lib/plist.c: enforce memory ordering in plist_check_list

There exists an iteration over a plist in plist_check_list(), and memory
dependency exists between variables "prev", "next" and "prev->next".  As
plist is used in the scheduling subsystem, we should guarantee the memory
ordering between multiple processors.

Using macro "WRITE_ONCE()" can help us to ensure the memory ordering as
it was stated in "Documentation/memory-barriers.txt".

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: I Hsin Cheng <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/plist.c b/lib/plist.c
index 0d86ed7a76ac..2e51829d3db9 100644
--- a/lib/plist.c
+++ b/lib/plist.c
@@ -47,8 +47,8 @@ static void plist_check_list(struct list_head *top)
 
 	plist_check_prev_next(top, prev, next);
 	while (next != top) {
-		prev = next;
-		next = prev->next;
+		WRITE_ONCE(prev, next);
+		WRITE_ONCE(next, prev->next);
 		plist_check_prev_next(top, prev, next);
 	}
 }