Re: [PATCH] io_uring: consider cgroup setting when binding sqpoll cpu

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/8/15 下午11:10, Hao Xu 写道:
> 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.
> 
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
> ---
>   fs/io_uring.c | 41 +++++++++++++++++++++++++++++++++++++----
>   1 file changed, 37 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 51c4166f68b5..35d0e7bc283b 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -79,6 +79,7 @@
>   #include <linux/pagemap.h>
>   #include <linux/io_uring.h>
>   #include <linux/tracehook.h>
> +#include <linux/cpuset.h>
>   
>   #define CREATE_TRACE_POINTS
>   #include <trace/events/io_uring.h>
> @@ -6903,15 +6904,35 @@ static int io_sq_thread(void *data)
>   	struct io_ring_ctx *ctx;
>   	unsigned long timeout = 0;
>   	char buf[TASK_COMM_LEN];
> +	cpumask_var_t cpus_allowed;
>   	DEFINE_WAIT(wait);
>   
>   	snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
>   	set_task_comm(current, buf);
>   
> -	if (sqd->sq_cpu != -1)
> -		set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu));
> -	else
> -		set_cpus_allowed_ptr(current, cpu_online_mask);
> +	if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
> +		mutex_lock(&sqd->lock);
> +		sqd->thread = NULL;
> +		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
> +			io_ring_set_wakeup_flag(ctx);
> +		io_run_task_work();
> +		mutex_unlock(&sqd->lock);
> +
> +		complete(&sqd->exited);
> +		do_exit(1);
> +	}
> +	cpuset_cpus_allowed(current, cpus_allowed);
> +	if (sqd->sq_cpu != -1) {
> +		if (!cpumask_test_cpu(sqd->sq_cpu, cpus_allowed)) {
Here comes a small race with cpus_allowed updating. If this is the case,
it means the cpus_allowed are changing frequently, in this situation
sqthread's cpumask will be setup to cpus_allowed anyway, so it's still
in the correct range.
(considering the aim of this patch is to limit sqthread to the cpuset
where its cgroup allows. If cpuset of its cgroup is changing frequently
we cannot bind sqthread to some cpu anyway.)
> +			sqd->sq_cpu = -1;
> +			pr_warn("sqthread %d: bound cpu not allowed\n", current->pid);
> +		} else {
> +			set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu));
> +		}
> +	}
> +	if (sqd->sq_cpu == -1)
> +		set_cpus_allowed_ptr(current, cpus_allowed);
> +	free_cpumask_var(cpus_allowed);
>   	current->flags |= PF_NO_SETAFFINITY;
>   
>   	mutex_lock(&sqd->lock);
> @@ -8060,11 +8081,23 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
>   
>   		if (p->flags & IORING_SETUP_SQ_AFF) {
>   			int cpu = p->sq_thread_cpu;
> +			cpumask_var_t cpus_allowed;
>   
>   			ret = -EINVAL;
>   			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
>   				goto err_sqpoll;
> +			if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
> +				ret = -ENOMEM;
> +				goto err_sqpoll;
> +			}
> +			cpuset_cpus_allowed(current, cpus_allowed);
> +			if (!cpumask_test_cpu(cpu, cpus_allowed)) {
> +				free_cpumask_var(cpus_allowed);
> +				goto err_sqpoll;
> +			}
> +
>   			sqd->sq_cpu = cpu;
> +			free_cpumask_var(cpus_allowed);
>   		} else {
>   			sqd->sq_cpu = -1;
>   		}
>