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

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Date: Sat, 23 Mar 2024 23:30:24 +0800
From: Wen Yang <wenyang.linux@...mail.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...nel.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: [PATCH v3] exit: move trace_sched_process_exit earlier in
 do_exit()



On 2024/3/20 05:57, Andrew Morton wrote:
> On Sun, 10 Mar 2024 13:25:29 +0800 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.
> 
> If userspace is awaiting this notification to say "it's now OK to read
> the dump file" then it could break things?
> 

Thanks for your comments.

This could also be achieved in the nearby proc_exit_connector().

In addition, this issue has been discussed in detail in the following link:
https://lkml.org/lkml/2024/2/23/1018


>> Move trace_sched_process_exit() earlier in do_exit().
>> This way a user-space monitor could detect the exits and
>> potentially make some preparations in advance.
>>
>> Oleg initially proposed this suggestion, and Steven further provided some
>> detailed suggestions, and Mathieu carefully checked the historical code
>> and said:
>> : I've checked with Matthew Khouzam (maintainer of Trace Compass)
>> : which care about this tracepoint, and we have not identified any
>> : significant impact of moving it on its model of the scheduler, other
>> : than slightly changing its timing.
>> : I've also checked quickly in lttng-analyses and have not found
>> : any code that care about its specific placement.
>> : So I would say go ahead and move it earlier in do_exit(), it's
>> : fine by me.
> 
> I'm not seeing a clear need for this change.  "maybe inconveniant" is
> quite thin.  Please fully describe what motivated you to work on this?
> 

Thanks.
We hope to address this issue in our Advanced Driver Assistance System:
When certain critical processes exit abnormally, prompt information can 
be reported to the monitoring program as soon as possible.

We have also attempted to add a new TP, as follows:
https://lkml.org/lkml/2024/2/23/5

But after some discussion, it is still considered more reasonable to 
move trace_sched_process_exit() earlier.

We also look forward to your suggestions, thanks again.


--
Best wishes,
Wen