linux-kernel - Re: [PATCH] coredump debugging: add a tracepoint to report the coredumping

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Date: Sat, 17 Feb 2024 11:49:24 +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] coredump debugging: add a tracepoint to report the
 coredumping

On 02/17, 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 the new trace_sched_process_coredump() into coredump_task_exit(),
> this way a user-space monitor could easily wait for the exits and
> potentially make some preparations in advance.

Can't comment, I never know when the new tracepoint will make sense.

Stupid question. Can we simply shift trace_sched_process_exit() up
before coredump_task_exit() ?

Oleg.


> Signed-off-by: Wen Yang <wenyang.linux@...mail.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> 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 | 7 +++++++
>  kernel/exit.c                | 1 +
>  2 files changed, 8 insertions(+)
>
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index dbb01b4b7451..ce7448065986 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -334,6 +334,13 @@ DEFINE_EVENT(sched_process_template, sched_process_exit,
>  	     TP_PROTO(struct task_struct *p),
>  	     TP_ARGS(p));
>
> +/*
> + * Tracepoint for a task coredumping:
> + */
> +DEFINE_EVENT(sched_process_template, sched_process_coredump,
> +	     TP_PROTO(struct task_struct *p),
> +	     TP_ARGS(p));
> +
>  /*
>   * Tracepoint for waiting on task to unschedule:
>   */
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 493647fd7c07..c11e12d73f4e 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -425,6 +425,7 @@ static void coredump_task_exit(struct task_struct *tsk)
>  			self.next = xchg(&core_state->dumper.next, &self);
>  		else
>  			self.task = NULL;
> +		trace_sched_process_coredump(tsk);
>  		/*
>  		 * Implies mb(), the result of xchg() must be visible
>  		 * to core_state->dumper.
> --
> 2.25.1
>