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Date: Mon, 18 Aug 2014 17:09:16 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Kirill Tkhai <tkhai@yandex.ru>
Cc: Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
        Frank Mayhar <fmayhar@google.com>,
        Frederic Weisbecker <fweisbec@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Sanjay Rao <srao@redhat.com>, Larry Woodman <lwoodman@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] sched: tasklist_lock cleanups (Was: don't use
	while_each_thread())
Message-ID: <20140818150916.GA19364@redhat.com>
References: <20140813191938.GA19301@redhat.com> <20140817152549.GA17984@redhat.com> <53F11B45.8070105@yandex.ru>
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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.