From a8af7246c114bfd939e539f9566b872c06f6225c Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 21 Aug 2009 13:58:54 +0200 Subject: [PATCH] sched: Avoid division by zero Patch a5004278f0525dcb9aa43703ef77bf371ea837cd (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 Signed-off-by: Peter Zijlstra Cc: Jes Sorensen Cc: Jens Axboe Cc: Linus Torvalds LKML-Reference: <1250855934.7538.30.camel@twins> Signed-off-by: Ingo Molnar --- kernel/sched.c | 23 ++++++++++------------- 1 file changed, 10 insertions(+), 13 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 1b529ef..8f8a98e 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -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; } -- 2.7.4