ring-buffer: Check for end of page in iterator

[deliverable/linux.git] / kernel / trace / ring_buffer.c

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index edefe3b2801b746d794316eba5e2259fac8751af..8c1b2d290718cfc1a14c99b8ab1ca5408821b4b5 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;
 }
 
 /**
@@ -3060,13 +3064,22 @@ 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;
 
+       /*
+        * 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:
+       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
@@ -3081,6 +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) {