linux-kernel - Re: WARNING: at arch/x86/kernel/smp.c:119 native_smp_send

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Date:	Fri, 23 Mar 2012 09:26:48 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Josh Boyer <jwboyer@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Avi Kivity <avi@...hat.com>, kvm <kvm@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: WARNING: at arch/x86/kernel/smp.c:119
 native_smp_send_reschedule+0x25/0x43()

On Fri, Mar 23, 2012 at 12:47:38PM +0200, Sasha Levin wrote:
> I'm just wondering about the status of the patches to fix this issue,
> this is still happening on linux-next.

I got distracted with other stuff.  I have been running code that does the
following in the shutdown path:

foreach_online_cpu
    cpu_down

but I get occasional hangs on reboot that I haven't gotten around to
debugging.  I assumed this is the approach Peter was suggesting though I
don't think he was sure if it was going to be reliable.

Cheers,
Don

> 
> On Fri, Feb 10, 2012 at 11:04 PM, Don Zickus <dzickus@...hat.com> wrote:
> > On Fri, Feb 10, 2012 at 09:36:03PM +0100, Peter Zijlstra wrote:
> >> On Fri, 2012-02-10 at 15:31 -0500, Don Zickus wrote:
> >> > So my second patch which I will eventually post will just skip the WARN_ON
> >> > if the system is going down.  Not sure if that is the proper way to address
> >> > this problem or change all of the stop_this_cpu code to use a different
> >> > bitmask than the cpu_online bitmask (but then you run the risk of a stuck
> >> > IPI I guess if the cpu is halted without notifying anyone).
> >>
> >> Yeah, the async hard kill of all cpus is bound to make problems.. what
> >> I'm wondering is, why is this in the normal shutdown path and not
> >> specific to a hard panic?
> >
> > I didn't write the original code, I just changed it from REBOOT_IRQ to
> > NMI and left all the stop_this_cpu stuff alone.
> >
> >>
> >> Trying to make this work is just not going to be pretty, and in the
> >> panic case we really don't care much.
> >
> > Sure.
> >
> > Cheers,
> > Don
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