From c4c0ce5c57ef0ca47a4428a14de6b5c8cdf8de8a Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ilpo=20J=C3=A4rvinen?= Date: Fri, 4 Aug 2006 16:36:18 -0700 Subject: [PATCH] [PKT_SCHED] RED: Fix overflow in calculation of queue average MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Overflow can occur very easily with 32 bits, e.g., with 1 second us_idle is approx. 2^20, which leaves only 11-Wlog bits for queue length. Since the EWMA exponent is typically around 9, queue lengths larger than 2^2 cause overflow. Whether the affected branch is taken when us_idle is as high as 1 second, depends on Scell_log, but with rather reasonable configuration Scell_log is large enough to cause p->Stab to have zero index, which always results zero shift (typically also few other small indices result in zero shift). Signed-off-by: Ilpo Järvinen Signed-off-by: David S. Miller --- include/net/red.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/net/red.h b/include/net/red.h index 5ccdbb3d4722..a4eb37946f2c 100644 --- a/include/net/red.h +++ b/include/net/red.h @@ -212,7 +212,7 @@ static inline unsigned long red_calc_qavg_from_idle_time(struct red_parms *p) * Seems, it is the best solution to * problem of too coarse exponent tabulation. */ - us_idle = (p->qavg * us_idle) >> p->Scell_log; + us_idle = (p->qavg * (u64)us_idle) >> p->Scell_log; if (us_idle < (p->qavg >> 1)) return p->qavg - us_idle; -- 2.20.1