linux-kernel - Re: [PATCH v2] exit: add exit_code to trace_sched_process_exit and move it earlier in do

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Date: Mon, 26 Feb 2024 20:44:35 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: wenyang.linux@...mail.com
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] exit: add exit_code to trace_sched_process_exit and
 move it earlier in do_exit()

Well. since I have already participated in the previous discussions...

As I said, I can't ack this (user-visible) patch even if I tried to
suggest this from the very beginning, I leave it to the maintainers.

I see nothing wrong in this change, but let me ask: do we really need
to report the exit code? this makes this patch even more user-visible
and I have no idea if it can break the current users.

On 02/23, wenyang.linux@...mail.com wrote:
>
> From: Wen Yang <wenyang.linux@...mail.com>
> 
> Currently coredump_task_exit() takes some time to wait for the generation
> of the dump file. But if the user-space wants to receive a notification
> as soon as possible it maybe inconvenient.
> 
> Add exit_code to the TP trace_sched_process_exit() and move it earlier in
> do_exit(). This way a user-space monitor could detect the exits and
> potentially make some preparations in advance.
> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Wen Yang <wenyang.linux@...mail.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: linux-kernel@...r.kernel.org
> ---
>  include/trace/events/sched.h | 28 +++++++++++++++++++++++++---
>  kernel/exit.c                |  2 +-
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index dbb01b4b7451..c2e8655fd453 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -330,9 +330,31 @@ DEFINE_EVENT(sched_process_template, sched_process_free,
>  /*
>   * Tracepoint for a task exiting:
>   */
> -DEFINE_EVENT(sched_process_template, sched_process_exit,
> -	     TP_PROTO(struct task_struct *p),
> -	     TP_ARGS(p));
> +TRACE_EVENT(sched_process_exit,
> +
> +	TP_PROTO(struct task_struct *task, long code),
> +
> +	TP_ARGS(task, code),
> +
> +	TP_STRUCT__entry(
> +		__array(	char,	comm,	TASK_COMM_LEN	)
> +		__field(	pid_t,	pid			)
> +		__field(	int,	prio			)
> +		__field(	long,	code			)
> +	),
> +
> +	TP_fast_assign(
> +		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
> +		__entry->pid		= task->pid;
> +		__entry->prio		= task->prio;
> +		__entry->code		= code;
> +	),
> +
> +	TP_printk("comm=%s pid=%d prio=%d exit_code=0x%lx",
> +		  __entry->comm, __entry->pid, __entry->prio,
> +		  __entry->code)
> +);
> +
>  
>  /*
>   * Tracepoint for waiting on task to unschedule:
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 493647fd7c07..48b6ed7f7760 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -826,6 +826,7 @@ void __noreturn do_exit(long code)
>  
>  	WARN_ON(tsk->plug);
>  
> +	trace_sched_process_exit(tsk, code);
>  	kcov_task_exit(tsk);
>  	kmsan_task_exit(tsk);
>  
> @@ -866,7 +867,6 @@ void __noreturn do_exit(long code)
>  
>  	if (group_dead)
>  		acct_process();
> -	trace_sched_process_exit(tsk);
>  
>  	exit_sem(tsk);
>  	exit_shm(tsk);
> -- 
> 2.25.1
>