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author | Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> | 2007-10-18 17:56:27 +0200 |
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committer | Adrian Bunk <bunk@kernel.org> | 2007-10-18 17:56:27 +0200 |
commit | c94861ff9759f5f73b49fb4f0fe0c000b82c703a (patch) | |
tree | 66a4ad3facf0e7918e712f9182b110cbad1dfa5a | |
parent | 06f529d5fa3b8ea0b84d327b6fdda988d4b63a62 (diff) | |
download | linux-stable-c94861ff9759f5f73b49fb4f0fe0c000b82c703a.tar.gz linux-stable-c94861ff9759f5f73b49fb4f0fe0c000b82c703a.tar.bz2 linux-stable-c94861ff9759f5f73b49fb4f0fe0c000b82c703a.zip |
[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>
-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 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; |