sched: fair-group: fix a Div0 error of the fair group scheduler (cb4ad1ff) · Commits · 戴 / test

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>

kernel/sched.c

+11 −6

Original line number	Diff line number	Diff line
		@@ -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);
		}

		/*

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