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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Thu, 24 Sep 2020 09:18:33 +0200
Message-ID: <CAKfTPtAgzcSZekb1D_Gm55vHpm4-9z5OyUxuoRTzx-_5icf5Ew@mail.gmail.com>
Subject: Re: [PATCH RESEND] sched/fair: Fix wrong cpu selecting from isolated domain
To:     Xunlei Pang <xlpang@linux.alibaba.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Jiang Biao <benbjiang@tencent.com>,
        Wetp Zhang <wetp.zy@linux.alibaba.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Thu, 24 Sep 2020 at 08:48, Xunlei Pang <xlpang@linux.alibaba.com> wrote:
>
> 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: 10e2f1acd010 ("sched/core: Rewrite and improve select_idle_siblings())
> Reported-by: Wetp Zhang <wetp.zy@linux.alibaba.com>
> Reviewed-by: Jiang Biao <benbjiang@tencent.com>
> Signed-off-by: Xunlei Pang <xlpang@linux.alibaba.com>

Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>

> ---
>  kernel/sched/fair.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a05..fa942c4 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6075,7 +6075,7 @@ 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;
>
> @@ -6083,7 +6083,8 @@ 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;
> @@ -6099,7 +6100,7 @@ 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;
>  }
> @@ -6274,7 +6275,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>         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;
>
> --
> 1.8.3.1
>