linux-kernel - Re: [PATCH][RFC] kernel/cpu: do not change the cpus_allowed of the current task when unplugging cpus

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Date:	Fri, 7 Jun 2013 11:05:43 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Zhao Chenhui <chenhui.zhao@...escale.com>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, leoli@...escale.com, scottwood@...escale.com,
	Priyanka.Jain@...escale.com
Subject: Re: [PATCH][RFC] kernel/cpu: do not change the cpus_allowed of the
 current task when unplugging cpus

* Zhao Chenhui | 2013-05-16 18:17:19 [+0800]:

>We found a problem. When a cpu is brought down using _cpu_down(),
>the corresponding cpu bit in the cpus_allowed of the current task is
>cleared. But this bit will not be set when the same cpu is online again.
>Then, the current task and its child processes will not be allowed to
>run on this cpu.

Isn't this what should happen? This also happens on mainline if you
leave the RT bits out, right? You should be able to put the task back on
the CPU once the CPU is up again.

Sebastian
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