From: Ilpo Järvinen Date: Fri, 4 Aug 2006 23:36:18 +0000 (-0700) Subject: [PKT_SCHED] RED: Fix overflow in calculation of queue average X-Git-Tag: v2.6.18-rc4~3^2~2 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c4c0ce5c57ef0ca47a4428a14de6b5c8cdf8de8a;p=linux-2.6 [PKT_SCHED] RED: Fix overflow in calculation of queue average 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 --- diff --git a/include/net/red.h b/include/net/red.h index 5ccdbb3d47..a4eb37946f 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;