tracing: Fix unmapping loop in tracing_mark_write

commit 7215853e985a4bef1a6c14e00e89dfec84f1e457 upstream.

Commit 6edb2a8a385f0cdef51dae37ff23e74d76d8a6ce introduced
an array map_pages that contains the addresses returned by
kmap_atomic. However, when unmapping those pages, map_pages[0]
is unmapped before map_pages[1], breaking the nesting requirement
as specified in the documentation for kmap_atomic/kunmap_atomic.

This was caught by the highmem debug code present in kunmap_atomic.
Fix the loop to do the unmapping properly.

Link: http://lkml.kernel.org/r/1418871056-6614-1-git-send-email-markivx@codeaurora.org
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Reported-by: Lime Yang <limey@codeaurora.org>
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 01603e48742ebb4687d3ff3aafc761e5047aa408..8b924fb7f915fb443430bc9000412bab59646130 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4894,7 +4894,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
        *fpos += written;
 
  out_unlock:
-       for (i = 0; i < nr_pages; i++){
+       for (i = nr_pages - 1; i >= 0; i--) {
                kunmap_atomic(map_page[i]);
                put_page(pages[i]);
        }