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| author | Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> | 2006-08-04 16:36:18 -0700 |
|---|---|---|
| committer | David S. Miller <davem@sunset.davemloft.net> | 2006-08-04 22:59:51 -0700 |
| commit | c4c0ce5c57ef0ca47a4428a14de6b5c8cdf8de8a (patch) | |
| tree | 762530925f75495b9d2b8bb35702060e7e2fa9ae /include/net/red.h | |
| parent | 30a584d944fbd599d4a8f470f75bf7af1a15b466 (diff) | |
| download | linux-c4c0ce5c57ef0ca47a4428a14de6b5c8cdf8de8a.tar.bz2 | |
[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>
Diffstat (limited to 'include/net/red.h')
| -rw-r--r-- | include/net/red.h | 2 |
1 files changed, 1 insertions, 1 deletions
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; |