Re: [PATCH v3] exit: move trace_sched_process_exit earlier in do_exit()

[Wen Yang]

On 2024/3/20 05:57, Andrew Morton wrote:
> On Sun, 10 Mar 2024 13:25:29 +0800 wenyang.linux@xxxxxxxxxxx wrote:
>
> > From: Wen Yang <wenyang.linux@xxxxxxxxxxx>
> >
> > 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