linux-kernel - Re: [RESEND PATCH v3] exit: move trace_sched_process_exit earlier in do

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Message-ID: <ZgfpPFYmvSg4WC+c@gmail.com>
Date: Sat, 30 Mar 2024 11:28:12 +0100
From: Ingo Molnar <mingo@...nel.org>
To: wenyang.linux@...mail.com
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v3] exit: move trace_sched_process_exit earlier in
 do_exit()


* wenyang.linux@...mail.com <wenyang.linux@...mail.com> wrote:

> From: Wen Yang <wenyang.linux@...mail.com>
> 
> In a safety critical system, when some processes exit abnormally, it 
> is hoped that prompt information can be reported to the monitor as 
> soon as possible.

If this event is so critical to catch, a probe can be put on do_exit(). 
This will be superior to your patch, because it will notify about the 
event even sooner.

> 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.

Could you point out an example of such third-party kernel modules, and 
why we should care about them?

> Compared to adding an extra tracking point, it is better to move the 
> existing trace_sched_process_exit() earlier in do_exit(), since any 
> tracer interested in knowing the point where a task is really 
> reclaimed is trace_sched_process_free() called from 
> delayed_put_task_struct().[1]

I disagree, I think this scheduler tracepoint should be moved even 
*later* in the exit sequence, and be combined with 
sched_autogroup_exit_task(), so that the scheduler only has a single 
exit-notification callback in essence.

Until this is all done cleanly no tree should pick up this change:

    NAKed-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo