux_pages[pgoff - rb->aux_pgoff]);
 	}

 	return __perf_mmap_to_page(rb, pgoff);
 }
	/*
	* Performance events ring-buffer code:
	*
	* Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
	* Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
	* Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
	* Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
	*
	* For licensing details see kernel-base/COPYING
	*/

	#include <linux/perf_event.h>
	#include <linux/vmalloc.h>
	#include <linux/slab.h>
	#include <linux/circ_buf.h>
	#include <linux/poll.h>

	#include "internal.h"

	static void perf_output_wakeup(struct perf_output_handle *handle)
	{
	atomic_set(&handle->rb->poll, POLLIN);

	handle->event->pending_wakeup = 1;
	irq_work_queue(&handle->event->pending);
	}

	/*
	* We need to ensure a later event_id doesn't publish a head when a former
	* event isn't done writing. However since we need to deal with NMIs we
	* cannot fully serialize things.
	*
	* We only publish the head (and generate a wakeup) when the outer-most
	* event completes.
	*/
	static void perf_output_get_handle(struct perf_output_handle *handle)
	{
	struct ring_buffer *rb = handle->rb;

	preempt_disable();
	local_inc(&rb->nest);
	handle->wakeup = local_read(&rb->wakeup);
	}

	static void perf_output_put_handle(struct perf_output_handle *handle)
	{
	struct ring_buffer *rb = handle->rb;
	unsigned long head;

	again:
	head = local_read(&rb->head);

	/*
	* IRQ/NMI can happen here, which means we can miss a head update.
	*/

	if (!local_dec_and_test(&rb->nest))
	goto out;

	/*
	* Since the mmap() consumer (userspace) can run on a different CPU:
	*
	* kernel user
	*
	* if (LOAD ->data_tail) { LOAD ->data_head
	* (A) smp_rmb() (C)
	* STORE $data LOAD $data
	* smp_wmb() (B) smp_mb() (D)
	* STORE ->data_head STORE ->data_tail
	* }
	*
	* Where A pairs with D, and B pairs with C.
	*
	* In our case (A) is a control dependency that separates the load of
	* the ->data_tail and the stores of $data. In case ->data_tail
	* indicates there is no room in the buffer to store $data we do not.
	*
	* D needs to be a full barrier since it separates the data READ
	* from the tail WRITE.
	*
	* For B a WMB is sufficient since it separates two WRITEs, and for C
	* an RMB is sufficient since it separates two READs.
	*
	* See perf_output_begin().
	*/
	smp_wmb(); /* B, matches C */
	rb->user_page->data_head = head;

	/*
	* Now check if we missed an update -- rely on previous implied
	* compiler barriers to force a re-read.
	*/
	if (unlikely(head != local_read(&rb->head))) {
	local_inc(&rb->nest);
	goto again;
	}

	if (handle->wakeup != local_read(&rb->wakeup))
	perf_output_wakeup(handle);

	out:
	preempt_enable();
	}

	int perf_output_begin(struct perf_output_handle *handle,
	struct perf_event *event, unsigned int size)
	{
	struct ring_buffer *rb;
	unsigned long tail, offset, head;
	int have_lost, page_shift;
	struct {
	struct perf_event_header header;
	u64 id;
	u64 lost;
	} lost_event;

	rcu_read_lock();
	/*
	* For inherited events we send all the output towards the parent.
	*/
	if (event->parent)
	event = event->parent;

	rb = rcu_dereference(event->rb);
	if (unlikely(!rb))
	goto out;

	if (unlikely(!rb->nr_pages))
	goto out;

	handle->rb = rb;
	handle->event = event;

	have_lost = local_read(&rb->lost);
	if (unlikely(have_lost)) {
	size += sizeof(lost_event);
	if (event->attr.sample_id_all)
	size += event->id_header_size;
	}

	perf_output_get_handle(handle);

	do {
	tail = READ_ONCE(rb->user_page->data_tail);
	offset = head = local_read(&rb->head);
	if (!rb->overwrite &&
	unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
	goto fail;

	/*
	* The above forms a control dependency barrier separating the
	* @tail load above from the data stores below. Since the @tail
	* load is required to compute the branch to fail below.
	*
	* A, matches D; the full memory barrier userspace SHOULD issue
	* after reading the data and before storing the new tail
	* position.
	*
	* See perf_output_put_handle().
	*/

	head += size;
	} while (local_cmpxchg(&rb->head, offset, head) != offset);

