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authorIlpo Järvinen <ilpo.jarvinen@helsinki.fi>2006-08-04 16:36:18 -0700
committerDavid S. Miller <davem@sunset.davemloft.net>2006-08-04 22:59:51 -0700
commitc4c0ce5c57ef0ca47a4428a14de6b5c8cdf8de8a (patch)
tree762530925f75495b9d2b8bb35702060e7e2fa9ae
parent30a584d944fbd599d4a8f470f75bf7af1a15b466 (diff)
downloadop-kernel-dev-c4c0ce5c57ef0ca47a4428a14de6b5c8cdf8de8a.zip
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[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 <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/red.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/net/red.h b/include/net/red.h
index 5ccdbb3..a4eb379 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;
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