Re: [PATCH for-5.15 v2] io_uring: consider cgroup setting when binding sqpoll cpu

[Jens Axboe <axboe@kernel.dk>]

On 8/27/21 8:13 AM, Hao Xu wrote:
> Since sqthread is userspace like thread now, it should respect cgroup
> setting, thus we should consider current allowed cpuset when doing
> cpu binding for sqthread.

In general, this looks way better than v1. Just a few minor comments
below.

> @@ -7000,6 +7001,16 @@ static bool io_sqd_handle_event(struct io_sq_data *sqd)
>  	return did_sig || test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
>  }
>  
> +static int io_sq_bind_cpu(int cpu)
> +{
> +	if (!test_cpu_in_current_cpuset(cpu))
> +		pr_warn("sqthread %d: bound cpu not allowed\n", current->pid);
> +	else
> +		set_cpus_allowed_ptr(current, cpumask_of(cpu));
> +
> +	return 0;
> +}

This should not be triggerable, unless the set changes between creation
and the thread being created. Hence maybe the warn is fine. I'd probably
prefer terminating the thread at that point, which would result in an
-EOWNERDEAD return when someone attempts to wake the thread.

Which is probably OK, as we really should not hit this path.

> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 04c20de66afc..fad77c91bc1f 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -116,6 +116,8 @@ static inline int cpuset_do_slab_mem_spread(void)
>  
>  extern bool current_cpuset_is_being_rebound(void);
>  
> +extern bool test_cpu_in_current_cpuset(int cpu);
> +
>  extern void rebuild_sched_domains(void);
>  
>  extern void cpuset_print_current_mems_allowed(void);
> @@ -257,6 +259,11 @@ static inline bool current_cpuset_is_being_rebound(void)
>  	return false;
>  }
>  
> +static inline bool test_cpu_in_current_cpuset(int cpu)
> +{
> +	return false;
> +}
> +
>  static inline void rebuild_sched_domains(void)
>  {
>  	partition_sched_domains(1, NULL, NULL);
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index adb5190c4429..a63c27e9430e 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1849,6 +1849,17 @@ bool current_cpuset_is_being_rebound(void)
>  	return ret;
>  }
>  
> +bool test_cpu_in_current_cpuset(int cpu)
> +{
> +	bool ret;
> +
> +	rcu_read_lock();
> +	ret = cpumask_test_cpu(cpu, task_cs(current)->effective_cpus);
> +	rcu_read_unlock();
> +
> +	return ret;
> +}
> +
>  static int update_relax_domain_level(struct cpuset *cs, s64 val)
>  {
>  #ifdef CONFIG_SMP

In terms of review and so forth, I'd split this into a prep patch. Then
patch 2 just becomes the io_uring consumer of it.

-- 
Jens Axboe