From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Dalton Subject: [PATCH net-next v4 5/6] lib: Ensure EWMA does not store wrong intermediate values Date: Thu, 16 Jan 2014 11:52:29 -0800 Message-ID: <1389901950-3854-5-git-send-email-mwdalton@google.com> References: <1389901950-3854-1-git-send-email-mwdalton@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Michael Dalton , "Michael S. Tsirkin" , netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, Eric Dumazet , Ben Hutchings To: "David S. Miller" Return-path: In-Reply-To: <1389901950-3854-1-git-send-email-mwdalton@google.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org To ensure ewma_read() without a lock returns a valid but possibly out of date average, modify ewma_add() by using ACCESS_ONCE to prevent intermediate wrong values from being written to avg-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 Signed-off-by: Michael Dalton --- 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