linux-kernel - Re: [PATCH 0/2] sched: tasklist_lock cleanups (Was: don't use while_each

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Date:	Mon, 18 Aug 2014 17:09:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Frank Mayhar <fmayhar@...gle.com>,
	Frederic Weisbecker <fweisbec@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sanjay Rao <srao@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] sched: tasklist_lock cleanups (Was: don't use
	while_each_thread())

On 08/18, Kirill Tkhai wrote:
>
> On 17.08.2014 19:25, Oleg Nesterov wrote:
> >
> > And I can't understand tg_has_rt_tasks(). Don't we need something
> > like the patch below? If not, please do not ask me why I think so,
> > I don't understand this black magic ;) But the usage of the global
> > "runqueues" array looks suspicious.
>
> This function searches RT task which is related to this tg. It's
> opaquely because it looks that there is an error.
>
> task_rq(p)->rt.tg is a task group of a top rt_rq, while the task may
> be queued on a child rt_rq instead of this. So, your patch is a BUGFIX,
> not a cleanup.

Yes, thanks, this was my (vague) understanding. But since I don't know
even the terminology I wasn't able to explain my concerns.

OK, I am going to shamelessly steal your words and turn them into the
changelog.

Thanks.

Oleg.

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