perf: Fix vmalloc ring buffer pages handling

If we allocate perf ring buffer with the size of single (user)
page, we will get memory corruption when releasing itin
rb_free_work function (for CONFIG_PERF_USE_VMALLOC option).

For single page sized ring buffer the page_order is -1 (because
nr_pages is 0). This needs to be recognized in the rb_free_work
function to release proper amount of pages.

Adding data_page_nr function that returns number of allocated
data pages. Customizing the rest of the code to use it.

Reported-by: Jan Stancek <jstancek@redhat.com>
Original-patch-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20130319143509.GA1128@krava.brq.redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 97fddb09762b0dc815af7d1f674993d87cd45574..cd55144270b5401030f4b5ce5576f97b6b976b63 100644 (file)
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -326,11 +326,16 @@ void rb_free(struct ring_buffer *rb)
 }
 
 #else
+static int data_page_nr(struct ring_buffer *rb)
+{
+       return rb->nr_pages << page_order(rb);
+}
 
 struct page *
 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
 {
-       if (pgoff > (1UL << page_order(rb)))
+       /* The '>' counts in the user page. */
+       if (pgoff > data_page_nr(rb))
                return NULL;
 
        return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
@@ -350,10 +355,11 @@ static void rb_free_work(struct work_struct *work)
        int i, nr;
 
        rb = container_of(work, struct ring_buffer, work);
-       nr = 1 << page_order(rb);
+       nr = data_page_nr(rb);
 
        base = rb->user_page;
-       for (i = 0; i < nr + 1; i++)
+       /* The '<=' counts in the user page. */
+       for (i = 0; i <= nr; i++)
                perf_mmap_unmark_page(base + (i * PAGE_SIZE));
 
        vfree(base);
@@ -387,7 +393,7 @@ struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
        rb->user_page = all_buf;
        rb->data_pages[0] = all_buf + PAGE_SIZE;
        rb->page_order = ilog2(nr_pages);
-       rb->nr_pages = 1;
+       rb->nr_pages = !!nr_pages;
 
        ring_buffer_init(rb, watermark, flags);