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Message-ID: <c411eda5-5378-4511-bea3-d1566174c8c7@efficios.com>
Date: Thu, 22 Feb 2024 11:25:36 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: wenyang.linux@...mail.com, Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>, Ingo Molnar <mingo@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Mel Gorman
<mgorman@...hsingularity.net>, Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] exit: add a tracepoint for profiling a task that is
starting to exit
On 2024-02-22 11:04, 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.
>
> Commit 2d4bcf886e42 ("exit: Remove profile_task_exit & profile_munmap")
> simplified the code, but also removed profile_task_exit(), which may
> prevent third-party kernel modules from detecting process exits timely.
>
> Add the new trace_sched_profile_task_exit() this way a user-space monitor
> could detect the exits and potentially make some preparations in advance.
I don't see any explanation justifying adding an extra tracepoint
rather than just moving trace_sched_process_exit() earlier in do_exit().
Why is moving trace_sched_process_exit() earlier in do_exit() an issue,
considering that any tracer interested in knowing the point where a task
is really reclaimed (from zombie state) is trace_sched_process_free()
called from delayed_put_task_struct() ?
Thanks,
Mathieu
>
> 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 | 28 ++++++++++++++++++++++++++++
> kernel/exit.c | 1 +
> 2 files changed, 29 insertions(+)
>
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index dbb01b4b7451..750b2f0bdf69 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -341,6 +341,34 @@ DEFINE_EVENT(sched_process_template, sched_wait_task,
> TP_PROTO(struct task_struct *p),
> TP_ARGS(p));
>
> +/*
> + * Tracepoint for profiling a task that is starting to exit:
> + */
> +TRACE_EVENT(sched_profile_task_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 a waiting task:
> */
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 493647fd7c07..f675f879a1b2 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_profile_task_exit(tsk, code);
> kcov_task_exit(tsk);
> kmsan_task_exit(tsk);
>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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