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

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Date: Fri, 1 Mar 2024 16:54:34 +0800
From: zhengzucheng <zhengzucheng@...wei.com>
To: Abel Wu <wuyun.abel@...edance.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

Ah yes indeed. I didn't notice that it was fixed，thanks！

在 2024/3/1 11:28, Abel Wu 写道:
> 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;
>>           }
>
> .