	/*
	* We rely on the implied barrier() by local_cmpxchg() to ensure
	* none of the data stores below can be lifted up by the compiler.
	*/

	if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
	local_add(rb->watermark, &rb->wakeup);

	page_shift = PAGE_SHIFT + page_order(rb);

	handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
	offset &= (1UL << page_shift) - 1;
	handle->addr = rb->data_pages[handle->page] + offset;
	handle->size = (1UL << page_shift) - offset;

	if (unlikely(have_lost)) {
	struct perf_sample_data sample_data;

	lost_event.header.size = sizeof(lost_event);
	lost_event.header.type = PERF_RECORD_LOST;
	lost_event.header.misc = 0;
	lost_event.id = event->id;
	lost_event.lost = local_xchg(&rb->lost, 0);

	perf_event_header__init_id(&lost_event.header,
	&sample_data, event);
	perf_output_put(handle, lost_event);
	perf_event__output_id_sample(event, handle, &sample_data);
	}

	return 0;

	fail:
	local_inc(&rb->lost);
	perf_output_put_handle(handle);
	out:
	rcu_read_unlock();

	return -ENOSPC;
	}

	unsigned int perf_output_copy(struct perf_output_handle *handle,
	const void *buf, unsigned int len)
	{
	return __output_copy(handle, buf, len);
	}

	unsigned int perf_output_skip(struct perf_output_handle *handle,
	unsigned int len)
	{
	return __output_skip(handle, NULL, len);
	}

	void perf_output_end(struct perf_output_handle *handle)
	{
	perf_output_put_handle(handle);
	rcu_read_unlock();
	}

	static void rb_irq_work(struct irq_work *work);

	static void
	ring_buffer_init(struct ring_buffer *rb, long watermark, int flags)
	{
	long max_size = perf_data_size(rb);

	if (watermark)
	rb->watermark = min(max_size, watermark);

	if (!rb->watermark)
	rb->watermark = max_size / 2;

	if (flags & RING_BUFFER_WRITABLE)
	rb->overwrite = 0;
	else
	rb->overwrite = 1;

	atomic_set(&rb->refcount, 1);

	INIT_LIST_HEAD(&rb->event_list);
	spin_lock_init(&rb->event_lock);
	init_irq_work(&rb->irq_work, rb_irq_work);
	}

	static void ring_buffer_put_async(struct ring_buffer *rb)
	{
	if (!atomic_dec_and_test(&rb->refcount))
	return;

	rb->rcu_head.next = (void *)rb;
	irq_work_queue(&rb->irq_work);
	}

	/*
	* This is called before hardware starts writing to the AUX area to
	* obtain an output handle and make sure there's room in the buffer.
	* When the capture completes, call perf_aux_output_end() to commit
	* the recorded data to the buffer.
	*
	* The ordering is similar to that of perf_output_{begin,end}, with
	* the exception of (B), which should be taken care of by the pmu
	* driver, since ordering rules will differ depending on hardware.
	*/
	void perf_aux_output_begin(struct perf_output_handle handle,
	struct perf_event *event)
	{
	struct perf_event *output_event = event;
	unsigned long aux_head, aux_tail;
	struct ring_buffer *rb;

	if (output_event->parent)
	output_event = output_event->parent;

	/*
	* Since this will typically be open across pmu::add/pmu::del, we
	* grab ring_buffer's refcount instead of holding rcu read lock
	* to make sure it doesn't disappear under us.
	*/
	rb = ring_buffer_get(output_event);
	if (!rb)
	return NULL;

	if (!rb_has_aux(rb) \|\| !atomic_inc_not_zero(&rb->aux_refcount))
	goto err;

	/*
	* Nesting is not supported for AUX area, make sure nested
	* writers are caught early
	*/
	if (WARN_ON_ONCE(local_xchg(&rb->aux_nest, 1)))
	goto err_put;

	aux_head = local_read(&rb->aux_head);

	handle->rb = rb;
	handle->event = event;
	handle->head = aux_head;
	handle->size = 0;

