linux-kernel - Re: [PATCH v3] sched: print parent comm in sched_show

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Date:   Tue, 28 Mar 2023 11:40:46 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     yu.c.chen@...el.com, akpm@...ux-foundation.org,
        juri.lelli@...hat.com, mingo@...hat.com, peterz@...radead.org,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        zyhtheonly@...il.com, zwp10758@...il.com, zyhtheonly@...h.net
Subject: Re: [PATCH v3] sched: print parent comm in sched_show_task()

On Tue 2023-03-28 11:44:59, 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.
> Also, we move the parent info to a following new line.
> It would be better to solve the situation when the task
> is not alive and we could not get information about the parent.
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8865,14 +8864,19 @@ void sched_show_task(struct task_struct *p)
>  #ifdef CONFIG_DEBUG_STACK_USAGE
>  	free = stack_not_used(p);
>  #endif
> -	ppid = 0;
> +
> +	pr_cont(" stack:%-5lu pid:%-5d flags:0x%08lx\n",
> +		free, task_pid_nr(p), read_task_thread_flags(p));
> +
>  	rcu_read_lock();
> -	if (pid_alive(p))
> -		ppid = task_pid_nr(rcu_dereference(p->real_parent));
> +	if (pid_alive(p)) {
> +		struct task_struct *parent = rcu_dereference(p->real_parent);
> +
> +		pr_info("parent:%-15.15s ppid:%-6d", parent->comm, task_pid_nr(parent));

There is a missing new line delimiter "\n".

> +	} else {
> +		pr_info("parent:unknown         ppid:<NULL>\n");
> +	}
>  	rcu_read_unlock();
> -	pr_cont(" stack:%-5lu pid:%-5d ppid:%-6d flags:0x%08lx\n",
> -		free, task_pid_nr(p), ppid,
> -		read_task_thread_flags(p));
>  
>  	print_worker_info(KERN_INFO, p);
>  	print_stop_info(KERN_INFO, p);

Otherwise, it looks good. With the added new line delimiter:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr