Merge tag 'trace-ring-buffer-v7.1-3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull ring-buffer fix from Steven Rostedt:

 - Fix accounting of persistent ring buffer rewind

   On boot up, the head page is moved back to the earliest point of the
   saved ring buffer. This is because the ring buffer being read by user
   space on a crash may not save the part it read. Rewinding the head
   page back to the earliest saved position helps keep those events from
   being lost.

   The number of events is also read during boot up and displayed in the
   stats file in the tracefs directory. It's also used for other
   accounting as well. On boot up, the "reader page" is accounted for
   but a rewind may put it back into the buffer and then the reader page
   may be accounted for again.

   Save off the original reader page and skip accounting it when
   scanning the pages in the ring buffer.

* tag 'trace-ring-buffer-v7.1-3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Do not double count the reader_page

Author: torvalds

kernel/trace/ring_buffer.c

@@ -1884,7 +1884,7 @@ static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu)
 static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 {
 	struct ring_buffer_cpu_meta *meta = cpu_buffer->ring_meta;
-	struct buffer_page *head_page, *orig_head;
+	struct buffer_page *head_page, *orig_head, *orig_reader;
 	unsigned long entry_bytes = 0;
 	unsigned long entries = 0;
 	int ret;
@@ -1895,16 +1895,17 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 		return;
 
 	orig_head = head_page = cpu_buffer->head_page;
+	orig_reader = cpu_buffer->reader_page;
 
 	/* Do the reader page first */
-	ret = rb_validate_buffer(cpu_buffer->reader_page->page, cpu_buffer->cpu);
+	ret = rb_validate_buffer(orig_reader->page, cpu_buffer->cpu);
 	if (ret < 0) {
 		pr_info("Ring buffer reader page is invalid\n");
 		goto invalid;
 	}
 	entries += ret;
-	entry_bytes += local_read(&cpu_buffer->reader_page->page->commit);
-	local_set(&cpu_buffer->reader_page->entries, ret);
+	entry_bytes += local_read(&orig_reader->page->commit);
+	local_set(&orig_reader->entries, ret);
 
 	ts = head_page->page->time_stamp;
 
@@ -2007,8 +2008,8 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
 	/* Iterate until finding the commit page */
 	for (i = 0; i < meta->nr_subbufs + 1; i++, rb_inc_page(&head_page)) {
 
-		/* Reader page has already been done */
-		if (head_page == cpu_buffer->reader_page)
+		/* The original reader page has already been checked/counted. */
+		if (head_page == orig_reader)
 			continue;
 
 		ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu);