Commit df3cb4ea authored Sep 24, 2020 by Xunlei Pang Committed by Peter Zijlstra Sep 25, 2020

sched/fair: Fix wrong cpu selecting from isolated domain



We've met problems that occasionally tasks with full cpumask
(e.g. by putting it into a cpuset or setting to full affinity)
were migrated to our isolated cpus in production environment.

After some analysis, we found that it is due to the current
select_idle_smt() not considering the sched_domain mask.

Steps to reproduce on my 31-CPU hyperthreads machine:
1. with boot parameter: "isolcpus=domain,2-31"
   (thread lists: 0,16 and 1,17)
2. cgcreate -g cpu:test; cgexec -g cpu:test "test_threads"
3. some threads will be migrated to the isolated cpu16~17.

Fix it by checking the valid domain mask in select_idle_smt().

Fixes: 10e2f1ac ("sched/core: Rewrite and improve select_idle_siblings())
Reported-by: Wetp Zhang <wetp.zy@linux.alibaba.com>
Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jiang Biao <benbjiang@tencent.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/1600930127-76857-1-git-send-email-xlpang@linux.alibaba.com

parent 51bd5121

kernel/sched/fair.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -6080,7 +6080,7 @@ static int select_idle_core(struct task_struct p, struct sched_domain sd, int
		/*
		* Scan the local SMT mask for idle CPUs.
		*/
		static int select_idle_smt(struct task_struct *p, int target)
		static int select_idle_smt(struct task_struct p, struct sched_domain sd, int target)
		{
		int cpu;

		@@ -6088,7 +6088,8 @@ static int select_idle_smt(struct task_struct *p, int target)
		return -1;

		for_each_cpu(cpu, cpu_smt_mask(target)) {
		if (!cpumask_test_cpu(cpu, p->cpus_ptr))
		if (!cpumask_test_cpu(cpu, p->cpus_ptr) \|\|
		!cpumask_test_cpu(cpu, sched_domain_span(sd)))
		continue;
		if (available_idle_cpu(cpu) \|\| sched_idle_cpu(cpu))
		return cpu;
		@@ -6104,7 +6105,7 @@ static inline int select_idle_core(struct task_struct p, struct sched_domain s
		return -1;
		}

		static inline int select_idle_smt(struct task_struct *p, int target)
		static inline int select_idle_smt(struct task_struct p, struct sched_domain sd, int target)
		{
		return -1;
		}
		@@ -6279,7 +6280,7 @@ symmetric:
		if ((unsigned)i < nr_cpumask_bits)
		return i;

		i = select_idle_smt(p, target);
		i = select_idle_smt(p, sd, target);
		if ((unsigned)i < nr_cpumask_bits)
		return i;

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