linux-kernel - Re: Qemu & KVM bug

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Message-ID: <47B3217D.7040903@qumranet.com>
Date:	Wed, 13 Feb 2008 18:57:33 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Marcelo Tosatti <marcelo@...ck.org>
CC:	Jiri Kosina <jkosina@...e.cz>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Qemu & KVM bug

Marcelo Tosatti wrote:
> On Wed, Feb 13, 2008 at 04:24:53PM +0100, Jiri Kosina wrote:
>   
>> On Wed, 13 Feb 2008, Zdenek Kabelac wrote:
>>
>>     
>>> I get this bug in my log whenever I start qemu-kvm - I do not use kqemu 
>>> module - so it's with plain kernel modules. If more details are needed - 
>>> just ask. (Cpu; C2D)
>>> BUG: sleeping function called from invalid context at kernel/rwsem.c:48
>>> in_atomic():1, irqs_disabled():0
>>> INFO: lockdep is turned off.
>>> Pid: 26600, comm: qemu-kvm Not tainted 2.6.25-rc1 #29
>>>       
>> This has been obviously caused by Marcelo's (added to CC) commit 
>> 10589a4699b, which added down_write(mmap_sem) to alloc_apic_access_page(), 
>> which is called with preempt disabled from vmx_create_vcpu().
>>     
>
> alloc_apic_access_page() called mutex_lock, so the warning would trigger
> before that change.
>
> I think it's fine to allocate the APIC page after put_cpu(), since no vcpu 
> state is required.
>
>   


Looks right, but wants a changelog and signoff, of course.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.

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