linux-kernel - Re: [PATCH] release_task: kill the no longer needed get/put_pid(thread

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Message-ID: <20250415-haare-kroch-2c11f03bd81d@brauner>
Date: Tue, 15 Apr 2025 09:35:49 +0200
From: Christian Brauner <brauner@...nel.org>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>, 
	"Eric W. Biederman" <ebiederm@...ssion.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] release_task: kill the no longer needed
 get/put_pid(thread_pid)

On Mon, Apr 14, 2025 at 11:26:35PM +0200, Mateusz Guzik wrote:
> On Mon, Apr 14, 2025 at 10:46 PM Oleg Nesterov <oleg@...hat.com> wrote:
> > I'd prefer to move add_device_randomness() after release_thread(),
> > but perhaps this needs another minor cleanup?
> >
> 
> I have no opinion on that front. As far as cosmetics go I would not
> touch it past the nit I mentioned in my previous e-mail, but I'm not
> going to protest any other changes.
> 
> imo the real thing to do concerning the routine is to figure out if
> the call is even of any benefit -- it very well may be this is call is
> only there because nobody with random-fu bothered to remove it.
> Personally I have epsilon knowledge of that area, so I'm not even
> going to try to evaluate it. But it would be nice if someone(tm)
> reached out to random folk concerning it. Worst case, even if it still
> has to be there, maybe the sucker can trylock and bail. It does
> contribute to contention, likely for no good reason.

Afaict, add_device_randomness() cannot block. So why can't we just move
this into put_task_struct_rcu_user() (or some variant that's local to
kernel/exit.c)? I see no reason why this would need to be done
synchronously?