	/*
	* In overwrite mode, AUX data stores do not depend on aux_tail,
	* therefore (A) control dependency barrier does not exist. The
	* (B) <-> (C) ordering is still observed by the pmu driver.
	*/
	if (!rb->aux_overwrite) {
	aux_tail = ACCESS_ONCE(rb->user_page->aux_tail);
	handle->wakeup = local_read(&rb->aux_wakeup) + rb->aux_watermark;
	if (aux_head - aux_tail < perf_aux_size(rb))
	handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb));

	/*
	* handle->size computation depends on aux_tail load; this forms a
	* control dependency barrier separating aux_tail load from aux data
	* store that will be enabled on successful return
	*/
	if (!handle->size) { /* A, matches D */
	event->pending_disable = 1;
	perf_output_wakeup(handle);
	local_set(&rb->aux_nest, 0);
	goto err_put;
	}
	}

	return handle->rb->aux_priv;

	err_put:
	rb_free_aux(rb);

	err:
	ring_buffer_put_async(rb);
	handle->event = NULL;

	return NULL;
	}

	/*
	* Commit the data written by hardware into the ring buffer by adjusting
	* aux_head and posting a PERF_RECORD_AUX into the perf buffer. It is the
	* pmu driver's responsibility to observe ordering rules of the hardware,
	* so that all the data is externally visible before this is called.
	*/
	void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size,
	bool truncated)
	{
	struct ring_buffer *rb = handle->rb;
	bool wakeup = truncated;
	unsigned long aux_head;
	u64 flags = 0;

	if (truncated)
	flags \|= PERF_AUX_FLAG_TRUNCATED;

	/* in overwrite mode, driver provides aux_head via handle */
	if (rb->aux_overwrite) {
	flags \|= PERF_AUX_FLAG_OVERWRITE;

	aux_head = handle->head;
	local_set(&rb->aux_head, aux_head);
	} else {
	aux_head = local_read(&rb->aux_head);
	local_add(size, &rb->aux_head);
	}

	if (size \|\| flags) {
	/*
	* Only send RECORD_AUX if we have something useful to communicate
	*/

	perf_event_aux_event(handle->event, aux_head, size, flags);
	}

	aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);

	if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
	wakeup = true;
	local_add(rb->aux_watermark, &rb->aux_wakeup);
	}

	if (wakeup) {
	if (truncated)
	handle->event->pending_disable = 1;
	perf_output_wakeup(handle);
	}

	handle->event = NULL;

	local_set(&rb->aux_nest, 0);
	rb_free_aux(rb);
	ring_buffer_put_async(rb);
	}

	/*
	* Skip over a given number of bytes in the AUX buffer, due to, for example,
	* hardware's alignment constraints.
	*/
	int perf_aux_output_skip(struct perf_output_handle *handle, unsigned long size)
	{
	struct ring_buffer *rb = handle->rb;
	unsigned long aux_head;

	if (size > handle->size)
	return -ENOSPC;

	local_add(size, &rb->aux_head);

	aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
	if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
	perf_output_wakeup(handle);
	local_add(rb->aux_watermark, &rb->aux_wakeup);
	handle->wakeup = local_read(&rb->aux_wakeup) +
	rb->aux_watermark;
	}

	handle->head = aux_head;
	handle->size -= size;

	return 0;
	}

	void perf_get_aux(struct perf_output_handle handle)
	{
	/* this is only valid between perf_aux_output_begin and _end /
	if (!handle->event)
	return NULL;

	return handle->rb->aux_priv;
	}

	#define PERF_AUX_GFP (GFP_KERNEL \| __GFP_ZERO \| __GFP_NOWARN \| __GFP_NORETRY)

	static struct page *rb_alloc_aux_page(int node, int order)
	{
	struct page *page;

	if (order > MAX_ORDER)
	order = MAX_ORDER;

	do {
	page = alloc_pages_node(node, PERF_AUX_GFP, order);
	} while (!page && order--);

	if (page && order) {
	/*
	* Communicate the allocation size to the driver:
	* if we managed to secure a high-order allocation,
	* set its first page's private to this order;
	* !PagePrivate(page) means it's just a normal page.
	*/
	split_page(page, order);
	SetPagePrivate(page);
	set_page_private(page, order);
	}

	return page;
	}

	static void rb_free_aux_page(struct ring_buffer *rb, int idx)
	{
	struct page *page = virt_to_page(rb->aux_pages[idx]);

