ring-buffer: Check if ring buffer iterator has stale data

[safe/jmp/linux-2.6] / kernel / trace / ring_buffer.c

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index edefe3b..503b630 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -464,6 +464,8 @@ struct ring_buffer_iter {
        struct ring_buffer_per_cpu      *cpu_buffer;
        unsigned long                   head;
        struct buffer_page              *head_page;
+       struct buffer_page              *cache_reader_page;
+       unsigned long                   cache_read;
        u64                             read_stamp;
 };
 
@@ -2716,6 +2718,8 @@ static void rb_iter_reset(struct ring_buffer_iter *iter)
                iter->read_stamp = cpu_buffer->read_stamp;
        else
                iter->read_stamp = iter->head_page->page->time_stamp;
+       iter->cache_reader_page = cpu_buffer->reader_page;
+       iter->cache_read = cpu_buffer->read;
 }
 
 /**
@@ -3066,6 +3070,15 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
        cpu_buffer = iter->cpu_buffer;
        buffer = cpu_buffer->buffer;
 
+       /*
+        * Check if someone performed a consuming read to
+        * the buffer. A consuming read invalidates the iterator
+        * and we need to reset the iterator in this case.
+        */
+       if (unlikely(iter->cache_read != cpu_buffer->read ||
+                    iter->cache_reader_page != cpu_buffer->reader_page))
+               rb_iter_reset(iter);
+
  again:
        /*
         * We repeat when a timestamp is encountered.