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sched: fair-group: fix a Div0 error of the fair group scheduler

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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 <miaox@cn.fujitsu.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Miao Xie 2008-04-28 12:54:56 +08:00 committed by Ingo Molnar
parent 712555ee4f
commit cb4ad1ffc7
1 changed files with 11 additions and 6 deletions
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17
kernel/sched.c
View file

@ -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);
}
/*