	ClearPagePrivate(page);
	page->mapping = NULL;
	__free_page(page);
	}

	int rb_alloc_aux(struct ring_buffer rb, struct perf_event event,
	pgoff_t pgoff, int nr_pages, long watermark, int flags)
	{
	bool overwrite = !(flags & RING_BUFFER_WRITABLE);
	int node = (event->cpu == -1) ? -1 : cpu_to_node(event->cpu);
	int ret = -ENOMEM, max_order = 0;

	if (!has_aux(event))
	return -ENOTSUPP;

	if (event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) {
	/*
	* We need to start with the max_order that fits in nr_pages,
	* not the other way around, hence ilog2() and not get_order.
	*/
	max_order = ilog2(nr_pages);

	/*
	* PMU requests more than one contiguous chunks of memory
	* for SW double buffering
	*/
	if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_SW_DOUBLEBUF) &&
	!overwrite) {
	if (!max_order)
	return -EINVAL;

	max_order--;
	}
	}

	rb->aux_pages = kzalloc_node(nr_pages * sizeof(void *), GFP_KERNEL, node);
	if (!rb->aux_pages)
	return -ENOMEM;

	rb->free_aux = event->pmu->free_aux;
	for (rb->aux_nr_pages = 0; rb->aux_nr_pages < nr_pages;) {
	struct page *page;
	int last, order;

	order = min(max_order, ilog2(nr_pages - rb->aux_nr_pages));
	page = rb_alloc_aux_page(node, order);
	if (!page)
	goto out;

	for (last = rb->aux_nr_pages + (1 << page_private(page));
	last > rb->aux_nr_pages; rb->aux_nr_pages++)
	rb->aux_pages[rb->aux_nr_pages] = page_address(page++);
	}

	/*
	* In overwrite mode, PMUs that don't support SG may not handle more
	* than one contiguous allocation, since they rely on PMI to do double
	* buffering. In this case, the entire buffer has to be one contiguous
	* chunk.
	*/
	if ((event->pmu->capabilities & PERF_PMU_CAP_AUX_NO_SG) &&
	overwrite) {
	struct page *page = virt_to_page(rb->aux_pages[0]);

	if (page_private(page) != max_order)
	goto out;
	}

	rb->aux_priv = event->pmu->setup_aux(event->cpu, rb->aux_pages, nr_pages,
	overwrite);
	if (!rb->aux_priv)
	goto out;

	ret = 0;

	/*
	* aux_pages (and pmu driver's private data, aux_priv) will be
	* referenced in both producer's and consumer's contexts, thus
	* we keep a refcount here to make sure either of the two can
	* reference them safely.
	*/
	atomic_set(&rb->aux_refcount, 1);

	rb->aux_overwrite = overwrite;
	rb->aux_watermark = watermark;

	if (!rb->aux_watermark && !rb->aux_overwrite)
	rb->aux_watermark = nr_pages << (PAGE_SHIFT - 1);

	out:
	if (!ret)
	rb->aux_pgoff = pgoff;
	else
	rb_free_aux(rb);

	return ret;
	}

	static void __rb_free_aux(struct ring_buffer *rb)
	{
	int pg;

	if (rb->aux_priv) {
	rb->free_aux(rb->aux_priv);
	rb->free_aux = NULL;
	rb->aux_priv = NULL;
	}

	if (rb->aux_nr_pages) {
	for (pg = 0; pg < rb->aux_nr_pages; pg++)
	rb_free_aux_page(rb, pg);

	kfree(rb->aux_pages);
	rb->aux_nr_pages = 0;
	}
	}

	void rb_free_aux(struct ring_buffer *rb)
	{
	if (atomic_dec_and_test(&rb->aux_refcount))
	irq_work_queue(&rb->irq_work);
	}

	static void rb_irq_work(struct irq_work *work)
	{
	struct ring_buffer *rb = container_of(work, struct ring_buffer, irq_work);

	if (!atomic_read(&rb->aux_refcount))
	__rb_free_aux(rb);

	if (rb->rcu_head.next == (void *)rb)
	call_rcu(&rb->rcu_head, rb_free_rcu);
	}

	#ifndef CONFIG_PERF_USE_VMALLOC

	/*
	* Back perf_mmap() with regular GFP_KERNEL-0 pages.
	*/

	static struct page *
	__perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
	{
	if (pgoff > rb->nr_pages)
	return NULL;

