linux-kernel - Re: [PATCH v2] exit: perform randomness and pid work without tasklist

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Message-ID: <20250128192224.GD24845@redhat.com>
Date: Tue, 28 Jan 2025 20:22:25 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: brauner@...nel.org, akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v2] exit: perform randomness and pid work without
 tasklist_lock

On 01/28, Mateusz Guzik wrote:
>
> On Tue, Jan 28, 2025 at 7:30 PM Oleg Nesterov <oleg@...hat.com> wrote:
> >
> no problem, will send a v3 provided there are no issues reported
> concerning the pid stuff

Great, thanks.

BTW, I didn't look at the pid stuff yet, I _feel_ that this can be simplified
too, but I am already sleeping, most probably I am wrong.

> > As for add_device_randomness(). I must have missed something, but I still can't
> > understand why we can't simply shift add_device_randomness(p->sum_exec_runtime)
> > to release_release_task() and avoid release_task_post->randomness.
> >
> > You said:
> >
> >         I wanted to keep the load where it was
> >
> > but why??? Again, I must have missed something, but to me this simply adds the
> > unnecessary complications. Either way, ->sum_exec_runtime is not stable even if
> > task-to-release != current, so what is the point?
> >
>
> Perhaps I should preface this is not a hill I'm going to die on. :->
>
> This is the spot which is known to work and release_task does not
> access the area otherwise. So for all I know someone will change it
> later to be freeable, zeroed for "hardening"

sum_exec_runtime can't be freed/zeroed/etc in any case.

Again, please note that task-to-release can still be running, especially
if it is current.

> always add the same value.

I don't think that "add the same value" does matter at all in this case,
but please correct me.

> So by default I don't want to change aspect.
>
> However, if you insist on the read to just moving, I'll be more than
> happy to do that in v3.

Thanks, see above ;)

Oleg.