linux-kernel - Re: [BUG] sched: tip/master show panic while booting/rebooting

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Date:	Wed, 19 Feb 2014 11:12:11 +0800
From:	Michael wang <wangyun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	paulus@...ba.org, Ingo Molnar <mingo@...hat.com>,
	acme@...stprotocols.net, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] sched: tip/master show panic while booting/rebooting

On 02/18/2014 07:22 PM, Peter Zijlstra wrote:
> On Tue, Feb 18, 2014 at 01:12:03PM +0800, Michael wang wrote:
>> Hi, Folks
>>
>> Got below panic while testing tip/master on x86 box, it randomly
>> occur while booting or rebooting, any ideas?
> 
> The obvious pick would be the relocation of the idle_balance call, but
> I'm not sure how that'll end up stalling.

I've review the code again, seems like it was caused by the same issue
we discussed (RT/DL enqueued issue), I found that idle_balance() will
return 1 in such cases:

        /*
         * While browsing the domains, we released the rq lock.
         * A task could have be enqueued in the meantime
         */
        if (this_rq->nr_running && !pulled_task)
                return 1;

And if no more fair task to be pulled, we will do balance again and
again in pick_next_task_fair() until panic in NMI...

The solution we discussed could solve the problem I suppose, it was
already in progress, correct?

Please let me know if there are any thing I could help with ;-)

Regards,
Michael Wang

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