linux-kernel - Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

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Date:	Tue, 22 Apr 2008 19:12:45 -0400
From:	Mark Lord <lkml@....ca>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	npiggin@...e.de, torvalds@...ux-foundation.org
Subject: Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

Jens,

While you're in there, :)

Could you perhaps fix this bug (below) if it still exists?

> Date:	Thu, 15 Nov 2007 12:07:48 -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
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> Content-Transfer-Encoding: 7bit
> Sender: linux-kernel-owner@...r.kernel.org
> 
> ... < snip > ...
> 
> 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.
> 
> Maybe it's related, maybe not.
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