linux-kernel - Re: [PATCH] sched: print parent comm in sched_show

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Message-ID: <Y60WrwuM43HcNVC7@chenyu5-mobl1>
Date:   Thu, 29 Dec 2022 12:25:19 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     <mingo@...hat.com>, <peterz@...radead.org>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <linux-kernel@...r.kernel.org>, <pmladek@...e.com>,
        <zyhtheonly@...il.com>, <zyhtheonly@...h.net>, <zwp10758@...il.com>
Subject: Re: [PATCH] sched: print parent comm in sched_show_task()

On 2022-12-28 at 00:14:00 +0800, Tio Zhang wrote:
> Knowing who the parent is might be useful for debugging.
> For example, we can sometimes resolve kernel hung tasks by stopping
> the person who begins those hung tasks.
> With the parent's name printed in sched_show_task(),
> it might be helpful to let people know which "service" should be operated.
> 
> Signed-off-by: Tio Zhang <tiozhang@...iglobal.com>
> ---
>  kernel/sched/core.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index cb2aa2b54c7a..6f4aef0fed58 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8854,6 +8854,7 @@ void sched_show_task(struct task_struct *p)
>  {
>  	unsigned long free = 0;
>  	int ppid;
> +	char pcomm[TASK_COMM_LEN];
>  
>  	if (!try_get_task_stack(p))
>  		return;
> @@ -8867,11 +8868,13 @@ void sched_show_task(struct task_struct *p)
>  #endif
>  	ppid = 0;
>  	rcu_read_lock();
> -	if (pid_alive(p))
> +	if (pid_alive(p)) {
>  		ppid = task_pid_nr(rcu_dereference(p->real_parent));
> +		get_task_comm(pcomm, rcu_dereference(p->real_parent));
Maybe struct task_struct *parent = rcu_dereference(p->real_parent);
and use parent directly to get its pid and comm?
Maybe off-topic, what if the parent is a kernel thread/worker? It might have extra
name information such as kthread->full_name or worker->desc according to proc_task_name().

thanks,