Message-ID: <20120530231541.4c13433a@feng-i7>
Date:	Wed, 30 May 2012 23:15:41 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH]x86, reboot: Fix a warning message triggered by
 stop_other_cpus()

On Wed, 30 May 2012 10:51:10 +0200
Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Feng Tang <feng.tang@...el.com> wrote:
> 
> > Hi Don,
> > 
> > On Tue, 22 May 2012 09:33:56 -0400
> > Don Zickus <dzickus@...hat.com> wrote:
> > 
> > > On Tue, May 22, 2012 at 10:52:33AM +0800, Feng Tang wrote:
> > > > 
> > > > The root cause seems to be the default_send_IPI_mask_allbutself_phys()
> > > > takes quiet some time (I measured it could be several ms) to complete
> > > > sending NMIs to all the other 23 CPUs, and for HZ=250/1000 system, the
> > > 
> > > I sent Ingo a patch (which he took in), that reverts this path to
> > > interrupts again (and NMIs as a fallback if it fails).  The problem will
> > > still exist I assume though I don't know if it changes the timing
> > > characteristics.
> > 
> > Thanks for your review and letting me know the revert which I just saw in
> > the latest Linus' tree. And I think this new mechanism will greatly reduce
> > the possibility, but it still exist as the old nmi_stop_other_cpus's
> > implementation still exist. So
> > 
> > Ingo,
> > 
> > Could you review this patch? thanks,
> 
> It doesn't apply anymore, so please merge and add Don's 
> Acked-by.

Hi Ingo,

Following is the updated patch, which could be applied to Linus's tree
and tip tree's master branch.

Thanks,
Feng
-------------------------

>From 9c4fc1b95da9cf35e1b1e8a71a67fc594adfdd78 Mon Sep 17 00:00:00 2001
From: Feng Tang <feng.tang@...el.com>
Date: Wed, 30 May 2012 21:01:49 +0800
Subject: [PATCH] x86, reboot: Fix a warning message triggered by
 stop_other_cpus()

When rebooting our 24 CPU Westmere servers with 3.4-rc6, we can always see
such warning msg:

Restarting system.
machine restart
------------[ cut here ]------------
WARNING: at arch/x86/kernel/smp.c:125 native_smp_send_reschedule+0x74/0xa7()
Hardware name: X8DTN
Modules linked in: igb [last unloaded: scsi_wait_scan]
Pid: 1, comm: systemd-shutdow Not tainted 3.4.0-rc6+ #22
Call Trace:
 <IRQ>  [<ffffffff8102a41f>] warn_slowpath_common+0x7e/0x96
 [<ffffffff8102a44c>] warn_slowpath_null+0x15/0x17
 [<ffffffff81018cf7>] native_smp_send_reschedule+0x74/0xa7
 [<ffffffff810561c1>] trigger_load_balance+0x279/0x2a6
 [<ffffffff81050112>] scheduler_tick+0xe0/0xe9
 [<ffffffff81036768>] update_process_times+0x60/0x70
 [<ffffffff81062f2f>] tick_sched_timer+0x68/0x92
 [<ffffffff81046e33>] __run_hrtimer+0xb3/0x13c
 [<ffffffff81062ec7>] ? tick_nohz_handler+0xd0/0xd0
 [<ffffffff810474f2>] hrtimer_interrupt+0xdb/0x198
 [<ffffffff81019a35>] smp_apic_timer_interrupt+0x81/0x94
 [<ffffffff81655187>] apic_timer_interrupt+0x67/0x70
 <EOI>  [<ffffffff8101a3c4>] ? default_send_IPI_mask_allbutself_phys+0xb4/0xc4
 [<ffffffff8101c680>] physflat_send_IPI_allbutself+0x12/0x14
 [<ffffffff81018db4>] native_nmi_stop_other_cpus+0x8a/0xd6
 [<ffffffff810188ba>] native_machine_shutdown+0x50/0x67
 [<ffffffff81018926>] machine_shutdown+0xa/0xc
 [<ffffffff8101897e>] native_machine_restart+0x20/0x32
 [<ffffffff810189b0>] machine_restart+0xa/0xc
 [<ffffffff8103b196>] kernel_restart+0x47/0x4c
 [<ffffffff8103b2e6>] sys_reboot+0x13e/0x17c
 [<ffffffff8164e436>] ? _raw_spin_unlock_bh+0x10/0x12
 [<ffffffff810fcac9>] ? bdi_queue_work+0xcf/0xd8
 [<ffffffff810fe82f>] ? __bdi_start_writeback+0xae/0xb7
 [<ffffffff810e0d64>] ? iterate_supers+0xa3/0xb7
 [<ffffffff816547a2>] system_call_fastpath+0x16/0x1b
---[ end trace 320af5cb1cb60c5b ]---

The root cause seems to be the default_send_IPI_mask_allbutself_phys()
takes quiet some time (I measured it could be several ms) to complete
sending NMIs to all the other 23 CPUs, and for HZ=250/1000 system, the
time is long enough for a timer interrupt to happen, which will in
turn trigger to kick load balance to a stopped CPU and cause this
warning in native_smp_send_reschedule().

So disabling the local irq before stop_other_cpu() can fix this
problem (tested 25 times reboot ok), and it is fine as there should
be nobody caring the timer interrupt in such reboot stage.

The latest 3.4 kernel slightly change this behavior by sending
REBOOT_VECTOR first and only send NMI_VECTOR if the REBOOT_VCTOR
fails, and this patch is still needed to prevent the problem.

Signed-off-by: Feng Tang <feng.tang@...el.com>
Acked-by: Don Zickus <dzickus@...hat.com>
---
 arch/x86/kernel/reboot.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 77215c2..ba823c8 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -658,9 +658,11 @@ void native_machine_shutdown(void)
 	set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));
 
 	/*
-	 * O.K Now that I'm on the appropriate processor,
-	 * stop all of the others.
+	 * O.K Now that I'm on the appropriate processor, stop all of the
+	 * others. Also disable the local irq to not receive the per-cpu
+	 * timer interrupt which may trigger scheduler's load balance.
 	 */
+	local_irq_disable();
 	stop_other_cpus();
 #endif
 
-- 
1.7.9

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