From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: kvm-85 sometimes not starting on 2.6.30-rc5
Date: Sun, 17 May 2009 23:27:42 +0300
Message-ID: <4A10733E.5000905@redhat.com>
References: <20090513192249.GA5760@nik-comp.linuxbox.cz>
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Cc: Nikola Ciprich <extmaillist@linuxbox.cz>,
	KVM list <kvm@vger.kernel.org>, nikola.ciprich@linuxbox.cz
To: Andrea Arcangeli <aarcange@redhat.com>
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Andrea, looks like the mother of all locks below.

Nikola Ciprich wrote:
> Hi,
> sometimes trying to start kvm on 2.6.30-rc5 (with kvm module v85, userspace v85) fails with:
> kvm_create_vm: Interrupted system call
> Could not create KVM context
>
> and following backtrace appears in dmesg:
> [  309.546138] BUG: MAX_LOCK_DEPTH too low!
> [  309.549964] turning off the locking correctness validator.
> [  309.549964] Pid: 2833, comm: qemu-kvm Not tainted 2.6.30lb.00_01_PRE08 #1
> [  309.549964] Call Trace:
> [  309.549964]  [<ffffffff80269aa9>] __lock_acquire+0x4a9/0xb70
> [  309.549964]  [<ffffffff802c54ef>] ? mm_take_all_locks+0x2f/0x130
> [  309.549964]  [<ffffffff8026b825>] lock_acquire+0xa5/0x150
> [  309.549964]  [<ffffffff802c55ac>] ? mm_take_all_locks+0xec/0x130
> [  309.549964]  [<ffffffff80505c96>] _spin_lock_nest_lock+0x36/0x50
> [  309.549964]  [<ffffffff802c55ac>] ? mm_take_all_locks+0xec/0x130
> [  309.549964]  [<ffffffff802c55ac>] mm_take_all_locks+0xec/0x130
> [  309.549964]  [<ffffffff802d43ab>] do_mmu_notifier_register+0x7b/0x1d0
> [  309.549964]  [<ffffffff802d451e>] mmu_notifier_register+0xe/0x10
> [  309.549964]  [<ffffffffa02a8dd9>] kvm_dev_ioctl+0x189/0x2f0 [kvm]
> [  309.549964]  [<ffffffff802f0171>] vfs_ioctl+0x31/0x90
> [  309.549964]  [<ffffffff802f03fb>] do_vfs_ioctl+0x22b/0x550
> [  309.549964]  [<ffffffff802f07a2>] sys_ioctl+0x82/0xa0
> [  309.549964]  [<ffffffff8020b442>] system_call_fastpath+0x16/0x1b
>
> It happened to me when I didn't have storage with kernel mounted.
> Further attempts are usually successfull.
> BR
> nik
>
>
>   


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.