ring_buffer: reset buffer page when freeing

Mathieu Desnoyers pointed out that the freeing of the page frame needs
to be reset otherwise we might trigger BUG_ON in the page free code.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 95ca9338cb6c090c3fdefa9998b111542965d1d4..cfa711374d9a6284bc6392cca4f6b4af3509dc8f 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -127,6 +127,17 @@ struct buffer_page {
        };
 };
 
+/*
+ * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
+ * this issue out.
+ */
+static inline void free_buffer_page(struct buffer_page *bpage)
+{
+       reset_page_mapcount(&bpage->page);
+       bpage->page.mapping = NULL;
+       __free_page(&bpage->page);
+}
+
 /*
  * We need to fit the time_stamp delta into 27 bits.
  */
@@ -240,7 +251,7 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
  free_pages:
        list_for_each_entry_safe(page, tmp, &pages, list) {
                list_del_init(&page->list);
-               __free_page(&page->page);
+               free_buffer_page(page);
        }
        return -ENOMEM;
 }
@@ -284,7 +295,7 @@ static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
 
        list_for_each_entry_safe(page, tmp, head, list) {
                list_del_init(&page->list);
-               __free_page(&page->page);
+               free_buffer_page(page);
        }
        kfree(cpu_buffer);
 }
@@ -393,7 +404,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
                p = cpu_buffer->pages.next;
                page = list_entry(p, struct buffer_page, list);
                list_del_init(&page->list);
-               __free_page(&page->page);
+               free_buffer_page(page);
        }
        BUG_ON(list_empty(&cpu_buffer->pages));
 
@@ -520,7 +531,7 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
  free_pages:
        list_for_each_entry_safe(page, tmp, &pages, list) {
                list_del_init(&page->list);
-               __free_page(&page->page);
+               free_buffer_page(page);
        }
        return -ENOMEM;
 }