linux-kernel - Re: EIP is at device

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Message-ID: <473C8FF0.4050702@rtr.ca>
Date:	Thu, 15 Nov 2007 13:29:04 -0500
From:	Mark Lord <lkml@....ca>
To:	Greg KH <gregkh@...e.de>
Cc:	Yasunori Goto <y-goto@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexey Dobriyan <adobriyan@...ru>, linux-kernel@...r.kernel.org
Subject: Re: EIP is at device_shutdown+0x32/0x60

Greg KH wrote:
> On Thu, Nov 15, 2007 at 12:07:48PM -0500, Mark Lord wrote:
..
>> Greg, I don't know if this is relevant or not,
>> but x86 has bugs in the halt/reboot code for SMP.
>>
>> Specifically, in native_smp_send_stop() the code now uses
>> spin_trylock() to "lock" the shared call buffers,
>> but then ignores the result.
>>
>> This means that multiple CPUs can/will clobber each other
>> in that code.
>>
>> The second bug, is that this code does not wait for the
>> target CPUs to actually stop before it continues.
>>
>> This was the real cause of the failure-to-poweroff problems
>> I was having with 2.6.23, which we fixed by using CPU hotplug
>> to disable_nonboot_cpus() before the above code ever got run.
> 
> I have noticed that the shutdown path is quite weird, shutting down
> sysdev devices differently depending on the type of shutdown, which is
> probably not good.
> 
> But what change are you talking about for the poweroff problem?  I have
> a _lot_ of people reporting that 2.6.22 is not powering off for them and
> I can't seem to figure it out.  Do you have a changeset for something
> that went in to fix this issue?
..

Well, the real bugs that cause the problem are described by me above.
I don't have a fix for those, but the workaround is in 2.6.23
under git 4047727e5ae33f9b8d2b7766d1994ea6e5ec2991 Fix SMP poweroff hangs.

With that workaround, there's no more hanging on halt,
though there could still be a hang on reboot.

A problem with that workaround is that it has no effect unless
the CPU hotplug code is configured (CONFIG_PM_SLEEP_SMP and pals).

Cheers
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