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Subject: Re: WARNING: cpu_is_offline() at native_smp_send_reschedule()
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Michael Wang <wangyun@linux.vnet.ibm.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>, LKML <linux-kernel@vger.kernel.org>,
        x86@kernel.org, Suresh Siddha <suresh.b.siddha@intel.com>,
        Venkatesh Pallipadi <venki@google.com>
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Date: Wed, 05 Sep 2012 12:54:40 +0200
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On Wed, 2012-09-05 at 12:35 +0800, Michael Wang wrote:
> > [   10.968565] reboot: machine restart
> > [   10.983510] ------------[ cut here ]------------
> > [   10.984218] WARNING: at /c/kernel-tests/src/stable/arch/x86/kernel/smp.c:123 native_smp_send_reschedule+0x46/0x50()
> > [   10.985880] Pid: 88, comm: kpktgend_0 Not tainted 3.6.0-rc3-00005-gb374aa1 #10
> > [   10.987185] Call Trace:
> > [   10.987506]  [<7902f42a>] warn_slowpath_common+0x5a/0x80
> > [   10.987506]  [<7901ee16>] ? native_smp_send_reschedule+0x46/0x50
> > [   10.987506]  [<7901ee16>] ? native_smp_send_reschedule+0x46/0x50
> > [   10.987506]  [<7902f4fd>] warn_slowpath_null+0x1d/0x20
> > [   10.987506]  [<7901ee16>] native_smp_send_reschedule+0x46/0x50
> 
> So this cpu try to fire a nohz balance kick ipi to an offline cpu?
> 
> May be we are choosing a wrong cpu to kick but that's not the point,
> what I can't understand is why this cpu could do this kick.
> 
> We have nohz_kick_needed() to check whether current cpu should do kick ,
> and the first condition we need to match is that current cpu should be
> idle, but the trace show current pid is 88 not 0.
> 
> We should add Peter to cc list, may be he will be interested on what
> happened.

> > [   10.987506]  [<7905fdad>] trigger_load_balance+0x1bd/0x250
> > [   10.987506]  [<79056d14>] scheduler_tick+0xd4/0x100
> > [   10.987506]  [<7903bde5>] update_process_times+0x55/0x70 

Hmm, added both venki and suresh as they touched it last ;-)

I suppose you're running a hotplug loop along with your workload?