[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-ID: <473A4C0F.6070504@redhat.com>
Date: Tue, 13 Nov 2007 20:14:55 -0500
From: Chuck Ebbert <cebbert@...hat.com>
To: linux-kernel <linux-kernel@...r.kernel.org>
CC: Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Divide-by-zero in the 2.6.23 scheduler code
https://bugzilla.redhat.com/show_bug.cgi?id=340161
The problem code has been removed in 2.6.24. The below patch disables
SCHED_FEAT_PRECISE_CPU_LOAD which causes the offending code to be skipped
but does not prevent the user from enabling it.
The divide-by-zero is here in kernel/sched.c:
static void update_cpu_load(struct rq *this_rq)
{
u64 fair_delta64, exec_delta64, idle_delta64, sample_interval64, tmp64;
unsigned long total_load = this_rq->ls.load.weight;
unsigned long this_load = total_load;
struct load_stat *ls = &this_rq->ls;
int i, scale;
this_rq->nr_load_updates++;
if (unlikely(!(sysctl_sched_features & SCHED_FEAT_PRECISE_CPU_LOAD)))
goto do_avg;
/* Update delta_fair/delta_exec fields first */
update_curr_load(this_rq);
fair_delta64 = ls->delta_fair + 1;
ls->delta_fair = 0;
exec_delta64 = ls->delta_exec + 1;
ls->delta_exec = 0;
sample_interval64 = this_rq->clock - ls->load_update_last;
ls->load_update_last = this_rq->clock;
if ((s64)sample_interval64 < (s64)TICK_NSEC)
sample_interval64 = TICK_NSEC;
if (exec_delta64 > sample_interval64)
exec_delta64 = sample_interval64;
idle_delta64 = sample_interval64 - exec_delta64;
======> tmp64 = div64_64(SCHED_LOAD_SCALE * exec_delta64, fair_delta64);
tmp64 = div64_64(tmp64 * exec_delta64, sample_interval64);
this_load = (unsigned long)tmp64;
do_avg:
/* Update our load: */
for (i = 0, scale = 1; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {
unsigned long old_load, new_load;
/* scale is effectively 1 << i now, and >> i divides by scale */
old_load = this_rq->cpu_load[i];
new_load = this_load;
this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
}
}
---
kernel/sched_fair.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-2.6.23.noarch.orig/kernel/sched_fair.c
+++ linux-2.6.23.noarch/kernel/sched_fair.c
@@ -93,7 +93,7 @@ unsigned int sysctl_sched_features __rea
SCHED_FEAT_FAIR_SLEEPERS *1 |
SCHED_FEAT_SLEEPER_AVG *0 |
SCHED_FEAT_SLEEPER_LOAD_AVG *1 |
- SCHED_FEAT_PRECISE_CPU_LOAD *1 |
+ SCHED_FEAT_PRECISE_CPU_LOAD *0 |
SCHED_FEAT_START_DEBIT *1 |
SCHED_FEAT_SKIP_INITIAL *0;
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists