linux-kernel - Re: [Bug #13116] Can't boot with nosmp

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Message-ID: <4A2EAA53.7060006@redhat.com>
Date:	Tue, 09 Jun 2009 21:30:43 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Dan Williams <dan.j.williams@...el.com>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [Bug #13116] Can't boot with nosmp

Dan Williams wrote:
> On Mon, Jun 8, 2009 at 5:04 PM, Stephen Hemminger<shemminger@...tta.com> wrote:
>   
>> I did some more debugging, and the problem appears to be that
>> booting with nosmp still leaves all the CPU's present in the cpu
>> possible mask. So code like dma engine (or loopback device), that
>> use alloc_percpu get broken.
>>
>> Not sure why all the cpu's are still showing up in the possible mask.
>> Rusty? do you have an answer.
>>     
>
> Would this recent commit also fix this issue?
>
> commit a4c0364be3f43d3e17fe19270f8b3d64881606e6
> Author: Avi Kivity <avi@...hat.com>
> Date:   Sat Jun 6 12:34:39 2009 +0300
>
>     KVM: Explicity initialize cpus_hardware_enabled
>
>     Under CONFIG_MAXSMP, cpus_hardware_enabled is allocated from the heap and
>     not statically initialized.  This causes a crash on reboot when kvm thinks
>     vmx is enabled on random nonexistent cpus and accesses nonexistent percpu
>     lists.
>
>     Fix by explicitly clearing the variable.
>
>     Cc: stable@...nel.org
>     Reported-and-tested-by: Yinghai Lu <yinghai@...nel.org>
>     Signed-off-by: Avi Kivity <avi@...hat.com>
>   

This only affects reboots.  But yes, the cpumask code has bugs.  Does 
the .config involved select MAXSMP?

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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