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

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Message-ID: <20080423072432.GX12774@kernel.dk>
Date:	Wed, 23 Apr 2008 09:24:32 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Mark Lord <lkml@....ca>
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

On Tue, Apr 22 2008, Mark Lord wrote:
> Jens,
> 
> While you're in there, :)
> 
> Could you perhaps fix this bug (below) if it still exists?

I don't understand the bug - what are the shared call buffers you are
talking of?

With the changes, there's not even an spin_trylock() in there anymore.
But I don't see the original bug either, so...


> 
> >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.

-- 
Jens Axboe

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