From: Miao Xie Date: Mon, 28 Apr 2008 04:54:56 +0000 (+0800) Subject: sched: fair-group: fix a Div0 error of the fair group scheduler X-Git-Tag: v2.6.26-rc2~62^2~4 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cb4ad1ffc7c0d8ea7dc8cd8ba303d83551716d46;p=linux-2.6 sched: fair-group: fix a Div0 error of the fair group scheduler When I echoed 0 into the "cpu.shares" file, a Div0 error occured. We found it is caused by the following calling. sched_group_set_shares(tg, shares) set_se_shares(tg->se[i], shares/nr_cpu_ids) __set_se_shares(se, shares) div64_64((1ULL<<32), shares) When the echoed value was less than the number of processores, the result of the sentence "shares/nr_cpu_ids" was 0, and then the system called div64() to divide the result, the Div0 error occured. It is unnecessary that the shares value is divided by nr_cpu_ids, I think. Because in the function __update_group_shares_cpu() and init_tg_cfs_entry(), the shares value isn't divided by nr_cpu_ids when setting shares of the sched entity. This patch fixes this bug. And echoing ULONG_MAX value into cpu.shares also causes Div0 error, so we set a macro MAX_SHARES to limit the max value of shares. Signed-off-by: Miao Xie Acked-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched.c b/kernel/sched.c index 561b3b39bd..f98f75f3c7 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -321,7 +321,13 @@ static DEFINE_SPINLOCK(task_group_lock); # define INIT_TASK_GROUP_LOAD NICE_0_LOAD #endif +/* + * A weight of 0, 1 or ULONG_MAX can cause arithmetics problems. + * (The default weight is 1024 - so there's no practical + * limitation from this.) + */ #define MIN_SHARES 2 +#define MAX_SHARES (ULONG_MAX - 1) static int init_task_group_load = INIT_TASK_GROUP_LOAD; #endif @@ -1804,6 +1810,8 @@ __update_group_shares_cpu(struct task_group *tg, struct sched_domain *sd, if (shares < MIN_SHARES) shares = MIN_SHARES; + else if (shares > MAX_SHARES) + shares = MAX_SHARES; __set_se_shares(tg->se[tcpu], shares); } @@ -8785,13 +8793,10 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares) if (!tg->se[0]) return -EINVAL; - /* - * A weight of 0 or 1 can cause arithmetics problems. - * (The default weight is 1024 - so there's no practical - * limitation from this.) - */ if (shares < MIN_SHARES) shares = MIN_SHARES; + else if (shares > MAX_SHARES) + shares = MAX_SHARES; mutex_lock(&shares_mutex); if (tg->shares == shares) @@ -8816,7 +8821,7 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares) * force a rebalance */ cfs_rq_set_shares(tg->cfs_rq[i], 0); - set_se_shares(tg->se[i], shares/nr_cpu_ids); + set_se_shares(tg->se[i], shares); } /*