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sched: Avoid division by zero

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Patch a5004278f0 (sched: Fix
cgroup smp fairness) introduced the possibility of a
divide-by-zero because load-balancing is not synchronized
between sched_domains.

This can cause the state of cpus to change between the first
and second loop over the sched domain in tg_shares_up().

Reported-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jes Sorensen <jes@sgi.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <1250855934.7538.30.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-08-21 13:58:54 +02:00 committed by Ingo Molnar
parent cde7e5ca4e
commit a8af7246c1
1 changed files with 10 additions and 13 deletions
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23
kernel/sched.c
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@ -1522,7 +1522,8 @@ static void __set_se_shares(struct sched_entity *se, unsigned long shares);
*/
static void
update_group_shares_cpu(struct task_group *tg, int cpu,
unsigned long sd_shares, unsigned long sd_rq_weight)
unsigned long sd_shares, unsigned long sd_rq_weight,
unsigned long sd_eff_weight)
{
unsigned long rq_weight;
unsigned long shares;
@ -1535,13 +1536,15 @@ update_group_shares_cpu(struct task_group *tg, int cpu,
if (!rq_weight) {
boost = 1;
rq_weight = NICE_0_LOAD;
if (sd_rq_weight == sd_eff_weight)
sd_eff_weight += NICE_0_LOAD;
sd_rq_weight = sd_eff_weight;
}
/*
* \Sum shares * rq_weight
* shares = -----------------------
* \Sum rq_weight
*
* \Sum_j shares_j * rq_weight_i
* shares_i = -----------------------------
* \Sum_j rq_weight_j
*/
shares = (sd_shares * rq_weight) / sd_rq_weight;
shares = clamp_t(unsigned long, shares, MIN_SHARES, MAX_SHARES);
@ -1593,14 +1596,8 @@ static int tg_shares_up(struct task_group *tg, void *data)
if (!sd->parent || !(sd->parent->flags & SD_LOAD_BALANCE))
shares = tg->shares;
for_each_cpu(i, sched_domain_span(sd)) {
unsigned long sd_rq_weight = rq_weight;
if (!tg->cfs_rq[i]->rq_weight)
sd_rq_weight = eff_weight;
update_group_shares_cpu(tg, i, shares, sd_rq_weight);
}
for_each_cpu(i, sched_domain_span(sd))
update_group_shares_cpu(tg, i, shares, rq_weight, eff_weight);
return 0;
}