From 03144b5869d2921dafbea477246aeb5d4eb5fc38 Mon Sep 17 00:00:00 2001 From: Michael Dalton Date: Thu, 16 Jan 2014 22:23:29 -0800 Subject: lib: Ensure EWMA does not store wrong intermediate values To ensure ewma_read() without a lock returns a valid but possibly out of date average, modify ewma_add() by using ACCESS_ONCE to prevent intermediate wrong values from being written to avg->internal. Suggested-by: Eric Dumazet Acked-by: Michael S. Tsirkin Acked-by: Eric Dumazet Signed-off-by: Michael Dalton Signed-off-by: David S. Miller --- lib/average.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'lib/average.c') diff --git a/lib/average.c b/lib/average.c index 99a67e662b3c..114d1beae0c7 100644 --- a/lib/average.c +++ b/lib/average.c @@ -53,8 +53,10 @@ EXPORT_SYMBOL(ewma_init); */ struct ewma *ewma_add(struct ewma *avg, unsigned long val) { - avg->internal = avg->internal ? - (((avg->internal << avg->weight) - avg->internal) + + unsigned long internal = ACCESS_ONCE(avg->internal); + + ACCESS_ONCE(avg->internal) = internal ? + (((internal << avg->weight) - internal) + (val << avg->factor)) >> avg->weight : (val << avg->factor); return avg; -- cgit v1.2.3