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Date: Tue, 14 Apr 2009 11:20:37 +0300
From: Avi Kivity <avi@redhat.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Luis Henriques <henrix@sapo.pt>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: Problem with kvm on -tip
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Peter Zijlstra wrote:
> On Sat, 2009-04-11 at 15:08 +0300, Avi Kivity wrote:
>   
>>> [ 3293.134688] BUG: MAX_LOCK_DEPTH too low!
>>>   
>>>       
>> Looks like a genuine issue, need to increase MAX_LOCK_DEPTH.  Andrea?
>>
>>     
>>> [ 3293.134704] turning off the locking correctness validator.
>>> [ 3293.134718] Pid: 5117, comm: kvm Not tainted 2.6.30-rc1-tip-01420-g58e70a8
>>> #18
>>> [ 3293.134727] Call Trace:
>>> [ 3293.134749]  [<ffffffff802805f6>] __lock_acquire+0x4c6/0xbf0
>>> [ 3293.134764]  [<ffffffff80280e2e>] lock_acquire+0x10e/0x160
>>> [ 3293.134780]  [<ffffffff802f3760>] ? mm_take_all_locks+0x110/0x150
>>> [ 3293.134798]  [<ffffffff80580c3b>] _spin_lock_nest_lock+0x3b/0x50
>>> [ 3293.134811]  [<ffffffff802f3760>] ? mm_take_all_locks+0x110/0x150
>>> [ 3293.134823]  [<ffffffff802f3760>] mm_take_all_locks+0x110/0x150
>>> [ 3293.134838]  [<ffffffff803093af>] do_mmu_notifier_register+0xdf/0x1f0
>>> [ 3293.134852]  [<ffffffff803094f3>] mmu_notifier_register+0x13/0x20
>>> [ 3293.134899]  [<ffffffffa02edede>] kvm_dev_ioctl+0x1ae/0x360 [kvm]
>>> [ 3293.134914]  [<ffffffff80327a16>] vfs_ioctl+0x36/0xb0
>>> [ 3293.134927]  [<ffffffff80327b22>] do_vfs_ioctl+0x92/0x5c0
>>> [ 3293.134942]  [<ffffffff80273d9b>] ? up_read+0x2b/0x40
>>> [ 3293.134955]  [<ffffffff8032809f>] sys_ioctl+0x4f/0x80
>>> [ 3293.134971]  [<ffffffff8020c1f2>] system_call_fastpath+0x16/0x1b request
>>>       
>
> Thing is, its grabbing all vma locks, and we have a lock depth limit of
> 48. Now when we started this, the claim was that kvm would only need
> this when the process was very fresh and would thus not yet have many
> vma, ergo we should never run into this limit.
>
> Has that changed?
>   

Hasn't changed; this is on VM creation.

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

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