[PATCH 3/5] ring-buffer: Check for end of page in iterator

[Steven Rostedt <rostedt@goodmis.org>]

[-- Attachment #1: 0003-ring-buffer-Check-for-end-of-page-in-iterator.patch --]
[-- Type: text/plain, Size: 1589 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

If the iterator comes to an empty page for some reason, or if
the page is emptied by a consuming read. The iterator code currently
does not check if the iterator is pass the contents, and may
return a false entry.

This patch adds a check to the ring buffer iterator to test if the
current page has been completely read and sets the iterator to the
next page if necessary.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/ring_buffer.c |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 503b630..8c1b2d2 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3064,9 +3064,6 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 	struct ring_buffer_event *event;
 	int nr_loops = 0;
 
-	if (ring_buffer_iter_empty(iter))
-		return NULL;
-
 	cpu_buffer = iter->cpu_buffer;
 	buffer = cpu_buffer->buffer;
 
@@ -3080,6 +3077,9 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 		rb_iter_reset(iter);
 
  again:
+	if (ring_buffer_iter_empty(iter))
+		return NULL;
+
 	/*
 	 * We repeat when a timestamp is encountered.
 	 * We can get multiple timestamps by nested interrupts or also
@@ -3094,6 +3094,11 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 	if (rb_per_cpu_empty(cpu_buffer))
 		return NULL;
 
+	if (iter->head >= local_read(&iter->head_page->page->commit)) {
+		rb_inc_iter(iter);
+		goto again;
+	}
+
 	event = rb_iter_head_event(iter);
 
 	switch (event->type_len) {
-- 
1.6.5