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Date:   Mon, 16 Jan 2023 17:26:03 +0800
From:   Chen Yu <yu.c.chen@intel.com>
To:     Tio Zhang <tiozhang@didiglobal.com>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Petr Mladek <pmladek@suse.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched: print parent comm in sched_show_task()
Message-ID: <Y8UYKzBJeejHCpgO@chenyu5-mobl1>
References: <20230113105413.GA30243@didi-ThinkCentre-M930t-N000>
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Hi Tio,
On 2023-01-13 at 18:54:13 +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.
> Also, we move the parent info to a following new line.
> It would better solve the situation when the task
> is not alive and we could not get information about the parent.
>
Maybe generate the patch via git format-patch -v2 because it is a second
one. Also Cced corresponding sched maintainers as they will make the decision.
> Signed-off-by: Tio Zhang <tiozhang@didiglobal.com>
> ---
>  kernel/sched/core.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index cb2aa2b54c7a..5be3f476ee5b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8853,7 +8853,6 @@ SYSCALL_DEFINE2(sched_rr_get_interval_time32, pid_t, pid,
>  void sched_show_task(struct task_struct *p)
>  {
>  	unsigned long free = 0;
> -	int ppid;
>  
>  	if (!try_get_task_stack(p))
>  		return;
> @@ -8865,14 +8864,16 @@ 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));
This might change the original scenario: if !pid_alive(p), the sched_show_task()
will print ppid = 0(init task?).

thanks,
Chenyu