1 files changed, 92 insertions, 43 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ff0a44aa578d..077d6940af0c 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -330,6 +330,11 @@ struct buffer_data_read_page {
 	struct buffer_data_page	*data;	/* actual data, stored in this page */
 };
 
+static __always_inline unsigned int rb_read_page_capacity(struct buffer_data_read_page *rpage)
+{
+	return (PAGE_SIZE << rpage->order) - BUF_PAGE_HDR_SIZE;
+}
+
 /*
  * Note, the buffer_page list must be first. The buffer pages
  * are allocated in cache lines, which means that each buffer
@@ -6998,56 +7003,78 @@ EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
  * ring_buffer_alloc_read_page - allocate a page to read from buffer
  * @buffer: the buffer to allocate for.
  * @cpu: the cpu buffer to allocate.
+ * @rpage: pointer to pass in an already allocated page (can be NULL)
+ *         and returns the allocated page.
  *
- * This function is used in conjunction with ring_buffer_read_page.
+ * This function is used in conjunction with ring_buffer_read_page().
  * When reading a full page from the ring buffer, these functions
  * can be used to speed up the process. The calling function should
  * allocate a few pages first with this function. Then when it
  * needs to get pages from the ring buffer, it passes the result
- * of this function into ring_buffer_read_page, which will swap
+ * of this function into ring_buffer_read_page(), which will swap
  * the page that was allocated, with the read page of the buffer.
  *
+ * If @rpage is provided, and it has a different order than the current
+ * subbuffer order, its payload will be freed and re-allocated. If it
+ * already matches the order, it is simply returned.
+ *
  * Returns:
- *  The page allocated, or ERR_PTR
+ *  0 on success, < 0 on error
  */
-struct buffer_data_read_page *
-ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
+int ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu,
+				struct buffer_data_read_page **rpage)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	struct buffer_data_read_page *bpage = NULL;
 	unsigned long flags;
+	unsigned int order;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return ERR_PTR(-ENODEV);
+		return -ENODEV;
 
-	bpage = kzalloc_obj(*bpage);
-	if (!bpage)
-		return ERR_PTR(-ENOMEM);
+	if (!rpage)
+		return -EINVAL;
+
+	order = READ_ONCE(buffer->subbuf_order);
 
-	bpage->order = buffer->subbuf_order;
+	if (*rpage) {
+		if ((*rpage)->order == order)
+			return 0;
+
+		/* We can reuse rpage, but we discard the payload */
+		free_pages((unsigned long)(*rpage)->data, (*rpage)->order);
+		(*rpage)->data = NULL;
+	} else {
+		*rpage = kzalloc_obj(**rpage);
+		if (!*rpage)
+			return -ENOMEM;
+	}
+
+	(*rpage)->order = order;
 	cpu_buffer = buffer->buffers[cpu];
+
 	local_irq_save(flags);
 	arch_spin_lock(&cpu_buffer->lock);
 
 	if (cpu_buffer->free_page.data) {
-		*bpage = cpu_buffer->free_page;
+		**rpage = cpu_buffer->free_page;
 		cpu_buffer->free_page.data = NULL;
 	}
 
 	arch_spin_unlock(&cpu_buffer->lock);
 	local_irq_restore(flags);
 
-	if (bpage->data) {
-		rb_init_data_page(bpage->data);
+	if ((*rpage)->data) {
+		rb_init_data_page((*rpage)->data);
 	} else {
-		bpage->data = alloc_cpu_data(cpu, bpage->order);
-		if (!bpage->data) {
-			kfree(bpage);
-			return ERR_PTR(-ENOMEM);
+		(*rpage)->data = alloc_cpu_data(cpu, (*rpage)->order);
+		if (!(*rpage)->data) {
+			kfree(*rpage);
+			*rpage = NULL;
+			return -ENOMEM;
 		}
 	}
 
-	return bpage;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
 
@@ -7055,21 +7082,30 @@ EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
  * ring_buffer_free_read_page - free an allocated read page
  * @buffer: the buffer the page was allocate for
  * @cpu: the cpu buffer the page came from
- * @data_page: the page to free
+ * @rpage: the buffer_data_read_page to free
  *
  * Free a page allocated from ring_buffer_alloc_read_page.
  */
 void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu,
-				struct buffer_data_read_page *data_page)
+				struct buffer_data_read_page *rpage)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	struct buffer_data_page *dpage = data_page->data;
-	struct page *page = virt_to_page(dpage);
+	struct buffer_data_page *dpage;
 	unsigned long flags;
+	struct page *page;
 
 	if (!buffer || !buffer->buffers || !buffer->buffers[cpu])
 		return;
 
+	if (!rpage)
+		return;
+
+	dpage = rpage->data;
+	if (!dpage)
+		goto out;
+
+	page = virt_to_page(dpage);
+
 	cpu_buffer = buffer->buffers[cpu];
 
