linux-kernel - Re: WARNING: cpu_is_offline() at native_smp_send

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Date:	Fri, 7 Sep 2012 16:17:29 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Venkatesh Pallipadi <venki@...gle.com>
Subject: Re: WARNING: cpu_is_offline() at native_smp_send_reschedule()

On Fri, Sep 07, 2012 at 09:23:16AM +0200, Peter Zijlstra wrote:
> On Fri, 2012-09-07 at 09:20 +0800, Fengguang Wu wrote:
> 
> > FYI, the bisect result is
> > 
> > commit 554cecaf733623b327eef9652b65965eb1081b81
> > Author: Diwakar Tundlam <dtundlam@...dia.com>
> > Date:   Wed Mar 7 14:44:26 2012 -0800
> > 
> >     sched/nohz: Correctly initialize 'next_balance' in 'nohz' idle balancer
> > 
> >     The 'next_balance' field of 'nohz' idle balancer must be initialized
> >     to jiffies. Since jiffies is initialized to negative 300 seconds the
> >     'nohz' idle balancer does not run for the first 300s (5mins) after
> >     bootup. If no new processes are spawed or no idle cycles happen, the
> >     load on the cpus will remain unbalanced for that duration.
> > 
> >     Signed-off-by: Diwakar Tundlam <dtundlam@...dia.com>
> >     Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> >     Link: http://lkml.kernel.org/r/1DD7BFEDD3147247B1355BEFEFE4665237994F30EF@HQMAIL04.nvidia.com
> >     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> Oh fun.. does the below 'fix' it?
> 
> The thing I'm thinking of a tick happening right after we set jiffies
> but before the zalloc (specifically the memset(0)) is complete. Since
> we've already registered the softirq we can end up in the load-balancer
> and see a completely weird idle mask.
> 
> Hmm?

The may be more causes, since I still get the warning:

[    9.816279] reboot: machine restart
[    9.835796] ------------[ cut here ]------------
[    9.836558] WARNING: at /c/wfg/linux/arch/x86/kernel/smp.c:123 native_smp_send_reschedule+0x46/0x50()
[    9.839792] Pid: 18, comm: kworker/0:1 Not tainted 3.6.0-rc3-bisect-00005-gb374aa1-dirty #49
[    9.839792] Call Trace:
[    9.839792]  [<7902f42a>] warn_slowpath_common+0x5a/0x80
[    9.839792]  [<7901ee16>] ? native_smp_send_reschedule+0x46/0x50
[    9.839792]  [<7901ee16>] ? native_smp_send_reschedule+0x46/0x50
[    9.839792]  [<7902f4fd>] warn_slowpath_null+0x1d/0x20
[    9.839792]  [<7901ee16>] native_smp_send_reschedule+0x46/0x50
[    9.839792]  [<7905fdad>] trigger_load_balance+0x1bd/0x250
[    9.839792]  [<79056d14>] scheduler_tick+0xd4/0x100
[    9.839792]  [<7903bde5>] update_process_times+0x55/0x70
[    9.839792]  [<79071187>] tick_sched_timer+0x57/0xb0
[    9.839792]  [<793accee>] ? do_raw_spin_unlock+0x4e/0x90
[    9.839792]  [<7904e0b7>] __run_hrtimer.isra.29+0x57/0x100
[    9.839792]  [<79071130>] ? tick_nohz_handler+0xe0/0xe0
[    9.839792]  [<7904ed45>] hrtimer_interrupt+0xe5/0x280
[    9.839792]  [<7905a5a7>] ? sched_clock_cpu+0xc7/0x150
[    9.839792]  [<7901f9a4>] smp_apic_timer_interrupt+0x54/0x90
[    9.839792]  [<79882631>] apic_timer_interrupt+0x31/0x40
[    9.839792]  [<7905007b>] ? call_srcu+0x2b/0x70
[    9.839792]  [<793a00e0>] ? __bitmap_intersects+0x10/0x80
[    9.839792]  [<7988194f>] ? _raw_spin_unlock_irq+0x1f/0x40
[    9.839792]  [<7905307f>] finish_task_switch+0x7f/0xd0
[    9.839792]  [<79053038>] ? finish_task_switch+0x38/0xd0
[    9.839792]  [<7988044a>] __schedule+0x38a/0x770
[    9.839792]  [<79045529>] ? worker_thread+0x1a9/0x380
[    9.839792]  [<793accee>] ? do_raw_spin_unlock+0x4e/0x90
[    9.839792]  [<7988084e>] schedule+0x1e/0x50
[    9.839792]  [<7904552e>] worker_thread+0x1ae/0x380
[    9.839792]  [<79056ed9>] ? complete+0x49/0x60
[    9.839792]  [<79045380>] ? manage_workers.isra.23+0x250/0x250
[    9.839792]  [<79049ff8>] kthread+0x78/0x80
[    9.839792]  [<79880000>] ? __up.isra.0+0xd/0x2d
[    9.839792]  [<79049f80>] ? insert_kthread_work+0x70/0x70
[    9.839792]  [<798830c6>] kernel_thread_helper+0x6/0xd

Thanks,
Fengguang

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