Re: [PATCH net-next v4 5/6] lib: Ensure EWMA does not store wrong intermediate values
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2014-01-16 20:25:22
Also in:
netdev
On Thu, Jan 16, 2014 at 11:52:29AM -0800, Michael Dalton wrote:
To ensure ewma_read() without a lock returns a valid but possibly out of date average, modify ewma_add() by using ACCESS_ONCE to prevent intermediate wrong values from being written to avg-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 <redacted> Signed-off-by: Michael Dalton <redacted>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
quoted hunk ↗ jump to hunk
--- lib/average.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)diff --git a/lib/average.c b/lib/average.c index 99a67e6..114d1be 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;-- 1.8.5.2