ring-buffer: Check for end of page in iterator

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>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 503b630e0bda6fdd246bd50b47b9d4f652100aae..8c1b2d290718cfc1a14c99b8ab1ca5408821b4b5 100644 (file)
--- 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) {