linux-kernel - Re: [PATCH -next] sched/fair: Fix task migrated to isolated cpus

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Message-ID: <d0977c14-2837-497b-896b-0a2ad20fb3d5@bytedance.com>
Date: Fri, 1 Mar 2024 11:28:59 +0800
From: Abel Wu <wuyun.abel@...edance.com>
To: Zheng Zucheng <zhengzucheng@...wei.com>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, joshdon@...gle.com
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] sched/fair: Fix task migrated to isolated cpus

Hi Zucheng, thanks for the bugfix. But it has already been addressed
by the following patches in tip/sched/core:

8aeaffef8c6e ("sched/fair: Take the scheduling domain into account in select_idle_smt()")
23d04d8c6b8e ("sched/fair: Take the scheduling domain into account in select_idle_core()")

On 3/1/24 10:31 AM, Zheng Zucheng Wrote:
> On the wakeup path with hyperthreading, select cpu only looks at
> task->cpus_ptr to see if the task can run on the target cpu. If isolcpus
> kernel parameter is set, and isolated cpus will be part of mask
> task->cpus_ptr, tasks were migrated to our isolated cpus.
> 
> Steps to reproduce on my 32-CPU hyperthreads machine:
> 1. with boot parameter: "isolcpus=0,1"
>     (thread lists: 0,16 and 1,17)
> 2. cgcreate -g cpuset:test
>     echo 0-31 > /sys/fs/cgroup/cpuset/test/cpuset.cpus
>     echo 0 > /sys/fs/cgroup/cpuset/test/cpuset.mems
>     cgexec -g cpuset:test "test_threads"
> 3. some threads will be migrated to the isolated cpu0/1.
> 
> Fix it by checking the valid domain mask in select_idle_smt() and
> select_idle_core()
> 
> Fixes: 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()")
> Fixes: 3e6efe87cd5c ("sched/fair: Remove redundant check in select_idle_smt()")
> Cc: stable@...r.kernel.org # v5.12+
> Signed-off-by: Zheng Zucheng <zhengzucheng@...wei.com>
> ---
>   kernel/sched/fair.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 533547e3c90a..e6552c77e0f1 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7289,7 +7289,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
>   		if (!available_idle_cpu(cpu)) {
>   			idle = false;
>   			if (*idle_cpu == -1) {
> -				if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, p->cpus_ptr)) {
> +				if (sched_idle_cpu(cpu) && cpumask_test_cpu(cpu, cpus)) {
>   					*idle_cpu = cpu;
>   					break;
>   				}
> @@ -7297,7 +7297,7 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
>   			}
>   			break;
>   		}
> -		if (*idle_cpu == -1 && cpumask_test_cpu(cpu, p->cpus_ptr))
> +		if (*idle_cpu == -1 && cpumask_test_cpu(cpu, cpus))
>   			*idle_cpu = cpu;
>   	}
>   
> @@ -7311,12 +7311,12 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
>   /*
>    * 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;
>   
>   	for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
> -		if (cpu == target)
> +		if (cpu == target || !cpumask_test_cpu(cpu, sched_domain_span(sd)))
>   			continue;
>   		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
>   			return cpu;
> @@ -7341,7 +7341,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
>   	return __select_idle_cpu(core, p);
>   }
>   
> -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;
>   }
> @@ -7591,7 +7591,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>   		has_idle_core = test_idle_cores(target);
>   
>   		if (!has_idle_core && cpus_share_cache(prev, target)) {
> -			i = select_idle_smt(p, prev);
> +			i = select_idle_smt(p, sd, prev);
>   			if ((unsigned int)i < nr_cpumask_bits)
>   				return i;
>   		}