[PATCH] tracing: Fix unmapping loop in tracing_mark_write

[Vikram Mulukutla]

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.

Reviewed-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Reported-by: Lime Yang <limey@xxxxxxxxxxxxxx>
Signed-off-by: Vikram Mulukutla <markivx@xxxxxxxxxxxxxx>
---
 kernel/trace/trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ab76b7b..bceed34 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4931,7 +4931,7 @@ 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]);
 	}
-- 
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a Linux Foundation Collaborative Project

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