1 files changed, 51 insertions, 5 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 54e7a90db848..4ae268e687fe 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -438,6 +438,7 @@ struct ring_buffer_per_cpu {
 	raw_spinlock_t			reader_lock;	/* serialize readers */
 	arch_spinlock_t			lock;
 	struct lock_class_key		lock_key;
+	struct buffer_data_page		*free_page;
 	unsigned long			nr_pages;
 	unsigned int			current_context;
 	struct list_head		*pages;
@@ -3405,11 +3406,23 @@ EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
 int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
+	struct buffer_page *reader;
+	struct buffer_page *head_page;
+	struct buffer_page *commit_page;
+	unsigned commit;
 
 	cpu_buffer = iter->cpu_buffer;
 
-	return iter->head_page == cpu_buffer->commit_page &&
-		iter->head == rb_commit_index(cpu_buffer);
+	/* Remember, trace recording is off when iterator is in use */
+	reader = cpu_buffer->reader_page;
+	head_page = cpu_buffer->head_page;
+	commit_page = cpu_buffer->commit_page;
+	commit = rb_page_commit(commit_page);
+
+	return ((iter->head_page == commit_page && iter->head == commit) ||
+		(iter->head_page == reader && commit_page == head_page &&
+		 head_page->read == commit &&
+		 iter->head == rb_page_commit(cpu_buffer->reader_page)));
 }
 EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
 
@@ -4377,9 +4390,25 @@ EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
  */
 void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
 {
-	struct buffer_data_page *bpage;
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+	struct buffer_data_page *bpage = NULL;
+	unsigned long flags;
 	struct page *page;
 
+	local_irq_save(flags);
+	arch_spin_lock(&cpu_buffer->lock);
+
+	if (cpu_buffer->free_page) {
+		bpage = cpu_buffer->free_page;
+		cpu_buffer->free_page = NULL;
+	}
+
+	arch_spin_unlock(&cpu_buffer->lock);
+	local_irq_restore(flags);
+
+	if (bpage)
+		goto out;
+
 	page = alloc_pages_node(cpu_to_node(cpu),
 				GFP_KERNEL | __GFP_NORETRY, 0);
 	if (!page)
@@ -4387,6 +4416,7 @@ void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
 
 	bpage = page_address(page);
 
+ out:
 	rb_init_page(bpage);
 
 	return bpage;
@@ -4396,13 +4426,29 @@ 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: the page to free
  *
  * Free a page allocated from ring_buffer_alloc_read_page.
  */
-void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
+void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data)
 {
-	free_page((unsigned long)data);
+	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
+	struct buffer_data_page *bpage = data;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	arch_spin_lock(&cpu_buffer->lock);
+
+	if (!cpu_buffer->free_page) {
+		cpu_buffer->free_page = bpage;
+		bpage = NULL;
+	}
+
+	arch_spin_unlock(&cpu_buffer->lock);
+	local_irq_restore(flags);
+
+	free_page((unsigned long)bpage);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);