linux-kernel - Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are dealocked when cpu is set to offline

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Message-ID: <b647ffbd0803070502m28355751rd526ed8ca4dd90a@mail.gmail.com>
Date:	Fri, 7 Mar 2008 14:02:20 +0100
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	ego@...ibm.com, "Ingo Molnar" <mingo@...e.hu>
Cc:	"Oleg Nesterov" <oleg@...sign.ru>, "Yi Yang" <yi.y.yang@...el.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Thomas Gleixner" <tglx@...utronix.de>
Subject: Re: [BUG 2.6.25-rc3] scheduler/hotplug: some processes are dealocked when cpu is set to offline

Hi,

'watchdog' is of SCHED_FIFO class. The standard load-balancer doesn't
move RT tasks between cpus anymore and there is a special mechanism in
scher_rt.c instead (I think, it's .25 material).

So I wonder, whether __migrate_task() is still capable of properly
moving a RT task to another CPU (e.g. for the case when it's in
TASK_RUNNING state) without breaking something in the rt migration
mechanism (or whatever else) that would leave us with a runqueue in
the 'inconsistent' state...
(I've taken a quick look at the relevant code so can't confirm it yet)

maybe it'd be faster if somebody could do a quick test now with the
following line commented out in kernel/softlockup.c :: watchdog()

-         sched_setscheduler(current, SCHED_FIFO, &param);

-- 
Best regards,
Dmitry Adamushko
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