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authorIlpo Järvinen <ilpo.jarvinen@helsinki.fi>2007-10-18 17:56:27 +0200
committerAdrian Bunk <bunk@kernel.org>2007-10-18 17:56:27 +0200
commitc94861ff9759f5f73b49fb4f0fe0c000b82c703a (patch)
parent06f529d5fa3b8ea0b84d327b6fdda988d4b63a62 (diff)
[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: Adrian Bunk <bunk@kernel.org>
1 files changed, 1 insertions, 1 deletions
diff --git a/include/net/red.h b/include/net/red.h
index 2ed4358e3295..cfc262549871 100644
--- a/include/net/red.h
+++ b/include/net/red.h
@@ -213,7 +213,7 @@ 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;