tree 762530925f75495b9d2b8bb35702060e7e2fa9ae
parent 30a584d944fbd599d4a8f470f75bf7af1a15b466
author Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> 1154734578 -0700
committer David S. Miller <davem@sunset.davemloft.net> 1154757591 -0700

[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>