linux-kernel - Re: Circular vma locking with kvm, seems to be mmu notifiers related

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Message-ID: <87od3x9u61.fsf@skyscraper.fehenstaub.lan>
Date:	Wed, 13 Aug 2008 10:49:10 +0200
From:	Johannes Weiner <hannes@...urebad.de>
To:	Avi Kivity <avi@...ranet.com>
Cc:	Max Krasnyansky <maxk@...lcomm.com>,
	LKML <linux-kernel@...r.kernel.org>, andrea@...ranet.com,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: Circular vma locking with kvm, seems to be mmu notifiers related

Hi Avi,

Avi Kivity <avi@...ranet.com> writes:

> Max Krasnyansky wrote:
>> Got this on the latest mainline git.
>> There are already a couple of lockdep/kvm threads. So maybe it's known.
>>
>> =============================================
>> [ INFO: possible recursive locking detected ]
>> 2.6.27-rc2 #36
>> ---------------------------------------------
>> qemu-system-x86/3445 is trying to acquire lock:
>>  (&anon_vma->lock){--..}, at: [<ffffffff8029f84d>] mm_take_all_locks+0x8d/0xf0
>>
>> but task is already holding lock:
>>  (&anon_vma->lock){--..}, at: [<ffffffff8029f84d>] mm_take_all_locks+0x8d/0xf0
>>
>>   
>
> Seems to be a false positive.  mmu_take_all_locks takes (surprise!)
> all anon_vma->locks belonging to an mm, and takes special care not to
> deadlock while doing this.
>
> We need to communicate this to lockdep somehow.

I think Peter already annotated this in
454ed842d55740160334efc9ad56cfef54ed37bc .

	Hannes
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