linux-kernel - Re: [PATCH 0/1] kthreads: simplify !kthreadd_task logic, kill kthreadd_task_init

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Message-ID: <20090918232215.GA25517@redhat.com>
Date:	Sat, 19 Sep 2009 01:22:15 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Wu Fei <at.wufei@...il.com>, Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, arjan@...radead.org,
	jeremy@...p.org, mschmidt@...hat.com, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org, tj@...nel.org,
	tglx@...utronix.de, Andrew Morton <akpm@...ux-foundation.org>,
	linux-tip-commits@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 0/1] kthreads: simplify !kthreadd_task logic, kill
	kthreadd_task_init_done

On 09/18, Linus Torvalds wrote:
>
> As to why pid == 0 wouldn't work, I don't know, but I'll take your word
> for it.

Say, admin wants to renice kthreadd or change its affinity. And we can't
show kthread in /proc if its pid is 0.

This can be changed afaics, we can even remove pidmap_init()->set_bit(0) so
that the first copy_process()->alloc_pid() will create the pid with nr == 0.
We don't care about unhashed init_struct_pid which also has nr == 0.

But I don't think this would be good, currently the code can safely assume
that the valid pid can't be 0. For example, find_process_by_pid(0) returns
current.

Oleg.

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