 	/*
@@ -7077,14 +7113,14 @@ void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu,
 	 * is different from the subbuffer order of the buffer -
 	 * we can't reuse it
 	 */
-	if (page_ref_count(page) > 1 || data_page->order != buffer->subbuf_order)
+	if (page_ref_count(page) > 1 || rpage->order != READ_ONCE(buffer->subbuf_order))
 		goto out;
 
 	local_irq_save(flags);
 	arch_spin_lock(&cpu_buffer->lock);
 
 	if (!cpu_buffer->free_page.data) {
-		cpu_buffer->free_page = *data_page;
+		cpu_buffer->free_page = *rpage;
 		dpage = NULL;
 	}
 
@@ -7092,8 +7128,8 @@ void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu,
 	local_irq_restore(flags);
 
  out:
-	free_pages((unsigned long)dpage, data_page->order);
-	kfree(data_page);
+	free_pages((unsigned long)dpage, rpage->order);
+	kfree(rpage);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
 
@@ -7164,10 +7200,9 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	if (!dpage)
 		return -1;
 
-	guard(raw_spinlock_irqsave)(&cpu_buffer->reader_lock);
+	len = min_t(size_t, len, rb_read_page_capacity(data_page));
 
-	if (data_page->order != cpu_buffer->reader_page->order)
-		return -1;
+	guard(raw_spinlock_irqsave)(&cpu_buffer->reader_lock);
 
 	reader = rb_get_reader_page(cpu_buffer);
 	if (!reader)
@@ -7182,16 +7217,18 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	/* Check if any events were dropped */
 	missed_events = cpu_buffer->lost_events;
 
-	/*
-	 * If this page has been partially read or
-	 * if len is not big enough to read the rest of the page or
-	 * a writer is still on the page, then
-	 * we must copy the data from the page to the buffer.
-	 * Otherwise, we can simply swap the page with the one passed in.
-	 */
+	 /*
+	  * It is not possible to swap the reader page if:
+	  *   - It has been partially read
+	  *   - len is not big enough to read it entirely
+	  *   - A writer is still on it
+	  *   - The ring buffer is static
+	  *   - The order doesn't match
+	  */
 	if (read || (len < (size - read)) ||
 	    cpu_buffer->reader_page == cpu_buffer->commit_page ||
-	    rb_is_static(cpu_buffer)) {
+	    rb_is_static(cpu_buffer) ||
+	    data_page->order != reader->order) {
 		struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
 		unsigned int rpos = read;
 		unsigned int pos = 0;
@@ -7285,7 +7322,7 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 		 * missed events, then record it there.
 		 */
 		if (missed_events > 0 &&
-		    rb_page_capacity(reader) - size >= sizeof(missed_events)) {
+		    rb_read_page_capacity(data_page) - size >= sizeof(missed_events)) {
 			memcpy(&dpage->data[size], &missed_events,
 			       sizeof(missed_events));
 			local_add(RB_MISSED_STORED, &dpage->commit);
@@ -7305,8 +7342,8 @@ int ring_buffer_read_page(struct trace_buffer *buffer,
 	/*
 	 * This page may be off to user land. Zero it out here.
 	 */
-	if (size < rb_page_capacity(reader))
-		memset(&dpage->data[size], 0, rb_page_capacity(reader) - size);
+	if (size < rb_read_page_capacity(data_page))
+		memset(&dpage->data[size], 0, rb_read_page_capacity(data_page) - size);
 
 	return read;
 }
@@ -7325,6 +7362,18 @@ void *ring_buffer_read_page_data(struct buffer_data_read_page *page)
 EXPORT_SYMBOL_GPL(ring_buffer_read_page_data);
 
 /**
+ * ring_buffer_read_page_size - get size of the read page.
+ * @page:  the page to get the size from
+ *
+ * Returns size of the page in bytes.
+ */
+unsigned int ring_buffer_read_page_size(struct buffer_data_read_page *rpage)
+{
+	return rpage ? PAGE_SIZE << rpage->order : 0;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_read_page_size);
+
+/**
  * ring_buffer_subbuf_size_get - get size of the sub buffer.
  * @buffer: the buffer to get the sub buffer size from
  *
@@ -7409,7 +7458,7 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 	/* Make sure all commits have finished */
 	synchronize_rcu();
 
-	buffer->subbuf_order = order;
+	WRITE_ONCE(buffer->subbuf_order, order);
 
 	/* Make sure all new buffers are allocated, before deleting the old ones */
 	for_each_buffer_cpu(buffer, cpu) {
@@ -7513,7 +7562,7 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
 	return 0;
 
 error:
-	buffer->subbuf_order = old_order;
+	WRITE_ONCE(buffer->subbuf_order, old_order);
 
 	atomic_dec(&buffer->record_disabled);