	if (pgoff == 0)
	return virt_to_page(rb->user_page);

	return virt_to_page(rb->data_pages[pgoff - 1]);
	}

	static void *perf_mmap_alloc_page(int cpu)
	{
	struct page *page;
	int node;

	node = (cpu == -1) ? cpu : cpu_to_node(cpu);
	page = alloc_pages_node(node, GFP_KERNEL \| __GFP_ZERO, 0);
	if (!page)
	return NULL;

	return page_address(page);
	}

	struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
	{
	struct ring_buffer *rb;
	unsigned long size;
	int i;

	size = sizeof(struct ring_buffer);
	size += nr_pages * sizeof(void *);

	rb = kzalloc(size, GFP_KERNEL);
	if (!rb)
	goto fail;

	rb->user_page = perf_mmap_alloc_page(cpu);
	if (!rb->user_page)
	goto fail_user_page;

	for (i = 0; i < nr_pages; i++) {
	rb->data_pages[i] = perf_mmap_alloc_page(cpu);
	if (!rb->data_pages[i])
	goto fail_data_pages;
	}

	rb->nr_pages = nr_pages;

	ring_buffer_init(rb, watermark, flags);

	return rb;

	fail_data_pages:
	for (i--; i >= 0; i--)
	free_page((unsigned long)rb->data_pages[i]);

	free_page((unsigned long)rb->user_page);

	fail_user_page:
	kfree(rb);

	fail:
	return NULL;
	}

	static void perf_mmap_free_page(unsigned long addr)
	{
	struct page page = virt_to_page((void )addr);

	page->mapping = NULL;
	__free_page(page);
	}

	void rb_free(struct ring_buffer *rb)
	{
	int i;

	perf_mmap_free_page((unsigned long)rb->user_page);
	for (i = 0; i < rb->nr_pages; i++)
	perf_mmap_free_page((unsigned long)rb->data_pages[i]);
	kfree(rb);
	}

	#else
	static int data_page_nr(struct ring_buffer *rb)
	{
	return rb->nr_pages << page_order(rb);
	}

	static struct page *
	__perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
	{
	/* The '>' counts in the user page. */
	if (pgoff > data_page_nr(rb))
	return NULL;

	return vmalloc_to_page((void )rb->user_page + pgoff PAGE_SIZE);
	}

	static void perf_mmap_unmark_page(void *addr)
	{
	struct page *page = vmalloc_to_page(addr);

	page->mapping = NULL;
	}

	static void rb_free_work(struct work_struct *work)
	{
	struct ring_buffer *rb;
	void *base;
	int i, nr;

	rb = container_of(work, struct ring_buffer, work);
	nr = data_page_nr(rb);

	base = rb->user_page;
	/* The '<=' counts in the user page. */
	for (i = 0; i <= nr; i++)
	perf_mmap_unmark_page(base + (i * PAGE_SIZE));

	vfree(base);
	kfree(rb);
	}

	void rb_free(struct ring_buffer *rb)
	{
	schedule_work(&rb->work);
	}

	struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
	{
	struct ring_buffer *rb;
	unsigned long size;
	void *all_buf;

	size = sizeof(struct ring_buffer);
	size += sizeof(void *);

	rb = kzalloc(size, GFP_KERNEL);
	if (!rb)
	goto fail;

	INIT_WORK(&rb->work, rb_free_work);

	all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
	if (!all_buf)
	goto fail_all_buf;

	rb->user_page = all_buf;
	rb->data_pages[0] = all_buf + PAGE_SIZE;
	rb->page_order = ilog2(nr_pages);
	rb->nr_pages = !!nr_pages;

	ring_buffer_init(rb, watermark, flags);

	return rb;

	fail_all_buf:
	kfree(rb);

	fail:
	return NULL;
	}

	#endif

	struct page *
	perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
	{
	if (rb->aux_nr_pages) {
	/* above AUX space */
	if (pgoff > rb->aux_pgoff + rb->aux_nr_pages)
	return NULL;

	/* AUX space */
	if (pgoff >= rb->aux_pgoff)
	return virt_to_page(rb->aux_pages[pgoff - rb->aux_pgoff]);
	}

	return __perf_mmap_to_page(rb, pgoff);
	}